Probable S-adenosylmethionine-dependent methyltransferase required for the 6-O-methylation of the polysaccharide backbone of 6-O-methylglucosyl lipopolysaccharides (MGLP). Inactivation of this gene results in a dramatic reduction in the amounts of 6-O-methylglucosyl lipopolysaccharides (MGLP) synthesized and in the accumulation of precursors of these molecules. Cells lacking this gene do not grow at high temperature (42 degrees Celsius) in Sauton's medium, although their growth is comparable to that of wild-type at 30 and 37 degrees Celsius in this medium. Belongs to the methyltransferase superfamily. Extended N-terminus.