production of exopolysaccharide by Pseudomonas putida GAP-P45 under various abiotic stress conditions and its role in soil aggregation

Exopolysaccharides (EPS) production is modified in response to environmental changes and is believed to protect bacteria. In the present study Pseudomonas putida strain GAP-P45 identified by 16S rDNA sequence analysis was exposed to stresses such as drought, temperature and salt to test the ability to tolerate and produce EPS. Strain GAP-P45 could tolerate matric stress up to −0.73 MPa, Temperature of 50°C and 1.4 M salt and produced EPS, which increased with increase in stress levels. Among all stress conditions, the production was high under drought stress. HPLC analysis revealed that monosaccharide composition and ratio of sugars in EPS increased under stress that might induce osmotic and thermal tolerance in GAP-P45. Rhamnose was reported as major sugar under all stress conditions. Among the different carbon sources tested, glycerol was found to be best for EPS production under stressed as well as non-stressed conditions. Inoculation with GAP-P45 resulted in better soil aggregation and aggregate stability under different stress conditions. However inoculation effect was more under drought-stress. The significance of these findings shows that abiotic stresses influence the EPS composition and ratios of sugars, which influence the tolerance of the microorganisms which can be employed for improvement in water holding capacity under unfavorable environmental conditions.