We've Moved!
Visit SDSU’s new digital collections website at https://digitalcollections.sdsu.edu
Description
Methylotrophic bacteria are defined by their ability to use reduced single carbon (C1)- compounds such as methanol, methane, or methylamine as their sole carbon and energy source. While methylotrophs evolve different metabolic routes for the primary C1-substrate oxidation, most reactions lead to the formation of formaldehyde, a highly toxic intermediate. Several cellular mechanisms have been identified for sensing, detoxification, oxidation and assimilation of formaldehyde amongst the Methylotrophs. One of them is the formaldehyde activating enzyme (Fae), which enhances the condensation of formaldehyde with tetrahydromethanopterin (H4MPT) for further oxidation. Many methylotrophs have several Fae-homologues. This study focuses on the role of additional fae-homologues in methylotrophy. The metabolic capabilities of Methylotenera species were explored using published physiological, genomic, and gene expression data. Like many methylotrophs, Methylotenera species possess several homologues of Fae. One of them (fae3) clusters with the Nmethylglutamate (NMG) pathway genes. The reactions of the NMG pathway produce methylene-tetrahydrofolate instead of formaldehyde. Expression of fae3 strongly correlates with the expression of the pathway. A phylogenetic tree of 78 Fae and Fae-like proteins from different bacteria and archaea was constructed (MEGAX). Five groups were named. Canonical Fae (Group 1), is best studied in Methylorubrum extorquens AM1 and is associated with function in the H4MPT pathway. Group 2 and 3 represent Fae 2 and Fae 3 of unknown function from different bacterial phyla. Group 4 consists of Fae from gram positive bacteria. Group 5 represents only archaeal homologues of Fae. The roles of three fae-homologues (fae, fae1-2 and fae3) from Methylotuvimicrobium alcaliphilum 20ZR were investigated via complementation tests and mutagenesis. Complementation with plasmids expressing 20ZRfae and 20ZRfae1-2 genes restored the AM1Δfae-mutant growth on solid media. While 20ZRfae also rescued the growth of the AM1Δfae cells in liquid culture, the 20ZRfae1-2 failed to complement. 20ZR fae3 did not improve AM1Δfae tolerance to methanol. Mutants of M. alcaliphilum 20ZR, lacking fae1-2, and fae3 do not display any significant defects in methane or methanol-dependent growth at both regular and copper limited conditions. Expression data for M. alcaliphilum 20ZR show that fae and fae3 genes are constitutively expressed. The expression of fae1-2 correlates with copper limitation.
