3 New CF Virulence Factors ID’d in Genome-wide Screen of Pathogen

In a new study, researchers describe the results of a genome-wide screen of Pseudomonas aeruginosa in a yeast, which led to the identification of three potential new Pseudomonas virulence factors. The research paper, entitled “Genome-wide Screen of Pseudomonas aeruginosa in Saccharomyces cerevisiae Identifies New Virulence Factors,” was published in Frontiers in Cellular and Infection Microbiology.

The opportunistic gram-negative bacterium Pseudomonas aeruginosa is the major pathogen that affects the lungs of cystic fibrosis (CF) patients, presenting high prevalence and often leading to chronic infection in immuno-compromised patients. It affects and damages host cellular processes through the secretion of effector proteins into the host’s cells. Great progress has been made in identifying these pathogenic effector proteins through a series of high throughput techniques and bioinformatics, allowing a deeper understanding of the infection process and the advancing research toward new therapies.

The yeast Saccharomyces cerevisiae has been regarded has an extremely useful model for the discovery of bacterial effector proteins of human pathogens, due to the fact that these pathogens target cellular processes that are conserved among eukaryotes, a class of organisms that comprises, among others, yeasts and humans.

Researchers performed an unbiased screen of a specific P. aeruginosa strain (PA14) in order to identify bacterial effector proteins that alter yeast cellular pathways and result in impaired growth. This experiment differed from previous approaches that relied on specific study of selected candidates — in this study, researchers performed a whole genome screen in order to identify unsuspected new virulence factors. Following a three-stage selection, the scientists experimentally selected 51 potential independent candidates.  Among these, the team recovered a known P. aeruginosa virulence factor, the protease LepA, a result that adds to the validation of the screen. Moreover, among the 51 candidates, the researchers validated three P. aeruginosa effector candidates (Pecs) never before described and theorize that these are secreted virulence factors.

All three Pecs were shown to greatly contribute to virulence in the C. elegans, and two of them (Pec 1 and 3) were also shown to contribute to P. aeruginosa acute cytotoxicity toward macrophages (immune system cells). Pec 1 and 2 were found to be associated with host cellular organelles, a fact that, the researchers conclude, “might lead us to investigate the role of the new host targets which will extend our understanding of the molecular mechanisms involved in the P. aeruginosa infection.”