Honggang Wei

Effects of milling and surfactants on suspensibility and spore viability in Paenibacillus polymyxa powder formulations

Abstract Two milling methods and five surfactants were tested for their effects on the suspensibility of a wettable powder formulation of Paenibacillus polymyxa HY96-2 (P. polymyxa original powder or PPOP). Both hammer milling and jet milling significantly improved suspensibility of PPOP (from 8.1 to 26.4% and 58.3%, respectively), and did not decrease spore viability. Five surfactants (EFW®, D-425®, sodium dodecyl benzene sulfonate, tea saponin and sodium lignosulphonate) were each mixed with jet milled powder (JMP). The best results were obtained with sodium lignosulphonate and D425. These gave equal improvement in suspensibility. Sodium lignosulphonate had the best biocompatibility; spore viability values of JMP mixed with this at 1, 3, 5, or 10% (w/w) were all over 95.0%. Addition of sodium lignosulphonate to hammer milled powder (HMP) or JMP at 5% (w/w) increased suspensibility from 26.4 to 38.6% and from 58.3 to 81.1%, respectively. Our results suggest that jet milling and sodium lignosulphonate can synergistically improve the suspensibility of P. polymyxa wettable powder without adverse effects on spore viability. These findings will accelerate the commercialization of P. polymyxa wettable powder and provide a basis for the development of other biopesticides.

Optimization of the spray drying of a Paenibacillus polymyxa-based biopesticide on pilot plant and production scales

Spore survival and moisture content are two important properties of biopesticides, and both are related to field biocontrol efficacy and storage shelf life. In this study, Paenibacillus polymyxa (HY96-2) was spray-dried on both pilot plant and production scales, and the effects of inlet and outlet temperatures on spore survival and moisture content were investigated. The results showed that inlet temperatures ranging from 170 to 230 °C (at an outlet temperature of 80 °C) had no obvious effect on the two properties during pilot scale processing, although an inlet temperature of 230 °C resulted in higher feed speed. When the outlet temperature on the pilot scale was reduced from 100 to 80 °C, no obvious variations in spore survival and moisture content were found, while a further reduction from 80 to 65 °C resulted in a decline in spore survival from 81.0 to 67.0% and an increase in moisture content from 2.3 to 31.7%. These results indicate that both outlet temperature and moisture content have an effect on spore survival. Optimum inlet and outlet temperatures for P. polymyxa processing were 230 °C and 85–90 °C on a production scale. Under these conditions, spore survival and moisture content were 83.5–86.6% and 2.73––4.12%, respectively.