Bacillus subtilis and other Bacilli have long been used as biological control agents against plant
bacterial diseases but the mechanisms by which the bacteria confer protection are not well
understood. Our goal in this study was to isolate strains of B. subtilis that exhibit high levels of
biocontrol efficacy from natural environments and to investigate the mechanisms by which these
strains confer plant protection. We screened a total of sixty isolates collected from various
locations across China and obtained six strains that exhibited above 50% biocontrol efficacy on
tomato plants against the plant pathogen Ralstonia solanacearum under greenhouse conditions.
These wild strains were able to form robust biofilms both in defined medium and on tomato plant
roots and exhibited strong antagonistic activities against various plant pathogens in plate assays.
We show that plant protection by those strains depended on widely conserved genes required for
biofilm formation, including regulatory genes and genes for matrix production. We provide
evidence suggesting that matrix production is critical for bacterial colonization on plant root
surfaces. Finally, we have established a model system for studies of B. subtilis-tomato plant
interactions in protection against a plant pathogen