Bacillus amyloliquefaciens subsp. plantarum FZB42 is a Gram-positive model bacterium
for unraveling plant–microbe interactions in Bacilli. In addition, FZB42 is used
commercially as biofertilizer and biocontrol agent in agriculture. Genome analysis of
FZB42 revealed that nearly 10% of the FZB42 genome is devoted to synthesizing
antimicrobial metabolites and their corresponding immunity genes. However, recent
investigations in planta demonstrated that – except surfactin – the amount of such
compounds found in vicinity of plant roots is relatively low, making doubtful a
direct function in suppressing competing microflora including plant pathogens. These
metabolites have been also suspected to induce changes within the rhizosphere
microbial community, which might affect environment and plant health. However,
sequence analysis of rhizosphere samples revealed only marginal changes in the
root microbiome, suggesting that secondary metabolites are not the key factor in
protecting plants from pathogenic microorganisms. On the other hand, adding FZB42
to plants compensate, at least in part, changes in the community structure caused
by the pathogen, indicating an interesting mechanism of plant protection by beneficial
Bacilli. Sub-lethal concentrations of cyclic lipopeptides and volatiles produced by plantassociated
Bacilli trigger pathways of induced systemic resistance (ISR), which protect
plants against attacks of pathogenic microbes, viruses, and nematodes. Stimulation
of ISR by bacterial metabolites is likely the main mechanism responsible for biocontrol
action of FZB42.