Abstract
ABSTRACTThere is a growing appreciation for the impact that bacteria have on higher organisms. Plant roots often harbor beneficial microbes, such as the Gram-positive rhizobacterium Bacillus subtilis, that influence their growth and susceptibility to disease. The ability to form surface-attached microbial communities called biofilms is crucial for the ability of B. subtilis to adhere to and protect plant roots. In this study, strains harboring deletions of the B. subtilis genes known to synthesize and degrade the second messenger cyclic di-adenylate monophosphate (c-di-AMP) were examined for their involvement in biofilm formation and plant attachment. We found that intracellular production of c-di-AMP impacts colony biofilm architecture, biofilm gene expression, and plant attachment in B. subtilis. We also show that B. subtilis secretes c-di-AMP and that putative c-di-AMP transporters impact biofilm formation and plant root colonization. Taken together, our data describe a new role for c-di-AMP as a chemical signal that affects important cellular processes in the environmentally and agriculturally important soil bacterium B. subtilis. These results suggest that the “intracellular” signaling molecule c-di-AMP may also play a previously unappreciated role in interbacterial cell-cell communication within plant microbiomes.
Highlights
There is a growing appreciation for the impact that bacteria have on higher organisms
We demonstrated that c-di-AMP signaling plays an important role in biofilm formation and plant attachment in B. subtilis through the phenotypic characterization of B. subtilis diadenylate cyclases (DACs) and PDE mutants
Biofilm formation is important for environmental fitness and adaptation in many bacteria
Summary
There is a growing appreciation for the impact that bacteria have on higher organisms. We found that B. subtilis secretes c-di-AMP and that the ability to produce, degrade, or transport cyclic di-adenylate monophosphate (c-di-AMP; a common bacterial second messenger) affects B. subtilis biofilm gene expression and plant attachment. To our knowledge, this is the first demonstration of c-di-AMP impacting a mutualist host-microbe association and suggests that c-di-AMP may function as a previously unappreciated extracellular signal able to mediate interactions within plant microbiomes. Plant root colonization is beneficial to the bacteria because root exudates provide a rich fixed-carbon source [12] These interkingdom interactions are highly relevant to environmental ecology and agriculture. These matrix components are encoded by the epsA-epsO (epsA-O) operon, the tapA operon, and the bslA gene, respectively
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