Differences among Bacillus velezensis Strains from Biofilm Formation to Competition in Niche Determination on Plant Roots

Biofilm formation and rhizosphere colonization of the plants are the main infrastructures for the biological control of the plant diseases. Bacteria accumulation in the protective layer, which results from their self-production of Exopolysaccharides (EPS), is called the biofilm. The formation of these complex structures originates from the multicellular behaviors of bacteria. Various elements can play a role in these mechanisms. In this study, we examined biofilm formation, root colonization, and salt tolerance to four concentrations of NaCl in the strains of Bacillus velezensis (Q12, US1, and UR1). The results showed that the biofilm strength plays an important role in the efficiency of tomato root colonization. Furthermore, UR1 that had defects in producing the surfactin, iturin, and fengycin using Ultrahigh-Performance Liquid Chromatography-High Resolution Electrospray Ionization Mass Spectrometry (UHPLC-HRESIMS), was incapable of tolerance to salinity, biofilm formation, competition, and rhizosphere colonization. Confocal Laser Scanning Microscopy (CLSM) studies showed that strains US1 and Q12 differed in the biofilm strength, the position of the bacteria that are located laterally, polar, or both, and root colonization. Q12 was introduced as the best strain in all these experiments. Also, based on the findings of this and previous studies, the possibility to create the subpopulations influenced by genetic diversity in Bacillus velezensis strains during biofilm formation is suggested.