Analysis of the Plasmid-Based ts -Mutant Δ fabA/pTS-fabA Reveals Its Lethality under Aerobic Growth Conditions That Is Suppressed by Mild Overexpression of desA at a Restrictive Temperature in Pseudomonas aeruginosa.

It is uncertain whether PA1610|fabA is essential or dispensable for growth on LB-agar plates under aerobic conditions in Pseudomonas aeruginosa PAO1. To examine its essentiality, we disrupted fabA in the presence of a native promoter-controlled complementary copy on ts -plasmid. In this analysis, we showed that the plasmid-based ts -mutant Δ fabA / pTS-fabA failed to grow at a restrictive temperature, consistent with the observation by Hoang and Schweizer (T. T. Hoang, H. P. Schweizer, J Bacteriol 179:5326-5332, 1997, https://doi.org/10.1128/jb.179.17.5326-5332.1997), and expanded on this by showing that Δ fabA exhibited curved cell morphology. On the other hand, strong induction of fabA-OE or PA3645|fabZ-OE impeded the growth of cells displaying oval morphology. Suppressor analysis revealed a mutant sup gene that suppressed a growth defect but not cell morphology of Δ fabA . Genome resequencing and transcriptomic profiling of sup identified PA0286 | desA , whose promoter carried a single-nucleotide polymorphism (SNP), and transcription was significantly upregulated (level increase of >2-fold, P < 0.05). By integration of the SNP-bearing promoter-controlled desA gene into the chromosome of Δ fabA / pTS-fabA , we showed that the SNP is sufficient for Δ fabA to phenocopy the sup mutant. Furthermore, mild induction of the araC -P BAD -controlled desA gene but not desB rescued Δ fabA . These results validated that mild overexpression of desA fully suppressed the lethality but not the curved cell morphology of Δ fabA . Similarly, Zhu et al. (Zhu K, Choi K-H, Schweizer HP, Rock CO, Zhang Y-M, Mol Microbiol 60:260-273, 2006, https://doi.org/10.1111/j.1365-2958.2006.05088.x) showed that multicopy desA partially alleviated the slow growth phenotype of Δ fabA , the difference in which was that Δ fabA was viable. Taken together, our results demonstrate that fabA is essential for aerobic growth. We propose that the plasmid-based ts -allele is useful for exploring the genetic suppression interaction of essential genes of interest in P. aeruginosa. IMPORTANCE Pseudomonas aeruginosa is an opportunistic pathogen whose multidrug resistance demands new drug development. Fatty acids are essential for viability, and essential genes are ideal drug targets. However, the growth defect of essential gene mutants can be suppressed. Suppressors tend to be accumulated during the construction of essential gene deletion mutants, hampering the genetic analysis. To circumvent this issue, we constructed a deletion allele of fabA in the presence of a native promoter-controlled complementary copy in the ts -plasmid. In this analysis, we showed that Δ fabA / pTS-fabA failed to grow at a restrictive temperature, supporting its essentiality. Suppressor analysis revealed desA , whose promoter carried a SNP and whose transcription was upregulated. We validated that both the SNP-bearing promoter-controlled and regulable P BAD promoter-controlled desA suppressed the lethality of Δ fabA . Together, our results demonstrate that fabA is essential for aerobic growth. We propose that plasmid-based ts -alleles are suitable for genetic analysis of essential genes of interest.