RocS drives chromosome segregation and nucleoid protection in Streptococcus pneumoniae

The divisome but not the elongasome organizes capsule synthesis in Streptococcus pneumoniae

The bacterial cell envelope consists of multiple layers, including the peptidoglycan cell wall, one or two membranes, and often an external layer composed of capsular polysaccharides (CPS) or other components. How the synthesis of all these layers is precisely coordinated remains unclear. Here, we identify a mechanism that coordinates the synthesis of CPS and peptidoglycan in Streptococcus pneumoniae. We show that CPS synthesis initiates from the division septum and propagates along the long axis of the cell, organized by the tyrosine kinase system CpsCD. CpsC and the rest of the CPS synthesis complex are recruited to the septum by proteins associated with the divisome (a complex involved in septal peptidoglycan synthesis) but not the elongasome (involved in peripheral peptidoglycan synthesis). Assembly of the CPS complex starts with CpsCD, then CpsA and CpsH, the glycosyltransferases, and finally CpsJ. Remarkably, targeting CpsC to the cell pole is sufficient to reposition CPS synthesis, leading to diplococci that lack CPS at the septum. We propose that septal CPS synthesis is important for chain formation and complement evasion, thereby promoting bacterial survival inside the host.

New insights into the Undecaprenol monophosphate recycling pathway of Streptococcus pneumoniae

Recycling of undecaprenol pyrophosphate is critical to regenerate the pool of undecaprenol monophosphate required for cell wall biosynthesis. Undecaprenol pyrophosphate is dephosphorylated by membrane-associated undecaprenyl pyrophosphate phosphatases such as UppP or type 2 Phosphatidic Acid Phosphatases (PAP2) and then transferred across the cytoplasmic membrane by Und-P flippases such as PopT (DUF368-containing protein) or UptA (a DedA family protein). While the deletion of uppP in S. pneumoniae has been reported to increase susceptibility to bacitracin and reduce infectivity in a murine infection model, the presence of PAP2 family proteins or Und-P flippases and their potential interplay with UppP in S. pneumoniae remained unknown. In this report, we identified two PAP2 family proteins and a DUF368-containing protein and investigated their roles together with that of UppP in cell growth, cell morphology and susceptibility to bacitracin in S. pneumoniae. Our results suggest that the undecaprenol monophosphate recycling pathway in S. pneumoniae could result from a functional redundancy between UppP, the PAP2-family protein Spr0434 and the DUF368-containing protein Spr0889.

The balance between gyrase and topoisomerase I activities determines levels of supercoiling, nucleoid compaction, and viability in bacteria

Two enzymes are responsible for maintaining supercoiling in the human pathogen Streptococcus pneumoniae, gyrase (GyrA₂GyrB₂) and topoisomerase I. To attain diverse levels of topoisomerase I (TopoI, encoded by topA), two isogenic strains derived from wild-type strain R6 were constructed: P_Zn topA, carrying an ectopic topA copy under the control of the ZnSO₄-regulated P_Zn promoter and its derivative ΔtopAP_Zn topA, which carries a topA deletion at its native chromosomal location. We estimated the number of TopoI and GyrA molecules per cell by using Western-blot and CFUs counting, and correlated these values with supercoiling levels. Supercoiling was estimated in two ways. We used classical 2D-agarose gel electrophoresis of plasmid topoisomers to determine supercoiling density (σ) and we measured compaction of nucleoids using for the first time super-resolution confocal microscopy. Notably, we observed a good correlation between both supercoiling calculations. In R6, with σ = -0.057, the average number of GyrA molecules per cell (2,184) was higher than that of TopoI (1,432), being the GyrA:TopoI proportion of 1:0.65. In ΔtopAP_Zn topA, the number of TopoI molecules depended, as expected, on ZnSO₄ concentration in the culture media, being the proportions of GyrA:TopoI molecules in 75, 150, and 300 μM ZnSO₄ of 1:0.43, 1:0.47, and 1:0.63, respectively, which allowed normal supercoiling and growth. However, in the absence of ZnSO₄, a higher GyrA:TopoI ratio (1:0.09) caused hyper-supercoiling (σ = -0.086) and lethality. Likewise, growth of ΔtopAP_Zn topA in the absence of ZnSO₄ was restored when gyrase was inhibited with novobiocin, coincidentally with the resolution of hyper-supercoiling (σ change from -0.080 to -0.068). Given that TopoI is a monomer and two molecules of GyrA are present in the gyrase heterotetramer, the gyrase:TopoI enzymes proportion would be 1:1.30 (wild type R6) or of 1:1.26-0.86 (ΔtopAP_Zn topA under viable conditions). Higher proportions, such as 1:0.18 observed in ΔtopAP_Zn topA in the absence of ZnSO₄ yielded to hyper-supercoiling and lethality. These results support a role of the equilibrium between gyrase and TopoI activities in supercoiling maintenance, nucleoid compaction, and viability. Our results shed new light on the mechanism of action of topoisomerase-targeting antibiotics, paving the way for the use of combination therapies.

