Ingmer, H. | Search bioRxiv

bioRxiv2018

SosA inhibits cell division in Staphylococcus aureus in response to DNA damage

Inhibition of cell division is critical for cell viability under DNA damaging conditions. In bacterial cells, DNA damage induces the SOS response, a process that inhibits cell division while repairs are being made. In coccoid bacteria, such as the human pathogen Staphylococcus aureus, the process remains poorly understood. Here we have characterized an SOS-induced cell-division inhibitor, SosA, in S. aureus. We find that in contrast to the wildtype, sosA mutant cells continue division under DNA damaging conditions with decreased viability as a consequence. Conversely, overproduction of SosA leads to cell division inhibition and reduced growth. The SosA protein is localized in the bacterial membrane and mutation of an extracellular amino acid, conserved between homologs of other staphylococcal species, abolished the inhibitory activity as did truncation of the C-terminal 30 amino acids. In contrast, C-terminal truncation of 10 amino acids lead to SosA accumulation and a strong cell division inhibitory activity. A similar phenotype was observed upon expression of wildtype SosA in a mutant lacking the membrane protease, CtpA. Thus, the extracellular C-terminus of SosA is required both for cell-division inhibition and for turnover of the protein. Functional studies showed that SosA is likely to interact with one or more divisome components and, without interfering with early cell-division events, halts cell division at a point where septum formation is initiated yet being unable to progress to septum closure. Our findings provide important insights into cell-division regulation in staphylococci that may foster development of new classes of antibiotics targeting this essential process. ImportanceStaphylococcus aureus is a serious human pathogen and a model organism for cell-division studies in spherical bacteria. We show that SosA is the DNA-damage-inducible cell-division inhibitor in S. aureus that upon expression causes cell swelling and cessation of the cell cycle at a characteristic stage post septum initiation but prior to division plate completion. SosA appears to function via an extracellular activity and is likely to do so by interfering with the essential membrane-associated division proteins, while at the same time being negatively regulated by the membrane protease CtpA. This report represents the first description of the process behind cell-division inhibition in coccoid bacteria. As several pathogens are included in this category, uncovering the molecular details of SosA activity and control can lead to identification of new targets for development of valuable anti-bacterial drugs.

microbiology↗

bioRxiv2018

Modelling bacteria-phage interactions driving predation and horizontal gene transfer

Bacteriophages shape microbial communities by predating on them and by accelerating their adaptation through horizontal gene transfer. The former is the basis of phage therapy, whereas the latter drives the evolution of numerous bacterial pathogens. We present a novel computational approach (eVIVALDI - eco-eVolutionary mIcrobial indiViduAL-baseD sImulations) to study phage-bacteria ecological interactions that integrates a large number of processes, including population dynamics, environmental structure, genome evolution, and phage-mediated horizontal transfer. We validate and illustrate the relevance of the model by focusing on three specific questions: the ecological interactions between bacteria and virulent phage during phage and antibiotic therapy, the role of prophages as competitive weapons, and how autotransduction facilitates bacterial acquisition of antibiotic resistance genes upon lysis of antibiotic resistant competitors. Our model recapitulates experimental and theoretical observations and provides novel insights. In particular, we find that environmental structure has a strong effect on community dynamics and evolutionary outcomes in all three case studies. Strong environmental structure, relative to well-mixed environments and especially if antibiotics are heterogeneously distributed, enhances the rate of acquisition of resistance to both phages and antibiotics, and leads to more accurate predictions of the dynamics of lysogen invasion in the gastrointestinal tract. We predicted the co-existence of invaders and resident lysogens in autotransduction under a range of parameters, and validated this key prediction experimentally. By linking ecological and evolutionary dynamics, our modelling approach sheds light on the factors that influence the dynamics of phage-bacteria interactions. It can also be expanded to put forward novel hypotheses, facilitating the design of phage therapy treatments and the assessment of the role of phages in the spread of antibiotic resistance.\n\nAUTHOR SUMMARYIn the face of a growing threat of antibiotic resistant bacteria, bacteriophages have re-emerged as a potential alternative to clinical treatments of infections, as they are efficient bacterial predators. However, bacteriophages can also promote, through a mechanism called transduction, the dissemination of adaptive traits between bacteria, including antibiotic resistance genes. Importantly, these two types of interactions (predation and transduction) can co-occur, which creates difficulties in predicting their outcome. We have developed eVIVALDI (eco-eVolutionary mIcrobial indiViduAL-baseD sImulations), a computational model that allows the simulation of microbial communities with a focus on the mechanisms involved in phage-bacteria interactions, across time and in different types of environments. eVIVALDI can be used to understand the conditions where phages are more likely to be successfully used to eliminate bacteria or, in the other hand, the conditions where they increase the probability of dissemination of adaptive traits. Our research highlights the importance of considering the diverse ways that phage and bacteria interact, and the relevant ecological conditions where these interactions take place, to understand how bacteriophages shape microbial communities and how they can be used as a clinical tool.

microbiology↗