A Novel Starch Digesting Halo-Acid-Alkali-Tolerant and Surfactant Stable Amylase from Newly Isolated Halophilic Bacterium Bacillus Siamensis Sp. F2: Application in Waste Valorization to Ethanol Fermentation

Abstract

The extracellular amylase production level by the moderate halophile Bacillus siamensis sp. F2 was optimized, and the enzyme was biochemically characterized. The culture parameters for NaCl, carbon, nitrogen, pH, and temperature were optimized for high titers of amylase production. Growing Bacillus siamensis sp. F2 cultures in Great Salt Lake-2 medium with additions of (in g/l) NaCl (100), starch (30), yeast extract (2), KNO3 (2), and MgSO4 (1) at pH 8, 30°C resulted in the maximum amylase production (4.2 U/ml). The amylase was active across a wide range of salinities (0 to 30% NaCl), pH (5.0–10.0), and temperatures (20–70oC), and showed good stability with surfactants (SDS and Triton X-100); hence identified as halo-acid-alkali-tolerant and surfactant stable. Temperature, pH, and salinity were optimal for amylase activity at 50°C, pH 7, and 5% NaCl, respectively. It also generates amylase utilizing agricultural wastes like sugarcane bagasse, wheat bran, and rice husk. Based on the performance of Bacillus siamensis sp. F2 using sugarcane bagasse and synthesizing amylase, the current study attempted to produce bioethanol by co-culturing with baker's yeast, which yielded 157 g/L of bioethanol. This novel amylase may have many potential applications in industrial waste-valorization and biorefinery sectors.