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.
Highlights
Thermophiles thrive at austere and unusual conditions and their evolutionary significance and biotechnological potential have triggered microbiological research over the last decades (Turner et al, 2007; Wagner and Wiegel, 2008; Yoneda et al, 2015)
Strain PCO was isolated from the thermophilic syngasconverting enrichment described by Alves et al (2013)
Strain PCO has a G+C content of the DNA of 34.5 mol % and shares 98% identity with the 16S rRNA gene of Thermoanaerobacter thermohydrosulfuricus
Summary
Thermophiles thrive at austere and unusual conditions and their evolutionary significance and biotechnological potential have triggered microbiological research over the last decades (Turner et al, 2007; Wagner and Wiegel, 2008; Yoneda et al, 2015). Thermophilic bacteria of the class Clostridia, such as members of the genera Clostridium, Thermoanaerobacter, Thermoanaerobacterium, and Caldicellulosiruptor, are currently used as biocatalysts for the production of biofuels or other chemicals of interest (Hemme et al, 2010; Carere et al, 2012). Members of the Thermoanaerobacter genus are utilized to produce ethanol and hydrogen (H2) from a variety of saccharides (Jessen and Orlygsson, 2012). An organism from Thermoanaerobacter genus—T. ethanolicus—is one of the most well-studied ethanol-producing bacteria (Wiegel and Ljungdahl, 1981; Lacis and Lawford, 1991). A less common substrate, carbon monoxide (CO), is used by T. thermohydrosulfuricus subsp. Carboxydovorans can grow with CO as sole electron donor (25% in the headspace), producing H2 and CO2 (Balk et al, 2009). T. thermohydrosulfuricus shares 99% similarity of the 16S rRNA gene sequence and over 70%
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