Involved in the biosynthesis of the exopolysaccharide acetan, a water-soluble polysaccharide involved in production of bacterial cellulose (BC). beta-D-Glc-(1->4)-alpha-D-Glc-di-trans,octa-cis-undecaprenyl diphosphate + GDP-alpha-D-mannose = alpha-D-Man-(1->3)-beta-D-Glc-(1->4)-alpha-D-Glc-1-di-trans,octa-cis-undecaprenyl diphosphate + GDP + H(+) Belongs to the glycosyltransferase group 1 family. Glycosyltransferase 4 subfamily. The gene has been independently discovered by another group, who referred to it as aceA, causing confusion with the aceA gene which encodes a undecaprenyl-phosphate glucose phosphotransferase.