Effect of Salt Concentration on the Production of α-Amylase and Protease by Bacillus coagulans and Wastewater Treatment Potential

Abstract

Bacillus coagulans is a moderately halotolerant bacterium with potential applications in enzyme production and wastewater treatment in brackish aquaculture systems. In this study, we examined how different NaCl concentrations (0 - 5%) affect the growth and extracellular α-amylase and protease activities of the strain B. coagulans PILS15.4. We also evaluated its ability to reduce chemical oxygen demand (COD) in real shrimp-pond wastewater with a salinity of 2.2%. The bacterium maintained relatively good growth up to about 3% NaCl, although cell density declined steadily as salinity increased. α-Amylase and protease activities were highest at low salinity (0 - 0.5% NaCl; 13.4 - 13.6 U/mL and 31.9 - 32.2 U/mL, respectively) and dropped sharply at salt levels above 3%. In the wastewater experiment, the inoculated treatment consistently achieved higher COD removal than the control, with the greatest improvement observed during the first 24 hours (20.7 - 21.4% compared with 2.3 - 3.8%). Both incubation time and bacterial addition significantly influenced COD reduction. Overall, B. coagulans showed promising potential for improving the early-stage degradation of organic matter in shrimp-pond wastewater under moderate salinity, although its enzyme production and treatment efficiency were clearly limited at higher salt concentrations. In shrimp pond wastewater with a salinity of 2.2%, the addition of B. coagulans significantly improved the effectiveness of COD elimination in the first 24 hours compared to the control.