Galactosyltransferase involved in the biosynthesis of the core oligosaccharide region of lipopolysaccharide (LPS). Catalyzes the addition of galactose from UDP-galactose to the first glucose residue of the LPS outer core. Cannot use other sugar donors, such as UDP-glucose, UDP-glucuronic acid, UDP-galacuronic acid, GDP-mannose, ADP-glucose and GDP-glucose. In the absence of a lipid acceptor, can hydrolyze UDP-galactose to UDP and galactose