Oxidative Reactions Catalyzed by Hydrogen Peroxide Produced by Streptococcus pneumoniae and Other Streptococci Cause the Release and Degradation of Heme from Hemoglobin

Streptococcus pneumoniae (Spn) strains cause pneumonia that kills millions every year worldwide. Spn produces Ply, a hemolysin that lyses erythrocytes releasing hemoglobin, and also produces the pro-oxidant hydrogen peroxide (Spn-H2O2) during growth. The hallmark of the pathophysiology of hemolytic diseases is the oxidation of hemoglobin, but oxidative reactions catalyzed by Spn-H2O2 have been poorly studied. We characterized the oxidation of hemoglobin by Spn-H2O2. We prepared a series of single-mutant (ΔspxB or ΔlctO), double-mutant (ΔspxB ΔlctO), and complemented strains in TIGR4, D39, and EF3030. We then utilized an in vitro model with oxyhemoglobin to demonstrate that oxyhemoglobin was oxidized rapidly, within 30 min of incubation, by Spn-H2O2 to methemoglobin and that the main source of Spn-H2O2 was pyruvate oxidase (SpxB). Moreover, extended incubation caused the release and the degradation of heme. We then assessed oxidation of hemoglobin and heme degradation by other bacterial inhabitants of the respiratory tract. All hydrogen peroxide-producing streptococci tested caused the oxidation of hemoglobin and heme degradation, whereas bacterial species that produce <1 μM H2O2 neither oxidized hemoglobin nor degraded heme. An ex vivo bacteremia model confirmed that oxidation of hemoglobin and heme degradation occurred concurrently with hemoglobin that was released from erythrocytes by Ply. Finally, gene expression studies demonstrated that heme, but not red blood cells or hemoglobin, induced upregulated transcription of the spxB gene. Oxidation of hemoglobin may be important for pathogenesis and for the symbiosis of hydrogen peroxide-producing bacteria with other species by providing nutrients such as iron.

Exploration of Streptococcus core genome to reveal druggable targets and novel therapeutics against S. pneumoniae

Streptococcus pneumoniae (S. pneumoniae), the major etiological agent of community-acquired pneumonia (CAP) contributes significantly to the global burden of infectious diseases which is getting resistant day by day. Nearly 30% of the S. pneumoniae genomes encode hypothetical proteins (HPs), and better understandings of these HPs in virulence and pathogenicity plausibly decipher new treatments. Some of the HPs are present across many Streptococcus species, systematic assessment of these unexplored HPs will disclose prospective drug targets. In this study, through a stringent bioinformatics analysis of the core genome and proteome of S. pneumoniae PCS8235, we identified and analyzed 28 HPs that are common in many Streptococcus species and might have a potential role in the virulence or pathogenesis of the bacteria. Functional annotations of the proteins were conducted based on the physicochemical properties, subcellular localization, virulence prediction, protein-protein interactions, and identification of essential genes, to find potentially druggable proteins among 28 HPs. The majority of the HPs are involved in bacterial transcription and translation. Besides, some of them were homologs of enzymes, binding proteins, transporters, and regulators. Protein-protein interactions revealed HP PCS8235_RS05845 made the highest interactions with other HPs and also has TRP structural motif along with virulent and pathogenic properties indicating it has critical cellular functions and might go under unconventional protein secretions. The second highest interacting protein HP PCS8235_RS02595 interacts with the Regulator of chromosomal segregation (RocS) which participates in chromosome segregation and nucleoid protection in S. pneumoniae. In this interacting network, 54% of protein members have virulent properties and 40% contain pathogenic properties. Among them, most of these proteins circulate in the cytoplasmic area and have hydrophilic properties. Finally, molecular docking and dynamics simulation demonstrated that the antimalarial drug Artenimol can act as a drug repurposing candidate against HP PCS8235_RS 04650 of S. pneumoniae. Hence, the present study could aid in drugs against S. pneumoniae.

