Cyclic Lipopeptide Biosynthetic Genes and Products, and Inhibitory Activity of Plant- Associated Bacillus against Phytopathogenic Bacteria
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The antibacterial activity against bacterial plant pathogens and its relationships with the
presence of the cyclic lipopeptide (cLP) biosynthetic genes ituC (iturin), bmyB (bacillomycin),
fenD (fengycin) and srfAA (surfactin), and their corresponding antimicrobial peptide
products have been studied in a collection of 64 strains of Bacillus spp. isolated from plant
environments. The most frequent antimicrobial peptide (AMP) genes were bmyB, srfAAand
fenD (34-50% of isolates). Most isolates (98.4%) produced surfactin isoforms, 90.6%iturins
and 79.7% fengycins. The antibacterial activity was very frequent and generally intense
among the collection of strains because 75% of the isolates were active against at least 6 of
the 8 bacterial plant pathogens tested. Hierarchical and correspondence analysis confirmed
the presence of two clearly differentiated groups. One group consisted of Bacillus strains
that showed a strong antibacterial activity, presented several cLPs genes and produced
several isoforms of cLPs simultaneously, mainly composed of B. subtilisand B. amyloliquefaciens,
although the last one was exclusive to this group. Another group was characterized
by strains with very low or none antibacterial activity, that showed one or none of the cLP
genes and produced a few or none of the corresponding cLPs, and was the most heterogenous
group including B. subtilis, B. licheniformis, B. megaterium, B. pumilus, B. cereusand
B. thuringiensis, although the last two were exclusive to this group. This work demonstrated
that the antagonistic capacity of plant-associated Bacillusagainst plant pathogenic bacteria
is related to the presence of cLP genes and to the production of the corresponding cLPs,
and it is mainly associated to the species B. subtilisand B. amyloliquefaciens. Our findings
would help to increase the yield and efficiency of screening methods to obtain candidate
strains to biocontrol agents with a mechanism of action relaying on the production of antimicrobial
cLPs