Active extracellular substances of Bacillus thuringiensis ITRI-G1 induce microalgae self-disruption for microalgal biofuel

Microalgal cultures are a clean and sustainable means to use solar energy for CO₂ fixation and fuel production. Microalgae grow efficiently and are rich in oil, but recovering that oil is typically expensive and consumes much energy. Therefore, effective and low-cost techniques for microalgal disruption and oil or lipid extraction are required by the algal biofuel industry. This study introduces a novel technique that uses active extracellular substances to induce microalgal cell disruption. A bacterium indigenous to Taiwan, Bacillus thuringiensis, was used to produce the active extracellular substances, which were volatile compounds with high thermal stability. Approximately 74% of fresh microalgal cells were disrupted after a 12-h treatment with the active extracellular substances. Algal lipid extraction efficiency was improved and the oil extraction time was decreased by approximately 37.5% compared with the control treatment. The substances effectively disrupted fresh microalgal cells but not dehydrated microalgal cells. An analysis of microalgal DNA from fresh cells after disruption treatment demonstrated typical DNA laddering, indicating that disruption may have resulted from programmed cell death. This study revealed that biological treatments are environmentally friendly methods for increasing microalgal lipid extraction efficiency, and introduced a microalgal cell self-disruption mechanism.