RESUMO
Several intracellular pathogens, including Salmonella enterica and Mycobacterium tuberculosis, require the virulence protein MgtC to survive within macrophages and to cause a lethal infection in mice. We now report that, unlike secreted virulence factors that target the host vacuolar ATPase to withstand phagosomal acidity, the MgtC protein acts on Salmonella's own F1Fo ATP synthase. This complex couples proton translocation to ATP synthesis/hydrolysis and is required for virulence. We establish that MgtC interacts with the a subunit of the F1Fo ATP synthase, hindering ATP-driven proton translocation and NADH-driven ATP synthesis in inverted vesicles. An mgtC null mutant displays heightened ATP levels and an acidic cytoplasm, whereas mgtC overexpression decreases ATP levels. A single amino acid substitution in MgtC that prevents binding to the F1Fo ATP synthase abolishes control of ATP levels and attenuates pathogenicity. MgtC provides a singular example of a virulence protein that promotes pathogenicity by interfering with another virulence protein.
Assuntos
Proteínas de Bactérias/metabolismo , Proteínas de Transporte de Cátions/metabolismo , ATPases Translocadoras de Prótons/antagonistas & inibidores , Infecções por Salmonella/microbiologia , Salmonella typhimurium/citologia , Salmonella typhimurium/patogenicidade , Fatores de Virulência/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Feminino , Concentração de Íons de Hidrogênio , Macrófagos/microbiologia , Potenciais da Membrana , Camundongos , Camundongos Endogâmicos C3H , Subunidades Proteicas/antagonistas & inibidores , Salmonella typhimurium/enzimologia , VirulênciaRESUMO
Phosphorus is an essential element assimilated largely as orthophosphate (Pi). Cells respond to Pi starvation by importing Pi from their surroundings. We now report that impaired protein synthesis alone triggers a Pi starvation response even when Pi is plentiful in the extracellular milieu. In the bacterium Salmonella enterica serovar Typhimurium, this response entails phosphorylation of the regulatory protein PhoB and transcription of PhoB-dependent Pi transporter genes and is eliminated upon stimulation of adenosine triphosphate (ATP) hydrolysis. When protein synthesis is impaired due to low cytoplasmic magnesium (Mg2+), Salmonella triggers the Pi starvation response because ribosomes are destabilized, which reduces ATP consumption and thus free cytoplasmic Pi. This response is transient because low cytoplasmic Mg2+ promotes an uptake in Mg2+ and a decrease in ATP levels, which stabilizes ribosomes, resulting in ATP consumption and Pi increase, thus ending the response. Notably, pharmacological inhibition of protein synthesis also elicited a Pi starvation response in the bacterium Escherichia coli and the yeast Saccharomyces cerevisiae Our findings identify a regulatory connection between protein synthesis and Pi homeostasis that is widespread in nature.
Assuntos
Proteínas de Bactérias/metabolismo , Fosfatos/metabolismo , Biossíntese de Proteínas , Adenosina Trifosfatases/fisiologia , Proteínas de Bactérias/fisiologia , Proteínas de Transporte de Cátions/fisiologia , Escherichia coli/efeitos dos fármacos , Escherichia coli/metabolismo , Homeostase , Magnésio/metabolismo , Proteínas de Membrana Transportadoras/fisiologia , Inibidores da Síntese de Proteínas/farmacologia , Saccharomyces cerevisiae/efeitos dos fármacos , Saccharomyces cerevisiae/metabolismo , Salmonella typhimurium/genética , Salmonella typhimurium/metabolismo , Transcrição GênicaRESUMO
The synthesis of ribosomes is regulated by both amino acid abundance and the availability of ATP, which regenerates guanosine triphosphate (GTP), powers ribosomes, and promotes transcription of rRNA genes. We now report that bacteria supersede both of these controls when experiencing low cytosolic magnesium (Mg2+), a divalent cation essential for ribosome stabilization and for neutralization of ATP's negative charge. We uncover a regulatory circuit that responds to low cytosolic Mg2+ by promoting expression of proteins that import Mg2+ and lower ATP amounts. This response reduces the levels of ATP and ribosomes, making Mg2+ ions available for translation. Mutants defective in Mg2+ uptake and unable to reduce ATP levels accumulate non-functional ribosomal components and undergo translational arrest. Our findings establish a paradigm whereby cells reduce the amounts of translating ribosomes to carry out protein synthesis.
