difficidin and bacilysin

Bacterial blight and bacterial leaf streak are serious, economically damaging, diseases of rice caused by the bacteria Xanthomonas oryzae pv. oryzae and X. oryzae pv. oryzicola. Bacillus amyloliquefaciens FZB42 was shown to possess biocontrol activity against these Xanthomonas strains by producing the antibiotic compounds difficidin and bacilysin. Analyses using fluorescence, scanning electron and transmission electron microscopy revealed difficidin and bacilysin caused changes in the cell wall and structure of Xanthomonas. Biological control experiments on rice plants demonstrated the ability of difficidin and bacilysin to suppress disease. Difficidin and bacilysin caused downregulated expression of genes involved in Xanthomonas virulence, cell division, and protein and cell wall synthesis. Taken together, our results highlight the potential of B. amyloliquefaciens FZB42 as a biocontrol agent against bacterial diseases of rice, and the utility of difficidin and bacilysin as antimicrobial compounds.

Topics: Anti-Bacterial Agents; Bacillus; Cell Wall; Dipeptides; Lactones; Oryza; Plant Diseases; Plant Leaves; Xanthomonas

The plant-growth-promoting-rhizobacteria Bacillus amyloliquefaciens FZB42 possess an enormous potential to synthesize a wide range of antimicrobial, antiviral and nematocidal compounds. One of them, the dipeptide antibiotic bacilysin, is synthesized by FZB42 during exponential growth. Here, we have demonstrated that bacilysin is positively regulated by the two-component response regulator DegU at the transcriptional level. In addition, ScoC (Hpr), a transition state regulator, negatively controlled expression of the bacA gene, which is the first gene within the bacilysin operon. Both DegU and ScoC were bound directly at the bacA promoter region. Furthermore, a monocistronic gene located in close vicinity of the bac operon and essential for bacilysin production, ywfH, was also regulated by DegU. Transcription of the bac operon and of the ywfH gene in B. amyloliquefaciens FZB42 was positively controlled by the DegU global regulator protein. The role of interactions within a ternary complex formed by the antagonistically acting regulators DegU and ScoC as well as the bacA promoter sequence remains to be elucidated.

Topics: Bacillus; Bacterial Proteins; Base Sequence; Binding Sites; Chromosome Mapping; Dipeptides; Electrophoretic Mobility Shift Assay; Gene Expression Regulation, Bacterial; Genes, Bacterial; Lactones; Molecular Sequence Data; Operon; Promoter Regions, Genetic; Protein Binding; Regulon; Transcription Factors; Transcription Initiation Site; Transcription, Genetic

Representatives of Bacillus amyloliquefaciens were shown to possess biocontrol activity against fire blight, a serious disease of orchard trees caused by Erwinia amylovora. Genome analysis of B. amyloliquefaciens FZB42 identified gene clusters responsible for synthesis of several polyketide compounds with antibacterial action. We show here that the antibacterial polyketides difficidin and to a minor extent bacillaene act efficiently against E. amylovora. Surprisingly, a mutant strain blocked in the production of difficidin (CH8 Deltadfn) inhibited growth of E. amylovora and suppressed fire blight disease nearly in the same range as the wild type. In addition, a sfp mutant (CH3 Deltasfp) unable to synthesize non-ribosomally lipopeptides and polyketides did still suppress growth of E. amylovora, suggesting that besides action of polyketides another antagonistic principle exist. A double mutant (RS06 Deltasfp Deltabac) devoid in polyketide and bacilysin synthesis was unable to suppress growth of E. amylovora indicating that the additional inhibitory effect is due to production of bacilysin, a dipeptide whose synthesis does not depend on Sfp. We propose to use B. amyloliquefaciens strains with enhanced synthesis of difficidin and/or bacilysin for development of biocontrol agents efficient against fire blight disease.

Topics: Bacillus; Chromatography, High Pressure Liquid; Dipeptides; Erwinia amylovora; Lactones; Macrolides; Mutation; Pest Control, Biological; Plant Diseases