Growth of Dehalococcoides mccartyi species in an autotrophic consortium producing limited acetate

Abstract

The dechlorinating Dehalococcoides mccartyi species requires acetate as carbon source, but little is known on its growth under acetate limiting conditions. In this study, we observed growth and dechlorination of a D. mccartyi-containing mixed consortium in a fixed-carbon-free medium with trichloroethene in the aqueous phase and H/CO in the headspace. Around 4 mM formate was produced by day 40, while acetate was constantly below 0.05 mM. Microbial community analysis of the consortium revealed dominance by D. mccartyi and Desulfovibrio sp. (57 and 22% 16S rRNA gene copies, respectively). From this consortium, Desulfovibrio sp. strain F1 was isolated and found to produce formate and acetate (1.2 mM and 48 µM, respectively, by day 24) when cultivated alone in the above mentioned medium without trichloroethene. An established co-culture of strain F1 and D. mccartyi strain 195 demonstrated that strain 195 could grow and dechlorinate using acetate produced by strain F1; and that acetate was constantly below 25 µM in the co-culture. To verify that such low level of acetate is utilizable by D. mccartyi, we cultivated strain 195 alone under acetate-limiting conditions and found that strain 195 consumed acetate to below detection (5 µM). Based on the acetate consumption and cell yield of D. mccartyi, we estimated that on average 1.2 × 10 acetate molecules are needed to supply carbon for one D. mccartyi cell. Our study suggests that Desulfovibrio may supply a steady but low amount of fixed carbon to dechlorinating bacteria, exhibiting important implications for natural bio-attenuation when fixed carbon is limited.

The reductive glycine pathway allows autotrophic growth of Desulfovibrio desulfuricans

“…Acetate excretion was observed previously also in an autotrophic co-culture of D. desulfuricans strain F1 with the non-autotrophic dechlorinating bacterium Dehalococcoides mccartyi. The CO 2 assimilation pathway in Desulfovibrio strain F1 was not investigated, but it produced formate and acetate when grown autotrophically 8 , suggesting that it may use the same pathway as described here for D. desulfuricans strain G11. Further research is needed to shed light on the metabolic and ecologic significance of acetate secretion.…”

“…The lack of genes for known pathways for CO 2 fixation is also observed in other Desulfovibrio members (Supplementary Data 3 ). Indeed, most Desulfovibrio members do not grow autotrophically with hydrogen, with a few exceptions mentioned above 8 – 10 . The observed autotrophic growth of D. desulfuricans indicates the presence of an unknown CO 2 fixation pathway in this microorganism.…”

“…on formate and hydrogen was thought to be dependent on the presence of an organic carbon source (e.g., acetate) [2][3][4][5][6][7] . However, D. desulfuricans strain F1 8 and the Desulfovibrio strains HRM1 and P23 9,10 were reported to grow autotrophically, though insight into the CO 2 fixation pathway was not obtained.…”

Alleviating Chlorinated Alkane Inhibition on Dehalococcoides to Achieve Detoxification of Chlorinated Aliphatic Cocontaminants

“…Beyond microbial reductive dechlorination, a variety of biological processes (e.g., acidogenesis, hydrogenesis, and methanogens) usually occur synchronously in dechlorinating consortia and at pollution sites, which can affect the rate of microbial reductive dechlorination. ,, The comprehensive analyses conducted in this study revealed that fermentation of organics to acetate and hydrogen can naturally tolerate cocontaminant inhibition. This resilience may arise from the apparent functional redundancy of putative fermenters, thereby contributing to the maintenance of fermentation activity under cocontaminant stress .…”

“…Hydrogen was measured using a GC instrument (7890A; Agilent) equipped with a thermal conductivity detector and a Varian PLT-5A column (30 m × 0.530 mm × 0.25 μm; Omega Scientific, Singapore). Short-chain volatile fatty acids were measured on an HPLC system (Agilent 1260) equipped with a UV detector (210 nm) and a Rezex ROA-Organic Acid H + (8%) HPLC column (30 cm × 7.8 mm × 8 μm; Phenomenex, Singapore) …”