Applied Microbiology and Biotechnology, Vol.102, No.10, 4467-4475, 2018
The effects of gene disruption of Kre6-like proteins on the phenotype of beta-glucan-producing Aureobasidium pullulans
Killer toxin resistant 6 (Kre6) and its paralog, suppressor of Kre null 1 (Skn1), are thought to be involved in the biosynthesis of cell wall beta-(1 -> 6)-D-glucan in baker's yeast, Saccharomyces cerevisiae. The Delta kre6 Delta skn1 mutant of S. cerevisiae and other fungi shows severe growth defects due to the failure to synthesize normal cell walls. In this study, two homologs of Kre6, namely, K6LP1 (Kre6-like protein 1) and K6LP2 (Kre6-like protein 2), were identified in Aureobasidium pullulans M-2 by draft genome analysis. The Delta k6lp1, Delta k6lp2, and Delta k6lp1 Delta k6lp2 mutants were generated in order to confirm the functions of the Kre6-like proteins in A. pullulans M-2. The cell morphologies of Delta k6lp1 and Delta k6lp1 Delta k6lp2 appeared to be different from those of wild type and Delta k6lp2 in both their yeast and hyphal forms. The productivity of the extracellular polysaccharides, mainly composed of beta-(1 -> 3),(1 -> 6)-D-glucan (beta-glucan), of the mutants was 5.1-17.3% less than that of wild type, and the degree of branching in the extracellular beta-glucan of mutants was 14.5-16.8% lower than that of wild type. This study showed that the gene disruption of Kre6-like proteins affected the cell morphology, the productivity of extracellular polysaccharides, and the structure of extracellular beta-glucan, but it did not have a definite effect on the cell viability even in Delta k6lp1 Delta k6lp2, unlike in the Delta kre6 Delta skn1 of S. cerevisiae.