FtsZ-Ring Regulation and Cell Division Are Mediated by Essential EzrA and Accessory Proteins ZapA and ZapJ in Streptococcus pneumoniae

The bacterial FtsZ-ring initiates division by recruiting a large repertoire of proteins (the divisome; Z-ring) needed for septation and separation of cells. Although FtsZ is essential and its role as the main orchestrator of cell division is conserved in most eubacteria, the regulators of Z-ring presence and positioning are not universal. This study characterizes factors that regulate divisome presence and placement in the ovoid-shaped pathogen, Streptococcus pneumoniae (Spn), focusing on FtsZ, EzrA, SepF, ZapA, and ZapJ, which is reported here as a partner of ZapA. Epi-fluorescence microscopy (EFm) and high-resolution microscopy experiments showed that FtsZ and EzrA co-localize during the entire Spn cell cycle, whereas ZapA and ZapJ are late-arriving divisome proteins. Depletion and conditional mutants demonstrate that EzrA is essential in Spn and required for normal cell growth, size, shape homeostasis, and chromosome segregation. Moreover, EzrA(Spn) is required for midcell placement of FtsZ-rings and PG synthesis. Notably, overexpression of EzrA leads to the appearance of extra Z-rings in Spn. Together, these observations support a role for EzrA as a positive regulator of FtsZ-ring formation in Spn. Conversely, FtsZ is required for EzrA recruitment to equatorial rings and for the organization of PG synthesis. In contrast to EzrA depletion, which causes a bacteriostatic phenotype in Spn, depletion of FtsZ results in enlarged spherical cells that are subject to LytA-dependent autolysis. Co-immunoprecipitation and bacterial two-hybrid assays show that EzrA(Spn) is in complexes with FtsZ, Z-ring regulators (FtsA, SepF, ZapA, MapZ), division proteins (FtsK, StkP), and proteins that mediate peptidoglycan synthesis (GpsB, aPBP1a), consistent with a role for EzrA at the interface of cell division and PG synthesis. In contrast to the essentiality of FtsZ and EzrA, ZapA and SepF have accessory roles in regulating pneumococcal physiology. We further show that ZapA interacts with a non-ZapB homolog, named here as ZapJ, which is conserved in Streptococcus species. The absence of the accessory proteins, ZapA, ZapJ, and SepF, exacerbates growth defects when EzrA is depleted or MapZ is deleted. Taken together, these results provide new information about the spatially and temporally distinct proteins that regulate FtsZ-ring organization and cell division in Spn.

The bacterial tyrosine kinase system CpsBCD governs the length of capsule polymers

Many pathogenic bacteria are encased in a layer of capsular polysaccharide (CPS). This layer is important for virulence by masking surface antigens, preventing opsonophagocytosis, and avoiding mucus entrapment. The bacterial tyrosine kinase (BY-kinase) regulates capsule synthesis and helps bacterial pathogens to survive different host niches. BY-kinases autophosphorylate at the C-terminal tyrosine residues upon external stimuli, but the role of phosphorylation is still unclear. Here, we report that the BY-kinase CpsCD is required for growth in Streptococcus pneumoniae Cells lacking a functional cpsC or cpsD accumulated low molecular weight CPS and lysed because of the lethal sequestration of the lipid carrier undecaprenyl phosphate, resulting in inhibition of peptidoglycan (PG) synthesis. CpsC interacts with CpsD and the polymerase CpsH. CpsD phosphorylation reduces the length of CPS polymers presumably by controlling the activity of CpsC. Finally, pulse-chase experiments reveal the spatiotemporal coordination between CPS and PG synthesis. This coordination is dependent on CpsC and CpsD. Together, our study provides evidence that BY-kinases regulate capsule polymer length by fine-tuning CpsC activity through autophosphorylation.

