Supplementary Information (doc 74K)

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Supplementary materials
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METHODS
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Total Nucleic Acids Extraction
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The same total nucleic extraction protocol (Dempster et al., 1999) was followed for all of
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the samples. The quarter of each filter dedicated to molecular work was stored in separate
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microcentrifuge tubes at -80°C in a cetyl trimethylammonium bromide (CTAB) solution
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consisting of 100 mM TrisHCl at pH 8.0, 1.4 M NaCl, 2% (w/v) CTAB, 1.0% polyvinyl
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pyrrolidone, and 20 mM Ethylenediaminetetraacetic acid. The filters and solution were
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thawed at room temperature, and 0.4% (v/v) beta-mercaptoethanol was added to each
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tube. The samples were vortexed briefly and incubated at 65°C for 15 min with
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occasional inversion. The samples were cooled to room temperature, and an equal
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volume of chloroform/isoamyl alcohol (24:1) was added, briefly mixed, and incubated at
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room temperature for 20 min. The aqueous and the organic phases were separated by
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centrifugation at 12,500 rpm for 20 min at 4°C. The aqueous layer was transferred to a
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new tube, an equal volume of chloroform/isoamyl alcohol was added and briefly mixed,
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and the phases were separated by centrifugation for 5 min. The aqueous layer was again
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moved to a new tube, and ½ volume 5 M NaCl and 1 volume isopropanol were added and
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briefly mixed. The samples were frozen at -80°C for at least 2 hours and then thawed and
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centrifuged at 4°C for 45 min. The pellet was washed with 70% ethanol and resuspended
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in 50 µL of RNase free water.
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PCR, RT-PCR and Cleaning
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All of the PCR reactions for the generation of clone libraries used the same bacterial 16S
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rRNA primers-- 8F (5’-AGRGTTTGATCCTGGCT CAG-3’) and 1492R (5’-
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CGGCTACCTTGTTACGACTT-3’; Teske, et al., 2002). Each PCR reaction contained 1
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µL of DNA template, 2.0 µL of each primer solution (10 µM each), 0.25 µL of
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SpeedSTAR Polymerase (Takara, Shiga, Japan), 2.0 µL of deoxynucleotide triphosphate
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(2.5 mM of each dATP, dCTP, dGTP and dTTP) and 2.5 µL of 10X Fast Buffer I; the
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volume was adjusted to 25 µL with molecular biology-grade water. Conditions for the
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PCR in the Bio-Rad iCycler (Hercules, CA, USA) were as follows: heat activation at
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94°C for 2 min, followed by 25 cycles consisting of 10 s denaturation at 98°C, 15 s
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primer annealing at 60°C, and 20 s elongation at 72°C. The PCR terminated with a 72°C
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extension at 10 min.
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For the production of the 16S rRNA clone libraries, an aliquot of the extracted total
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nucleic acids was treated with RNase-free DNase I using the Turbo DNA-free kit
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(Ambion, Austin, TX, USA). The DNA-free samples (1 µL) were used in a 25 µL reverse
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transcriptase chain reaction (RT-PCR) with a Real-Time One-Step RNA PCR Kit,
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Version 2.0 (Takara) with 12.5 µL of 2X One Step RNA PCR Buffer, 2.0 µL of each
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primer solution (of 10 µM), 0.5 µL of RNase inhibitor, 0.5 µL of TaKaRa Ex Taq HS,
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and 0.5 µL of Reverse Transcriptase XL (AMV). Conditions for the RT-PCR in the Bio-
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Rad iCycler were as follows: reverse transcription at 42°C for 15 min, reverse
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transcriptase inactivation at 95°C for 2 min, followed by 25 cycles consisting of 20 s
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denaturation at 98°C, 25 s primer annealing at 60°C, and 1 min elongation at 72°C. The
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RT-PCR terminated with an extension at 72°C for 10 min. The coastal PCR (DNA) and
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RT-PCR (cDNA) products were cleaned using a Wizard SV Gel and PCR Clean-Up
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system (Promega, Madison, WI, USA) using either the gel purification or the PCR
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product purification protocols provided with the kit. The offshore DNA and cDNA were
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cleaned using an UltraClean GelSpin DNA Extraction Kit (MoBio Laboratories, Solana
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Beach, CA, USA). Samples that gave >30% chimeric results were re-processed using a
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reconditioning PCR (Thompson et al., 2002). The PCR product (1 µL) was used in a new
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PCR reaction with new reagents for 3 more cycles, and the resulting PCR product was
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not cleaned before cloning.
