Improvement of the secretion of extracellular proteins and isolation and characterization of the amylase I (amy1) gene from Ophiostoma floccosum

UV mutagenesis was applied to improve protein secretion in Ophiostoma floccosum. Amylase activity was used as an indicator for enhanced protein production after repeated rounds of mutagenic treatment. The amylase activity in the culture supernatant of the best mutant (MQ.5.1) was increased by more than 240-fold compared to the initial parental strain. At the same time, the increase in total secreted protein was about six times greater than the parental strain. Secreted proteinase and lipase activities of the parental strain and four key mutants were also investigated. N-terminal sequencing of the five dominant protein bands separated by SDS-PAGE from the culture supernatant was conducted. Two of the proteins identified were subtilisin-like proteinases and one was a pepsin-like proteinase. In addition, one protein was identified as an α-amylase and one remained unidentified. A 6.5 kb DNA fragment was isolated by Genomic Walking PCR using primers based on the α-amylase amino acid sequence. The amplified fragment contained the entire gene encoding α-amylase (amy1) and its regulatory sequences. Analysis showed that multiple transcripts were generated from the single α-amylase gene locus.