Beta-mannosyltransferase involved in cell wall biosynthesis. Required for beta-1,2-mannose transfer on phospholipomannan. Required for pro-inflammatory response in macrophages through phospholipomannan-induced TNF-alpha production. Expression is induced in biofilm. Leads to the production of phospholipomannan with short truncated oligomannosidic chain and impairs induction of TNF-alpha production in macrophages. Belongs to the BMT family.