Phenotypic diversification in vivo: Pseudomonas aeruginosa gacS− strains generate small colony variants in vivo that are distinct from in vitro variants

Abstract

Pseudomonas aeruginosa has long been known to produce phenotypic variants during chronic mucosal surface infections. These variants are thought to be generated to ensure bacterial survival against the diverse challenges in the mucosal environment. Studies have begun to elucidate the mechanisms by which these variants emerge in vitro; however, too little information exists on phenotypic variation in vivo to draw any links between variants generated in vitro and in vivo. Consequently, in this study, the P. aeruginosa gacS gene, which has previously been linked to the generation of small colony variants (SCVs) in vitro, was studied in an in vivo mucosal surface infection model. More specifically, the rat prostate served as a model mucosal surface to test for the appearance of SCVs in vivo following infections with P. aeruginosa gacS− strains. As in in vitro studies, deletion of the gacS gene led to SCV production in vivo. The appearance of these in vivo SCVs was important for the sustainability of a chronic infection. In the subset of rats in which P. aeruginosa gacS− did not convert to SCVs, clearance of the bacteria took place and healing of the tissue ensued. When comparing the SCVs that arose at the mucosal surface (MS-SCVs) with in vitro SCVs (IV-SCVs) from the same gacS− parent, some differences between the phenotypic variants were observed. Whereas both MS-SCVs and IV-SCVs formed dense biofilms, MS-SCVs exhibited a less diverse resistance profile to antimicrobial agents than IV-SCVs. Additionally, MS-SCVs were better suited to initiate an infection in the rat model than IV-SCVs. Together, these observations suggest that phenotypic variation in vivo can be important for maintenance of infection, and that in vivo variants may differ from in vitro variants generated from the same genetic parent.

A gacS Deletion in Pseudomonas aeruginosa Cystic Fibrosis Isolate CHA Shapes Its Virulence

“…Interestingly, gacS mutants in PA14 are prone to generate stable SCVs when growing in biofilm or exposed to stresses [63] as well as in vivo [64]. When CHA was grown in static conditions in vitro , we also observed the emergence of stable SCV-like colonies (not shown).…”

Coexistence and Within-Host Evolution of Diversified Lineages of Hypermutable Pseudomonas aeruginosa in Long-term Cystic Fibrosis Infections

“…, betalactams, aminoglycoside, quinolones, chloramphenicol, trimethoprim, and imipenem [29] , [47] , [48] , [49] , [50] , [51] , [52] , [53] . Even though the GacA/GacS system is required for activation of genes involved in chronic persistence, gacS mutants are prone to generate stable and stress-tolerant small colony variants (SCVs) when growing in biofilms, exposed to stress factors [54] , [55] , or in vivo [56] , suggesting that the absence of GacS may confer some additional advantage for persistence in the CF lung. fusA1 encodes the elongation factor EF-G1A, which confers resistance to the antibiotic argyrin in P. aeruginosa [57] , [58] .…”

Waddington’s Landscapes in the Bacterial World

“…Variation of mutation rates in response to environmental factors is an old prediction of population genetics (Fitch, 1982) and has been validated by experimental studies (Oliver et al, 2000;Saint-Ruf and Matic, 2006;Pribis et al, 2019). Formation of small colony variants of pathogenic bacteria in animal cells and tissues may be also a manifestation of increased mutation rates (Proctor et al, 1994;Cano et al, 2003;Nelson et al, 2010). The notion of stress-induced mutation has raised concerns about mutational burden (Roth et al, 2006).…”