Assuntos
Regulação Bacteriana da Expressão Gênica , Magnésio/farmacologia , Biossíntese de Proteínas/efeitos dos fármacos , Proteínas Ribossômicas/biossíntese , Ribossomos/efeitos dos fármacos , Salmonella typhimurium/efeitos dos fármacos , Trifosfato de Adenosina/metabolismo , Cátions Bivalentes , Meios de Cultura/química , Meios de Cultura/farmacologia , Escherichia coli/genética , Escherichia coli/metabolismo , Guanosina Trifosfato/biossíntese , Magnésio/metabolismo , Biogênese de Organelas , Proteínas Ribossômicas/genética , Ribossomos/genética , Ribossomos/metabolismo , Salmonella typhimurium/genética , Salmonella typhimurium/metabolismo , Eletricidade Estática , Estresse Fisiológico/genéticaRESUMO
Phosphorus (P) is an essential component of core biological molecules. In bacteria, P is acquired mainly as inorganic orthophosphate (Pi) and assimilated into adenosine triphosphate (ATP) in the cytoplasm. Although P is essential, excess cytosolic Pi hinders growth. We now report that bacteria limit Pi uptake to avoid disruption of Mg2+-dependent processes that result, in part, from Mg2+ chelation by ATP. We establish that the MgtC protein inhibits uptake of the ATP precursor Pi when Salmonella enterica serovar Typhimurium experiences cytoplasmic Mg2+ starvation. This response prevents ATP accumulation and overproduction of ribosomal RNA that together ultimately hinder bacterial growth and result in loss of viability. Even when cytoplasmic Mg2+ is not limiting, excessive Pi uptake increases ATP synthesis, depletes free cytoplasmic Mg2+, inhibits protein synthesis, and hinders growth. Our results provide a framework to understand the molecular basis for Pi toxicity. Furthermore, they suggest a regulatory logic that governs P assimilation based on its intimate connection to cytoplasmic Mg2+ homeostasis.
Assuntos
Citoplasma/metabolismo , Homeostase , Magnésio/metabolismo , Fosfatos/metabolismo , Trifosfato de Adenosina/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Transporte Biológico , Proteínas de Transporte de Cátions/genética , Proteínas de Transporte de Cátions/metabolismo , Regulação Bacteriana da Expressão Gênica , Viabilidade Microbiana , Mutação , Fosfatos/toxicidade , Biossíntese de Proteínas , Salmonella typhimurium/genética , Salmonella typhimurium/crescimento & desenvolvimento , Salmonella typhimurium/metabolismoRESUMO
The mechanism of action and contribution to pathogenesis of many virulence genes are understood. By contrast, little is known about anti-virulence genes, which contribute to the start, progression, and outcome of an infection. We now report how an anti-virulence factor in Salmonella enterica serovar Typhimurium dictates the onset of a genetic program that governs metabolic adaptations and pathogen survival in host tissues. Specifically, we establish that the anti-virulence protein CigR directly restrains the virulence protein MgtC, thereby hindering intramacrophage survival, inhibition of ATP synthesis, stabilization of cytoplasmic pH, and gene transcription by the master virulence regulator PhoP. We determine that, like MgtC, CigR localizes to the bacterial inner membrane and that its C-terminal domain is critical for inhibition of MgtC. As in many toxin/anti-toxin genes implicated in antibiotic tolerance, the mgtC and cigR genes are part of the same mRNA. However, cigR is also transcribed from a constitutive promoter, thereby creating a threshold of CigR protein that the inducible MgtC protein must overcome to initiate a virulence program critical for pathogen persistence in host tissues.
