Comparative Analysis of Carbon Monoxide Tolerance among Thermoanaerobacter Species

Abstract

An anaerobic thermophilic strain (strain PCO) was isolated from a syngas-converting enrichment culture. Syngas components cannot be used by strain PCO, but the new strain is very tolerant to carbon monoxide (pCO = 1.7 × 105 Pa, 100% CO). 16S rRNA gene analysis and DNA-DNA hybridization revealed that strain PCO is a strain of Thermoanaerobacter thermohydrosulfuricus. The physiology of strain PCO and other Thermoanaerobacter species was compared, focusing on their tolerance to carbon monoxide. T. thermohydrosulfuricus, T. brockii subsp. finnii, T. pseudethanolicus, and T. wiegelii were exposed to increased CO concentrations in the headspace, while growth, glucose consumption and product formation were monitored. Remarkably, glucose conversion rates by Thermoanaerobacter species were not affected by CO. All the tested strains fermented glucose to mainly lactate, ethanol, acetate, and hydrogen, but final product concentrations differed. In the presence of CO, ethanol production was generally less affected, but H2 production decreased with increasing CO partial pressure. This study highlights the CO resistance of Thermoanaerobacter species.

Co‐cultivation of Thermoanaerobacter strains with a methanogenic partner enhances glycerol conversion

“…and hydrogenotrophic methanogens (mainly Methanothermobacter thermautotrophicus ) were the dominant microorganisms in the community developed in a continuous bioreactor operated with glycerol at 70°C. However, as previously mentioned, Alves et al () reported that glycerol was only poorly utilized by T. brockii subsp. finnii .…”

“…Within the Thermoanaerobacter genus, only T. wiegelii , T. siderophilus , T. brockii subsp. finnii and T. subterraneus were reported to grow with glycerol (Cook et al , ; Slobodkin et al , ; Fardeau et al , ; Alves et al , ), although growth of T. brockii subsp. finnii was described as poor (Alves et al , ).…”

“…finnii and T. subterraneus were reported to grow with glycerol (Cook et al , ; Slobodkin et al , ; Fardeau et al , ; Alves et al , ), although growth of T. brockii subsp. finnii was described as poor (Alves et al , ). Therefore, to further assess the possible positive effect of methanogens on glycerol fermentation, T. brockii subsp.…”

“…). The main bacterial genera identified were probably involved in glycerol conversion, since some of the characterized strains within the genera Pseudothermotoga , Acetomicrobium and Thermoanaerobacter have been reported as glycerol degraders (Rees et al , ; Menes and Muxí, ; Maru et al , ; Alves et al , ) . Acetate and methane were the main products of glycerol conversion, indicating that methane was produced from formate or H 2 /CO 2 (Fig.…”

“…Enrichments (coded Gly(x), where 9 represents the number of transfers) were started by inoculating 120 ml serum bottles, containing 50 ml BM, with 10% (v/v) of the sludge. Glycerol was added from a sterile stock solution to a final concentration of 10 mM, based on the works of Fardeau et al (2000) and Alves et al (2016). Successive transfers of the cultures to new medium (10% v/v) and serial dilutions were made after confirming microbial growth and activity, based on microscopic observations and methane measurements (more than 30% of the theoretical value expected).…”