A bioencapsulation and drying method increases shelf life and efficacy of Metarhizium brunneum conidia.

This study reports the development of encapsulated and dried entomopathogenic fungus Metarhiuzm brunneum with reduced conidia content, increased conidiation, a high drying survival and enhanced shelf life. Dried beads prepared with the fillers corn starch, potato starch, carboxymethylcellulose or autoclaved baker's yeast, showed enhanced survival with increasing filler content. The maximum survival of 82% was found for beads with 20% corn starch at <0.1 water activity. While increasing starch content inhibits the conidiation, autoclaved baker's yeast and a combination with starch enhanced the conidiation to 1.0 × 108 conidia/bead. Beads with conidia content reduced to 0.01% multiplied conidia in a "microfermentation" by the factor 1000. A bioassay confirmed that conidia formed from rehydrated beads were virulent against Tenebrior molitor larvae. After six months of storage, encapsulated conidia showed improved shelf life compared to non-formulated conidia. This "microfermenter" will pave the way for encapsulated fungi to be used as cost-effective biocontrol agents.

Calcium gluconate as cross-linker improves survival and shelf life of encapsulated and dried Metarhizium brunneum and Saccharomyces cerevisiae for the application as biological control agents.

Calcium chloride (CC) is the most common cross-linker for the encapsulation of biocontrol microorganisms in alginate beads. The aim of this study was to evaluate if calcium gluconate (CG) can replace CC as cross-linker and at the same time improve viability after drying and rehydration, hygroscopic properties, shelf life and nutrient supply. Hence, the biocontrol fungi Metarhizium brunneum and Saccharomyces cerevisiae were encapsulated in Ca-alginate beads supplemented with starch. Beads were dried and maximum survival was found in beads cross-linked with CG. Beads prepared with CG showed lower hygroscopic properties, but a higher shelf life for encapsulated fungi. Moreover, we demonstrated that gluconate has a nutritive effect on encapsulated fungi, leading to increased mycelium growth of M. brunneum and to enhanced CO2 release from beads containing Saccharomyces cerevisiae. The application of CG as cross-linker will pave the way towards increasing drying survival and shelf life of various, especially drying-sensitive microbes.