Regulation of antibiotics production in biocontrol strains of pseudomonas spp

Abstract

Pseudomonas are ubiquitous aerobic, gram-negative rod-shaped motile bacteria. Their ability to survive in a variety of environments, and metabolic versatility, make them organisms of choice to explore a metabolic function. Among the myriad functions, their ability to suppress the pathogens (biological control) has made them highly popular. Pseudomonas spp. produce a range of secondary metabolites including antibiotics, siderophores, and HCN, a function often hypothesized to confer a selective advantage in the bacterial persistence in soil and the rhizosphere. Secondary metabolite production is regulated through multi-tier mechanisms. Feasibility of molecular genetic analysis and availability of genome sequences make them attractive model system to study the antibiotic production and its regulation. Secondary metabolism is regulated through various mechanisms acting at transcriptional and post-transcriptional levels. The highly conserved GacA/GacS two-component signal transduction is a universal global regulatory mechanism in fluorescent Pseudomonas spp. Stationary-phase gene expression is interwoven with this regulatory circuit, wherein stationary-phase sigma factor, RpoS is a central regulator controlling the stress tolerance and environmental fitness of a strain. A third pathway, consisting of small RNAs ensures secondary metabolism and biocontrol at post-transcriptional level. They scavenge small RNA binding proteins thereby relieving the translational repression of the target genes. Several functions and their regulatory network feed directly into the broad framework of quorum sensing (QS). In Pseudomonads, identified regulatory elements of QS include the RpoS, the GacS/GacA, and other two-component regulatory systems, the small RNA-binding regulator and many others. The discovery of new regulators of QS will help in elucidating the signal transduction mechanism in bacteria as a whole, and understanding the regulation of biocontrol function in Pseudomonads in particular. This is a pre-requisite for predicting the optimal environmental conditions for such bacteria to materialize their desired functions.