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The clean PCR and RT-PCR products were cloned into chemically competent E. coli
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cells using a TOPO TA Cloning Kit that contained TOP 10 cells and either a pCR 2.1-
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TOPO vector or a pCR 4.0 TOPO vector (Invitrogen, San Diego, CA, USA). Sanger
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sequencing of the bacterial colonies was performed in the forward and reverse direction
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by GENEWIZ, Inc. (South Plainfield, NJ) on an ABI 3730xl sequencer using universal
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primers M13F(-21) and M13F(-47). Contiguous sequences were constructed and edited
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using Sequencher (Genecodes, Ann Arbor, MI, USA). Clean, full-length sequences were
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sent to greengenes.lbl.gov for chimera checking using the default settings of Bellerophon
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version 3 (Huber et al., 2004).
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RESULTS AND DISCUSSION
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Surface/ Subsurface, DNA/RNA, and Particle-Associated Partitioning
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The OTUs that represented five or more sequences (28 OTUs total) are shown in the heat
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map (Fig. S3) with the percentage of each library for which they account. For all OTUs
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that were represented in more than one library (57 OTUs total), 95% showed partitioning
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into surface waters (both coastal and offshore) and deeper (mid-depth and bottom)
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waters. Of the top 28 OTUs, 18% were exclusively found in particle-associated or free-
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living libraries, and 43% were exclusively found in DNA or RNA libraries. Five OTUs
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were only found in DNA libraries: the ‘Candidatus Pelagibacter ubique’ (Fig. S5a),
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Actinobacteria gp. OCS155 (Fig. S5d), SAR11-Surface 1 (Fig. S5a), Micromonas (Fig.
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S5d), and SAR86 (II) (Fig. S5b) groups. Seven OTUs were only found in RNA libraries:
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Thalassospira (Fig. S5a), the Eastern North Pacific Ocean SUP05 cluster (Fig. S5b), the
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MGB / SAR324 Clade – Group II (Fig. S5d), Sulfitobacter (Fig. S5a), Arctic BD96
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Group (Fig. S5b), Flavobacterial Marine Group NS9 (Fig. S5c), and the SAR324-
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Chesapeake Bay group (Fig. S5d).
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Of the top 28 most common OTUs, only two were found in both a surface (coastal or
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offshore) library and a mid-depth or bottom depth offshore library. One was an OTU
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closely related to Pseudoalteromonas undia (Fig. S5b), of which most strains are capable
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of protease, lipase, and amylase activity, and possibly galactosidase activity (Yu et al.,
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2009). The other OTU in this category grouped with Hyphomonas (Fig. S5a), some
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members of which have been characterized by an approximate 0.9 µm diameter and a
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reproduction method of budding from the tip of a hypha that is up to three times longer
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than the parent cell (Weiner et al., 1985). The OTU was found exclusively in the particle-
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associated offshore surface and mid-depth libraries.
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Coastal and Offshore Surface Partitioning
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Several OTUs were preferentially found in the coastal libraries. Two of these OTUs are
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closely related to a Roseobacter clone (Fig. S5a) and to a Marine Group B / SAR 324
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Clade clone (Fig. S5d) recently identified in the Chesapeake Bay (Kan et al., 2008). An
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OTU closely related to the “Candidatus Pelagibacter ubique” strain HTCC1002 (Fig.
