Fatty Acid Biosynthesis in Pseudomonas aeruginosa: Cloning and Characterization of the fabAB Operon Encoding b-Hydroxyacyl- Acyl Carrier Protein Dehydratase (FabA) and b-Ketoacyl-Acyl Carrier Protein Synthase I (FabB)

The Pseudomonas aeruginosa fabA and fabB genes, encoding b-hydroxyacyl-acyl carrier protein dehydratase and b-ketoacyl-acyl carrier protein synthase I, respectively, were cloned, sequenced, and expressed in Escherichia coli. Northern analysis demonstrated that fabA and fabB are cotranscribed and most probably form a fabAB operon. The FabA and FabB proteins were similar in size and amino acid composition to their counterparts from Escherichia coli and to the putative homologs from Haemophilus influenzae. Chromosomal fabA and fabB mutants were isolated; the mutants were auxotrophic for unsaturated fatty acids. A temperaturesensitive fabA mutant was obtained by site-directed mutagenesis of a single base that induced a G101D change; this mutant grew normally at 30°C but not at 42°C, unless the growth medium was supplemented with oleate. By physical and genetic mapping, the fabAB genes were localized between 3.45 and 3.6 Mbp on the 5.9-Mbp chromosome, which corresponds to the 58to 59.5-min region of the genetic map.