ISOLATION AND CHARACTERIZATION OF AN OBLIGATELY ANAEROBIC, PECTINOLYTIC, MEMBER OF THE GENUS EUBACTERIUM FROM MULLET GUT

A gram positive, motile rod-shaped strictly anaerobic non sporulating bacterium was isolated from an enrichment initiated with mullet gut contents. The organism grew optimally at 30-degrees-C at pH 6.5 and at a salinity of 10/10(3). Out of a variety of mono-, di-, and polysaccharides tested only pectin, cellobiose and starch actively supported growth in either semi defined medium or peptone-yeast extract (PY) medium. Galacturonic acid and maltose were less effective as substrates. Mol product per 100 mol of pectin monomer degraded were: acetate, 163; ethanol, 30; methanol, 88 and formate, 48. Per 100 mol of hexose in cellobiose or starch degraded, the amounts were acetate, 39; ethanol, 128 and formate, 41. Hydrogen was not detectable in the incubations (detection limit, < 10(-5) atm) and propionate, butyrate, lactate or succinate were not produced as fermentation end-products (< 2 mol per 100 mol monomer). The guanine plus cytosine content of DNA from the bacterium was 31 mol%, and the cell walls contained meso-diaminopimelic acid. A phylogenetic analysis of the organism by 16S rDNA sequencing and DNA-DNA homology indicated that the organism grouped more closely with several species of Clostridium than with Eubacterium. The phenotypic characteristics of the organism indicated that it did not fit within the genus Clostridium and more closely resembled Eubacterium. The organism is therefore designated as a species of Eubacterium; the type strain is P-1 (DSM 6788).