Metarhizium robertsii protease and conidia production, response to heat stress and virulence against Aedes aegypti larvae

Abstract

Nutritional factors exert significant influence on the growth of entomopathogenic fungi, one of the main agents employed commercially in the biological control of arthropods. Thus, the objective of this work is to optimize the culture medium and solid fermentation time for production of proteases and conidia of Metarhizium robertsii ARSEF 2575 and to evaluate the interference of riboflavin and salts on virulence and resistance to abiotic stress factors. In the first step, nine groups were separated: negative control, positive control, and seven supplementation groups: ammonium nitrate, ammonium chloride, potassium nitrate, sodium nitrate, ammonium sulfate, ammonium phosphate, urea. Sodium nitrate showed significant difference in protease production at the time of 20 days of solid fermentation. Then, different concentrations of sodium nitrate and riboflavin as supplement were evaluated. Response surface methodology demonstrated that riboflavin and sodium nitrate influence proteolytic activity and conidia production, but without synergism. Supplementation of the medium with the optimal concentration of sodium nitrate and riboflavin did not interfere with the germination of conidia without exposure to abiotic stress, but did increase the thermotolerance of conidia. The presence of riboflavin and sodium nitrate at optimal concentrations in the culture medium did not alter fungal virulence with and without exposure to heat stress, varying according to the presence or absence of the supernatant during exposure, evidencing that resistance to heat exposure is multifactorial and dependent on intra- and extracellular factors. Moreover, the supplementation increased the larvicidal activity of the supernatant against Aedes aegypti.

Performance of Metarhizium rileyi Nm017: nutritional supplementation to improve production and quality conidia

“…4 b). Comparably, Ferreira et al ( 2021 ) showed that culture medium supplemented with sodium nitrate and riboflavin enhanced protease activity and conidia production of Metarhizium robertsii . Similarly, additives such as soybean protein combined with wheat bran induced the protease activity of M. anisopliae (Kim et al 2020 ), and the supplementation with yeast extract improved the chitinase composition of M. anisopliae (Dhar and Kaur 2009 ).…”

Solid-State Fermentation: Applications and Future Perspectives for Biostimulant and Biopesticides Production

“…Most of the scientific papers deal with the use of SSF to grow fungi and oomycetes ( Supplementary Table S1 , Refs. [ 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , …”