Role of Partially Saturated Canthaxanthin and Ergosterol in the Survival of Aspergillus carbonarius Mutant at Extreme Acidic Condition.

Unlike the wild type, the mutant Aspergillus carbonarius synthesized a yellow pigment, partially
saturated canthaxanthin (PSC) when the growth medium acidified to low pH. Since the pigment found pharmaceutical
applications, the possible mechanism involved in its ability to grow at extreme acidic conditions
is described. To understand the mutation in the pathway, specific inhibitors affecting carotenoid biosynthesis
were used in the medium and PSC synthesis and cell integrity were studied. Results suggested that the possible
occurrence of mutation in the isoprenoid pathway for higher production of carotenoid as well as ergosterol
caused the mutant to grow in extremely acidic conditions. The results also suggested that the flow of carbon
for sterol biosynthesis and that of carotenoids are dependent. The deposition of carotenoids and ergosterol in
the cell membrane causing the cells to maintain pH homeostasis under the acidic growth conditions is of significant
importance. In A. carbonarius, understanding the cause of stress induced PSC accumulation is
essential for efficient expression and production of the pharmaceutically significant carotenoid and this will
further facilitate research into the role of carotenoids in stress tolerance of other filamentous fungi.