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Differential possession of type 6 secretion system effector genes in exoU and exoS Pseudomonas aeruginosa in
Tanzina Akter1, Abrar Maswood Haider2, Fiona Stapleton3
1School of Optometry and Vision Science, Faculty of Medicine and Health, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia; Microbial Biotechnology Division, National Institute of Biotechnology (NIB), Dhaka, 1349, Bangladesh.
Abstract:
Corneal infection (microbial keratitis; MK) is most frequently caused by Pseudomonas aeruginosa, which can utilize an array of secreted virulence factors for pathogenesis. Invasive strains of P. aeruginosa possessing the exoS gene, invade mammalian cells, while cytotoxic strains with the exoU gene rapidly kill host cells. This study investigated the presence of the type six secretion system (T6SS) effector genes in exoU and exoS strains isolated from MK. Fourteen different T6SS effector genes within 20 exoU and 19 exoS P. aeruginosa were explored using whole genome sequence data by BLAST search. To confirm the BLAST search result, PCR was used to detect exoU, exoS and those genes significantly different in the BLAST search, in a separate set of 56 MK isolates from India (24) and Australia (32). The phospholipase D (PLD) activity was measured using the Amplex Red Phospholipase D Assay kit. Three effector genes, tse7, tle1, and pldA, were differentially possessed in the exoU and exoS strains in the BLAST search (p < 0.05). When combining the BLAST search and PCR results, pldA was significantly more common in exoU (81.8%) than the exoS strains (37.3%) (p < 0.01) and trends were similar in Indian (81% exoU vs 45.5% exoS) and Australian (82.6% exoU vs 23% exoS) isolates. PldA expression was associated with detectable PLD activity. Irrespective of geographical region, pldA was more commonly found in exoU P. aeruginosa. While MK due to exoU is generally more severe than those due to exoS, the association between expression of pldA and its function requires further investigation.
Insights
Pseudomonas aeruginosa strains causing corneal infections were analyzed for type VI secretion system (T6SS) genes. The pldA gene was significantly more prevalent in cytotoxic exoU strains than invasive exoS strains, suggesting a role in microbial keratitis pathogenesis.
Area of Science:
- Microbiology
- Ophthalmology
- Genetics
Background:
- Corneal infections, or microbial keratitis (MK), are often caused by Pseudomonas aeruginosa.
- P. aeruginosa strains are categorized by virulence factors: invasive exoS strains and cytotoxic exoU strains.
- The type VI secretion system (T6SS) plays a role in bacterial pathogenesis.
Purpose of the Study:
- To investigate the presence and distribution of T6SS effector genes in P. aeruginosa strains isolated from MK.
- To determine if specific T6SS effector genes correlate with the presence of exoS or exoU genes.
- To assess the phospholipase D (PLD) activity associated with identified effector genes.
Main Methods:
- Whole genome sequencing and BLAST searches were used to identify T6SS effector genes in 20 exoU and 19 exoS P. aeruginosa strains.
- Polymerase Chain Reaction (PCR) was employed to confirm the presence of specific genes in an additional 56 MK isolates.
- Phospholipase D (PLD) activity was measured using a commercial assay kit.
Main Results:
- Three T6SS effector genes (tse7, tle1, pldA) showed differential distribution between exoU and exoS strains.
- The pldA gene was significantly more common in exoU strains (81.8%) compared to exoS strains (37.3%) across all isolates.
- This association between pldA and exoU strains was consistent in isolates from both India and Australia.
- PldA expression correlated with detectable PLD activity.
Conclusions:
- The pldA gene is more frequently found in exoU P. aeruginosa strains associated with microbial keratitis, irrespective of geographical origin.
- The presence of pldA in exoU strains suggests a potential role in the pathogenesis of severe corneal infections.
- Further research is needed to elucidate the functional significance of pldA and its association with PLD activity in P. aeruginosa keratitis.
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