Effects of different light wavelengths on Bacillus subtilis and Bacillus velezensis, two biocontrol agents isolated from the maize phyllosphere

In previous studies, two strains isolated from the maize phyllosphere were identified as Bacillus subtilis (EM-A7) and Bacillus velezensis (EM-A8) and selected as potential biocontrol agents against Exserohilum turcicum. This study aimed to assess the ability of EM-A7 and EM-A8 to form biofilm and have antagonistic activity under varying light conditions. LED sources were custom-designed so that each corresponded to a given spectrum at a specific photosynthetically active photon flux density. Significant differences were observed in growth parameters (generation time and constant growth rate) under different LED sources. Blue light inhibited the growth of both strains. Red increased k rate in EM-A8, while the g values increased in EM-A7. Red and white light generally increased biofilm formation, and blue light inhibited it. EM-A7 and EM-A8 significantly reduced their ability to swim under blue LED, but it was not affected by red, green, or white light. The ability to swarm was negatively affected. Fungal growth decreased significantly compared to the control when the bacterium growing on the same plate had been previously incubated under red and white light or in the dark. These results indicate that different light wavelengths clearly influenced the aspects assessed in B. subtilis and B. velezensis, with the effects of blue light being overall negative and those of red and white overall positive. Given that, all these factors can be important for the establishment and survival of Bacillus strains on leaves, as well as for their effectiveness against pathogens, light could be a significant factor to consider in the design of biocontrol strategies.