Assuntos
Proteínas de Bactérias/biossíntese , Regulação Bacteriana da Expressão Gênica , Salmonella typhimurium/crescimento & desenvolvimento , Salmonella typhimurium/genética , Fatores de Virulência/biossíntese , Adaptação Fisiológica , Trifosfato de Adenosina/biossíntese , Animais , Linhagem Celular , Macrófagos/microbiologia , Camundongos , Viabilidade Microbiana , VirulênciaRESUMO
The majority of cellular phosphate (PO4-3; Pi) exists as nucleoside triphosphates, mainly adenosine triphosphate (ATP), and ribosomal RNA (rRNA). ATP and rRNA are also the largest cytoplasmic reservoirs of magnesium (Mg2+), the most abundant divalent cation in living cells. The co-occurrence of these ionic species in the cytoplasm is not coincidental. Decades of work in the Pi and Mg2+ starvation responses of two model enteric bacteria, Escherichia coli and Salmonella enterica, have led to the realization that the metabolisms of Pi and Mg2+ are interconnected. Bacteria must acquire these nutrients in a coordinated manner to achieve balanced growth and avoid loss of viability. In this chapter, we will review how bacteria sense and respond to fluctuations in environmental and intracellular Pi and Mg2+ levels. We will also discuss how these two compounds are functionally linked, and how cells elicit physiological responses to maintain their homeostasis.
Assuntos
Fosfatos , Salmonella enterica , Trifosfato de Adenosina/metabolismo , Homeostase , Magnésio , Fosfatos/metabolismo , Salmonella enterica/metabolismoRESUMO
Organisms must maintain physiological levels of Mg(2+) because this divalent cation is critical for the stabilization of membranes and ribosomes, for the neutralization of nucleic acids, and as a cofactor in a variety of enzymatic reactions. In this review, we describe the mechanisms that bacteria utilize to sense the levels of Mg(2+) both outside and inside the cytoplasm. We examine how bacteria achieve Mg(2+) homeostasis by adjusting the expression and activity of Mg(2+) transporters and by changing the composition of their cell envelope. We discuss the connections that exist between Mg(2+) sensing, Mg(2+) transport, and bacterial virulence. Additionally, we explore the logic behind the fact that bacterial genomes encode multiple Mg(2+) transporters and distinct sensing systems for cytoplasmic and extracytoplasmic Mg(2+). These analyses may be applicable to the homeostatic control of other cations.
Assuntos
Bactérias/metabolismo , Proteínas de Bactérias/metabolismo , Magnésio/metabolismo , Bactérias/crescimento & desenvolvimento , Proteínas da Membrana Bacteriana Externa/metabolismo , Ligação Competitiva , Transporte Biológico , Proteínas de Transporte/metabolismo , Cátions/metabolismo , Regulação Bacteriana da Expressão Gênica , Homeostase , Interações Hospedeiro-Patógeno , Riboswitch , Transdução de Sinais , VirulênciaRESUMO
Flagella are multiprotein complexes necessary for swimming and swarming motility. In Salmonella enterica serovar Typhimurium, flagella-mediated motility is repressed by the PhoP/PhoQ regulatory system. We now report that Salmonella can move on 0.3% agarose media in a flagella-independent manner when experiencing the PhoP/PhoQ-inducing signal low Mg(2+). This motility requires the PhoP-activated mgtA, mgtC, and pagM genes, which specify a Mg(2+) transporter, an inhibitor of Salmonella's own F1Fo ATPase, and a small protein of unknown function, respectively. The MgtA and MgtC proteins are necessary for pagM expression because pagM mRNA levels were lower in mgtA and mgtC mutants than in wild-type Salmonella, and also because pagM expression from a heterologous promoter rescued motility in mgtA and mgtC mutants. PagM promotes group motility by a surface protein(s), as a pagM-expressing strain conferred motility upon a pagM null mutant, and proteinase K treatment eliminated motility. The pagM gene is rarely found outside subspecies I of S. enterica and often present in nonfunctional allelic forms in organisms lacking the identified motility. Deletion of the pagM gene reduced bacterial replication on 0.3% agarose low Mg(2+) media but not in low Mg(2+) liquid media. Our findings define a form of motility that allows Salmonella to scavenge nutrients and to escape toxic compounds in low Mg(2+) semisolid environments.
