Characterization of a Phenazine and Hexanoyl Homoserine Lactone Producing Pseudomonas aurantiaca Strain PB-St2, Isolated from Sugarcane Stem

Abstract

A novel strain of fluorescent pseudomonad (PB-St2) was isolated from surface-sterilized stems of sugarcane grown in Pakistan. The bacterium was identified as Pseudomonas aurantiaca on the basis of 16S rRNA gene sequence analysis and results from physiological and biochemical characteristics carried out with API50 CH and QTS 24 bacterial identification kits. Assays using substrate-specific media for enzymes revealed lipase and protease activities but cellulase, chitinase, or pectinase were not detected. The bacterium was unable to solubilize phosphate or produce indole acetic acid. However, it did produce HCN, siderophores, and homoserine lactones. In dual culture assays on agar, the bacterium showed antifungal activity against an important pathogen of sugarcane in Pakistan, namely Colletotrichum falcatum, as well as for pathogenic isolates of Fusarium oxysporium and F. lateritium but not against F. solani. The antifungal metabolites were identified using thin-layer chromatography, UV spectra, and MALDI-TOFF spectra and shown to be phenazine-1-carboxylic acid (PCA), 2-hydroxyphenazine(2-OH-PHZ), and Nhexanoyl homoserine lactone (HHL) (assessed using only TLC data). The capacity of this bacterium to produce HCN and 2-OH-PHZ, as well as to inhibit the growth of C. falcatum, has not been previously reported.

Secondary Metabolites of Pseudomonas aurantiaca and Their Role in Plant Growth Promotion

“…Isolated PB-St2 has been thoroughly investigated for the production of secondary metabolites. Information about most of its secondary metabolites has been published separately (Mehnaz et al 2009(Mehnaz et al , 2013; some unpublished information have been included in this manuscript. Complete profi le of PB-St2 secondary metabolites is not characterized yet.…”

“…BL915, SR1, and PB-St2 strains of P . aurantiaca are reported as HCN producers (Gaffney et al 1994 ;Mehnaz et al 2009 ;Andres et al 2011 ).…”

“…Siderophore production is reported for S1, SR1, and PB-St2 strains of P . aurantiaca (Mandryk et al 2007 ;Mehnaz et al 2009 ;Andres et al 2011 ). PB-St2 produces hydroxamate-type siderophores (Mehnaz et al 2009 ).…”

“…aurantiaca (Mandryk et al 2007 ;Mehnaz et al 2009 ;Andres et al 2011 ). PB-St2 produces hydroxamate-type siderophores (Mehnaz et al 2009 ). For other strains, the information about type or nature of siderophores is not available.…”

“…aurantiaca , PB-St2 and IB5-10. PB-St2 was isolated from a stem of a local variety of sugarcane growing in Punjab, Pakistan (Mehnaz et al 2009 ), and IB5-10 was isolated from a coastal sand dune in east coast of Korea. PCA and 2-OH-Phz are major secondary metabolites of PB-St2 ( Fig.…”