Effect of NaCl concentration on enzyme activities of halophilic bacteria in saltpans, Hambantota, Sri Lanka

Abstract

Halophilic bacteria are able to thrive in hypersaline environments and produce industrially important enzymes such as amylases and proteases, which can function under high salt concentrations. The present study aimed at screening amylase- and protease-producing bacteria isolated from sediments of the Hambantota saltpan. Screening of amylase and protease activity was performed on 11 bacterial isolates. Bacterial cultures were inoculated onto starch agar and skim milk agar to identify amylase- and protease-producing bacteria, respectively, and were incubated at 37 °C for 48 hours. One strain showed positive results for both enzymes and was selected for quantitative analysis. Based on morphological and biochemical characterization, it was tentatively identified as Bacillus spp. Protease and amylase activity of the crude enzyme extract were determined under different NaCl concentrations using the Folin method and the DNS (3,5-dinitrosalicylic acid) method, respectively. Amylase activity was assessed by growing the bacterium in starch broth with NaCl concentrations ranging from 1% to 10%. The highest amylase activity (0.311 U/mL) was observed at 6% NaCl, while the lowest activity (0.040 U/mL) was recorded at 1% NaCl. Similarly, protease activity was measured by growing the bacterium in skim milk broth. The highest protease activity (0.097 U/mL) was detected at 2% NaCl, and the lowest (0.050 U/mL) at 6% NaCl. These findings highlight the potential of this strain to produce amylase and protease enzymes across a broad range of salt concentrations, making it suitable for industrial applications that require high-salt conditions. Future studies could focus on optimizing enzyme production for commercial use.