Enterobacter agglomerans, phosphate solubilizing bacteria, and microbial activity in soil: Effect of carbon sources

Soil contains large amount of phosphorus that exists in insoluble forms. Some soil bacteria like Enterobacter agglomerans may have the capability to solubilize insoluble P and hydrolyze organic P for plant growth. These phosphate-solubilizing bacteria (PSB) may be stimulated by organic energy sources added to or found in soils. To examine the effect of organic energy sources on the survival of E. agglomerans and soil microbial activities, E. agglomerans were introduced into unsterilized soil containing 1% hydroxyapatite (HA) and either 1% glucose (GL), phytic acid dodecasodium salt (PA), glycerol-2-phosphate disodium salt (GP), soluble starch (SS) or no addition. Two controls were used: control 1: without E. agglomerans (C1) and control 2: with E. agglomerans (C2). E. agglomerans introduced in C2 treatment increased soil microbial biomass, phosphatase activity, and P solubilization compared to C1 at 2 d; however, with time there was no significant difference in treatments. Acid and alkaline phosphatase activities in GL and SS treatments were greater when compared to PA and GP; however, P concentration was greater in PA and GP treatments. Phytic acid and glycerol-2-phosphate may provide the necessary energy to solubilize HA as well as organic phosphate which is hydrolyzed by phosphatase. Soil microbial biomass C in GL and SS treatments were higher compared to PA and GP treatments. When only LB culture was added, E. agglomerans was not detectable after 22 d. Any additional mineralizable C contributes to the survival of E. agglomerans with time.