Effect of Carbon Substrates on Rock Phosphate Solubilization by Bacteria from Composts and Macrofauna

Abstract

Five of the 207 isolates from different composts, farm waste compost (FWC), rice straw compost (RSC), Gliricidia vermicompost (GVC), and macrofauna, showed rock phosphate (RP) solubilization in buffered medium in plate culture. When tested in RP broth medium, all five strains, Enterobacter cloacae EB 27, Serratia marcescens EB 67, Serratia sp. EB 75, Pseudomonas sp. CDB 35, and Pseudomonas sp. BWB 21, showed gluconic acid production and solubilized RP. Based on cellulose-degrading and P-solubilizing ability, two strains were selected for further studies. In the presence of different carbon sources, both strains showed a drop in pH and solubilized RP. P released was maximum with glucose (1212 and 522 micromol) and minimum with cellobiose (455 and 306 micromol) by S. marcescens EB 67 and Pseudomonas sp. CDB 35, respectively. Glucose dehydrogenase (GDH) activity was 63 and 77% with galactose and 35 and 46% with cellobiose when compared to glucose (100%) by EB 67 and CDB 35, respectively. Both strains solubilized RP in the presence of different crop residues. EB 67 and CDB 35 showed maximum cellulase activity (0.027 units) in the presence of rice straw and a mixture of rice straw and root. P solubilized from RP in the presence of pigeonpea root was 134 and 140 micromol with EB 67 and CDB 35. Significantly, these bacteria isolated from composts and macrofauna solubilized rock phosphate in the presence of various pure carbon substrates and crop residues and their importance in soil/rhizosphere conditions is discussed.

Origanum syriacum ssp. sinaicum associated Growth Promoting Bacteria

“…High phosphate solubilization activity by Serratia sp. was reported by previous studies [48][49][50] that supported observation that gave Serratia isolates higher grade of phosphate solubilization compared with Bacillus isolates. The isolation of B2 Serratia SK3 as endophyte from cultivated root and B5 Serratia SK1a from the rhizospere of the wild oregano supports that it might be associated with the plant to enhance phosphate uptake.…”

Interactions between arbuscular mycorrhizal fungi and phosphate-solubilizing fungus (Mortierella sp.) and their effects on Kostelelzkya virginica growth and enzyme activities of rhizosphere and bulk soils at different salinities

“…The P solubilization occurs in the rhizosphere soil where organic compounds are released by roots or mycorrhizae (Nguyen 2003;Amos and Walters 2006). Many rhizosphere microorganisms are heterotrophs and might use these organic substrates to produce organic acids, which would increase P concentrations in solution (Hameeda et al 2006;Reyes et al 2006). Probably Gm was more effective than Ga in stimulating P solubilization by Ms, but we are unable to explain the underlying mechanisms.…”

Biological Control of Chickpea Collar Rot by Co-inoculation of Antagonistic Bacteria and Compatible Rhizobia

“…The soil mix consisted of RP as the P source, as Pseudomonas sp. CDB 35 was known to solubilize P from our previous study [13]. Inoculation of Rhizobium IC 59 and antagonistic bacterial isolate Pseudomonas sp.…”