H-NS family protein MvaU downregulates phenazine-1-carboxylic acid(PCA)biosynthesis via binding to an AT-rich region within the promoter of the phz2 gene cluster in the rhizobacterium Pseudomonas strain PA1201

Histone-like nucleoid-structuring(H-NS)proteins are key regulators in gene expression silencing and in nucleoid compaction.The H-NS family member proteins MvaU in Pseudomonas aeruginosa are thought to bind the same AT-rich regions of chromosomes and function to coordinate the control of a common set of genes.Here,we explored the molecular mechanism by which MvaU controls PCA biosynthesis in P.aeruginosa PA1201.We present evidence suggesting that MvaU is self-regulated.Deletion of mvaU significantly increased PCA production,and PCA production sharply decreased when mvaU was over-expressed.MvaU transcriptionally repressed phz2 cluster expression and consequently reduced PCA biosynthesis.β-galactosidase assays confirmed that base pairing near the35 box is required when MvaU regulates PCA production in PA1201.Electrophoretic mobility shift assays(EMSA)and additional point mutation analysis demonstrated that MvaU directly bound to an AT-rich motif within the promoter of the phz2 cluster.Chromatin immunoprecipitation(ChIP)analysis also indicated that MvaU directly bound to the P5 region of the phz2 cluster promoter.MvaU repression of PCA biosynthesis was independent of QscR and OxyR in PA1201 and neither PCA or H2O2 were the environmental signals that induced mvaU expression.These findings detail a new MvaU-dependent regulatory pathway of PCA biosynthesis in PA1201 and provide a foundation to increase PCA fermentation titer by genetic engineering.

Las-like quorum-sensing system negatively regulates both pyoluteorin and phenazine-1-carboxylic acid production in Pseudomonas sp. M18

A las-like quorum-sensing system in Pseudomonas sp. M18 was identified, which consisted of lasI and lasR genes encoding LuxI-LuxR type regulator. Several functions of the las system from strain M18 were investigated in this study. The chromosomal inactivation of either lasI or lasR by recombination increased the production of both pyoluteorin (Plt) and phenazine-1-carboxylic acid (PCA) by 4-5 fold and 2-3 fold over that of the wild type strain of M18, respectively. Production of both antibiotics was restored to wild-type levels after in trans complementation with the wild-type lasI or lasR gene. Expression of the translational fusions pltA'-'lacZ and phzA'-'lacZ further confirmed the negative effect of lasI or lasR on both biosynthetic operons, and it was also demonstrated that the las system was related to the ability of swarming motility and the inhibition of cell growth.

Isolation and identifi cation of antimicrobial metabolites from sea anemone-derived fungus Emericella sp.SMA01

Marine symbiotic fungi represent an intriguing source of discovery of novel secondary metabolites with various biological activities.Sea anemones are benthic marine invertebrates,however,the cultivable symbiotic fungi residing in the sea anemones are paid few attentions compared to those derived from their cnidarian counterparts.Here we show the identification of antimicrobial secondary metabolites from the sea anemone-derived symbiotic fungi.Out offive isolated fungal strains,only the strain SMA01 showed strong antimicrobial activities,which was assigned into the genus Emericella based on the morphological characteristics and the ITS sequencing.Media swift from liquid fermentation to solid rice medium presented little influence on its antibacterial activity.A chemical investigation of the ethyl acetate extract of the Emericella sp.SMA01 led to discovery of the primary antibiotic metabolite phenazine-1-carboxylic acid.The IC_(50) values of the phenazine-1-carboxylic acid against Phytophthora capsici,Gibberella zeae,and Verticillium dahliae were determined to be 23.26-53.89μg/mL.To the best of our knowledge,this was the first report of Emericella sp.in sea anemones.The current study may benefit understanding of the defensive chemical interactions between the symbiotic fungi and their host sea anemones.