Profling of antimicrobial metabolites of plant growth promoting Pseudomonas spp. isolated from diferent plant hosts

Abstract

In this study, nine strains of Pseudomonas aurantiaca and P. chlororaphis, and two isolates of Pseudomonas sp.: At1RP4 and RS-1, were characterized for the in-vitro production of secondary metabolites in LB, DMB, and King’s B media, and of the genes responsible for the production of antagonistic metabolites. Based on 16S rRNA gene sequence, isolates At1RP4 and RS-1 were identifed as strains of P. aeruginosa and P. fuorescens. Five phenazine derivatives comprising phenazine, phenazine-1-carboxylic acid (PCA), 2-hydroxyphenazine-1-carboxylic acid (2-OH-Phz-1-COOH), phenazine 1,6-dicarboxylic acid (Phz-1,6-di-COOH), and 2-hydroxyphenazine (2-OH-Phz) were produced by all strains in all three culture media including DMB, King’s B and LB. However, 2,8-dihydroxyphenazine, 6-methylphenazine-1-carboxylic acid, pyrrolnitrin, and the ortho-dialkyl-aromatic acids, were produced by the P. aurantiaca and P. chlororaphis strains. In addi tion, all strains produced 2-acetamidophenol, pyochelin, and diketopiperazine derivatives in variable amounts in all three culture media used. Highest levels of quorum-sensing signal molecules including PQS, 2-Octyl-3-hydroxy-4(1H)-quinolone, and hexahydro-quinoxaline-1,4-dioxide were recorded for P. aeruginosa At1RP4. Moreover, all strains produced volatile hydrogen cyanide (0.95–6.68 µg/L) and the phytohormone indole-3-acetic acid (0.42–13.9 µM). Production of extracellular lipase and protease was recorded in all pseudomonads, whereas, cellulase production and phosphate solubilization were variable. Genes for hydrogen cyanide and phenazine-1-carboxylic acid were detected in all eleven strains while the gene for pyrrolnitrin biosynthesis was amplifed in P. aurantiaca and P. chlororaphis strains. Comparative metabolomic analysis provided detailed insights about the strain-specifc metabolites in pseudomonads, and their pseudo-relative quantifcation in diferent bacterial growth media to be used as single-strain biofertilizer and biocontrol inoculums