Project description:Streptococcus pneumoniae is a human commensal bacterium that causes serious diseases. Peptidoglycan (PG) is the critical component of bacteria that maintains cell shape, size, chaining, and turgor resistance. Because of its surface exposure and eubacterial-specific mechanism of biosynthesis, PG biosynthesis remains an outstanding target for discovery of new antibiotics to resistant “superbugs,” like S. pneumoniae. Pneumococcal PG biosynthesis is carried out by a balance of septal and peripheral (side-wall-like) PG synthesis mediated by bPBP2x and bPBP2b, respectively, that emanates from midcell regions. We selected for additional suppressor mutations, besides mltG, that eliminate the requirement for essential bPBP2b in peripheral PG synthesis. We found that mutations that inactivate a putative RNA binding protein, designated KhpA, suppressed the requirement for some, but not all of the essential proteins required for peripheral PG synthesis. KhpA was used as bait in co-IP experiments to demonstrate interactions with a second RNA binding protein, designated KhpB, in cells. Mutations in khpA or khpB phenocopy each other and result in slower growth rates, smaller cell size with normal aspect ratios, and induction of cell wall stress responses. RIP-Seq analyses confirmed KhpAB as RNA binding protein in cells. Another suppressor of Δpbp2b implicated induction of a cell division operon as a way to bypass the requirement for bPBP2b. We show that increased expression of this cell division operon occurs in ΔkhpAB mutants and that this induction is necessary and sufficient to account for suppression of Δpbp2b. Comparisons of relative transcript amounts and protein levels indicate that induction of this cell division operon in ΔkhpAB mutants occurs primarily at the post-transcriptional level. Together, our results show that KhpAB, which are virulence factors in S. pneumoniae and are conserved in other Gram-positive pathogens, acts as a new class of RNA binding protein, with properties analogous to Hfq in Gram-negative bacteria.

Project description:Pyruvate oxidase encoded by spxB is a major virulence factor in the human respiratory pathogen Streptococcus pneumoniae. During aerobic growth, SpxB synthesizes large amounts of H2O2 and acetyl phosphate, which can serve as a phosphoryl group donor to response regulators and be converted to ATP. SpxB is the main source of the millimolar concentrations of H2O2 produced and tolerated by pneumococcus, despite its lack of a catalase. We report here the first cis- and trans-acting regulatory elements for spxB transcription. These elements were identified in a genetic screen, similar to those used previously for phase variants, for spontaneous mutations that caused colonies of virulent serotype 2 strain D39 to change from a transparent to an opaque appearance. Six of the seven opaque colonies recovered (frequency of 3 x 10-5) were impaired for SpxB function. Modeling suggested that two mutations changed amino acids in SpxB required for FAD cofactor or subunit binding. One mutation deleted a cis-acting adjacent direct repeat required for optimal spxB transcription. The other three independent mutations created the same frameshift near the start of a trans-acting regulatory gene designated as spxR. The SpxR protein contains helix-turn-helix, CBS, and HotDog domains implicated in DNA, adenosine, and CoA compound binding, respectively, consistent with the idea that SpxR positively regulates spxB transcript amount in response to energy and metabolic state rather than oxidative state. Finally, microarray analyses of a null spxB or a spxR mutant revealed the presence of a new oxidative stress response in pneumococcus and unexpectedly demonstrated that SpxR strongly positively regulates the transcript amount of the strH exoglycosidase gene, which like spxB, has been implicated in host colonization. Keywords: genetic modification Bacterial strains were grown exponentially in rich (BHI) media at 37C and an atmosphere of 5% CO2, and were processed as described in the related Sample records. Samples were collected from three independent biological replicates and included one dye swap. Data were normalized using the Lowess (subgrid) method without background subtraction.

Project description:Bacteriophage infection of Lactococcus lactis strains used in the manufacture of fermented milk products is a major threat for the dairy industry. A greater understanding of the global molecular response of the bacterial host following phage infection has the potential to identify new targets for the design of phage control measures for biotechnological processes. In this study, we have used whole-genome oligonucleotide microarrays to gain insights into the genomic intelligence driving the instinctive response of L. lactis subsp. lactis IL1403 to the onset of a challenge with the lytic prolate-headed phage c2. Following phage adsorption, the bacterium differentially regulated the expression of 61 genes belonging to 14 functional categories, and mostly to cell envelope (12 genes), regulatory functions (11 genes), and carbohydrate metabolism (7 genes). The nature of the differentially regulated genes suggests the orchestration of a complex response involving induction of cell envelope stress proteins, D-alanylation of cell-wall lipoteichoic acids (LTAs), restoration of the proton motive force (PMF), and energy conservation. Increased D-alanylation of LTAs would act as an adsorption blocking mechanism, which we speculate may allow the survival of a small percent of the cell population when facing more realistic in vivo low titer-phage attacks. The modification of LTAs decoration in response to phage c2 adsorption also suggests these cell wall structures as possible primary receptors for this phage. Restoration of a physiological PMF is achieved by regulating the expression of genes affecting the two main components of the PMF, and serves to reverse a drastic depolarization of the host membrane caused by phage adsorption. Down-regulation of energy-consuming metabolic activities and a switch to anaerobic respiration helps the bacterium to save energy in order to sustain the PMF and the overall response to phage. We finally propose that the overall transcriptional response of L. lactis IL1403 to the phage stimuli is orchestrated by the concerted action of Phage Shock Proteins and of the bivalent transcriptional regulator SpxB following activation by the two-component system CesSR. To our knowledge, this represents the first detailed description in L. lactis, and probably in Gram-positive bacteria, of the molecular mechanisms involved in the host response to the membrane perturbation mediated by phage adsorption. Two-condition experiment: IL1403 vs. Bacteriophage c2-infected IL1403 cells. Biological replicates: 2 controls, 2 infected, independently grown and harvested. Two technical replicates per array.

