Polymyxin P is the active principle in suppressing phytopathogenic Erwinia spp. by the biocontrol rhizobacterium Paenibacillus polymyxa M-1

Abstract

BackgroundNine gene clusters dedicated to nonribosomal synthesis of secondary metabolites with possible antimicrobial action, including polymyxin and fusaricidin, were detected within the whole genome sequence of the plant growth-promoting rhizobacterium (PGPR) Paenibacillus polymyxa M-1. To survey the antimicrobial compounds expressed by M-1 we analyzed the active principle suppressing phytopathogenic Erwinia spp.ResultsP. polymyxa M-1 suppressed the growth of phytopathogenic Erwinia amylovora Ea 273, and E. carotovora, the causative agents of fire blight and soft rot, respectively. By MALDI-TOF mass spectrometry and reversed-phase high-performance liquid chromatography (RP-HPLC), two antibacterial compounds bearing molecular masses of 1190.9 Da and 1176.9 Da were detected as being the two components of polymyxin P, polymyxin P1 and P2, respectively. The active principle acting against the two Erwinia strains was isolated from TLC plates and identified by postsource decay (PSD)-MALDI-TOF mass spectrometry as polymyxin P1 and polymyxin P2. These findings were corroborated by domain structure analysis of the polymyxin (pmx) gene cluster detected in the M-1 chromosome which revealed that corresponding to the chemical structure of polymyxin P, the gene cluster is encoding D-Phe in position 6 and L-Thr in position 7.ConclusionsIdentical morphological changes in the cell wall of the bacterial phytopathogens treated with either crude polymyxin P or culture supernatant of M-1 corroborated that polymyxin P is the main component of the biocontrol effect exerted by strain M-1 against phytopathogenic Erwinia spp.

Characterization of Novel Fusaricidins Produced by Paenibacillus polymyxa-M1 Using MALDI-TOF Mass Spectrometry

“…Paenibacillus polymyxa strain M-1 isolated from surface sterilized wheat roots in China was kept frozen at -70 o C with 15% glycerol as laboratory stock and cultivated in glucose-starchCaCO 3 (GSC) liquid broth at 30 o C for 24 h, as described previously [4,34]. In addition, strain M1 was grown on GSCagar at 30 o C for at least 24 h.…”

“…The most frequent products are lipopeptides [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], peptide/polyketide hybrids [17,18], as well as lantibiotics [19,20]. Such products qualify Paenibacillus strains for applications in agriculture, medicine, and biotechnology.…”

“…The prominent products of this strain are two lipopeptide families, the polymyxins and the fusaricidins, which both are of industrial and medical interest. Recently, we investigated its polymyxin products in detail [4]. They efficiently inhibit Gram-negative bacteria.…”

“…They efficiently inhibit Gram-negative bacteria. M1 synthesizes two variants of polymyxin P which were revealed as efficient agents against phytopathogenic Erwinia strains in biocontrol [4,31].…”

Full genome sequence of Brevibacillus laterosporus strain B9, a biological control strain isolated from Zhejiang, China

“…These bacteria mainly use two strategies in biocontrol including biofilm formation and antibiotic secondary metabolism Niu et al, 2013). In order to investigate which mechanism was used by B9 strain, we made a local BLAST search based on the reference-associated genes.…”