Effect of Stress Inducer on the Morphology of the Riboflavin producer Eremothecium ashbyii

Abstract

Eremothecium ashbyii is a filamentous hemiascomycete fungus known for the overproduction of riboflavin and is therefore an industrially important micro organism. Riboflavin is required in trace amounts, but at high concentration it is toxic to the cell, causing photo-induced damage of the macromolecules. Although riboflavin acts as a protective agent for spores against UV radiation, at high concentrations it causes the same damage to the cell as UV radiation. Production of riboflavin is initiated by stress such as UV rays or limiting substrate. Thus stress induced riboflavin production is seen in this organism. Preliminary studies have shown that as a first line of defence against toxicity due to production of excess riboflavin, morphological changes are produced. Sporulation in this fungus has also been correlated with riboflavin overproduction. Non sporulating E.ashbyii produces less riboflavin. The morphology and physiology of different E.ahbyii UV mutants varied and showed distinct changes during their growth in the riboflavin production medium. The physiological characteristics of UV mutants and that of wild type E.ashbyii differed in terms of increased glucose utilization and higher biomass production. The mutants also showed higher riboflavin production. Highly flavinogenic mutants show good mycelial integrity and sporulation. In this study for the first time the morphological changes in E.ashbyii under conditions of stress are reported. The organism was grown in the presence used two stressors – riboflavin itself and the chemical mutagen ethidium bromide. It was found that when riboflavin itself was used as a stress compound, production was initiated at an early stage, increased production was obtained and the organism was able to tolerate upto 0.8mM riboflavin, but when ethidium bromide was used,a toxic effect was observed in the organism leading to a decreased riboflavin production. Thus a feed forward effect on riboflavin production was observed when riboflavin itself was used as a stress inducer.