Xanthomonas campestris, a novel stress tolerant, phosphate-solubilizing bacterial strain from saline-alkali soils

A total of 198 bacterial strains were isolated from various niches of saline-alkali soils, out of which 85 strains were able to solubilize phosphate on plates at 30 degrees C. The strain RMLU-26, identified as Xanthomonas campestris, was the most efficient with its ability to solubilize P, subjected to N-methyl-N'-nitro-N-nitrosoguanidine (NTG) for development of mutants. The P solubilizing ability of X. campestris is reported for the first time. The wild type and mutant strains of X. campestris revealed a differential response to various stress factors (high pH, temperature, and salt concentration). The mutant strain revealed maximum P solubilization (67.1%) at 30 degrees C and pH 8.0 while the wild type strain showed maximum solubilization (41.9%) at 35 degrees C and pH 7.0. Percent P2O5 solubilization by both strains revealed a steep decline in tricalcium phosphate solubilization with an increase in NaCl concentration from 0.5 to 10% along with a concomitant drop in pH of the medium from 8.0 to 4.5 in wild type and 4.0 in mutant strain. However, a 1.5- to 2-fold increase in 'P' solubilization was observed in the mutant strain when compared to the wild type strain in the presence of NaCl. The overall improved tolerance of the strains to alkalinity and salinity could be due to accumulation and/or secretion of specific solute (xanthan).