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S5A), a coastal SAR11 isolate that carries out glycolysis (Schwalbach et. al, 2010), was
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found in the coastal and offshore station libraries. It accounted for a greater percentage of
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the coastal libraries than the offshore libraries. An OTU belonging to the OCS155 clade
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of Actinobacteria (Fig. S5e) represented more of the coastal than the offshore surface
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libraries. This deeply branching group has been found in the Sargasso Sea, the
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continental shelf waters off North Carolina, the Northeastern Pacific Ocean, and the
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Columbia River mouth and estuary (Rappé et al., 2000). An OTU in the SAR116 group
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(Fig. S5a) was exclusively found in the coastal station libraries. The genome of the first
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cultured representative of this group, “Candidatus Puniceispirillum marinum” IMC1322,
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was recently sequenced. The genome suggests that the group is composed of metabolic
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generalists in ocean nutrient cycling (Oh et al., 2010). The Flavobacteria Marine Group
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NS9 OTU (Fig. S5c) was preferentially found in the coastal libraries. A SAR11 Surface
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1b group (Fig. S5a; Carlson et al., 2008) was found exclusively at the surface offshore, as
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were the OTUs from the genera Sulfitobacter (Fig. S5a), Prochlorococcus (Fig. S5e), and
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Thalassospira (Fig. S5a). One OTU was noticeably not preferentially found in the coastal
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or offshore surface libraries. This OTU was most closely related to Synechococcus sp.
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RS9905 (Fig. S5d), a member of clade III; this clade differs from the other clades
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because its members are motile (Toledo et al., 1999). The Synechococcus OTU was
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found in the coastal and offshore surface libraries.
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Notable Bacterial Groups
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The two most common OTUs were both Gammaproteobacteria that were only found at
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the mid-depth and bottom depths offshore. The first of these (Fig. S5b) was represented
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by 73 sequences (10.1% of the 723 total sequences from all libraries) and grouped with
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the genus Marinomonas, but did not match cultured isolates. A closely-related,
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uncultured species (AY028196) was identified in bacterioplankton samples exposed to
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diatom detritus (Bidle & Azam, 2001). The second-most observed OTU (Fig. S5b)
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grouped with Balneatrix. It was closely related to an uncultured endosymbiont of a cold-
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seep Mytilidas sp. (Duperron et al., 2008). An Alphaproteobacteria OTU grouping with
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the genus Thalassospira (Fig. S5a) was only found in a surface offshore library. It
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represented 51% of the free-living offshore surface RNA library and a small portion (5%)
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of the particle-associated surface RNA library. This OTU’s closest cultured
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representative is Thalassospira tepidiphila, a motile, facultatively anaerobic polycyclic
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aromatic hydrocarbon-degrading bacterium (Kodama et al., 2008).
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A gammaproteobacterial OTU (Fig. S5b) within the genus Oceanospirillales was found
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exclusively in the four offshore mid-depth libraries, and is very closely related to
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uncultured representatives (HM587889) of the DWH Oceanospirillales found in Gulf of
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Mexico Deepwater Horizon deep hydrocarbon plume (Hazen et al., 2010; Mason et al.
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2012). Interestingly, the mid-depth water mass might contain hydrocarbons from natural
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seeps, as was observed for the Subtropical Underwater in the southwest North Atlantic
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(Harvey et al., 1979; Requejo & Boeh, 1985). Because the subtropical underwater of the
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southwest North Atlantic extends into the Gulf of Mexico, it constitutes a potential source
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for the Oceanospirillales-related bacteria that responded quickly to the availability of
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dissolved hydrocarbons in the oil-polluted water column (Hazen et al. 2010). A second
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Oceaniserpentilla cluster was distinct from the first Oceaniserpentilla OTU, but was
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distributed among the libraries similarly.
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One OTU grouped with Marine Group B/SAR324 Clade Group II (Fig. S5d; Brown and
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Donachie, 2006). Group II has been found globally distributed in cold waters (<16°C;
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Wright et al., 1997), and enzyme sequencing has suggested that it is important in
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dissolved organic phosphorus cycling (Brown & Donachie 2006). It represented a
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considerable portion of the free-living offshore bottom RNA library (20%), and is also
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found in the free-living offshore mid-depth RNA library (3%). Only the Synechococcus
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sp. RS9905 OTU (Fig. S5d) was found in the coastal and offshore surface RNA and
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DNA libraries.
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One of the most dominant marine bacterial groups, the SAR11 cluster, was abundant in
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the DNA coastal and offshore libraries and noticeably missing from the corresponding
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RNA libraries (Fig. 2 and S5a). There are no obvious methodological reasons for this
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discrepancy. The total nucleic acid extraction protocol extracted both DNA and RNA at
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the same time, and the same primers were used for both DNA and RNA libraries.