The Pneumococcal Divisome: Dynamic Control of Streptococcus pneumoniae Cell Division

Cell division in Streptococcus pneumoniae (pneumococcus) is performed and regulated by a protein complex consisting of at least 14 different protein elements; known as the divisome. Recent findings have advanced our understanding of the molecular events surrounding this process and have provided new understanding of the mechanisms that occur during the division of pneumococcus. This review will provide an overview of the key protein complexes and how they are involved in cell division. We will discuss the interaction of proteins in the divisome complex that underpin the control mechanisms for cell division and cell wall synthesis and remodelling that are required in S. pneumoniae, including the involvement of virulence factors and capsular polysaccharides.

Bacterial cell proliferation: from molecules to cells

Bacterial cell proliferation is highly efficient, both because bacteria grow fast and multiply with a low failure rate. This efficiency is underpinned by the robustness of the cell cycle and its synchronization with cell growth and cytokinesis. Recent advances in bacterial cell biology brought about by single-cell physiology in microfluidic chambers suggest a series of simple phenomenological models at the cellular scale, coupling cell size and growth with the cell cycle. We contrast the apparent simplicity of these mechanisms based on the addition of a constant size between cell cycle events (e.g. two consecutive initiation of DNA replication or cell division) with the complexity of the underlying regulatory networks. Beyond the paradigm of cell cycle checkpoints, the coordination between the DNA and division cycles and cell growth is largely mediated by a wealth of other mechanisms. We propose our perspective on these mechanisms, through the prism of the known crosstalk between DNA replication and segregation, cell division and cell growth or size. We argue that the precise knowledge of these molecular mechanisms is critical to integrate the diverse layers of controls at different time and space scales into synthetic and verifiable models.

A Comprehensive Evolutionary Scenario of Cell Division and Associated Processes in the Firmicutes

The cell cycle is a fundamental process that has been extensively studied in bacteria. However, many of its components and their interactions with machineries involved in other cellular processes are poorly understood. Furthermore, most knowledge relies on the study of a few models, but the real diversity of the cell division apparatus and its evolution are largely unknown. Here, we present a massive in-silico analysis of cell division and associated processes in around 1,000 genomes of the Firmicutes, a major bacterial phylum encompassing models (i.e. Bacillus subtilis, Streptococcus pneumoniae, and Staphylococcus aureus), as well as many important pathogens. We analyzed over 160 proteins by using an original approach combining phylogenetic reconciliation, phylogenetic profiles, and gene cluster survey. Our results reveal the presence of substantial differences among clades and pinpoints a number of evolutionary hotspots. In particular, the emergence of Bacilli coincides with an expansion of the gene repertoires involved in cell wall synthesis and remodeling. We also highlight major genomic rearrangements at the emergence of Streptococcaceae. We establish a functional network in Firmicutes that allows identifying new functional links inside one same process such as between FtsW (peptidoglycan polymerase) and a previously undescribed Penicilin-Binding Protein or between different processes, such as replication and cell wall synthesis. Finally, we identify new candidates involved in sporulation and cell wall synthesis. Our results provide a previously undescribed view on the diversity of the bacterial cell cycle, testable hypotheses for further experimental studies, and a methodological framework for the analysis of any other biological system.

