Enhancement of DHA production from Aurantiochytrium sp. by atmospheric and room temperature plasma mutagenesis aided with microbial microdroplet culture screening

In order to achieve strain improvement and reduction of fermentation medium cost, atmospheric and room temperature plasma (ARTP) mutagenesis and microbial microdroplet culture (MMC) high-throughput screening were used to obtain high-yield Aurantiochytrium sp. strain. Meanwhile, low-cost food waste liquid was added into culture medium to reduce cost. The results showed that the optimal treatment time of ARTP mutagenesis for Aurantiochytrium sp. was 25 s, and 20 mutant strains were screened out by MMC to investigate their performance. The most significant increase in DHA yield was mutant Aurantiochytrium sp. MA20, whose biomass, lipid, and DHA yield were 29.0 +/- 0.24, 15.8 +/- 0.11, and 9.22 +/- 0.37 g/L and 5.77, 16.9, and 83.2% higher than those of original strain, respectively. Compared with the original strain, the DHA proportion in total fatty acids of Aurantiochytrium sp. MA20 increased from 37.2 to 58.3%, while the DHA proportion in biomass increased from 18.4 to 31.7%. The genetic stability for Aurantiochytrium sp. MA20 showed that the yield of biomass, lipid, and DHA of the 50th generation were 29.1 +/- 0.13, 16.2 +/- 0.31, and 9.47 +/- 0.26 g/L, respectively, which was no significant difference between original strain, indicating that the mutant MA20 could be inherited stably. Using food waste liquid to replace 100% yeast extract and 50% sea water of the fermentation medium, the DHA yield reached 9.54 g/L, which was equivalent to that of traditional medium, while the cost of medium was reduced by 45% that achieved the recycle of food waste resource.