Unraveling the conversion of methoxylated compounds in Tepidanaerobacter acetatoxydans

Methoxylated aromatic compounds (MACs) are components of lignin and are therefore very abundant on Earth. However, their impact on the global carbon cycle is not well understood. To convert these compounds microorganisms use O-demethylase systems that comprise four different enzymes. So far, the O-demethylase systems of some bacteria and one archaeon [1] have been characterized. The anaerobic bacterium Tepidanaerobacter acetatoxydans is known to use different organic compounds as carbon and energy source such as organic acids, alcohols, sugars and amino acids as well as acetate in syntrophy with methanogens [2]. Although the conversion of MACs has not been previously observed, the organism harbors a genomic region with several genes encoding components of O-demethylase systems in its genome. Chemolithotrophic growth and acetogenesis have not yet been described for T. acetatoxydans, which encodes most of the acetogenic key enzymes, but lacks for formate dehydrogenase [3]. The question rises if the O-demethylase systems in T. acetatoxydans are functional and if the organism can produce acetate from MACs. To answer this we studied several O-demethylase systems from T. acetatoxydans in regard to their biochemical properties and phylogeny. Furthermore, we performed growth studies with T. acetatoxydans to investigate it"s still underexplored metabolic potential. We were able to show the growth of T. acetatoxydans on various MACs. Furthermore, we observed that one O-demethylase system from T. acetatoxydans converts next to the MACs syringate and vanillate also 2-MB and TMB, which is different to all yet characterized bacterial O-demethylase systems but similar to the archaeal one [1]. Different O-demethylases encoded by T. acetatoxydans seem to build a yet uncharacterized phylogenetic clade, which could indicate the use of different substrates. This work will lead to a better understanding of MAC conversion and the involved enzyme systems in T. acetatoxydans and resolve the acetogenic metabolism using MACs as carbon source.

[1] Kurth JM et al. (2021). ISME J. 15:3549–65.

[2] Westerholm M, Roos S, Schnürer A. (2011). Syst Appl Microbiol. 34:260–6.

[3] Müller B et al. (2015). PLoS ONE. 10:e0121237.