A novel,symbiotic bacterium isolated from marine shipworm secretes proteolytic activity

Proteolytic activity was identified in cultures of the marine shipworm bacterium by monitoring of the release of acid-soluble azopeptides from azocasein. Activity was predominantly extracellular (>80%), and its production was coincident with logarithmic cell growth. The protease(s) appeared to be constitutive, since it was present even when the bacterium was grown under nitrogen-fixing conditions. However, activity was stimulated up to 8.6-fold by the addition of complex nitrogen (casein, amino acids) to the growth medium. Maximum activity was observed at 40°C and between pH 6.5 and 9.0. Relatively low concentrations (0.1 mM) of phenylmethylsulfonyl fluoride (PMSF) abolished activity, indicative of a serine protease(s).The mention of firm names or trade products does not imply that they are endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.