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Additionally, Moeseneder et al. (2005) found the SAR11 group using T-RFLP of both
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RNA and DNA, indicating that preferential SAR11 RNA degradation is unlikely. The
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SAR11 group simply may not have been very active in our samples, despite evidence that
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SAR11 bacteria can be relatively large and active off the North Carolina coast in April
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(Malmstrom et al., 2004). One other study, to the knowledge of the authors, has
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demonstrated low activity in SAR11 bacteria. In the Arctic, approximately 2% - 50% of
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SAR11 bacteria showed uptake of glucose and amino acids using micro-FISH, and even
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fewer were actively taking up ATP; other groups such as Roseobacter,
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Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria had higher
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percentages of active bacteria (Alonso-Sáez et al., 2008). The difference in SAR11
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representation between DNA and RNA surface water clone libraries does not cause the
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enhanced DNA and RNA division in the surface compared to the mid-depth and bottom
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libraries, as shown by FastUniFrac analysis excluding SAR11 (results not shown).
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Linkage between community composition and enzymatic activity.
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Comparing the potential of the microbial community to respond to addition of specific
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substrates with microbial community composition is a challenge for the experimental
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design of enzyme assays. Here we chose to assess the potential of living cells, gravity
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filtered onto different filter sizes, in time course experiments. After filtration, and
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incubation of the filter pieces in artificial seawater, initially only the activity of enzymes
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attached to cells (or detritus) on the filter is measured. Once hydrolytic enzymes are
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synthesized, they most likely remain active for several days or longer (Steen and Arnosti,
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2011); therefore, hydrolysis rates will, over the time course of an incubation, partially
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uncouple from the changing composition of the microbial community. Microbial
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community change during incubation time will depend on the average generation time of
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the community, and can modulate the spectrum of enzyme activities. The enzyme
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activities that dominate at any time point represent a time-integrated microbial
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community response over the length of the incubation. Conceptually, microbial
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community composition and potential hydrolysis rates are linked most directly at the start
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of an incubation, when the clone library composition reflects the “starter” bacterial
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community that had synthesized the enzymes whose integrated activity spectrum is
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assessed at the first time point after filtration (Fig. 1). In contrast, enzymes whose
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activities are detected later in the incubation likely reflect the development of enzymatic
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activity by enzyme production (Fig. 1, Fig. S2).
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The Shannon Index was used as previously described (Steen et al., 2010) to evaluate the
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evenness of the hydrolytic capabilities of a community, analyzed after 2 days incubation,
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as well as using the maximum rates that were observed over the timecourse of incubation
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(see Fig. S2). Using maximum hydrolysis rates, the evenness of hydrolysis rates for
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particle-associated and unfiltered water decreased (according to significant differences)
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in the following order: coastal, offshore mid-depth, surface, and bottom waters (Fig. S8).
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For the free-living community with maximum hydrolysis rates, the Shannon index was
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highest at the coastal station and did not vary with depth offshore. Similar results were
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obtained for analysis using the hydrolysis rates measured on day 2 (Fig. S8). The
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diversity/evenness of hydrolysis rates thus did not map directly to diversity of OTUs at
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the activity levels and phylogenetic levels we examined.
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The contrast between the community diversity and hydrolytic capability is particularly
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notable for the offshore bottom water communities. Though more diverse than the mid-
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depth communities (Fig. 2 and S4), the bottom communities hydrolyzed a narrower
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spectrum of substrates (Fig. 1), and evenness of hydrolysis rates were also generally
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lower, especially for the particle-associated community (Fig. S8). A similar disconnect is
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apparent in the comparison of community diversity and hydrolytic capability in coastal
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and offshore samples. The microbial community at the coastal station hydrolyzed all six
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fluorescently-labeled substrates at higher rates than at the offshore surface station, where
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fewer substrates were hydrolyzed (Fig. 1). These broad capabilities and higher rates of
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hydrolysis at the coast are not matched by greater bacterial 16S rRNA clone library
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diversity. Detailed understanding of the relationship between community composition
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and hydrolytic capabilities will likely require genomic and proteomic studies to identify
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the range of enzymes produced by specific phylogenetic groups (e.g., Wegner et al.
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2013), since extracellular enzymatic capabilities of bacteria are likely differentiated at
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fine-grained phylogenetic scales (Zimmerman et al. 2013).
