Mgl2 is a hypothetical methyltransferase involved in exopolysaccharide production, biofilm formation and motility in Rhizobium leguminosarum bv. trifolii.

In this study, functional characterization of the mgl2 gene located closely to the Pss-I exopolysaccharide biosynthesis region in Rhizobium leguminosarum bv. trifolii TA1 was described. The hypothetical protein encoded by the mgl2 gene was found to be similar to methyltransferases. Protein homology/template-based modeling facilitated prediction of the Mgl2 structure, which vastly resembled class I methyltransferases with a SAM-binding cleft. The Mgl2 protein was engaged in exopolysaccharide but not lipopolysaccharide synthesis. The mgl2 deletion mutant produced exopolysaccharide comprising only low molecular weight fractions, while overexpression of mgl2 caused overproduction of exopolysaccharide with a normal low to high molecular weight ratio. The deletion of the mgl2 gene resulted in disturbances in biofilm formation and slight increase in motility in minimal medium. Red clover (Trifolium pratense) inoculated with the mgl2 mutant formed effective nodules and the appearance of the plants indicated active nitrogen fixation. The mgl2 gene was shown to be preceded by an active and strong promoter. The Mgl2 was defined as an integral membrane protein and formed homodimers in vivo, however did not interact with Pss proteins encoded within the Pss-I region. The results were discussed in the context of the possible involvement of the newly described potential methyltransferase in various metabolic traits such as the exopolysaccharide synthesis and motility important for rhizobial saprophytic and symbiotic lifestyles.