Bacillus amyloliquefaciens FZB42 is a Gram-positive, plant-associated bacterium, which stimulates plant growth and produces secondary metabolites that suppress soil-borne plant pathogens. Its 3,918-kb genome, containing an estimated 3,693 protein-coding sequences, lacks extended phage insertions, which occur ubiquitously in the closely related Bacillus subtilis 168 genome. The B. amyloliquefaciens FZB42 genome reveals an unexpected potential to produce secondary metabolites, including the polyketides bacillaene and difficidin. More than 8.5% of the genome is devoted to synthesizing antibiotics and siderophores by pathways not involving ribosomes. Besides five gene clusters, known from B. subtilis to mediate nonribosomal synthesis of secondary metabolites, we identified four giant gene clusters absent in B. subtilis 168. The pks2 gene cluster encodes the components to synthesize the macrolactin core skeleton.

Although bacterial polyketides are of considerable biomedical interest, the molecular biology of polyketide biosynthesis in Bacillus spp., one of the richest bacterial sources of bioactive natural products, remains largely unexplored. Here we assign for the first time complete polyketide synthase (PKS) gene clusters to Bacillus antibiotics. Three giant modular PKS systems of the trans-acyltransferase type were identified in Bacillus amyloliquefaciens FZB 42. One of them, pks1, is an ortholog of the pksX operon with a previously unknown function in the sequenced model strain Bacillus subtilis 168, while the pks2 and pks3 clusters are novel gene clusters. Cassette mutagenesis combined with advanced mass spectrometric techniques such as matrixassisted laser desorption ionization-time of flight mass spectrometry and liquid chromatography-electrospray ionization mass spectrometry revealed that the pks1 (bae) and pks3 (dif) gene clusters encode the biosynthesis of the polyene antibiotics bacillaene and difficidin or oxydifficidin, respectively. In addition, B. subtilis OKB105 (pheA sfp 0 ), a transformant of the B. subtilis 168 derivative JH642, was shown to produce bacillaene, demonstrating that the pksX gene cluster directs the synthesis of that polyketide.Environmental Bacillus amyloliquefaciens strain FZB 42 is distinguished from the domesticated model organism Bacillus subtilis 168 (23) by several features important for rhizosphere competence particularly by its abilities to suppress competitive organisms present in the plant rhizosphere (17, 21) and to promote plant growth (16). In a previous contribution (20), we have reported that B. amyloliquefaciens FZB 42 is a producer of three families of lipopeptides, surfactins, bacillomycins D, and fengycins, which are well-known secondary metabolites with mainly antifungal activity. They are also produced by numerous B. subtilis strains (48). Furthermore, three giant gene clusters containing genes with homology to polyketide synthase (PKS) genes of modular organization were identified but not assigned functional roles. Mutants of FZB 42 deficient in the synthesis of cyclic lipopeptides were unable to suppress phytopathogenic fungi but still retained their antibacterial potency.Polyketides belong to a large family of secondary metabolites that include many bioactive compounds with antibacterial, immunosuppressive, antitumor, or other physiologically relevant bioactivities. Their biosynthesis is accomplished by stepwise decarboxylative Claisen condensations between the extender unit and the growing polyketide chain, generating enzyme-bound ␤-ketoacyl intermediates. Before a subsequent round of chain extension, a variable set of modifying enzymes can locally introduce structural variety. Similar to the nonribosomal synthesis of peptides, the PKS multienzyme system uses acyl carrier proteins (ACPs) that are posttranslationally modified with the 4Ј-phosphopantetheine prosthetic group to channel the growing polyketide intermediate during elongation processes (3). Type I PKSs...

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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.

Here we report on a novel thiazole/oxazole-modified microcin (TOMM) from Bacillus amyloliquefaciens FZB42, a Gram-positive soil bacterium. This organism is well known for stimulating plant growth and biosynthesizing complex small molecules that suppress the growth of bacterial and fungal plant pathogens. Like microcin B17 and streptolysin S, the TOMM from B. amyloliquefaciens FZB42 undergoes extensive posttranslational modification to become a bioactive natural product. Our data show that the modified peptide bears a molecular mass of 1,335 Da and displays antibacterial activity toward closely related Gram-positive bacteria. A cluster of 12 genes that covers ϳ10 kb is essential for the production, modification, export, and self-immunity of this natural product. We have named this compound plantazolicin (PZN), based on the association of several producing organisms with plants and the incorporation of azole heterocycles, which derive from Cys, Ser, and Thr residues of the precursor peptide.Bacillus amyloliquefaciens FZB42 is a Gram-positive, plant growth-promoting bacterium with an impressive capacity to produce secondary metabolites with antimicrobial activity (7). The nonribosomal syntheses of polyketides (bacillaene, difficidin, and macrolactin), lipopeptides (surfactin, fengycin, and bacillomycin D), and siderophores (bacillibactin and the product of the nrs cluster) are carried out by large gene clusters distributed over the entire genome of B. amyloliquefaciens FZB42. While these compounds are biosynthesized in a 4Ј-phosphopantetheine transferase (Sfp)-dependent fashion, the production of the antibacterial dipeptide bacilysin is independent of Sfp (8,9). In total, 8.5% of the entire genomic capacity of B. amyloliquefaciens FZB42 is devoted to the nonribosomal synthesis of secondary metabolites, exceeding that of the model Gram-positive bacterium Bacillus subtilis 168 by more than 2-fold (6). Prophage sequences that often harbor biosynthetic gene clusters of ribosomally synthesized peptides (microcins, lantibiotics/lantipeptides), which are common in B. subtilis strains, were not previously detected within the FZB42 genome. However, the presence of an antimicrobial compound(s) active against sigW mutant strain HB0042 of B. subtilis has been reported. SigW is an extracytoplasmic sigma factor that provides intrinsic resistance to antimicrobial compounds produced by other Bacilli (4).The driving force for the current report was the finding that FZB42 mutant RS6, which is deficient in the Sfp-dependent synthesis of lipopeptides and polyketides and in Sfp-independent bacilysin production (9), still produced an antibacterial substance active against Bacillus subtilis HB0042. This finding underscores the diversity of biosynthetic strategies employed by FZB42 and offers new possibilities for discovering novel natural products with biomedically relevant activities. Recent genomic analysis of FZB42 revealed a ribosomally encoded biosynthetic gene cluster that is conserved among many species across two domains of life ...