Genome Sequence of the Cellulolytic Gliding Bacterium Cytophaga hutchinsonii

Abstract

The complete DNA sequence of the aerobic cellulolytic soil bacterium Cytophaga hutchinsonii, which belongs to the phylum Bacteroidetes, is presented. The genome consists of a single, circular, 4.43-Mb chromosome containing 3,790 open reading frames, 1,986 of which have been assigned a tentative function. Two of the most striking characteristics of C. hutchinsonii are its rapid gliding motility over surfaces and its contact-dependent digestion of crystalline cellulose. The mechanism of C. hutchinsonii motility is not known, but its genome contains homologs for each of the gld genes that are required for gliding of the distantly related bacteroidete Flavobacterium johnsoniae. Cytophaga-Flavobacterium gliding appears to be novel and does not involve well-studied motility organelles such as flagella or type IV pili. Many genes thought to encode proteins involved in cellulose utilization were identified. These include candidate endo-β-1,4-glucanases and β-glucosidases. Surprisingly, obvious homologs of known cellobiohydrolases were not detected. Since such enzymes are needed for efficient cellulose digestion by well-studied cellulolytic bacteria, C. hutchinsonii either has novel cellobiohydrolases or has an unusual method of cellulose utilization. Genes encoding proteins with cohesin domains, which are characteristic of cellulosomes, were absent, but many proteins predicted to be involved in polysaccharide utilization had putative D5 domains, which are thought to be involved in anchoring proteins to the cell surface.