A novel operon encoding formaldehyde fixation: the ribulose monophosphate pathway in the gram-positive facultative methylotrophic bacterium Mycobacterium gastri MB19

A 4.2-kb PstI fragment harboring the gene cluster of the ribulose monophosp hate (RuMP) pathway for formaldehyde fixation was identified in the chromos ome of a gram-positive, facultative methylotroph, Mycobacterium gastri MB19 , by using the coding region of 3-hexulose-6-phosphate synthase (HPS) as th e hybridization probe, The PstI fragment contained three complete open read ing frames (ORFs) which encoded from the 5' end, a DNA-binding regulatory p rotein (rmpR), 6-phospho-3-hexuloisomerase (PHI; rmpB), and HPS (rmpA). Seq uence analysis suggested that rmpA and rmpB constitute an operon, and North ern blot analysis of RNA extracted from bacteria grown under various condit ions suggested that the expression of the two genes is similarly regulated at the transcriptional level. A similarity search revealed that the protein s encoded by rmpA and rmpB in M, gastri MB19 show high similarity to the un identified proteins of nonmethylotrophic prokaryotes, including bacteria an d anaerobic archaea. The clusters in the phylogenetic tree of the HPS prote in of M, gastri MB19 and those in the phylogenetic tree of the PHI protein were nearly identical, which implies that these two formaldehyde-fixing gen es evolved as a pair, These findings give new insight into the acquisition of the formaldehyde fixation pathway during the evolution of diverse microo rganisms.