Assuntos
Adenosina Trifosfatases/metabolismo , Proteínas de Bactérias/metabolismo , Proteínas de Transporte de Cátions/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Proteínas de Membrana Transportadoras/metabolismo , Movimento/fisiologia , Salmonella typhimurium/fisiologia , Sequência de Aminoácidos , Sequência de Bases , Biologia Computacional , Flagelos/metabolismo , Magnésio/metabolismo , ATPases Mitocondriais Próton-Translocadoras/antagonistas & inibidores , Dados de Sequência Molecular , Mutagênese , Alinhamento de Sequência , Análise de Sequência de DNARESUMO
Cellulose is the most abundant organic polymer on Earth. In bacteria, cellulose confers protection against environmental insults and is a constituent of biofilms typically formed on abiotic surfaces. We report that, surprisingly, Salmonella enterica serovar Typhimurium makes cellulose when inside macrophages. We determine that preventing cellulose synthesis increases virulence, whereas stimulation of cellulose synthesis inside macrophages decreases virulence. An attenuated mutant lacking the mgtC gene exhibited increased cellulose levels due to increased expression of the cellulose synthase gene bcsA and of cyclic diguanylate, the allosteric activator of the BcsA protein. Inactivation of bcsA restored wild-type virulence to the Salmonella mgtC mutant, but not to other attenuated mutants displaying a wild-type phenotype regarding cellulose. Our findings indicate that a virulence determinant can promote pathogenicity by repressing a pathogen's antivirulence trait. Moreover, they suggest that controlling antivirulence traits increases long-term pathogen fitness by mediating a trade-off between acute virulence and transmission.
Assuntos
Celulose/biossíntese , Salmonella typhimurium/patogenicidade , Trifosfato de Adenosina/metabolismo , Animais , Proteínas de Bactérias/metabolismo , Glucosiltransferases/metabolismo , Espaço Intracelular/efeitos dos fármacos , Espaço Intracelular/metabolismo , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Macrófagos/microbiologia , Magnésio/farmacologia , Camundongos , Mutação/genética , Fagócitos/efeitos dos fármacos , Fagócitos/metabolismo , Salmonella typhimurium/efeitos dos fármacos , Salmonella typhimurium/crescimento & desenvolvimento , VirulênciaRESUMO
Bacteria acquire P primarily as inorganic orthophosphate (Pi, PO43-). Once internalized, Pi is rapidly assimilated into biomass during the synthesis of ATP. Because Pi is essential, but excessive ATP is toxic, the acquisition of environmental Pi is tightly regulated. In the bacterium Salmonella enterica (Salmonella), growth in Pi-limiting environments activates the membrane sensor histidine kinase PhoR, leading to the phosphorylation of its cognate transcriptional regulator PhoB and subsequent transcription of genes involved in adaptations to low Pi. Pi limitation promotes PhoR kinase activity by altering the conformation of a membrane signaling complex comprised of PhoR, the multicomponent Pi transporter system PstSACB and the regulatory protein PhoU. However, the identity of the Pi-starvation signal and how it controls PhoR activity remain unknown. Here, we identify conditions where the PhoB and PhoR signal transduction proteins can be maintained in an inactive state when Salmonella is grown in media lacking Pi. Our results demonstrate that PhoB/PhoR is activated by an intracellular P-insufficiency signal.IMPORTANCEIn enteric bacteria, the transcriptional response to phosphorus (P) starvation is controlled by a specialized signal transduction system comprised of a membrane-bound, multicomponent signal sensor, and a cytoplasmic transcriptional factor. Whereas this system has been primarily studied in the context of phosphate (Pi) starvation, it is currently unknown how this stress initiates signal transduction. In the current study, we establish that this signaling system is regulated by a cytoplasmic signal arising from insufficient P. We demonstrate that rather than responding to extracellular conditions, cells couple the activation of their P starvation response to the availability of cytoplasmic P. This regulatory logic may enable cells to prevent toxicity resulting from excessive Pi acquisition and hinder the onset of a P starvation response when their metabolic demands are being met through the consumption of P sources other than Pi.
