Reduced TCA cycle rates at high hydrostatic pressure hinder hydrocarbon degradation and obligate oil degraders in natural, deep-sea microbial communities

Petroleum hydrocarbons reach the deep-sea following natural and anthropogenic factors. The process by which they enter deep-sea microbial food webs and impact the biogeochemical cycling of carbon and other elements is unclear. Hydrostatic pressure (HP) is a distinctive parameter of the deep sea, although rarely investigated. Whether HP alone affects the assembly and activity of oil-degrading communities remains to be resolved. Here we have demonstrated that hydrocarbon degradation in deep-sea microbial communities is lower at native HP (10 MPa, about 1000 m below sea surface level) than at ambient pressure. In long-term enrichments, increased HP selectively inhibited obligate hydrocarbon-degraders and downregulated the expression of beta-oxidation-related proteins (i.e., the main hydrocarbon-degradation pathway) resulting in low cell growth and CO2 production. Short-term experiments with HP-adapted synthetic communities confirmed this data, revealing a HP-dependent accumulation of citrate and dihydroxyacetone. Citrate accumulation suggests rates of aerobic oxidation of fatty acids in the TCA cycle were reduced. Dihydroxyacetone is connected to citrate through glycerol metabolism and glycolysis, both upregulated with increased HP. High degradation rates by obligate hydrocarbon-degraders may thus be unfavourable at increased HP, explaining their selective suppression. Through lab-scale cultivation, the present study is the first to highlight a link between impaired cell metabolism and microbial community assembly in hydrocarbon degradation at high HP. Overall, this data indicate that hydrocarbons fate differs substantially in surface waters as compared to deep-sea environments, with in situ low temperature and limited nutrients availability expected to further prolong hydrocarbons persistence at deep sea

Effects of high pressure on inactivation kinetics and events related to proton efflux in Lactobacillus plantarum

Knowledge of the mechanism of pressure-induced inactivation of microorganisms could be helpful in defining an effective, relatively mild pressure treatment as a means of decontamination, especially in combination with other physical treatments or antimicrobial agents. We have studied the effect of high pressure on Lactobacillus plantarum grown at pH 5.0 and 7.0. The classical inactivation kinetics were compared with a number of events related to the acid-base physiology of the cell, i.e., activity of F0F1 ATPase, intracellular pH, acid efflux, and intracellular ATP pool, Cells grown at pH 5.0 were more resistant to pressures of 250 MPa than were cells grown at pH 7.0. This difference in resistance may be explained by a higher F0F1 ATPase activity, better ability to maintain a Delta pH, or a higher acid efflux of the cells grown at pH 5,0, After pressure treatment at 250 MPa, the F0F1 ATPase activity was decreased, the ability to maintain a Delta pH was reduced, and the acid efflux was impaired. The ATP pool increased initially after mild pressure treatment and finally decreased after prolonged treatment, The observations on acid efflux and the ATP pool suggest that the glycolysis is affected by high pressure later than is the F0F1 ATPase activity. Although functions related to the membrane-bound ATPase activity were impaired, no morphological changes of the membrane could be observed