Characterization of halophilic bacterium NB2-1 from Pla-ra and its protease production

A halophilic proteolytic bacterium, NB2-1, isolated from Pla-ra, fermented fish in Thailand, was identified as Virgibacillus marismortui oil the basis of the genetic and phenotypic characteristics. NB2-1 produced a substantial level of extracellular proteolytic activity, corresponding with the growth and reaching the maximum at the end of the exponential phase (3 days). The optimum conditions required for maximum protease production were 15% (w/v) NaCl, pH at 9 and temperature at 30C. Of the media tested, maximum protease production occurred in a medium containing 15% NaCl, 0.5% yeast extract, 0.1% glutamic acid, 0.2% KCl, 0.3% trisodium citrate; 2% MgSO4 center dot 7H(2)O, 0.0036% FeCl2 center dot 4H(2)O and 0.000036% MnCl2-4H(2)O. The protease activity was optimally active at pH 10, 50C and 5% (w/v) NaCl when casein was used as a substrate. The activity was strongly inhibited by phenylmethane sulfonyl fluoride. Activity-stained substrate gel indicated the presence of several proteases with the estimated molecular weights of 17, 19, 24, 29 and 35 kDa in the crude NB2-1 extracellular protease. The results of the present investigation showed that the strain NB2-1 could be a potential source of thermoactive alkaline protease production.