Organization and characterization of genetic regions in Bacillus subtilis subsp. krictiensis ATCC55079 associated with the biosynthesis of iturin and surfactin compounds

Abstract

Bacillus subtilis subsp. krictiensis ATCC55079 produces the cyclic lipopeptide antibiotics iturin A–F as well as several surfactins. Here, we analyzed and characterized the biosynthetic genes associated with iturin and surfactin production in this strain. We aligned the sequences of each iturin and surfactin synthetase ORF obtained from a genomic library screen and next generation sequencing. The resulting 37,249-bp and 37,645-bp sequences associated with iturin and surfactin production, respectively, contained several ORFs that are predicted to encode proteins involved in iturin and surfactin biosynthesis. These ORFs showed higher sequence homologies with the respective iturin and surfactin synthetase genes of B. methylotrophicus CAU B946 than with those of B. subtilis RB14 and B. subtilis ATCC6633. Moreover, comparative analysis of the secondary metabolites produced by the wild-type and surfactin-less mutant (with a spectinomycin resistance cassette inserted into the srfAB gene within the putative surfactin gene region) strains demonstrated that the mutant strain showed significantly higher antifungal activity against Fusarium oxysporum than the wild-type strain. In addition, the wild-type strain-specific surfactin high performance liquid chromatography (HPLC) peaks were not observed in the surfactin-less mutant strain. In contrast, the iturin A peak detected by HPLC and liquid chromatography-mass spectrometry (LC/MS) in the surfactin-less mutant strain was 30% greater than that in the wild-type strain. These results suggested that the gene cluster we identified is involved in surfactin biosynthesis, and the biosynthetic pathways for iturin and surfactin in Bacillus strains producing both iturin and surfactin may utilize a common pathway.

Lipopeptide mediated biocontrol activity of endophytic Bacillus subtilis against fungal phytopathogens

“…shows structural similarities to surfactin [49]. The notable differences among these lipopeptides include the type of the amino acids, their peptide sequences, the branching of the fatty acid chain [63] and their biosynthetic genes present in different operons. The presence of fenA and other four polyketide genes have been detected in the bacterial genome, however, fengycin, bacillaene, difficidin, macrolactins and bacillomycin were not detected by LC-ESI-MS. Synthesis of these compounds may be condition specific and therefore were not synthesized during the antagonistic activity against the fungal pathogens.…”

Characterization of Antifungal Lipopeptide Biosurfactants Produced by Marine Bacterium Bacillus sp. CS30

“…Most Bacillus sp. can produce one type of lipopeptide and a few can produce two or three types of lipopeptides [13,14,15]. The biological activities of lipopeptides are closely related to the sequence of amino-acid residues, the cyclization of the peptide, and the length and branching of the fatty acid chain [16].…”

Fungal-bacterial interaction selects for quorum sensing mutants and a metabolic shift towards the production of natural antifungal compounds

“…Moreover, a Bacillus subtilis subsp. krictiensis surfactin-less mutant showed significantly higher antifungal activity against Fusarium oxysporum than its wild-type strain (41). Thus, we speculate that by reducing or preventing the biosynthesis of surfactin, BsA01 could avoid some negative impact on fitness while making an effective use of other inhibitory compounds against S. terrestris .…”

“…One could think that the lack of surfactin is a mere consequence of the metabolic change that arise along with the phenotype variation experienced by BsA01 and that is not directly related to the antagonism per se . However, it has been suggested that surfactins could interfere with the activity of other lipopeptides with proven antifungal activity such as fengycins/plipastatins and iturins (38, 41). In a study, B. amyloliquefaciens FZB42 mutants selectively repressed in the synthesis of one or two types of lipopeptides revealed that the co-production of surfactin and fengycin lowered the global antifungal activity (38).…”