Extracellular polysaccharide production by soil bacteria: Environmental control and significance in agricultural soils.

摘要

Environmental control of the production of microbial extracellular polysaccharides (EPS) was investigated in pure cultures of a soil Pseudomonas species and in an agricultural soil. Nitrogen limitation stimulated EPS production per unit microbial biomass in liquid culture, in unsaturated sand cultures (matric potential = ;Desiccation stimulated EPS production and depressed protein production while wetting decreased EPS and increased protein contents in sand cultures of the Pseudomonas. Carbon allocation, therefore, shifted from protein production after wetting to EPS production during desiccation. EPS produced by the Pseudomonas held several times its weight in water at low water potential. The high water holding capacity of the EPS matrix may improve nutrient availability during desiccation. The addition of 8 mg EPS/g sand significantly slowed the rate of drying of quartz sand. These properties of EPS may help EPS-producing microorganisms to survive desiccation.;Microbial EPS stabilize soil aggregates. The effects of management on EPS production and soil aggregation were examined. Two winter cover crops: Vicia dasycarpa L., a nitrogen fixer, and Avena sativa L., and three N fertilizer regimes: 0, 168, or 280 kg/ha (NH