Role of Multispecies Biofilms with a Dominance of Bacillus subtilis in the Rhizosphere

Bacillus subtilis is a soil-dwelling, spore-forming bacterium that is also a plant growth-promoting rhizobacterium (PGPR) and an excellent biological control agent with various beneficial activities in plant protection. Biological control by Bacillus subtilis is attributed to a number of important abilities of the bacterium, including antibiotic production, inhibition of pathogenic fungi and parasites, induction of plant systemic resistance, and formation of plant root-associated biofilms. Bacillus subtilis not only induce plant growth but also provide protection by the process known as biocontrol, whereas other bacteria in the biofilm mode of growth can create a nuisance for plants. The plant and the rhizomicrobiome strongly influence each other via the secretion and detection of signaling compounds. Interactions between microbes can be both cooperative or competitive, meaning that depending on co-occurring bacteria, root colonization by B. subtilis might be improved or reduced, or even successful or unsuccessful. Despite the fact that Bacillus is one of the most commonly used genera in microbial inocula, no studies have looked at the effect the of the natural plant microbiome on the distribution of B. subtilis strains in the structure of biofilms, formed in the rhizosphere, their root colonization and biocontrol activity. This article describe the major features of B. subtilis biofilms with a focus on the various signals and mechanisms that regulate expression of the matrix genes, which induce biofilm formation and focus on the importance of multiple species biofilms composed of either synergistically acting bacteria or Bacillus subtilis antagonistic strains, that compete for root colonization, as well as specific effects of these interactions on plant health, growth, and development, the ecological significance and the influence of root exudates on their interactions and biofilm forming ability.