Summary: Several strains of agar-degrading bacteria were isolated from the River Wey, Guildford, during the summer of 1976. All were Gram-negative rods and could be divided into two groups. Those which only softened the agar belonged to the genus and those which caused extensive liquefaction of the agar have been referred to the genus . Attempts to isolate, purify and characterize the enzymes showed some differences between the two taxa. The strains of produced at least two enzyme complexes, one cell-free and the other cell-bound, and hydrolysed agar with the formation of oligosaccharides. The strains of , on the other hand, readily released ‘agarase’ into the medium yielding monosaccharides as major end-products. The agar-degrading enzymes of both groups were inducible, not only by agar, but also by other galactans and polysaccharides associated with plants. The enzyme preparations also hydrolysed a wide range of plant-derived polysaccharides, including some associated with terrestrial and freshwater plants rather than with marine algae. These results suggest that there is no special ecological reason for the presence of agarolytic bacteria in fresh water but that their activity reflects the wide substrate spectrum of the polysaccharides of such organisms. The agar-softening strains are considered to belong to a new species for which the name is proposed.


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