Homoacetogenesis and microbial community composition are shaped by pH and total sulfide concentration

Abstract

Biological CO 2 sequestration through acetogenesis with H 2 as electron donor is a promising technology to reduce greenhouse gas emissions. Today, a major issue is the presence of impurities such as hydrogen sulfide (H 2 S) in CO 2 containing gases, as they are known to inhibit acetogenesis in CO 2 -based fermentations. However, exact values of toxicity and inhibition are not well-defined. To tackle this uncertainty, a series of toxicity experiments were conducted, with a mixed homoacetogenic culture, total dissolved sulfide concentrations ([TDS]) varied between 0 and 5 mM and pH between 5 and 7. The extent of inhibition was evaluated based on acetate production rates and microbial growth. Maximum acetate production rates of 0.12, 0.09 and 0.04 mM h -1 were achieved in the controls without sulfide at pH 7, pH 6 and pH 5. The half-maximal inhibitory concentration (IC 50 qAc ) was 0.86, 1.16 and 1.36 mM [TDS] for pH 7, pH 6 and pH 5. At [TDS] above 3.33 mM, acetate production and microbial growth were completely inhibited at all pHs. 16S rRNA gene amplicon sequencing revealed major community composition transitions that could be attributed to both pH and [TDS]. Based on the observed toxicity levels, treatment approaches for incoming industrial CO 2 streams can be determined.

Estimating microbial growth and hydrogen consumption in hydrogen storage in porous media

“…Exposure to hydrogen sulfide, H2S, and its bisulfide ion, HS -, causes damage to microbial proteins and coenzymes [89,162]. It remains unclear whether H2S or HSis responsible for the toxicity effect but there is general consensus that H2S can penetrate the microbial cell membrane more easily than HS - [162]. Hydrogen sulfide dissociates with a pK1 of 6.99 at 10…”

“…without however stopping all metabolic activity [164]. For methanogens and homoacetogens 3.8-7.5 mM H2S and total sulfide concentrations of 3.3 mM, respectively, stop the growth [162,166]. In systems with circumneutral pH and ferric ion concentrations above 1 mM, the concentrations of H2S are predicted to be kept below toxic levels due to its precipitation in makinawite [44].…”

¬Estimating Microbial Hydrogen Consumption in Hydrogen Storage in Porous Media as a Basis for Site Selection

“…Exposure to hydrogen sulfide, H2S, and its bisulfide ion, HS -, causes damage to microbial proteins and coenzymes [91,158]. It remains unclear whether H2S or HSis responsible for the toxicity effect but there is general consensus that H2S can penetrate the microbial cell membrane more easily than HS - [158]. Hydrogen sulfide dissociates with a pK1 of 6.99 at 10…”

“…At 5.0-6.3 mM H2S growth is completely inhibited for SSRM [160,162], without however stopping all metabolic activity [160]. For methanogens and homoacetogens 3.8-7.5 mM H2S and total sulfide concentrations of 3.3 mM, respectively, stop the growth [158,162]. In systems with circumneutral pH and ferric ion concentrations above 1 mM, the concentrations of H2S are predicted to be kept below toxic levels due to its precipitation in makinawite [46].…”

Effect of Humin and Chemical Factors on CO2-Fixing Acetogenesis and Methanogenesis

“…Under standard conditions, sulfate reduction is thermodynamically more favorable than methanogenesis and acetogenesis [ 21 , 22 ]. Furthermore, sulfide produced from sulfate reduction is toxic to acetogens and methanogens [ 23 , 24 ]. Salinity (sodium chloride (NaCl)) also affects the microbial CO 2 -fixing activities.…”