Effects of environmental factors on growth and sclerotium formation in Aspergillus ochraceus

Abstract

The effects of carbohydrates, amino acids, sulphur-containing compounds, temperature, pH, and light on growth and sclerotium production in Aspergillus ochraceus were studied. The maximal number of sclerotia was formed on medium containing sucrose at a concentration of 2 × 10−1 M, while on the lactose, galactose, and arabinose media no sclerotia were formed and poor mycelial growth was observed. Among the amino acids tested, glutamic acid (10−2 M) enhanced sclerotium formation, whereas there was complete inhibition when methionine (10−2 M) and ethionine (10−2 M) were added. Good production of sclerotia occurred on medium containing glutathione in all concentrations tested. Among the other sulphur-containing compounds tested, only sodium thiosulphate at a concentration of 10−1 M inhibited sclerotium formation without inhibition of mycelial growth. The pH at which sclerotia were formed ranged from 4.0 to 9.0. There was no growth at pH 3.0, and normal mycelial growth without sclerotium production occurred at a pH range of 11.0 to 13.0. Optimal temperatures for mycelial growth and sclerotium formation were 28 and 32 °C, while less growth and no sclerotium production occurred at 20 and 24 °C. Extensive production of sclerotia was observed when cultures were grown in the dark, while under continuous white, red, or blue light sclerotium production was sparse. It is suggested that sulphur-containing compounds can serve as a tool for studying the mechanism of sclerotium production in A. ochraceus.