Isolation of extremophilic bacteria from microbial mats and the applicability of their amylases for bioethanol production from food waste

The applicability of extremophilic amylases in hydrolyzing food waste for bioethanol production has not been investigated much. The current study aims to extract amylases from halophilic bacteria isolated from a hypersaline mat and to use them for the saccharification of food waste to produce bioethanol. Nine halophilic bacteria belonging to the genera Bacillus and Halomonas were isolated. Growth experiments showed that all isolates were moderately halophilic and mesophilic. The crude amylases from four selected Bacillus strains (i.e. NM1-NM4) were active under a temperature range of 40–60°C, pH of 9–10 and at 6–36% NaCl concentrations. Significant inhibition was noted in the presence of metal ions, especially Mn²⁺ (90–100%). The maximum activity of the crude amylases at their optimal temperature and pH ranged from 35.34 ± 0.01 to 38.78 ± 0.004 U/mL. The amylase obtained from Bacillus sp. NM2 was used to hydrolyze bread and rice waste (2% w/v). Subsequent fermentation of the rice and bread hydrolyzates using Saccharomyces cerevisiae resulted in 1.8 g/L (equivalent to 212.6 mg/g of sugar) and 0.5 g/L (60.2 mg/g of sugar) of bioethanol, respectively. This study demonstrates the potential of using extremophilic amylases for the saccharification and bioethanol production from inexpensive food waste.