Growth Characteristics ofMethanomassiliicoccus luminyensisand Expression of Methyltransferase Encoding Genes

Abstract

DNA sequence analysis of the human gut revealed the presence a seventh order of methanogens referred to as Methanomassiliicoccales.Methanomassiliicoccus luminyensisis the only member of this order that grows in pure culture. Here, we show that the organism has a doubling time of 1.8 d with methanol + H2and a growth yield of 2.4 g dry weight/mol CH4.M. luminyensisalso uses methylamines + H2(monomethylamine, dimethylamine, and trimethylamine) with doubling times of 2.1–2.3 d. Similar cell yields were obtained with equimolar concentrations of methanol and methylamines with respect to their methyl group contents. The transcript levels of genes encoding proteins involved in substrate utilization indicated increased amounts of mRNA from themtaBC2gene cluster in methanol-grown cells. When methylamines were used as substrates, mRNA of themtb/mttoperon and of themtmBC1cluster were found in high abundance. The transcript level ofmtaC2was almost identical in methanol- and methylamine-grown cells, indicating that genes for methanol utilization were constitutively expressed in high amounts. The same observation was made with resting cells where methanol always yielded the highest CH4production rate independently from the growth substrate. Hence,M. luminyensisis adapted to habitats that provide methanol + H2as substrates.