Activation of a signaling pathway by the physical translocation of a chromosome

In every organism, the cell cycle requires the execution of multiple processes in a strictly defined order. However, the mechanisms used to ensure such order remain poorly understood, particularly in bacteria. Here, we show that the activation of the essential CtrA signaling pathway that triggers cell division in Caulobacter crescentus is intrinsically coupled to the initiation of DNA replication via the physical translocation of a newly replicated chromosome, powered by the ParABS system. We demonstrate that ParA accumulation at the new cell pole during chromosome segregation recruits ChpT, an intermediate component of the CtrA signaling pathway. ChpT is normally restricted from accessing the selective PopZ polar microdomain until the new chromosome and ParA arrive. Consequently, any disruption to DNA replication initiation prevents ChpT polarization and, in turn, cell division. Collectively, our findings reveal how major cell-cycle events are coordinated in Caulobacter and, importantly, how chromosome translocation triggers an essential signaling pathway.

MetR is a molecular adaptor for pneumococcal carriage in the healthy upper airway

Streptococcus pneumoniae resides in the human upper airway as a commensal but also causes pneumonia, bacteremia, meningitis, and otitis media. It remains unclear how pneumococci adapt to nutritional conditions of various host niches. We here show that MetR, a LysR family transcriptional regulator, serves as a molecular adaptor for pneumococcal fitness, particularly in the upper airway. The metR mutant of strain D39 rapidly disappeared from the nasopharynx but was marginally attenuated in the lungs and bloodstream of mice. RNA-seq and ChIP-seq analyses showed that MetR broadly regulates transcription of the genes involved in methionine synthesis and other functions under methionine starvation. Genetic and biochemical analyses confirmed that MetR is essential for the activation of methionine synthesis but not uptake. Co-infection of influenza virus partially restored the colonization defect of the metR mutant. These results strongly suggest that MetR is particularly evolved for pneumococcal carriage in the upper airway of healthy individuals where free methionine is severely limited, but it becomes dispensable where environmental methionine is relatively more abundant (e.g., inflamed upper airway and sterile sites). To the best of our knowledge, MetR represents the first known regulator particularly for pneumococcal carriage in healthy individuals.

A conserved cell division protein directly regulates FtsZ dynamics in filamentous and unicellular actinobacteria

Bacterial cell division is driven by the polymerization of the GTPase FtsZ into a contractile structure, the so-called Z-ring. This essential process involves proteins that modulate FtsZ dynamics and hence the overall Z-ring architecture. Actinobacteria like Streptomyces and Mycobacterium lack known key FtsZ-regulators. Here we report the identification of SepH, a conserved actinobacterial protein that directly regulates FtsZ dynamics. We show that SepH is crucially involved in cell division in Streptomyces venezuelae and that it binds FtsZ via a conserved helix-turn-helix motif, stimulating the assembly of FtsZ protofilaments. Comparative in vitro studies using the SepH homolog from Mycobacterium smegmatis further reveal that SepH can also bundle FtsZ protofilaments, indicating an additional Z-ring stabilizing function in vivo. We propose that SepH plays a crucial role at the onset of cytokinesis in actinobacteria by promoting the assembly of FtsZ filaments into division-competent Z-rings that can go on to mediate septum synthesis.

CcrZ is a pneumococcal spatiotemporal cell cycle regulator that interacts with FtsZ and controls DNA replication by modulating the activity of DnaA

Most bacteria replicate and segregate their DNA concomitantly while growing, before cell division takes place. How bacteria synchronize these different cell cycle events to ensure faithful chromosome inheritance by daughter cells is poorly understood. Here, we identify Cell Cycle Regulator protein interacting with FtsZ (CcrZ) as a conserved and essential protein in pneumococci and related Firmicutes such as Bacillus subtilis and Staphylococcus aureus. CcrZ couples cell division with DNA replication by controlling the activity of the master initiator of DNA replication, DnaA. The absence of CcrZ causes mis-timed and reduced initiation of DNA replication, which subsequently results in aberrant cell division. We show that CcrZ from Streptococcus pneumoniae interacts directly with the cytoskeleton protein FtsZ, which places CcrZ in the middle of the newborn cell where the DnaA-bound origin is positioned. This work uncovers a mechanism for control of the bacterial cell cycle in which CcrZ controls DnaA activity to ensure that the chromosome is replicated at the right time during the cell cycle.

