Distribution and Potential Ecophysiological Roles of Multiple GroEL Chaperonins in Pink-Pigmented Facultative Methylotrophs

Abstract

The distribution and phylogeny of the GroEL chaperonin genes in the type strains of all described species of pink-pigmented methylotrophic bacteria (PPFM) belonging to the genera Methylobacterium and Methylorubrum were analyzed. Half of the bacterial strains tested (38 out of 69) were found to possess multiple groEL genes. Analysis of their translated amino acid sequences and promoter regions preceding the groESL operons that include them demonstrated that the GroEL chaperonins of these methylotrophs form three similarity groups typical of PPFM. The largest of these (GroEL1) combines, apparently, essential housekeeping chaperonins, and the other two consist of additional separately clustered proteins that differ in the composition of the elements regulating their gene expression. The strains encoding proteins of the GroEL2 group were isolated from various environments, including those contaminated with industrially produced C₁-compounds, while bacteria possessing GroEL3-like chaperonins are predominantly plant symbionts. It has been proposed that GroEL3 proteins may be involved in phytosymbiotic processes, whereas GroEL2 chaperonins can participate in response to specific stresses experienced by host cells in their habitats. At the same time, the GroEL chaperonin of Methylobacterium brachiatum B0021^T, atypical for PPFM, seem to be intended for folding of dinuclear iron monooxygenase, in whose gene cluster it is encoded. Further testing of these assumptions should elucidate the roles of multiple GroEL chaperonins in PPFM and allow more complete use of their biotechnological potential as plant growth stimulants and biodegradation/bioremediation agents.