Isolation and characterization of Clostridium hobsonii comb. nov.

A search for organisms yielding commercial products from bioresources resulted in a group of 37 isolates from a cattle-waste digester. Using strict anaerobic technique, the organisms were cultured by direct isolation and continuous perfusion on straw, ball-milled cellulose and dewaxed cotton as substrates. Gram-negatively staining rods (though showing a Gram-positive wall in electron micrographs) were straight to slightly-curved with tapering ends, 0•25-0•7 × 1•5-3•5 μm, with peritrichous flagellation. Cultures showed extensive degradation of filter paper; 27–42•7% and up to 31% solubilization of straw and cotton respectively. Cellobiose, -triose and -tetrose, but not glucose, resulted from cellulose hydrolysis. Fermentation products were ethanol, acetate, formate, lactate, succinate and, with some strains, propionate, with CO2 and H2 as fermentation gases. Though major tests were done on all, isolates U311, U191, T111, U62 and C400 were examined extensively. All the test strains showed strong to moderate fermentation of glucose, cellobiose, aesculin, maltose, fructose, lactose, mannose, melibiose, ribose, starch, xylose, xylan, raffinose and sucrose. The mol% G + C ratio of the DNA for three strains was 39•5–43•9 (Tm). Characteristics of the organisms isolated overlapped with those of Eubacterium cellulosolvens NCDO 2433, 2430, ATCC 43171; Clostridium cellobioparum ATCC 15832 and Clostridium thermocellum ATCC 27405. In the present investigation E. cellulosolvens strains produced ethanol, spores in sporulation medium (Lett. Appl. Microbiol., 1, 31, 1985) and a G + C ratio of 42•5 for strain 2433. C. thermocellum grew at 37•C. Under recommendations 3–4, rule 42 of the international code of nomenclature of bacteria, we propose the name Clostridium hobsonii for U311, a species of biotechnological importance, in honor of P. N. Hobson B.Sc., Ph.D., D.Sc., F.I.Biol., F.R.S.C., F.R.S.E.