CYTOPHAGA-XYLANOLYTICA SP-NOV, A XYLAN-DEGRADING, ANAEROBIC GLIDING BACTERIUM

Gliding bacteria attached in masses to, and dominated the fermentation of, xylan powder in methanogenic and sulfidogenic enrichments from various freshwater sediments. Isolates of such bacteria were all gram-negative, slender rods (0.4 x 4 24 mum) that formed no endospores, microcysts or fruiting bodies. Representative strain XM3 was a mesophilic, aeroduric anaerobe that grew by fermentation of mono-, di-, and polysaccharides (but not cellulose) in a mineral medium containing up to 3% NaCl. However, CO2/HCO3- was required in media for consistent initiation of growth. Fermentation products included acetate, propionate, succinate, CO2, and H-2. Xylan-grown cells had xylanase and various glycosidase activities that were mainly or almost entirely cell-associated, respectively. Strain XM3 was weakly catalase positive, but oxidase negative; it possessed sulphonolipids and carotenoid, but not flexirubin, pigments; and its total cellular fatty acids were dominated by C-15:0 anteiso (75%), n (13%) and iso (2%) isomers. Strain XM3 had 45.5 mol% G + C in its DNA, and partial sequencing of its 16S rRNA placed XM3 within the Bacteroides-Flavobacterium phylogenetic group. Similar strains were isolated from marine sediments. Strain XM3 is herewith proposed as the type strain of the new species, Cytophaga xylanolytica. Results, which are discussed in terms of our current concept of the genus Cytophaga, suggest that the importance of C. xylanolytica in anaerobic biopolymer decomposition has not been fully appreciated.