Adaptation during propagation improves Clostridium autoethanogenum tolerance towards benzene, toluene and xylenes during gas fermentation

Benzene, toluene and xylenes (BTX) are a group of compounds detected in many crude syngas mixtures. However, BTX have been identified to negatively affect microorganisms, including acetogenic species that are capable of fermenting syngas into valuable biocommodities. In order to overcome BTX inhibitory effects, we describe stepwise adaptation in Clostridium autoethanogenum that leads to tolerance to up to 0.5 mM benzene, 0.21 mM toluene and 0.07 mM xylenes. This is equivalent to eightfold of that which is found in a wood gasification plant syngas stream. Fully adapted cultures matched growth, acetate and ethanol product concentrations, and CO consumption compared to the control. The results demonstrate an efficient route towards producing a highly tolerant, industrially relevant acetogenic strain.