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Rationale for Time Course Experiments of Extracellular Enzymatic Activities
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The clone libraries constructed using 16S rRNA genes were intended to assess the
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bacterial community that potentially participates in polysaccharide degradation. These
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bacteria may be more likely to hydrolyze a specific substrate if they have the necessary
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enzymatic tools. If the active community does not possess these tools, then an inactive
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but relatively abundant group that is capable of hydrolysis may be activated.
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Alternatively, a relatively rare group with hydrolytic capability could increase in
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abundance. Because of these different possibilities, maximum rates of hydrolysis most
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likely do not correspond to the activity of initially active groups represented in the RNA
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libraries. However, the time course of hydrolysis can give important clues about the
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extent to which individual metabolic and/or community composition restructuring must
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take place for hydrolysis to occur. For example, despite the great diversity across all
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RNA libraries, laminarin was hydrolyzed quickly in all samples, supporting the
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hypothesis that a wide range of marine bacteria can hydrolyze laminarin. Mixed
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community incubations more accurately portray the hydrolytic capabilities of natural
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communities than experiments with individual isolates. Given the time scale of
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incubation, the response of a microbial community to a substrate could include enzyme
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induction, cellular growth, and changes in community composition. However, it is
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important to remember that even if a community hydrolyzes substrate quickly, the
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fraction of the metabolically active community performing the hydrolysis is unknown.
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Time Courses of Hydrolysis
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Among substrates hydrolyzed by particle-associated and free-living microbial
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communities of both the coastal station and the offshore station surface site, two
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substrates had noticeably different patterns of hydrolysis with time: chondroitin and
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xylan (Fig. S2). These different patterns likely reflect differing time-scales of response by
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the microbial communities. A rapid response suggests either the widespread presence of a
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gene(s) for the appropriate enzyme(s) among diverse members of the community, and/or
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the presence of the gene(s) for the enzyme among abundant members of the community.
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A slow response (increasing hydrolysis rates with time) likely indicates an increased
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growth response by a rare group capable of hydrolyzing the substrate, induction of
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enzymes among such community members, and/or a shift in metabolism as low
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concentrations of natural substrates in the incubation are exhausted.
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Laminarin hydrolysis rates were always maximal at the first time point, fitting the pattern
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discussed above for rapid response. In contrast, chondroitin only reached its maximum
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hydrolysis rate by the first time point once, in the particle-associated coastal station
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sample. For all other samples, maximum chondroitin hydrolysis rates occurred after an
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initial time lag, a response consistent with enzyme induction or slow growth. An
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experiment involving pre-exposure of a microbial community to chondroitin in fact
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suggested that enzyme induction can occur for chondroitin on the time scale of hours to
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days (Arnosti, 2004). Pure culture experiments with several organisms have also shown
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inducibility of chondroitin- hydrolyzing enzymes (Lipeski et al., 1986; Shain et al.,
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1996).
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The pattern of xylan hydrolysis over time differed between the coastal and offshore
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locations more than that of any other substrate. Xylan hydrolysis was still increasing on
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day 13 in the particle-associated and free-living coastal incubations, while it was steady
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in the particle-associated and free-living offshore station surface samples (Fig. S2). The
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coastal pattern is consistent with hydrolysis performed by an initially small portion of the
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population that grows over the time course of the incubation. The time course of xylan
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hydrolysis also differed with depth more than that of other substrates. Xylan hydrolysis
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was delayed in the bottom offshore station samples compared with the hydrolysis by the
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mid-depth and surface samples (Fig. S2). This delay is consistent with either induction by
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the substrate or the growth of a hydrolyzing population that was initially rare.
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The time course of hydrolysis varied between the particle-associated and free-living
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fractions for some substrates, even though particle-associated and free-living
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communities nearly always hydrolyzed the same substrates. The most sensitive
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information regarding differences in bacterial composition and enzymatic activity may be
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found in the time course of the hydrolysis of these substrates. Fucoidan hydrolysis at the
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coastal station occurred quickly in the free-living sample, but began on day 8 and was
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still increasing by day 13 in the particle-associated sample. The opposite was true for
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arabinogalactan and chondroitin hydrolysis, both of which reached their maximum rates
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of hydrolysis earlier in the particle-associated coastal station sample than in the free-
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living sample. The offshore stations had fewer differences between particle-associated
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and free-living hydrolysis rate patterns than the coastal station; the most notable
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difference was the delayed chondroitin hydrolysis in the particle-associated compared to
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the free-living fraction in the bottom site offshore station sample.
