Abstract
A number of agar-degrading bacteria were isolated from the River Wey, Guildford during the summer period of 1976. The isolates were all Gram-negative rods belonging to two genera; Alteromonas and Cytophaga. The strains of Cytophaqa caused considerable softening of agar. The Alteromonas, on the other hand, were found capable of liquefying agar. The results obtained indicate that the agar-softening strains of Cytophaga produced at least two enzymes systems, one cell-free and the other cell-bound while the agar-liquefying strains of Alteromonas produced a single, cell-free enzyme system which hydrolyses agar by an exocleavage mechanism. Both organisms grew well with inorganic nitrates as a nitrogen source but the Alteromonas did not grow well on ammonium sulphate. The extracellular enzymes were best obtained from cell-free culture fluid by cold acetone precipitation but further purification by affinity chromatography led to considerable loss of activity. The agar-degrading enzymes were inducible not only by agar but also by other galactans which are known to occur widely in plants. The enzymes also showed a broad spectrum of activity, liberating reducing compounds from many polygalactose polysaccharides. The K[M] values obtained for agarose (0.170mg ml[-1]); gum arabic (0. 073mg ml[-1]) and arabinogalactan (0.152mg ml[-1]) indicate that agarose is not the natural substrate for the enzyme. It seems quite possible that these organisms participate actively in the degradation of galactose polymers in fresh waters and that their evolution could be associated with the presence of these polysaccharides in the River Wey.