Chiang Mai Journal of Science

Four  strains  of  Bacillus sp.  designated  K52, K53, K61 and KK128 were  isolated  from Ka-pi  (shrimp  paste),  Pla-ra  (Fermented  fish)  Ka-pi  and  Pla-ra, respectively. They  showed maximum growth on nutrient agar containing 15% NaCl at 50-55 ^oC. Bacillus licheniformis K61 produced the highest protease activity in Medium 3 containing 1.0 % glucose, 0.25% yeast extract and 0.05% CaCl₂. H₂O (pH 7.0). Maximum protease activity was detected at the end of the exponential growth phase. The optimum pHs and tempearatures of crude proteases from all four bacteria were at pH 8.0 and 50-55 oC,  respectively. The four crude proteases were  stable  at  45  ^oC  for  24  h  and  unstable  at  60 oC.  The  crude  protease  activities  of  four bacteria were inhibited by EDTA, SDS and PMSF, but not by mercaptoethanol. They were activated by Co²⁺, glycerol, Mn²⁺, Ca²⁺ except for the enzyme from isolate K53 which was not activated by Co²⁺, K⁺ ions activated only the enzymes from strains K52 and K61. The crude  proteases  from four  isolates  were  inhibited  by  Ba²⁺, Fe²⁺, Hg²⁺ and Cu²⁺. The  crude protease activities from four bacteria decreased with increasing concentration of  NaCl. Egg albumin was the best substrate for protease activity from Bacillus licheniformis K61.