Interacting temperature and water activity modulate production of Destruxin A by Metarhizium anisopliae on Galleria larvae-modified agar based media invitro
Destruxin A produced by some strains of entomopathogenic Metarhizium anisopliae is an important secondary metabolite which has been reported as a virulence factor. This study evaluated the effect of temperature and water activity (aw) on destruxin A (DA) production by two strains of M. anisopliae (V275 and Ma 275.86) cultured on Oxoid Technical Agar modified with homogenized insect larvae invitro. Only one of the strains (V275) produced DA on the substrate and there were significant variabilities in the amount of DA at different aw and temperature regimes. Concentrations of DA were further modulated by interactions of temperature and aw. The retention time for DA in the HPLC profile was 15.5 minutes and the highest peak was at 0.98 aw and 35°C while the lowest was at 0.96 aw and 35°C. The abiotic interactions that supported biomass production appeared different from what was required for production of DA. The optimal temperatures for biomass formation varied significantly with aw. At 0.995 aw and 25°C, highest biomass was produced while at relatively lower aw levels (0.98 and 0.96) the optimum temperature was 30 °C. There was a strong positive correlation (r = 0.455, n = 25, p = 0.023) between temperature and DA concentration.