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Bacterial amidases are essential to split the shared envelope of adjunct daughter cells to allow cell separation. Their activity needs to be precisely controlled to prevent cell lysis. In

E. coli and many other bacterial species can alter their cell cycle according to nutrient availability. Under optimal conditions bacteria grow and divide very fast but they slow down the cell cycle when conditions deteriorate. This adaptability is underlined by mechanisms coordinating cell growth with duplication of genetic material and cell division. Several mechanisms regulating DNA replication process in E. coli have been described with biochemical details so far. Nevertheless we still don’t fully understand the source of remarkable precision that allows bacterial cells to coordinate their growth and chromosome replication. To shed light on regulation of E. coli DNA replication at systemic level, we used affinity purification coupled with mass spectrometry (AP-MS) to characterize protein-protein interactions (PPIs) formed by key E. coli replication proteins, under disparate bacterial growth conditions and phases. We present the resulting dynamic replication protein interaction network (PIN) and highlight links between DNA replication and several cellular processes, like outer membrane synthesis, RNA degradation and modification or starvation response.ImportanceDNA replication is a vital process, ensuring propagation of genetic material to progeny cells. Despite decades of studies we still don’t fully understand how bacteria coordinate chromosomal DNA duplication with cell growth and cell division under optimal and stressful conditions. At molecular level, regulation of processes, including DNA replication, is often executed through direct protein-protein interactions (PPIs). In this work we present PPIs formed by the key E. coli replication proteins under three different bacterial growth conditions. We show novel PPIs with confirmed impact on chromosomal DNA replication. Our results provide also alternative explanations of genetic interactions uncovered before by others for E.coli replication machinery.

Protein lysine acetylation, regulates a wide range of cellular functions and is controlled by protein deacetylases called sirtuins. In eukaryotes, sirtuins activity is coupled to the spatiotemporally-controlled NAD+ level. However, regulation of the bacterial sirtuin CobB and its coupling to the NAD+ metabolism is not well understood. In this work we show that such coordination in Escherichia coli cells is achieved through a CobB interaction with PRPP synthase Prs, an enzyme necessary for NAD+ synthesis. Probing CobB protein-protein interactions, we demonstrate that it forms a stable complex with Prs. This assembly stimulates CobB deacetylase activity and partially protects it from inhibition by nicotinamide. We provide evidence that Prs acetylation is not necessary for CobB binding but affects the global acetylome and CobB activity in vivo. Consequently, we show that Prs acetylation status affects bacterial growth under different metabolic regimes. Therefore, we propose that CobB-Prs crosstalk orchestrates the NAD+ metabolism and protein acetylation in response to environmental cues.

Shiga toxin-converting bacteriophages (or Stx phages) are responsible for virulence of enterohemorrhagic Escherichia coli strains. Although they belong to the group of lambdoid phages, which have served as models in studies on DNA replication mechanisms, details of regulation of replication of Stx phage genomes are poorly understood. Despite high similarity of their replication regions to that of phage lambda, considerable differences occur between them. Here, we present a comparison of origins of replication and O proteins of lambda and selected Stx phages (phages P27 and 933W). Stx initiator proteins, similarly to the lambda O protein, exist in the form of dimers. Only 4 iteron sequences are strongly bound in vitro by the O proteins, despite the presence of 6 such fragments in the Stx ori, while the function of the other two iterons is still crucial for transformation of E. coli wild-type strain by the P27-derived lambdoid plasmid. As these sequences are found in the gene coding for Stx O proteins, the sequences of these proteins themselves are also extended compared to lambda phage. Therefore, proteins O of Stx phages P27 and 933W have 13 additional amino acids. They can act as a space barrier, thus affecting the lesser packing of the O-some Stx complex compared to the structure found in lambda. Such structure of the DNA replication initiation complex may determine its lesser dependence on the processes occurring in the host cell, including transcriptional activation of the origin. Differences between molecular processes occurring during formation of replication complexes in lambda and Stx phages may indicate the specialization of the latter phages and their adaptation to specific environmental conditions where quick genetic switches are crucial.

Prs (phosphoribosyl pyrophosphate synthase) is a broadly conserved protein that synthesises 5-phosphoribosyl 1-pyrophospate (PRPP); a substrate for biosynthesis of at least 10 enzymatic pathways including biosynthesis of DNA building blocks – purines and pyrimidines. InEscherichia coli, it is a protein of homo-hexameric quaternary structure, which can be challenging to work with, due to frequent aggregation and activity loss. Several studies showed brief purification protocols for various bacterial PRPP synthases, in most cases involving ammonium sulfate precipitation.Here, we provide a protocol for expression ofE. coliPrs protein in Rosetta (DE3) and BL21 (DE3) pLysE strains and a detailed method for His-Prs and untagged Prs purification on nickel affinity chromatography columns. This protocol allows purification of proteins with high yield, purity and activity. We report here N-terminally His-tagged protein fusions, stable and active, providing that the temperature around 20 °C is maintained at all stages, including centrifugation. Moreover, we successfully applied this method to purify two enzyme variants with K194A and G9S alterations. The K194A mutation in conserved lysine residue results in protein variant unable to synthetize PRPP, while the G9S alteration originates fromprs-2allele variant which was previously related to thermo-sensitive growth. His-PrsG9S protein purified here, exhibited comparable activity as previously observedin-vivosuggesting the proteins purified with our protocol resemble their physiological state.The protocol for Prs purification showed here indicates guidance to improve stability and quality of the protein and to ensure more reliable results in further assaysin-vitro.

Bacterial cells often inhabit environments where conditions can change rapidly. Therefore, a lot of bacterial species developed control strategies allowing them to grow and divide very fast during feast and slow down both parameters during famine. Under rich nutritional conditions, fast-growing bacteria can divide with time interval equal to half of the period required to synthesize their chromosomes. This is possible due to multifork replication which allows ancestor cells to start copying genetic material for their descendants. This reproduction scheme was most likely selected for, since it enables maximization of growth rate and hence – effective competition for resources, while ensuring that DNA replication will not become limiting for cell division. Even with this complexity of cell cycle, isogenic bacterial cells grown under defined conditions display remarkably narrow distribution of sizes. This may suggest that mechanisms exists to control cell size at division step. Alternative view, with great support in experimental data is that the only step coordinated with cell growth is the initiation of DNA replication. Despite decades of research we are still not sure what the driving forces in bacterial cell cycle are. In this work we review recent advances in understanding coordination of growth with DNA replication coming from single cell studies and systems biology approaches.

To ensure faithful transmission of genetic material to progeny cells, DNA replication is tightly regulated, mainly at the initiation step. Escherichia coli cells regulate the frequency of initiation according to growth conditions. Results of the classical, as well as the latest studies, suggest that the DNA replication in E. coli starts at a predefined, constant cell volume per chromosome but the mechanisms coordinating DNA replication with cell growth are still not fully understood. Results of recent investigations have revealed a role of metabolic pathway proteins in the control of cell division and a direct link between metabolism and DNA replication has also been suggested both in Bacillus subtilis and E. coli cells. In this work we show that defects in the acetate overflow pathway suppress the temperature-sensitivity of a defective replication initiator-DnaA under acetogenic growth conditions. Transcriptomic and metabolic analyses imply that this suppression is correlated with pyruvate accumulation, resulting from alterations in the pyruvate dehydrogenase (PDH) activity. Consequently, deletion of genes encoding the pyruvate dehydrogenase subunits likewise resulted in suppression of the thermal-sensitive growth of the dnaA46 strain. We propose that the suppressor effect may be directly related to the PDH complex activity, providing a link between an enzyme of the central carbon metabolism and DNA replication.