RESUMO
IMPORTANCE: Phosphorus (P) is the fifth most abundant element in living cells. This element is acquired mainly as inorganic phosphate (Pi, PO4 3-). In enteric bacteria, P starvation activates a two-component signal transduction system which is composed of the membrane sensor protein PhoR and its cognate transcription regulator PhoB. PhoB, in turn, promotes the transcription of genes that help maintain Pi homeostasis. Here, we characterize the P starvation response of the bacterium Salmonella enterica. We determine the PhoB-dependent and independent transcriptional changes promoted by P starvation and identify proteins enabling the utilization of a range of organic substrates as sole P sources. We show that transcription and activity of a subset of these proteins are independent of PhoB and Pi availability. These results establish that Salmonella enterica can maintain Pi homeostasis and repress PhoB/PhoR activation even when cells are grown in medium lacking Pi.
Assuntos
Proteínas de Escherichia coli , Salmonella enterica , Fósforo/metabolismo , Proteínas de Bactérias/metabolismo , Escherichia coli/genética , Salmonella enterica/genética , Salmonella enterica/metabolismo , Organofosfatos/metabolismo , Regulação Bacteriana da Expressão Gênica , Fatores de Transcrição/metabolismo , Proteínas de Escherichia coli/genéticaRESUMO
Bacteria acquire P primarily as inorganic orthophosphate (Pi, PO43-). Once internalized, Pi is rapidly assimilated into biomass during the synthesis of ATP. Because Pi is essential, but excessive ATP is toxic, the acquisition of environmental Pi is tightly regulated. In the bacterium Salmonella enterica (Salmonella), growth in Pi-limiting environments activates the membrane sensor histidine kinase PhoR, leading to the phosphorylation of its cognate transcriptional regulator PhoB and subsequent transcription of genes involved in adaptations to low Pi. Pi limitation is thought to promote PhoR kinase activity by altering the conformation of a membrane signaling complex comprised by PhoR, the multicomponent Pi transporter system PstSACB and the regulatory protein PhoU. However, the identity of the low Pi signal and how it controls PhoR activity remain unknown. Here we characterize the PhoB-dependent and independent transcriptional changes elicited by Salmonella in response to P starvation, and identify PhoB-independent genes that are required for the utilization of several organic-P sources. We use this knowledge to identify the cellular compartment where the PhoR signaling complex senses the Pi-limiting signal. We demonstrate that the PhoB and PhoR signal transduction proteins can be maintained in an inactive state even when Salmonella is grown in media lacking Pi. Our results establish that PhoR activity is controlled by an intracellular signal resulting from P insufficiency.
RESUMO
In the current study, we adapted and optimized the lambda Red recombineering strategy to genetically manipulate the fastidious insect endosymbiont Sodalis glossinidius. This work greatly facilitates the application of genetics to the study of insect symbionts and should also prove useful in the context of long-awaited paratransgenic insect control strategies.
