Optimisation de la croissance et de la sporulation de Conidiobolus obscurus en milieu défini

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Abstract
Physical and nutritional factors influencing the growth and sporulation of Conidiobolus obscurus (Hall et Dunn) Remaudière et Keller were studied using simple and fragmented factorial designs and centered composite designs. Culture conditions allowing maximum sporulation were a temperature of 20 °C, complete darkness, and a near neutral pH of around 6.5. Under our experimental conditions, dextrose influenced neither the growth nor the sporulation of C. obscurus. The cations stimulating the formation of azygospores were magnesium and to a lesser extent zinc and manganese. Sulphur must be added to the medium in a reduced or oxydized form. Phosphates must be present in the culture medium, but at a concentration less than 30 mM/L. Vitamins stimulating sporulation were thiamine, biotin, and folic acid while pantothenic acid favoured growth. Among the 20 amino acids tested, proline, leucine, methionine, glutamic and aspartic acids, glutamine, asparagine, histidine, phenylalanine, lysine, and arginine were the most favourable for growth and sporulation of C. obscurus. Growth and sporulation in the optimized defined medium containing 11 amino acids, four vitamins, four salts, and dextrose were comparable to the best results obtained in a nondefined medium composed of dextrose and yeast extract.