Decoding capsule synthesis in Streptococcus pneumoniae

Streptococcus pneumoniae synthesizes more than one hundred types of capsular polysaccharides (CPS). While the diversity of the enzymes and transporters involved is enormous, it is not limitless. In this review, we summarized the recent progress on elucidating the structure-function relationships of CPS, the mechanisms by which they are synthesized, how their synthesis is regulated, the host immune response against them, and the development of novel pneumococcal vaccines. Based on the genetic and structural information available, we generated provisional models of the CPS repeating units that remain unsolved. In addition, to facilitate cross-species comparisons and assignment of glycosyltransferases, we illustrated the biosynthetic pathways of the known CPS in a standardized format. Studying the intricate steps of pneumococcal CPS assembly promises to provide novel insights for drug and vaccine development as well as improve our understanding of related pathways in other species.

Bacterial chromosome segregation by the ParABS system

Proper chromosome segregation during cell division is essential in all domains of life. In the majority of bacterial species, faithful chromosome segregation is mediated by the tripartite ParABS system, consisting of an ATPase protein ParA, a CTPase and DNA-binding protein ParB, and a centromere-like parS site. The parS site is most often located near the origin of replication and is segregated first after chromosome replication. ParB nucleates on parS before binding to adjacent non-specific DNA to form a multimeric nucleoprotein complex. ParA interacts with ParB to drive the higher-order ParB–DNA complex, and hence the replicating chromosomes, to each daughter cell. Here, we review the various models for the formation of the ParABS complex and describe its role in segregating the origin-proximal region of the chromosome. Additionally, we discuss outstanding questions and challenges in understanding bacterial chromosome segregation.

Chromosome Segregation Proteins as Coordinators of Cell Cycle in Response to Environmental Conditions

Chromosome segregation is a crucial stage of the cell cycle. In general, proteins involved in this process are DNA-binding proteins, and in most bacteria, ParA and ParB are the main players; however, some bacteria manage this process by employing other proteins, such as condensins. The dynamic interaction between ParA and ParB drives movement and exerts positioning of the chromosomal origin of replication (oriC) within the cell. In addition, both ParA and ParB were shown to interact with the other proteins, including those involved in cell division or cell elongation. The significance of these interactions for the progression of the cell cycle is currently under investigation. Remarkably, DNA binding by ParA and ParB as well as their interactions with protein partners conceivably may be modulated by intra- and extracellular conditions. This notion provokes the question of whether chromosome segregation can be regarded as a regulatory stage of the cell cycle. To address this question, we discuss how environmental conditions affect chromosome segregation and how segregation proteins influence other cell cycle processes.

Shedding Light on the Cell Biology of the Predatory Bacterium Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus is a predatory bacterium that feeds upon and proliferates inside other Gram-negative bacteria. Upon entry into the periplasmic space of the prey envelope, B. bacteriovorus initiates an exquisite developmental program in which it digests the host resources and grows as a filament, which eventually divides in a non-binary manner, releasing a variable number of daughter cells. The progeny then escape from the prey ghost to encounter new victims and resume the predation cycle. Owing to its unique biology, B. bacteriovorus undoubtedly represents an attractive model to unravel novel mechanisms of bacterial cell cycle control and cellular organization. Yet, the molecular factors behind the sophisticated lifestyle of this micro-predator are still mysterious. In particular, the spatiotemporal dynamics of proteins that control key cellular processes such as transmission of the genetic information, cell growth and division remain largely unexplored. In this Perspective article, I highlight outstanding fundamental questions related to these aspects and arising from the original biology of this bacterium. I also discuss available insights and potential cell biology approaches based on quantitative live imaging techniques, in combination with bacterial genetics and biochemistry, to shed light on the intracellular organization of B. bacteriovorus in space and time.