Project description:Bacteriophage infection of Lactococcus lactis strains used in the manufacture of fermented milk products is a major threat for the dairy industry. A greater understanding of the global molecular response of the bacterial host following phage infection has the potential to identify new targets for the design of phage control measures for biotechnological processes. In this study, we have used whole-genome oligonucleotide microarrays to gain insights into the genomic intelligence driving the instinctive response of L. lactis subsp. lactis IL1403 to the onset of a challenge with the lytic prolate-headed phage c2. Following phage adsorption, the bacterium differentially regulated the expression of 61 genes belonging to 14 functional categories, and mostly to cell envelope (12 genes), regulatory functions (11 genes), and carbohydrate metabolism (7 genes). The nature of the differentially regulated genes suggests the orchestration of a complex response involving induction of cell envelope stress proteins, D-alanylation of cell-wall lipoteichoic acids (LTAs), restoration of the proton motive force (PMF), and energy conservation. Increased D-alanylation of LTAs would act as an adsorption blocking mechanism, which we speculate may allow the survival of a small percent of the cell population when facing more realistic in vivo low titer-phage attacks. The modification of LTAs decoration in response to phage c2 adsorption also suggests these cell wall structures as possible primary receptors for this phage. Restoration of a physiological PMF is achieved by regulating the expression of genes affecting the two main components of the PMF, and serves to reverse a drastic depolarization of the host membrane caused by phage adsorption. Down-regulation of energy-consuming metabolic activities and a switch to anaerobic respiration helps the bacterium to save energy in order to sustain the PMF and the overall response to phage. We finally propose that the overall transcriptional response of L. lactis IL1403 to the phage stimuli is orchestrated by the concerted action of Phage Shock Proteins and of the bivalent transcriptional regulator SpxB following activation by the two-component system CesSR. To our knowledge, this represents the first detailed description in L. lactis, and probably in Gram-positive bacteria, of the molecular mechanisms involved in the host response to the membrane perturbation mediated by phage adsorption.

Project description:The bacterial cell envelope is the frontier line of the adaptational defense that protects cells against environmental and intrinsic stressors to maintain homeostasis. Deciphering the molecular pathways involved in envelope biology is of high importance for both fundamental sciences and translational applications. Peptidoglycan (PG) is one of the main structural components of bacterial cell envelopes. It protects bacteria against mechanical and osmotic stress, confers cell shape and physical integrity. In a previous study, we identified that the Escherichia coli ElyC protein containing a highly conserved domain of an unknown function is required for envelope integrity at low temperature. ElyC was shown to be essential for PG assembly at room temperature (21°C) and to be involved in the metabolism of the lipid carrier necessary for the membrane step of the biosynthesis pathways for PG and other bacterial envelope polysaccharides. PG assembly was completely blocked in ElyC-defective cells grown at 21°C, leading to a terminal phenotype of cell lysis. The physiological importance of ElyC in bacterial cells grown at the physiological temperature of 37°C had not yet been investigated. To study this, we performed phenotypic characterization and transcriptomic profiling of ElyC-defective E. coli cells were grown at 37°C and 21°C, compared to wild-type cells. Even if ∆elyC mutant cells grow as well as wild-type cells at 37°C, microscopic analysis revealed that cellular morphology is altered by the lack of ElyC at this temperature. PG quantification and analysis confirmed that PG biosynthesis is significantly inhibited in the absence of ElyC at 37°C. We further have shown that ∆elyC mutant cells are more sensitive to PG-targeting β-lactam antibiotics than wild-type cells at 37°C. The RNA-Seq transcriptomic study showed that elimination of the ElyC evokes a highly defective cellular envelope when elyC mutant grows at 21°C, whereas at 37°C, the absence of ElyC leads to a moderate cellular response. While the PG defect of cells inactivated for ElyC is lethal at 21°C, ElyC-defective cells maintain enough PG integrity to grow and survive at 37°C. However, those cells are morphologically defective, are coping with envelope stress and are more sensitive to PG-targeting antibiotics. Overall, our data support a crucial role for ElyC in the metabolic flux for the PG biosynthesis pathway at optimal and suboptimal temperatures.

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SpxB regulates O-acetylation dependent resistance of Lactococcus lactis peptidoglycan to hydrolysis

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