Adaptive Evolution of Aurantiochytrium limacinum for Efficient Production of Docosahexaenoic Acid Under Acidic and High-Temperature Conditions

Acid- and heat-tolerant industrial microbial strains are crucial for biotechnological production because they minimize the risk of microbial contamination and reduce energy consumption associated with cooling requirements. Here, adaptive laboratory evolution (ALE) of <i>Aurantiochytrium limacinum</i> was performed to improve the capability of the strain to produce docosahexaenoic acid (DHA) under acidic and high-temperature conditions. A stepwise increase from 30 to 38 °C was applied during cultivation at pH 4.5. After 30 cycles of high-temperature exposure (34 °C), an adaptive strain (BBF002) was obtained. Cell growth and DHA production of BBF002 were higher than those of the parental strain (BBF001) by 32.95 and 7.12%, respectively, at pH 4.5 and 30 °C. Based on the experimental data obtained using glucose as a carbon source, a kinetic model was developed to describe cell growth, biomass maintenance, and DHA, and we used other metabolite methods to produce the native, parental, and adaptive strains. The growth traits of the three strains could be adequately described through logistic modeling. DHA was found to be a mixed-growth product produced during exponential and stationary phases, according to the Luedeking-Piret equation.