Cloning and targeted disruption of two lipopolysaccharide biosynthesis genes, kdsA and waaG, of Pseudomonas aeruginosa PAO1 by site-directed mutagenesis.

The emergence of antibiotic resistance in bacterial pathogens poses a great challenge to public health and emphasizes the need for new antimicrobial targets. The recent development of microbial genomics and the availability of genome sequences allows for the identification of essential genes which could be novel and potential targets for antibacterial drugs. However, these predicted targets need experimental validation to confirm essentiality. Here, we report on experimental validation of a two potential targets in the lipopolysaccharide (LPS) biosynthesis pathway of the pathogen Pseudomonas aeruginosa PAO1 using insertion duplication. Two genes, kdsA and waaG, from LPS encoding proteins 2-dehydro-3-deoxyphosphooctonate aldolase and UDP-glucose (heptosyl) LPS α-1,3-glucosyltransferase were selected as putative target candidates for the gene disruption experiments using plasmid insertion mutagenesis to determine essentiality. The introduction of a selectable ampicillin and kanamycin resistance marker into the chromosome resulted in lack of recovery of antibiotic-resistant colonies suggesting the essentiality of these genes for the survival of P. aeruginosa. Several molecular analyses were carried out in order to confirm the essentiality of these genes. We propose that the above two validated drug targets are essential and can be screened for functional inhibitors for the discovery of novel therapeutic compounds against antibiotic-resistant opportunistic pathogen P. aeruginosa.