Pneumococcal Colonization and Virulence Factors Identified Via Experimental Evolution in Infection Models

Abstract

Streptococcus pneumoniae is a commensal of the human nasopharynx and a major cause of respiratory and invasive disease. We examined adaptation and evolution of pneumococcus, within nasopharynx and lungs, in an experimental system where the selective pressures associated with transmission were removed. This was achieved by serial passage of pneumococci, separately, in mouse models of nasopharyngeal carriage or pneumonia. Passaged pneumococci became more effective colonisers of the respiratory tract and we observed several examples of potential parallel evolution. The cell wall modifying glycosyltransferase LafA was under strong selection during lung passage, whilst the surface expressed pneumococcal vaccine antigen gene pvaA and the glycerol-3-phosphate dehydrogenase gene gpsA were frequent targets of mutation in nasopharynx-passaged pneumococci. These mutations were not identified in pneumococci that were separately evolved by serial passage on laboratory agar. We focussed on gpsA, in which the same single nucleotide polymorphism arose in two independently evolved nasopharynx-passaged lineages. We describe a new role for this gene in nasopharyngeal carriage and show that the identified single nucleotide change confers resistance to oxidative stress and enhanced nasopharyngeal colonisation potential. We demonstrate that polymorphisms in gpsA arise and are retained during human colonisation. These findings highlight how within-host environmental conditions can determine trajectories of bacterial evolution. Relative invasiveness or attack rate of pneumococcal lineages may be defined by genes that make niche-specific contributions to bacterial fitness. Experimental evolution in animal infection models is a powerful tool to investigate the relative roles played by pathogen virulence and colonisation factors within different host niches.

The glycerol-3-phosphate dehydrogenases GpsA and GlpD constitute the oxidoreductive metabolic linchpin for Lyme disease spirochete host infectivity and persistence in the tick

“…A recent study has implicated GpsA in resistance of Streptococcus pneumoniae to oxidative stress [ 30 ]. To examine if gpsA also protects B .…”

“…Recent studies have suggested that gpsA may be a virulence factor in other pathogens. Green et al, 2021 [ 30 ] found using a forward genetic screen that GpsA is important for S . pneumoniae to establish nasopharyngeal colonization and plays a role in resistance to oxidative stress.…”

“…A recent study has implicated GpsA in resistance of Streptococcus pneumoniae to oxidative stress [30]. To examine if gpsA also protects B. burgdorferi from oxidative stress, we measured the viability of wild-type, ΔgpsA and gpsA + strains following exposure to H 2 O 2 and found no significant differences between the strains, at least under the conditions tested (S2 Fig).…”

Lysine245 plays a crucial role in stability and function of glycerol 3‐phosphate dehydrogenase (Gpd1) in Saccharomyces cerevisiae

“…8 The role of Gpds in regulation of stress responses (especially oxidative stress) is conserved in prokaryotes. 9,10 The human enzyme (1X0V, 6E8Y, 6PYP) has been studied in some detail. [11][12][13] The binding of the cofactor (NAD + ) resulted in no significant change in the enzyme structure while formation of a ternary complex with DHAP resulted in discernible changes in conformation.…”

“…Expression of Gpd2 is induced under anaerobic conditions 8 . The role of Gpds in regulation of stress responses (especially oxidative stress) is conserved in prokaryotes 9,10 …”