Christofi, T. | Search bioRxiv

bioRxiv2019

Pseudomonas aeruginosa core metabolism exerts a widespread growth-independent control on virulence

Bacterial virulence may rely on secondary metabolism, but core metabolism genes are assumed to be necessary primarily for bacterial growth. To assess this assumption, we correlated the genome, the transcriptome and the pathogenicity of 30 fully sequenced Pseudomonas strains using two Drosophila and one mouse infection assay. In accordance with previous studies gene presence-absence does not explain differences in virulence among P. aeruginosa strains, but merely between P. aeruginosa and other Pseudomonas species. Similarly, classical gene expression analysis of highly vs. lowly pathogenic P. aeruginosa strains identifies many virulence factors, and only a few metabolism genes related to virulence. Nevertheless, assessing the virulence of 553 core metabolic and 95 random non-metabolic gene mutants of P. aeruginosa PA14, we found 16.5% of the core metabolic and 8.5% of the non-metabolic genes to be necessary for full virulence. Strikingly, 11.8% of the core metabolism genes exhibit defects in virulence that cannot be attributed to auxotrophy. The compromised in virulence metabolic gene mutants were mapped in multiple pathways and exhibited further defects in acute virulence phenotypes and in a mouse lung infection model. Functional transcriptomics re-analysis of core metabolism at the pathway level, reveals amino-acid, succinate, citramalate, and chorismate biosynthesis and beta-oxidation as important for full virulence and expression of these pathways indicative of virulence in various strains. Thus, P. aeruginosa virulence variation, which to this point remains unpredictably combinatorial at the gene level, can be dissected at the pathway level via combinatorial trancriptome and functional core metabolism analysis.

microbiology↗

bioRxiv2019

Defining Escherichia coli as a health-promoting microbe against intestinal Pseudomonas aeruginosa

Gut microbiota acts as a barrier against intestinal pathogens, but species-specific protection of the host from infection remains relatively unexplored. Taking a Kochs postulates approach in reverse to define health-promoting microbes we find that Escherichia coli naturally colonizes the gut of healthy mice, but it is depleted from the gut of antibiotic-treated mice, which become susceptible to intestinal colonization by Pseudomonas aeruginosa and concomitant mortality. Reintroduction of fecal bacteria and E. coli establishes a high titer of E. coli in the host intestine and increases defence against P. aeruginosa colonization and mortality. Moreover, diet is relevant in this process because high sugars or dietary fat favours E. coli fermentation to lactic acid and P. aeruginosa growth inhibition. To the contrary, low sugars allow P. aeruginosa to produce the oxidative agent pyocyanin that inhibits E. coli growth. Our results provide an explanation as to why P. aeruginosa doesnt commonly infect the human gut, despite being a formidable microbe in lung and wound infections.\n\nAuthor SummaryHere we interrogate the conundrum as to why Pseudomonas aeruginosa is not a clinical problem in the intestine as opposed to other tissues. P. aeruginosa interacts with Neisseria, Streptococcus, Staphylococcus and Actinomyces species found in the human lung. These are predominantly gram-positive bacteria that induce P. aeruginosa virulence. Moreover, peptidoglycan, which is abundant in gram-positive bacteria, can directly trigger the virulence of P. aeriginosa. We reasoned that P. aeruginosa might be benign in the human gut due to the inhibitory action of benign gram-negative intestinal bacteria, such as Escherichia coli. Therefore, we dissected the antagonism between E. coli and P. aeruginosa and the effect of a conventional, a fat-, a carbohydrate-and a protein-based diet in intestinal dysbiosis. Our findings support the notion that an unbalanced diet or antibiotics induces gut dysbiosis by the elimination of commensal E. coli, in addition to lactic acid bacteria, imposing a gut environment conducive to P. aeruginosa infection. Moreover, commensal E. coli provides an explanation as to why P. aeruginosa doesnt commonly infect the human gut, despite being a formidable microbe in lung and wound infections.

microbiology↗