Rules and Exceptions: The Role of Chromosomal ParB in DNA Segregation and Other Cellular Processes

The segregation of newly replicated chromosomes in bacterial cells is a highly coordinated spatiotemporal process. In the majority of bacterial species, a tripartite ParAB-parS system, composed of an ATPase (ParA), a DNA-binding protein (ParB), and its target(s) parS sequence(s), facilitates the initial steps of chromosome partitioning. ParB nucleates around parS(s) located in the vicinity of newly replicated oriCs to form large nucleoprotein complexes, which are subsequently relocated by ParA to distal cellular compartments. In this review, we describe the role of ParB in various processes within bacterial cells, pointing out interspecies differences. We outline recent progress in understanding the ParB nucleoprotein complex formation and its role in DNA segregation, including ori positioning and anchoring, DNA condensation, and loading of the structural maintenance of chromosome (SMC) proteins. The auxiliary roles of ParBs in the control of chromosome replication initiation and cell division, as well as the regulation of gene expression, are discussed. Moreover, we catalog ParB interacting proteins. Overall, this work highlights how different bacterial species adapt the DNA partitioning ParAB-parS system to meet their specific requirements.

¡vIVA la DivIVA!

Reproduction in the bacterial kingdom predominantly occurs through binary fission-a process in which one parental cell is divided into two similarly sized daughter cells. How cell division, in conjunction with cell elongation and chromosome segregation, is orchestrated by a multitude of proteins has been an active area of research spanning the past few decades. Together, the monumental endeavors of multiple laboratories have identified several cell division and cell shape regulators as well as their underlying regulatory mechanisms in rod-shaped Escherichia coli and Bacillus subtilis, which serve as model organisms for Gram-negative and Gram-positive bacteria, respectively. Yet our understanding of bacterial cell division and morphology regulation is far from complete, especially in noncanonical and non-rod-shaped organisms. In this review, we focus on two proteins that are highly conserved in Gram-positive organisms, DivIVA and its homolog GpsB, and attempt to summarize the recent advances in this area of research and discuss their various roles in cell division, cell growth, and chromosome segregation in addition to their interactome and posttranslational regulation.

Protein post-translational modifications in bacteria

Over the past decade the number and variety of protein post-translational modifications that have been detected and characterized in bacteria have rapidly increased. Most post-translational protein modifications occur in a relatively low number of bacterial proteins in comparison with eukaryotic proteins, and most of the modified proteins carry low, substoichiometric levels of modification; therefore, their structural and functional analysis is particularly challenging. The number of modifying enzymes differs greatly among bacterial species, and the extent of the modified proteome strongly depends on environmental conditions. Nevertheless, evidence is rapidly accumulating that protein post-translational modifications have vital roles in various cellular processes such as protein synthesis and turnover, nitrogen metabolism, the cell cycle, dormancy, sporulation, spore germination, persistence and virulence. Further research of protein post-translational modifications will fill current gaps in the understanding of bacterial physiology and open new avenues for treatment of infectious diseases.

The Tyrosine-Autokinase UbK Is Required for Proper Cell Growth and Cell Morphology of Streptococcus pneumoniae

Protein phosphorylation is a key post-translational modification required for many cellular functions of the bacterial cell. Recently, we identified a new protein-kinase, named UbK, in Bacillus subtilis that belongs to a new family of protein-kinases widespread in bacteria. In this study, we analyze the function of UbK in Streptococcus pneumoniae. We show that UbK displays a tyrosine-kinase activity and autophosphorylates on a unique tyrosine in vivo. To get insights into its cellular role, we constructed a set of pneumococcal ubk mutants. Using conventional and electron microscopy, we show that the ubk deficient strain, as well as an ubk catalytic dead mutant, display both severe cell-growth and cell-morphology defects. The same defects are observed with a mutant mimicking permanent phosphorylation of UbK whereas they are not detected for a mutant mimicking defective autophosphorylation of UbK. Moreover, we find that UbK phosphorylation promotes its ability to hydrolyze ATP. These observations show that the hydrolysis of ATP by UbK serves not only for its autophosphorylation but also for a distinct purpose essential for the optimal cell growth and cell-morphogenesis of the pneumococcus. We thus propose a model in which the autophosphorylation/dephosphorylation of UbK regulates its cellular function through a negative feedback loop.