Abstract
Secondary metabolites have an important impact on the biocontrol potential of soil-derived microbes. In addition, various microbe-produced chemicals have been suggested to impact the development and phenotypic differentiation of bacteria, including biofilms. The non-ribosomal synthesized lipopeptide of Bacillus subtilis, surfactin, has been described to impact the plant promoting capacity of the bacterium. Here, we investigated the impact of surfactin production on biofilm formation of B. subtilis using the laboratory model systems; pellicle formation at the air-medium interface and architecturally complex colony development, in addition to plant root-associated biofilms. We found that the production of surfactin by B. subtilis is not essential for pellicle biofilm formation neither in the well-studied strain, NCIB 3610, nor in the newly isolated environmental strains, but lack of surfactin reduces colony expansion. Further, plant root colonization was comparable both in the presence or absence of surfactin synthesis. Our results suggest that surfactin-related biocontrol and plant promotion in B. subtilis strains are independent of biofilm formation.
Highlights
Several species from the “Bacillus subtilis complex” are wellcharacterized plant growth-promoting rhizobacteria (PGPRs), providing various beneficial activities for plants and inhibiting fungal and bacterial pathogens [1]
A strain deleted for sfp, which is defective for synthesis of all non-ribosomal peptide synthetases (NRPS)-derived molecules, is able to form pellicle in both media
The B. subtilis produced surfactin has been reported to lead to induction of biofilm development under non-biofilm inducing conditions [26]
Summary
Several species from the “Bacillus subtilis complex” are wellcharacterized plant growth-promoting rhizobacteria (PGPRs), providing various beneficial activities for plants and inhibiting fungal and bacterial pathogens [1]. Many strains of Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus velezensis are currently used in organic and traditional agriculture to prevent infection and/or increase yields of various crops [2,3,4] These species are of particular interest because they can form stress-resistant endospores, a cell-type ideal for product formulation. Most PGPR Bacillus spp. produce a wide range of bioactive molecules, such as lipopeptides, which directly influences plant growth and defense [5]. Many of these molecules are synthesized by multienzyme-complexes called non-ribosomal peptide synthetases (NRPS) [6]. SrfAA-AD produces versatile molecules from the surfactin family [10]
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