Abstract
BackgroundPhenazine-1-carboxamide (PCN), a phenazine derivative, is strongly antagonistic to fungal phytopathogens. The high PCN biocontrol activity fascinated researcher’s attention in isolating and identifying novel bacterial strains combined with engineering strategies to target PCN as a lead molecule. The chemical route for phenazines biosynthesis employs toxic chemicals and display low productivities, require harsh reaction conditions, and generate toxic by-products. Phenazine biosynthesis using some natural phenazine-producers represent remarkable advantages of non-toxicity and possibly high yield in environmentally-friendlier settings.ResultsA biocontrol bacterium with antagonistic activity towards fungal plant pathogens, designated as strain HT66, was isolated from the rice rhizosphere. The strain HT66 was identified as Pseudomonas chlororaphis based on the colony morphology, gas chromatography of cellular fatty acids and 16S rDNA sequence analysis. The secondary metabolite produced by HT66 strain was purified and identified as PCN through mass spectrometry, and 1H, 13C nuclear magnetic resonance spectrum. The yield of PCN by wild-type strain HT66 was 424.87 mg/L at 24 h. The inactivation of psrA and rpeA increased PCN production by 1.66- and 3.06-fold, respectively, which suggests that psrA and rpeA are PCN biosynthesis repressors. qRT-PCR analysis showed that the expression of phzI, phzR, and phzE was markedly increased in the psrA and rpeA double mutant than in psrA or rpeA mutant. However, the transcription level of rpeA and rpeB in strain HT66ΔpsrA increased by 3.52- and 11.58-folds, respectively. The reduced psrA expression in HT66ΔrpeA strain evidenced a complex regulation mechanism for PCN production in HT66.ConclusionIn conclusion, the results evidence that P. chlororaphis HT66 could be modified as a potential cell factory for industrial-scale biosynthesis of PCN and other phenazine derivatives by metabolic engineering strategies.
Highlights
Phenazine-1-carboxamide (PCN), a phenazine derivative, is strongly antagonistic to fungal phytopathogens
The phylogenetic tree based on 16S rDNA indicates that strain HT66 is close to P. chlororaphis with 99% similarity (Fig. 1)
The report of fatty acid methyl ester analysis by Sherlock MIS database showed that the strain HT66 was at the highest Sim index to P. chlororaphis (Additional file 1: Fig. S3, Table S2)
Summary
Phenazine-1-carboxamide (PCN), a phenazine derivative, is strongly antagonistic to fungal phytopathogens. The high PCN biocontrol activity fascinated researcher’s attention in isolating and identifying novel bacterial strains combined with engineering strategies to target PCN as a lead molecule. During the past couple of decades, plant growth-promoting rhizobacteria (PGPR) have attracted a great deal of researcher’s attention in the field of agriculture. Majority of these bacteria function as biological control agents in various plant-pathogen systems and promote plant growth by protecting them from various soil-borne pathogens [1, 2]. The high biocontrol activity of PCN against many fungal plant pathogens fascinated researcher’s interest in isolating and identifying novel bacterial strains together with engineering strategies to target PCN as a lead molecule [3, 22]
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