Partial Purification and Characterization of the Inhibitory Substance of Bacillus subtilis against Common Bacterial Fish Pathogens

Abstract

The present investigation was carried out to study the active component of Bacillus subtilis, a gastrointestinal bacterium of mrigal (Cirrhinus mrigala) that shows inhibitory activity against a wide range of fish pathogens. The bacterium was found to inhibit all the fish pathogens and an extra cellular protein fraction (ECP) of 5-10 kD was found to be the active component responsible for inhibitory activity. The component was heat stable (60°C for 1 h) and a change in pH had no effect on the antibacterial activity. The protein fraction was sensitive to trypsin, chymotrypsin, lysozyme, and proteinase K at 2.5 mg/ml and resistant at 0.1 and 0.5 mg/ml. The present investigation confirmed that the active component of the B. subtilis responsible for antibacterial activities against common fish pathogens is a low molecular weight protein fraction (5-10 kD). A protein or peptide with such a low molecular weight has the potential to serve as an alternative health management strategy for combating disease in aquaculture.