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Response to low-level phage predation in Staphylococcus aureus biofilms

ABSTRACT: An important lesson from the war on pathogenic bacteria has been the need to understand the physiological responses and evolution of natural microbial communities. Bacterial populations in the environment are generally forming biofilms subject to some level of phage predation. These multicellular communities are notoriously resistant to antimicrobials and, consequently, very difficult to eradicate. This has sparked the search for new therapeutic alternatives, including phage therapy. This study demonstrates that S. aureus biofilms formed in the presence of a non-lethal dose of phage phiIPLA-RODI exhibit a unique physiological state that could potentially benefit both the host and the predator. Thus, biofilms formed under phage pressure are thicker and have a greater DNA content. Also, the virus-infected biofilm displayed major transcriptional differences compared to an untreated control. Significantly, RNA-seq data revealed activation of the stringent response, which could slow down the advance of the bacteriophage within the biofilm. The end result would be an equilibrium that would help bacterial cells to withstand environmental challenges, while maintaining a reservoir of sensitive bacterial cells available to the phage upon reactivation of the dormant carrier population.

ORGANISM(S): Staphylococcus aureus

PROVIDER: GSE87706 | GEO | 2017/01/20

SECONDARY ACCESSION(S): PRJNA345608

REPOSITORIES: GEO

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Project description:Purpose: Protozoan predators affect the structure of bacterial communities, but investigations into how predation influences bacterial evolution and antagonistic behaviours are scarce. We performed a 20-day predator-prey evolution experiment on solid media to investigate the adaptive traits that arise in bacterial prey under continuous protozoan predation. Methods: Pseudomonas fluorescens SBW25 and a wild Acanthamoeba sp. isolate as a predator prey pair co-evolved for 20 days yielded both previously described (Wrinkly Spreader; WS) and novel colony morphotype (Wrinkly Fried Egg; WFE) isolates with conferred grazing resistance. These isolates were subjected to RNAseq profiling with and without predation to determine transcriptional changes contributing to grazing resistance. Results: For differential gene expression the WT SBW25 without predation was used as a baseline. For the WS condition, a total of 881 differentially expressed genes (DEGs) were identified, of which 424 were upregulated and 457 were downregulated. In the WFE condition, a total of 908 DEGs were identified, of which 475 were upregulated and 434 were downregulated. Among all DEGs, 335 upregulated and 313 downregulated genes were shared between the WS1 and WFE conditions Conclusions: Our findings suggest that protozoan predation can profoundly influence the course of genetic and phenotypic evolution in a short period of time. Together, the differential expression results suggest expression of features that would be expected to increase biofilm formation in WFE according to previous studies. However, increased expression of these traits may not lead to a stronger biofilm, but may still provide predation resistance. For example, fibrils may increase the effective profile size of a bacterial cell. Increased Fap-mediated biofilm formation also induces increased alginate synthesis in P. aeruginosa PA01, an exopolysaccharide that protects mucoid P. aeruginosa against macrophage killing. Interestingly, we found increased expression of alginate biosynthesis genes in both WFE and WS1 (algA, algF), suggesting alternate mechanisms leading to increased alginate production in these two strains.

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Response to low-level phage predation in Staphylococcus aureus biofilms

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