Assuntos
Bacteriófago lambda/enzimologia , DNA Bacteriano/genética , Enterobacteriaceae/genética , Genética Microbiana/métodos , Recombinação Genética , Proteínas Virais/metabolismo , Animais , Engenharia Genética/métodos , Insetos/microbiologiaRESUMO
Bacteriophages (phages) are ubiquitous in nature. These viruses play a number of central roles in microbial ecology and evolution by, for instance, promoting horizontal gene transfer (HGT) among bacterial species. The ability of phages to mediate HGT through transduction has been widely exploited as an experimental tool for the genetic study of bacteria. As such, bacteriophage P1 represents a prototypical generalized transducing phage with a broad host range that has been extensively employed in the genetic manipulation of Escherichia coli and a number of other model bacterial species. Here we demonstrate that P1 is capable of infecting, lysogenizing, and promoting transduction in members of the bacterial genus Sodalis, including the maternally inherited insect endosymbiont Sodalis glossinidius While establishing new tools for the genetic study of these bacterial species, our results suggest that P1 may be used to deliver DNA to many Gram-negative endosymbionts in their insect host, thereby circumventing a culturing requirement to genetically manipulate these organisms.IMPORTANCE A large number of economically important insects maintain intimate associations with maternally inherited endosymbiotic bacteria. Due to the inherent nature of these associations, insect endosymbionts cannot be usually isolated in pure culture or genetically manipulated. Here we use a broad-host-range bacteriophage to deliver exogenous DNA to an insect endosymbiont and a closely related free-living species. Our results suggest that broad-host-range bacteriophages can be used to genetically alter insect endosymbionts in their insect host and, as a result, bypass a culturing requirement to genetically alter these bacteria.
Assuntos
DNA Bacteriano/genética , Enterobacteriaceae/genética , Enterobacteriaceae/virologia , Técnicas de Transferência de Genes , Genoma Bacteriano , Transdução Genética , Bacteriófagos/genética , Bacteriófagos/metabolismo , Enterobacteriaceae/classificação , Escherichia coli/genética , Especificidade de Hospedeiro , Filogenia , SimbioseRESUMO
Antibiotics constitute one of the cornerstones of modern medicine. However, individuals may succumb to a bacterial infection if a pathogen survives exposure to antibiotics. The ability of bacteria to survive bactericidal antibiotics results from genetic changes in the preexisting bacterial genome, from the acquisition of genes from other organisms, and from nonheritable phenomena that give rise to antibiotic tolerance. Nonheritable antibiotic tolerance can be exhibited by a large fraction of the bacterial population or by a small subpopulation referred to as persisters. Nonheritable resistance to antibiotics has been ascribed to the activity of toxins that are part of toxin-antitoxin modules, to the universal energy currency ATP, and to the signaling molecule guanosine (penta) tetraphosphate. However, these molecules are dispensable for nonheritable resistance to antibiotics in many organisms. By contrast, nutrient limitation, treatment with bacteriostatic antibiotics, or expression of genes that slow bacterial growth invariably promote nonheritable resistance. We posit that antibiotic persistence results from conditions promoting feedback inhibition among core cellular processes, resulting phenotypically in a slowdown or halt in bacterial growth.
Assuntos
Antibacterianos/farmacologia , Bactérias/efeitos dos fármacos , Bactérias/crescimento & desenvolvimento , Fenômenos Fisiológicos Bacterianos , Farmacorresistência Bacteriana Múltipla , Trifosfato de Adenosina/metabolismo , Animais , Bactérias/genética , Humanos , Camundongos , Testes de Sensibilidade MicrobianaRESUMO
Stable associations between insects and bacterial species are widespread in nature. This is the case for many economically important insects, such as tsetse flies. Tsetse flies are the vectors of Trypanosoma brucei, the etiological agent of African trypanosomiasis-a zoonotic disease that incurs a high socioeconomic cost in regions of endemicity. Populations of tsetse flies are often infected with the bacterium Sodalis glossinidius Following infection, S. glossinidius establishes a chronic, stable association characterized by vertical (maternal) and horizontal (paternal) modes of transmission. Due to the stable nature of this association, S. glossinidius has been long sought as a means for the implementation of anti-Trypanosoma paratransgenesis in tsetse flies. However, the lack of tools for the genetic modification of S. glossinidius has hindered progress in this area. Here, we establish that S. glossinidius is amenable to DNA uptake by conjugation. We show that conjugation can be used as a DNA delivery method to conduct forward and reverse genetic experiments in this bacterium. This study serves as an important step in the development of genetic tools for S. glossinidius The methods highlighted here should guide the implementation of genetics for the study of the tsetse-Sodalis association and the evaluation of S. glossinidius-based tsetse fly paratransgenesis strategies.IMPORTANCE Tsetse flies are the insect vectors of T. brucei, the causative agent of African sleeping sickness-a zoonotic disease that inflicts a substantial economic cost on a broad region of sub-Saharan Africa. Notably, tsetse flies can be infected with the bacterium S. glossinidius to establish an asymptomatic chronic infection. This infection can be inherited by future generations of tsetse flies, allowing S. glossinidius to spread and persist within populations. To this effect, S. glossinidius has been considered a potential expression platform to create flies which reduce T. brucei stasis and lower overall parasite transmission to humans and animals. However, the efficient genetic manipulation of S. glossinidius has remained a technical challenge due to its complex growth requirements and uncharacterized physiology. Here, we exploit a natural mechanism of DNA transfer among bacteria and develop an efficient technique to genetically manipulate S. glossinidius for future studies in reducing trypanosome transmission.
