ERL conceived the study, participated in its design and coordination, and helped with redaction of the manuscript. All authors read and approved the final manuscript.”
“Background The plant growth-promoting rhizobacterium

Paenibacillus polymyxa, formerly known as Bacillus polymyxa[1], can promote plant growth by producing indole-3-acetic acid (IAA) [2] and volatile compounds [3]. It is also known for controlling plant-parasitic nematodes [4, 5] and fungal phytopathogens including Fusarium oxysporum[6], Fusarium graminearum[7], Aspergillus niger[8], Penicillium expansum[9], Leptosphaeria maculans[10], Phytophthora palmivora and Pythium aphanidermatum[11]. P. polymyxa has been recently 5-Fluoracil mouse used to control bacterial

phytopathogens such as Xanthomonas campestris[12], and X. axonopodis[13]. The antagonistic effect of P. polymyxa against phytopathogens is mainly due to its capability to produce antimicrobial substances, such as peptide antibiotics and antimicrobial Selleckchem Venetoclax proteins. P. polymyxa can produce several kinds of peptide antibiotics, including polymyxins [14–22], gavaserin and saltavidin [23], jolipeptin [24], gatavalin [25] and fusaricidins [26, 27]. Polymyxins which are known for their strong inhibiting effects against gram-negative bacteria have been used to treat multidrug-resistant gram-negative bacteria [28] and to prevent septic shock [29]. The molecular structure of polymyxin is comprised of a cyclic peptide chain Leukotriene-A4 hydrolase and a hydrophobic

tail. Each member of polymyxins differs in the structures of fatty acids and the variations in the amino acid residues [30]. Polymyxins are synthesized by the nonribosomal peptide synthetase (NRPS) mechanism [31]. To date, two giant gene clusters responsible for synthesis of polymyxin A [28], and polymyxin B [32] are known. Among the 202 bacterial strains isolated from surface sterilized wheat plants collected from Beijing and Henan Province, China, one strain designated M-1 was selected due to its inhibiting effect against fungal phytopathogens. Growth of wheat was also enhanced in the presence of this strain indicating its plant growth promoting activity [33]. The whole genome of P. polymyxa M-1 has been sequenced, and nine giant gene clusters involved in non-ribosomal synthesis of antimicrobial lipopeptides and polyketides have been detected [34]. Due to its rich spectrum of secondary metabolites with antimicrobial action, P. polymyxa M-1 is a good candidate for bio-controlling fire blight, a serious disease in apple and pear caused by Erwinia amylovora. Previously, we have shown that the polyketide difficidin and the dipeptide bacilysin produced by Bacillus amyloliquefaciens suppress growth of E. amylovora[35]. Here, we report that P. polymyxa M-1 synthesizes two components of polymyxin P, polymyxin P1 and P2, which are efficient against E. amylovora.