Preformulation study as a basis for the development of Streptomyces sp. PNM-9 microparticles for biological control

The use of biocontrollers such as Streptomyces sp. PNM-9, which is effective against Burkholderia glumae and Colletotrichum gloeosporioides, the phytopathogens of yam and rice crops, serves as a promising alternative to pesticides. However, its effectiveness may be compromised by environmental stress. The preformulation of a microparticulate system that could contain the biocontroller was conducted to improve its stability. Streptomyces sp. PNM-9 was cultivated on rice husk and kaolin solid supports, subjecting them to temperatures of 60°C and 80°C for 10 minutes and desiccation stress for 6 hours at 25°C. To evaluate compatibility with wall materials, selected and inoculated solid support was used to prepare mixtures with maltodextrin, soy protein, and gum arabic. Each of these mixtures was subsequently spray-dried under predefined conditions. Solid supports demonstrated a protective effect on Streptomyces sp. PNM-9 against high temperature and drying conditions, in contrast to the broth. No statistically significant differences were found in the viability of Streptomyces sp. PNM-9 between the two supports after exposure to different temperatures and drying conditions. The rice husk, selected as the solid support, showed no incompatibilities with the wall materials. Therefore, subsequent studies focusing on microparticle formulation with rice husk and the evaluated polymer as wall material are strongly recommended.