Microbial piezophysiology: which role fo r high pressure in oil
degradation?
Scoma A lb e rto 1, Ramiro Vilchez-Vargas1, Marta Barbato2, Francesca M apelli2, Sara Borin2,
Daniele D affonchio2 and Nico Boon'
1 Laboratory o f M icrobial Ecology and T echnology (LabMET), Ghent U niversity
Coupure Links 653, B-9000, Gent, Belgium
E-mail: nico.boon@ uqent.be
2 D epartm ent o f Food, Environm ental and N utrition a l Sciences (DeFENS), U niversity o f Milan
via Celoria 2, 20133, Milano, Italy
Most o f the scientific research carried o ut so fa r in m icro biolo gy and biotechnology is focused on
the understanding o f biological kinetics at am bient pressure. This cond itio n may characterize the
large m a jo rity o f m icrobes on d ry land, w hile it does not apply to those living in the sea. Oceans are
populated by a large variety o f m icroorganism s th a t are able to survive in e xtre m ely harsh
co nditions (Kato e t a i, 1998). Here, m etabolic pathways are typ ically affected by high pressure (as
well as by low tem peratures) in a manner th a t is not com p le te ly clear. When oil spills occur, a
relevant am ount o f hydrocarbons (HCs) is released into the environm ent (A dcroft ex a!., 2010). In
the case o f marine accidents, such com pounds w ill spread horizontally, eventually reaching the
closest shores, and vertically, dro pp ing downwards to the sea flo or. Here, although HCs are present
in nature, marine ecosystems may be able to degrade only a very m inor fraction o f such spills.
Typically, one o f the main reasons fo r HCs low b io de gra da bility is th e ir low s o lu b ility in water,
preventing an e fficie n t m icrobial uptake. It is known th a t high pressure increases oil s o lu b ility in
w ater (Srivastan ex a!., 1992), while also su pp orting an increase in the flu id ity o f cells’ membrane
(Bartlett, 2000), both easing m icrobial access to HCs. M icroorganism s responsible fo r
biorem ediation are known to produce surfactants, which fu rth e r enhance oil solubility, a co ndition
known to feature the best degraders (Yakim ov ex a!., 1998). However, these factors are not
su fficien t to allow fu ll rem ediation, and the m a jo rity o f the spilled HCs persist fo r decades (Reddy ex
a i, 2002). In ord er to gain fu rth e r insights on the role o f hydrostatic pressure on the catabolic
pathways trigg ered during HCs degradation, we tested fo u r d iffe re n t HCs degraders (belonging to
the genera A lca nivo ra x and Marinobacxer, three o f which are new isolates fro m surface w ater and
sedim ent) at three d iffe re n t pressures (1, 55 and 105bars, correspondent to about 0, 550 and
1050m seawater-depth), using dodecane (Cl 2) as a m odel HC. Evaluation o f cells grow th (as optical
density) was coupled to a num ber o f biochem ical analyses, such as oxygen respiration, carbon
dioxide production, h ydro p h o b icity te st (in directly expressing the degree o f access to HCs) and
phospholipid fa tty acids (PLFA) analysis. Further, tra n scrip to m ic analyses have been conducted to
check the expression o f the alkane monooxygenase gene (alkB) and the cytochrom e P450 (CYP153),
the m ost known genes responsible fo r HC degradation, and to unravel which o th e r genes are
triggered by high pressure in such conditions and are pote ntia lly involved in the degradation o f
HCs.
References
A d cro ft A., R. Hallberg, J.P. Dunne, B.L. Samuels, J.A. Galt, C.H. Barker and D. Payton. 2010.
Sim ulations o f underw ater plumes o f dissolved oil in the G ulf o f Mexico. Geophysical Research
Letters 37(1 8): 1-10.
Bartlett D. 2000. M icrobial adaptation to the psychrosphere/piezosphere. In: M olecular Marine
M icrobiology. Douglas H.B. (Ed.). W ym ondham, N orfolk, England, UK: H orizon Scientific Press,
p. 1 85-202.
Kato C., L. Li, Y. Nogi, Y. Nakamura., J. Tamaoka. and K. H orikoshi. 1 998. Extrem ely Barophilic
Bacteria Isolated fro m the Mariana Trench, C hallenger Deep, at a Depth o f 11,000 Meters.
Applied Environm ental M icrobiology 64(4):1 510-1513.
Reddy C .M., T.l. Eglinton, A. Hounshell., H.K. White, L. Xu., R.B. Gaines, G.S. Frysinger. 2002. The
West Falmouth oil spill a fte r th irty years: The persistence o f petroleum hydrocarbons in marsh
sediments. Environm ental Science & T echnology 36(22):4754-4760.
Srivastan S., N.A. Darwish, K.A. Gasem and R.L. Robinson Jr. 1 992. S o lub ility o f methane in hexane,
decane, and dodecane at tem peratures from 311 to 423 K and pressures to 10.4 MPa. Journal
o f Chemical and Engineering Data 37(4):516-520.
Yakim ov M.M., P.N. Golyshin, S. Lang, E.R.B. Moore, W.R. Abraham , H. Lunsdorf and K.N. Tim m is.
1998. A lca nivo ra x b orkum en sis gen. now, sp. nov., a new, hydrocarbon-degrading and
surfactant-producing marine bacterium . International Journal o f Systematic Bacteriology
48:339-348.
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