Isolation of Actinomyces viscosus strain GA: characteristics of its cellular biological retardant(s)

Actinomyces viscosus strain GA produces an exocellular biological retardant(s) that prevents certain vegetable plants from becoming overgrown. The biological retardant(s) was assayed using the etiolated wheat coleoptile assay, and fractionation of culture supernatant fluid resulted in a partial purification of the retardant(s). The biological retardant(s) was most active around pH 7 in the bioassay and when applied to sterile soil mixture. The biological retardant(s) was tentatively identified as a derivative of a rare hexose carbohydrate (but not an amino sugar) but an exact structure was not determined. In a sterilized synthetic soil system, the biological retardant(s) has an effect on tomato cultivars similar to that observed by the synthetic plant growth regulators Alar (succinic acid 2,2-dimethylhydrazide) and Bonzi (paclobutrazol).