Characterization and stability of extracellular alkaline proteases from halophilic and alkaliphilic bacteria isolated from saline habitat of coastal Gujarat, India

The present study deals with the isolation and characterization of the moderately halophilic-alkaliphilic bacteria from a saline habitat in western India. Eight different bacterial strains were isolated using enrichment techniques at 20% (w/v) NaCl and pH 10. The isolates exhibited diversity towards gram's reaction, colony and cell morphology. They were able to grow and produce alkaline protease over a broad range of NaCl, 5-20% (w/v) and pH, 8-10. None of the isolates could grow at pH 7, and one could not grow even at pH 8. Crude and partially purified proteases from strain S-5 were subjected to characterization with reference to pH, salt stability and protein folding. Optimum protease activity and stability was recorded at 10% salt and pH 9-9.5. Denaturation kinetics of S5 alkaline protease along with a reference protease was studied at 8M urea followed by renaturation. The S5 alkaline protease could be partially renatured up to 32% of the original activity. Despite of the fact that all the 8 isolates were from the same site, they displayed significant diversity with respect to their salt requirement for growth and enzyme secretion. While the effect of pH was less demarcated on growth, the protease production was significantly affected. Isolate S5 produced substantial amount of halotolerant and alkaline protease. The activity and stability of the alkaline protease in a broader range of pH and salt would definitely make this enzyme an important candidate for various industrial applications.