Abstract A bacterium (strain A1) isolated from a ditch synthesized three kinds of intracellular alginate lyases: A1-I (molecular weight [M.W.] 60,000), A1-II-1 (M.W. 60,000) and A1-II-2 (M.W. 25,000) in laboratory-scale cultures. However, when cells of strain A1 were grown on an industrial scale, another lyase (A1-III) was produced other than A1-I, A1-II-1 and A1-II-2. The A1-III lyase was a monomer with a M.W. of about 38,000, and its activity toward bacterial (acetylated) alginates was much higher (2-fold) than that toward seaweed (non-acetylated) alginates. The N-terminal amino acid sequence of A1-III lyase was consistent with that of A1-I lyase.