Enhancing Activities of Salt-tolerant Proteases Secreted by Aspergillus oryzae using Atmospheric and Room Temperature Plasma Mutagenesis

Aspergillus oryzae (A. oryzae) 3.042 was mutagenized using Atmospheric and Room Temperature Plasma (ARTP) technology to enhance its salt-tolerant proteases activity. Compared to the starting strain, mutant H8 subjected to 180 s of ARTP treatment exhibited an excellent genetic stability (15 generations), growth rate and significantly increased activities of neutral proteases, alkaline proteases and aspartyl aminopeptidase during fermentation. Mutant H8 significantly enhanced the contents of 1–5 kDa peptides, aspartic acid, serine, threonine and cysteine in soy sauce by 16.61%, 7.69%, 17.30%, 8.61% and 45.00%, respectively. But it had no effects on the contents of other 14 free amino acids (FAAs) due to its slightly enhanced acidic proteases activity. Analyses of transcriptional expressions of salt-tolerant alkaline protease gene (AP, gi: 217809) and aspartyl aminopeptidase gene (AAP, gi: 6165646) indicated that their expression levels were increased by approximately 30% and 27%, respectively. But no mutati...