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Decomposition and Binding Action of Polysaccharides from Azotobacter Indicus (Beijerinckia) and Other Bacteria in Soil¹

ABSTRACT

The decomposition rate and binding effect in soil of a polysaccharide synthesized by A. indicus (Beijerinckia) were compared with those of other bacterial polysaccharides, including one from Chromobacterium violaceum and with other type organic materials. In acid and neutral soils an average of 19% of the A. indicus polysaccharide decomposed in 8 weeks. This compared with averages of 38%, 39%, 51%, 67%, and 84% decomposition for almond shells, C. violaceum polysaccharide, corn stalks, Azotobacter chroococcum polysaccharide, and glucose, respectively. Of these and additional organic materials tested, only peat moss was more resistant to decomposition than the A. indicus polysaccharide. All the bacterial polysaccharides were highly effective in binding soil particles into water stable aggregates. After 30 days of incubation A. indicus polysaccharide reduced numbers or had little effect on bacteria and fungi developing on soil dilution plates. Growth of fungi from soil dilutions on media containing no carbohydrate was as good or better than on the same medium containing poly-saccharide from A. indicus or C. violaceum. Polysaccharides from A. indicus, C. violaceum, and B. subtilis reduced germination and/or growth of soil bacteria on agar media.

¹ Paper no. 1608, University of California Citrus Research Center and Agr. Exp. Sta.

² Department of Soils and Plant Nutrition, University of California. Riverside, Calif.

Received for publication October 15, 1964. Accepted for publication April 1, 1965.