Characterisation of optimum cultural environmental conditions for the production of high numbers of Metarhizium anisopliae blastospores with enhanced ecological fitness
2005
Ypsilos, I.K. | Magan, N.
The aim of this study was the production of high numbers of M. anisopliae blastospores with enhanced germination efficiency under conditions of water-stress (ecological fitness). Different nitrogen sources and concentrations were screened for their ability to induce blastospore production while keeping pH and water activity (a(w)) at fixed levels (6.8, and 0.98 a(w), respectively). After optimum nitrogen status was determined (cornsteep solid (CS) + yeast extract (YE); or cottonseed flour (CF) + YE), the effect of interaction of nitrogen source, pH (3.5, 5, 6.8, 8, 9 and 10) and solutes for a(w) adjustment (KCl, NaCl, PEG 200) on blastospore production, endogenous polyol content (glycerol, erythritol, arabitol and mannitol) and total protein, were determined. For both ionic (NaCl, KCl) and non-ionic solutes (PEG 200), optimum blastospore production (between 4 x 10(7) and 2 x 10(8) blastospores ml(-1)) and growth occurred in the pH range 6.8-8, with the CF + YE nitrogen profile giving higher yields than CS + YE. Optimum conditions for high erythritol and total protein endogenous concentrations (40.37-73.44 and 14.33-18.90 mg g(-1) fresh weight, respectively) occurred between pH 6.8 and 8 by ionic a(w) modification (KCl, NaCl) and with the CF + YE nitrogen profile. Germination of blastospores produced under these cultural conditions was between 62 and 89% under conditions of water-stress (0.96 a(w)). On the other hand, blastospores with lower amounts of erythritol and total protein content had decreased germination (8-67%). These results could have significant implications for developing a liquid fermentation medium for the production of high numbers of fungal propagules with enhanced efficacy under non-optimum environmental conditions.
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