Characterization of Aspergillus Carbonarius In Relation To Polygalacturonase Secretion and Carotenoid Biosynthesis

Abstract

In the present study, the relationship between polygalacturonase (PG) secretion and partially saturated canthaxanthin (PSC) biosynthesis was studied using carotenogenic inhibitors and SDS-PAGE electrophoresis. Also the correlation between morphogenesis and PG secretion was investigated by analysing through microscopic studies. From the results, it was observed that secretion of PG was positively influenced by the PSC biosynthesis. The results also showed that the mutant with hairy mycelial structure resulted in higher PG activity when compared to the wild type that lacks hyper branching. From the results, it was confirmed that a mutation might have occurred in the isoprenoid pathway that has helped mutant for survival at acidic conditions. Further, an alteration in the morphogenesis and hyper branching development caused over secretion of PG enzyme in the mutant. The acidic stress under low pH is an important abiotic factor that affects the carotenoid biosynthesis in Aspergillus carbonarius. The carotenoid accumulation by A. carbonarius mutant was enhanced by low pH whereas the pH 5.5 was unable to promote the carotenoid biosynthesis. In this study, the transcriptome of A. carbonarius mutant grown in low pH (3.0) was compared with A. carbonarius mutant grown in normal pH (5.5), with the aim of identifying the key genes responsible for carotenoid biosynthesis through RNA sequencing. Results showed that for the mutant Aspergillus carbonarius that was grown in pH 5.5, a total of 1.58GB (~20 milion reads) and for the mutant that was grown in pH 3.0, 1.18GB (~ 15 million reads) data was generated. A total of 4220 genes were identified, out of which 927 genes were fetched as significantly expressed genes. There were about 173 genes that were up regulated and 754 genes that were down regulated in both control and coloured samples. The present transcriptomic study provides the basic understanding of carotenoid biosynthesis in A. carbonarius mutant under pH stress. It has been earlier reported that PSC from A.