Assuntos
Conjugação Genética , Enterobacteriaceae/genética , Herança Materna/genética , Simbiose , Moscas Tsé-Tsé/microbiologia , Animais , Escherichia coli/genética , Insetos Vetores/microbiologia , Trypanosoma brucei brucei/fisiologiaRESUMO
Bacteria can withstand killing by bactericidal antibiotics through phenotypic changes mediated by their preexisting genetic repertoire. These changes can be exhibited transiently by a large fraction of the bacterial population, giving rise to tolerance, or displayed by a small subpopulation, giving rise to persistence. Apart from undermining the use of antibiotics, tolerant and persistent bacteria foster the emergence of antibiotic-resistant mutants. Persister formation has been attributed to alterations in the abundance of particular proteins, metabolites, and signaling molecules, including toxin-antitoxin modules, adenosine triphosphate, and guanosine (penta) tetraphosphate, respectively. Here, we report that persistent bacteria form as a result of slow growth alone, despite opposite changes in the abundance of such proteins, metabolites, and signaling molecules. Our findings argue that transitory disturbances to core activities, which are often linked to cell growth, promote a persister state regardless of the underlying physiological process responsible for the change in growth.
Assuntos
Farmacorresistência Bacteriana , Salmonella enterica/crescimento & desenvolvimento , Salmonella enterica/genéticaRESUMO
Insects from many different taxonomic groups harbor maternally transmitted bacterial symbionts. Some of these associations are ancient in origin and obligate in nature whereas others originated more recently and are facultative. Previous research focused on the biology of ancient obligate symbionts with essential nutritional roles in their insect hosts. However, recent important advances in understanding the biology of facultative associations have been driven by the development of techniques for the culture, genetic modification and manipulation of facultative symbionts. In this review, we examine these available experimental techniques and illustrate how they have provided fascinating new insight into the nature of associations involving facultative symbionts. We also propose a rationale for future research based on the integration of genomics and experimentation.
Assuntos
Bactérias/crescimento & desenvolvimento , Insetos/microbiologia , Simbiose , Animais , Bactérias/isolamento & purificação , Bactérias/ultraestrutura , Técnicas Bacteriológicas , Insetos/crescimento & desenvolvimento , Microscopia EletrônicaRESUMO
Adenosine triphosphate (ATP) is the energy currency of living cells. Even though ATP powers virtually all energy-dependent activities, most cellular ATP is utilized in protein synthesis via tRNA aminoacylation and guanosine triphosphate regeneration. Magnesium (Mg(2+)), the most common divalent cation in living cells, plays crucial roles in protein synthesis by maintaining the structure of ribosomes, participating in the biochemistry of translation initiation and functioning as a counterion for ATP. A non-physiological increase in ATP levels hinders growth in cells experiencing Mg(2+) limitation because ATP is the most abundant nucleotide triphosphate in the cell, and Mg(2+) is also required for the stabilization of the cytoplasmic membrane and as a cofactor for essential enzymes. We propose that organisms cope with Mg(2+) limitation by decreasing ATP levels and ribosome production, thereby reallocating Mg(2+) to indispensable cellular processes.