The consecutive genes BF0771-BF0774 in the genome of Bacteroides fragilis NCTC 9343 were found to constitute an operon. The functional analysis of BF0772 showed that the gene encoded a novel enzyme, mannosylglucose phosphorylase that catalyzes the reaction, 4-O-beta-D-mannopyranosyl-D-glucose + Pi -> mannose-1-phosphate + glucose. Here we propose a new mannan catabolic pathway in the anaerobe, which involves 1,4-beta-mannanase (BF0771), a mannobiose and/or sugar transporter (BF0773), mannobiose 2-epimerase (BF0774), and mannosylglucose phosphorylase (BF0772), finally progressing to glycolysis. This pathway is distributed in microbes such as Bacteroides, Parabacteroides, Flavobacterium, and (C) 2011 Elsevier Inc. All rights reserved.