In vitro catalyzes the phosphorolysis of D-kojibiose into beta-D-glucose 1-phosphate and D-glucose. No other disaccharides tested substitute for D-kojibiose. In the reverse direction disaccharides can be formed from beta-D-glucose 1-phosphate plus D-glucose, L-sorbose, D-sorbitol, L-iditol or 1,5-anhydro-D-glucitol, but with low efficiency. The beta-D-glucose 1-phosphate product is the substrate for YcjU (AC P77366), the next apparent enzyme in the putative biochemical pathway encoded in this locus (yjcM to ycjW). kojibiose + phosphate = beta-D-glucose 1-phosphate + D-glucose kcat is 1.0 sec(-1) for phosphorolysis of kojibiose, and kcat is 0.8 sec(-1) for the reverse reaction. No visible phenotype when grown on glucose. Kojibiose does not support bacterial growth of K12 / BW25113 nor of BL-21(DE3), perhaps because it is not transported into E.coli. Belongs to the glycosyl hydrolase 65 family.