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

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 (R), D-425 (R), 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.