Supplementary text S1
Alternate pathways to account for reduced abundance of methanogenic archaea in MI
Sulfate-reducing bacteria.
Sulfate reducing bacteria (SRB) in the mammalian gut include the genera Desulfovibrio,
Desulfobacter, Desulfobulbus and Desulfotomaculum (MacFarlane and Gibson, 1997).
The predominant H2-utilizing SRB in the human colon belong to the genus Desulfovibrio
(70-90% of the total SRB counts). However, previous attempts to cultivate these bacteria
from the gut of marine iguanas on Postgate’s medium B (1984) containing lactate as
carbon source were unsuccessful. In order to verify the presence of SRB in the gut
population in the iguana colon, we have used a PCR approach that targets the APS
reductase (apsA) gene which is a useful phylogenetic marker for sulfate reducing bacteria
(Friedrich, 2002).
DNA was extracted from marine iguana (n=4) and land iguana (n=5) samples.
PCR amplification of apsA gene fragment was carried out using primers APS-FW and
APS-RV that amplify a ~390bp fragment, and APS7-F and APS8-R that amplify a
~900bp fragment of the -subunit of the APS reductase gene (Friedrich, 2002):
 APS-FW (5’-TGG CAG ATM ATG ATY MAC GG-3’)
 APS-RV (5’-GGG CCG TAA CCG TCC TTG AA-3’)
 APS7-F (5’-GGG YCT KTC CGC YAT CAA YAC-3’)
 APS8-R (5’-GCA CAT GTC GAG GAA GTC TTC-3’)
PCR products were cloned into the pGEM-T Easy vector and sequenced. Analysis
of the BLAST reports of the sequenced clones from the APS-FW/RW library (~390bp)
and APS-7F/8R library (~900bp) are summarized in Table S1A. All sequences recovered
thus far are associated with classical gram-negative, lactate-utilizing sulfate reducing
bacteria. Although Desulfomonas pigra and Desulfovibrio desulfuricans differ in
phenotypic traits (shape and motility), recent molecular analysis suggests that D. pigra
should be reclassified within the genus Desulfovibrio (Loubinoux et al., 2002).
Desulfovibrio termitidis is a carbohydrate-degrading, sulfate reducing bacterium isolated
from the hindgut of termites (Trinkerl et al., 1990). This species utilizes a wide variety of
carbohydrates in contrast to other Desulfovibrio species.
Table S1A. Summary of BLAST analysis for PCR amplification of apsA gene fragments
from marine and land iguanas. Values are reported as percentage amino acid sequence
identity (number of clones in parenthesis).
Species
Desulfovibrio termitidis
Desulfovibrio vulgaris
Desulfovibrio desulfuricans
Desulfomonas pigra
PCR product obtained from:
Marine iguana
Land iguana
~ 390 bp
~ 900 bp
~ 390 bp
~ 900 bp
93-95% (12)
94-95% (4)
95-96% (12)
68% (1)
86% (1)
91% (1)
91% (1)
1
Supplementary text S1
Alternate pathways to account for reduced abundance of methanogenic archaea in MI
Acetogen
We also aimed to provide a preliminary identification of bacterial targets producing
acetate (i.e., acetogens) in the iguana feces. Past studies had demonstrated that the
formyltetrahydrofolate synthetase (fthfs) gene encodes a key enzyme in reductive
acetogenesis, and can be used as a functional representation for acetogens. Therefore,
genomic DNA from an individual land and marine iguana was PCR amplified with
primer pairs (Leaphart and Lovell, 2001):
 FTHFS-F (5-TTY ACW GGH GAY TTC CAT GC-3), and
 FTHFS-R (5-GTA TTG DGT YTT RGC CAT ACA-3)
After amplification, PCR products were purified and cloned into competent E. coli
JM109 by using the pGEM-T Easy vector system, and plasmids were sequenced.
Table S1B revealed that the production of acetate is in part due to the presence of
acetogens related to phylum Firmicutes and a group of uncultured bacterium that are
present in the land and marine iguana feces.
Table S1B. Summary of BLAST results from FTHFS gene fragments (~1060 bp).
Values are reported as percentage amino acid sequence similarity (number of clones in
parenthesis).
PCR product obtained from:
Nearest matches
Marine iguana
Land iguana
Uncultured bacterium
62-68 % (3)
59-78 % (5)
Ruminococcus productus
51-69 % (4)
Clostridium thermaceticum
61 % (1)
References in this supplementary text
Friedrich MW. (2002). Phylogenetic analysis reveals multiple lateral transfers of
adenosine-5'-phosphosulfate reductase genes among sulfate-reducing
microorganisms. Journal of bacteriology 184: 278-289.
Leaphart AB, Lovell CR. (2001). Recovery and analysis of formyltetrahydrofolate
synthetase gene sequences from natural populations of acetogenic bacteria.
Applied and environmental microbiology 67: 1392-1395.
Loubinoux J, Valente FM, Pereira IA, Costa A, Grimont PA, Le Faou AE. (2002).
Reclassification of the only species of the genus Desulfomonas, Desulfomonas
pigra, as Desulfovibrio piger comb. nov. International journal of systematic and
evolutionary microbiology 52: 1305-1308.
MacFarlane GT, Gibson GR. (1997). Carbohydrate fermentation, energy transduction and
gas metabolism in the human large intestine. In: Mackie RI, White BA (ed.).
Gastrointestinal Microbiology. Chapman & Hall: New York, pp 269-318.
Trinkerl M, Breunig A, Schauder R, König H. (1990). Desulfovibrio termitidis sp. nov., a
carbohydrate-degrading sulfate-reducing bacterium from the hindgut of a termite.
Systematic and Applied Microbiology 13: 372-377.
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