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Toledo G, Palenik B, Brahamsha B. (1999). Swimming marine Synechococcus strains
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with widely different photosynthetic pigment ratios form a monophyletic group. Appl
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Weiner RM, Devine RA, Powell DM, Dagasan L, Moore RL. (1985). Hyphomonas
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oceanitis sp.nov., Hyphomonas hirschiana sp. nov., and Hyphomonas jannaschiana sp.
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nov. Int J Syst Bacteriol 35: 237–243.
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Yu Y, Li H, Zeng Y, Chen B. (2009). Extracellular enzymes of cold-adapted bacteria
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from Arctic sea ice, Canada Basin. Polar Biology 32: 1539–1547.
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Figure legends
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Figure S1. Sampling locations and water column profiles. a) Coastal and offshore
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station locations graphed using Ocean Data View (Schlitzer, 2002). b). CTD profiles.
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Line 1= temperature; Line 2 (bold) = salinity; Line 3 (grey) = oxygen concentration; and
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Line 4 (thin) = beam transmission. Horizontal dotted lines indicate the surface, mid-
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depth, and bottom sampling depths.
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Figure S2. Time course of hydrolysis of six different substrates by coastal and offshore
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communities. Error bars show deviation between two replicates. PA = Particle-
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associated; FL = Free-living.
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Figure S3. Distribution heat map of OTUs among all 16S rRNA and rRNA gene
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clone libraries. First letter and number of clone names indicate the tree
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(g=Gammaproteobacteria, a = Alphaproteobacteria, o = Other, b = Bacteroidetes) and
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position in tree. For example, clone g16Ys0Os112 is found in the Gammaproteobacteria
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tree. It is the 16th clone from the top, and it is found in the tree as g16Ys0Os112. ALL
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numbers represent percentage of each library the OTU composes. First bar = 73 seqs. PA
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= Particle-associated library; FL = Free-living library; D = DNA library; R = RNA
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library. OTU definition = 0.03. (DWH Oceanospirillales indicates the clone that showed
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99.6% nucleotide similarity to a prominent Oceanospirillales clone in the Deepwater
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Horizon subsurface hydrocarbon plume (Hazen et al., 2010).
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Figure S4. Rarefaction curves for all clone libraries. FL = Free-living; PA = Particle-
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associated. OTU definition = 0.03.
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Figure S5. Phylogenetic trees based on near-complete 16S rDNA and rRNA sequences,
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and calculated by empirically optimized distances following the General Time Reversible
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plus Invariant sites plus Gamma (GTR+I+G) distribution model. Bootstrap support was
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obtained by 200 replicates using the same model. The trees show the relationships
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between all clones in all sixteen 16S rRNA and rDNA clone libraries, separated into the
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following groups: a) Alphaproteobacteria, b) Gammaproteobacteria, c) Bacteroidetes, d)
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Delta-, Epsilon- and Betaproteobacteria, e) Other bacterial phyla. Asterisks* indicate
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clones that represent multiple similar sequences; numbers of sequences are given in
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parentheses.
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Figure S6. Cell counts and hydrolysis rates. Hydrolysis rates in whole water (same
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data as in Fig. 1a), plotted along with cell counts in whole water.
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Figure S7. Cluster diagram (unweighted) of all 16S rDNA and rRNA clone libraries,
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constructed with fast UniFrac using the unweighted option, which does not take into
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account OTU abundances. The scale bar shows the distance between clusters in UniFrac
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units: a distance of 0 means that two samples are identical, and a distance of 0.5 means
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that two samples contain mutually exclusive lineages. Particle-associated libraries are
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bolded. The numbers show the support for each node as determined by jackknife
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analysis. PA = Particle-associated; FL = Free-living.
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Figure S8. Shannon evenness. “Max” indicates that the maximum rates of hydrolysis
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for each substrate / incubation were used in the analysis, regardless of when the
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maximum occurred. Sample point of the maximum rate can be seen in Fig. S2. “Day 2”
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indicates that the hydrolysis rate for each substrate and incubation from day 2 was used in
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the analysis.
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