Inhibition of sulfate-reducing bacteria with formate

Abstract

Despite hostile environmental conditions, microbial communities have been found in µL-sized water droplets enclosed in heavy oil of the Pitch Lake, Trinidad. Some droplets showed high sulfate concentrations and surprisingly low relative abundances of sulfate-reducing bacteria in a previous study. Hence, we investigated here whether sulfate reduction might be inhibited naturally. Ion chromatography revealed very high formate concentrations around 2.37 mM in 21 out of 43 examined droplets. Since these concentrations were unexpectedly high, we performed growth experiments with the three sulfate-reducing type strains Desulfovibrio vulgaris, Desulfobacter curvatus, and Desulfococcus multivorans, and tested the effects of 2.5, 8 or 10 mM formate on sulfate reduction. Experiments demonstrated that 8 or 10 mM formate slowed down the growth rate of D. vulgaris and D. curvatus and the sulfate reduction rate of D. curvatus and D. multivorans. Concerning D. multivorans, increasing formate concentrations delayed the onsets of growth and sulfate reduction, which were even inhibited completely while formate was added constantly. Contrary to previous studies, D. multivorans was the only organism capable of formate consumption. Our study suggests that formate accumulates in the natural environment of the water droplets dispersed in oil and that such levels are very likely inhibiting sulfate-reducing microorganisms.

Imprints of ecological processes in the taxonomic core community: an analysis of naturally replicated microbial communities enclosed in oil

“…In most reservoirs, however, oil is the continuous fluid phase filling the pore volume with discontinuous water filling only a smaller portion of the interstitial pores (Head et al 2003 ). Moreover, Voskuhl et al ( 2021 , 2022 ) revealed strong variability in community composition as well as in ion composition in the water droplets, which by itself provides further evidence for considerable limitation of dispersal as well as diffusion. Together, this indicates that dispersal has had little influence on microbial community composition in the water droplets.…”

Assessing anaerobic microbial degradation rates of crude light oil with reverse stable isotope labelling and community analysis

“…Following the incubation of oil, heavy oil, or water from oil reservoirs, fermenters frequently emerge as the most prevalent microorganisms (Mbadinga et al, 2011;Zhou et al, 2019b;Pannekens et al, 2021). In most studies on oil reservoir microbiology, sulfate reduction was observed to take a subordinate role due to rapid depletion of sulfate (Jones et al, 2008) or potential inhibition of the sulfate-reducing bacteria (Voskuhl et al, 2022). Typically when sulfate concentrations exceed 50 μM, sulfate reduction becomes the prevailing degradation process (Jimenez et al, 2016).…”

A Hitchhiker’s Guide to Supplying Enzymatic Reducing Power into Synthetic Cells

“…While formate in high concentrations can be toxic to some living organisms, , it represents a harmless and highly soluble C 1 compound to readily provide reducing power to artificial cells designed in a bottom-up fashion. Since it does not require a membrane transporter to cross phospholipid bilayers in the millisecond time scale, formate provides the advantage of requiring exclusively a NAD­(P) + -dependent formate dehydrogenase (FDH) to reduce the nicotinamide cofactor, while CO 2 is formed as a reaction product.…”