High-throughput transposon sequencing highlights the cell wall as an important barrier for osmotic stress in methicillin resistantStaphylococcus aureusand underlines a tailored response to different osmotic stressors

Abstract

SummaryStaphylococcus aureus is an opportunistic pathogen that can cause soft tissue infections but is also a frequent cause of foodborne illnesses. One contributing factor for this food association is its high salt tolerance allowing this organism to survive commonly used food preservation methods. How this resistance is mediated is poorly understood, particularly during long-term exposure. In this study, we used TN-seq to understand how the responses to osmotic stressors differ. Our results revealed distinctly different long-term responses to NaCl, KCl and sucrose stresses. In addition, we identified the DUF2538 domain containing gene SAUSA300_0957 (gene 957) as essential under salt stress. Interestingly, a 957 mutant was less susceptible to oxacillin and showed increased peptidoglycan crosslinking. The salt sensitivity phenotype could be suppressed by amino acid substitutions in the transglycosylase domain of the penicillin binding protein Pbp2, and these changes restored the peptidoglycan crosslinking to WT levels. These results indicate that increased crosslinking of the peptidoglycan polymer can be detrimental and highlight a critical role of the bacterial cell wall for osmotic stress resistance. This study will serve as a starting point for future research on osmotic stress response and help develop better strategies to tackle foodborne staphylococcal infections.

Identification of the main glutamine and glutamate transporters in Staphylococcus aureus and their impact on c‐di‐AMP production

“…Such changes could also be an advantage during osmotic stress or c‐di‐AMP deficiency. Indeed, we have recently shown a correlation between specific changes in the peptidoglycan structure and the NaCl stress resistance in S. aureus (Schuster et al, ). In addition, since the cellular c‐di‐AMP levels are significantly higher in the gdpP as well as the alsT mutant strains compared to WT (Figures b and a), the underlying mechanistic bases for the decrease in eDNA release observed for the gdpP and alsT mutant strains might be related.…”

Impact of high salinity and the compatible solute glycine betaine on gene expression of Bacillus subtilis

“…Finally, expression of the yrkA gene encoding a putative magnesium transporter was fivefold higher in cells grown at high versus low salinity. It can be noted in this context that inactivation of the magnesium transporter MgtE of Staphylococcus aureus strongly impairs growth of the bacterium under hyperosmotic conditions (Schuster et al ., 2019).…”

Stress response modulation: the key to survival of pathogenic and spoilage bacteria during poultry processing

“…This can occur when preservatives such as salt are added to chicken meat, or can result from desiccation which may be encountered by bacteria on the external surfaces of carcasses during air chilling or crust freezing processes or on production surfaces [7]. Osmotic stress can result in protein misfolding, inducing macromolecular crowding and envelope stress, reducing the viability of bacterial cells in such environments [23]. Water loss can combine with low temperatures to enhance the stress exerted on microbes, which is a characteristic effect of applying multiple control hurdles within a process [17,24].…”

“…In alpha, beta and gamma-Proteobacteria, c-di-GMP instead tends to fill the role of c-di-AMP, which includes adaptation to osmotic stress through the control of transport of potassium ions through the downregulation of KtrAB, KtrCD or KimA systems at the genetic level and increasing compatible solute uptake such as OpuC carnitine transport in S. aureus and Bacillus spp. It is further involved in DNA damage response, via the DisA DNA integrity response protein, some control of central metabolism, biofilm formation and acid stress resistance [23,40,74]. The primary inducing signal for c-di-AMP is not known, although CdaA cyclase protein is transcribed as part of an operon with CdaR, an extracellular response protein, and GlmM, phosphoglucosamine mutase, seen in some species such as S. aureus, Lactococcus lactis and Bacillus subtilis.…”

“…aureus and Bacillus spp. It is further involved in DNA damage response, via the DisA DNA integrity response protein, some control of central metabolism, biofilm formation and acid stress resistance [23, 40, 74]. The primary inducing signal for c-di-AMP is not known, although CdaA cyclase protein is transcribed as part of an operon with CdaR, an extracellular response protein, and GlmM, phosphoglucosamine mutase, seen in some species such as S. aureus, Lactococcus lactis and Bacillus subtilis .…”