Hydrogen isotope fractionation in lipid biosynthesis by the piezophilic bacterium Moritella japonica DSK1

The delta D of fatty acids is emerging as an important marine biogeochemical proxy, but the microbiological and environmental factors controlling the variations of delta D of the lipids are not fully constrained. We report here the first measurement of D/H ratios of fatty acids in a piezophilic bacterium and show that hydrostatic pressure and the lipid biosynthetic pathway probably exerts dominant control over the delta D of fatty acids. Piezophilic bacterium Moritella japonica DSK1 was grown at a pressure of 30 MPa with glucose as substrate. Fatty acids in DSK1 showed vastly varied delta D, ranging from + 44.4 to - 171 parts per thousand. Short-chain fatty acids (SCFA), which are synthesized by the fatty acid synthase (FAS) pathway, had positive delta D (average + 3 parts per thousand), whereas long-chain polyunsaturated fatty acid (LC-PUFA) synthesized via the polyketide pathway exhibited much depleted delta D (- 171 parts per thousand). Our results suggest that the lipid biosynthetic pathways can exert first-order control on the hydrogen isotope signature of bacterial membrane lipids under elevated pressure. Our findings have important implications in marine biogeochemistry. D-depleted fatty acids in marine sediments and in the water column may be derived from piezophilic bacterial reworking and resynthesis of organic matter at high pressure condition. Thus, caution must be exercised in the interpretation of hydrogen isotope signatures of lipids in, e.g., deducing sources of organic matter and tracing microbial biogeochemical processes in the deep ocean and the deep biosphere. (C) 2014 Elsevier B.V. All rights reserved.