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Relationship between cardiolipin metabolism and oxygen availability in Bacillus subtilis.

ABSTRACT: We report changes of the content of anionic phospholipids in Bacillus subtilis in response to hypoxic conditions and inhibition of terminal respiration. Cardiolipin accumulates rapidly when bacteria are suspended in non-growth medium under reduced aeration or exposed to the inhibitor cyanide; the increase of cardiolipin occurs at the expense of its precursor phosphatidylglycerol and is temperature-dependent. Depending on the extent of hypoxic stress, membranes containing different levels of cardiolipin can be isolated from B. subtilis cells. The NADH oxidase activity in cardiolipin-enriched membranes is cyanide-resistant; furthermore O2 consumption measurements indicated that cardiolipin-enriched cells are resistant to cyanide. Results point out a possible interdependence between the effect of cyanide on cardiolipin metabolism and the effect of cardiolipin on the effectiveness of cyanide inhibition.

SUBMITTER: Lobasso S

PROVIDER: S-EPMC3668533 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Relationship between cardiolipin metabolism and oxygen availability in Bacillus subtilis.

Lobasso Simona S Palese Luigi L LL Angelini Roberto R Corcelli Angela A

FEBS open bio 20130219

We report changes of the content of anionic phospholipids in Bacillus subtilis in response to hypoxic conditions and inhibition of terminal respiration. Cardiolipin accumulates rapidly when bacteria are suspended in non-growth medium under reduced aeration or exposed to the inhibitor cyanide; the increase of cardiolipin occurs at the expense of its precursor phosphatidylglycerol and is temperature-dependent. Depending on the extent of hypoxic stress, membranes containing different levels of card ...[more]

PMID: 23772387

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Project description:BackgroundRiboflavin, an intermediate of primary metabolism, is one kind of important food additive with high economic value. The microbial cell factory Bacillus subtilis has already been proven to possess significant importance for the food industry and have become one of the most widely used riboflavin-producing strains. In the practical fermentation processes, a sharp decrease in riboflavin production is encountered along with a decrease in the dissolved oxygen (DO) tension. Influence of this oxygen availability on riboflavin biosynthesis through carbon central metabolic pathways in B. subtilis is unknown so far. Therefore the unveiled effective metabolic pathways were still an unaccomplished task till present research work.ResultsIn this paper, the microscopic regulation mechanisms of B. subtilis grown under different dissolved oxygen tensions were studied by integrating 13C metabolic flux analysis, metabolomics and transcriptomics. It was revealed that the glucose metabolic flux through pentose phosphate (PP) pathway was lower as being confirmed by smaller pool sizes of metabolites in PP pathway and lower expression amount of ykgB at transcriptional level. The latter encodes 6-phosphogluconolactonase (6-PGL) under low DO tension. In response to low DO tension in broth, the glucose metabolic flux through Embden-Meyerhof-Parnas (EMP) pathway was higher and the gene, alsS, encoding for acetolactate synthase was significantly activated that may result due to lower ATP concentration and higher NADH/NAD+ ratio. Moreover, ResE, a membrane-anchored protein that is capable of oxygen regulated phosphorylase activity, and ResD, a regulatory protein that can be phosphorylated and dephosphorylated by ResE, were considered as DO tension sensor and transcriptional regulator respectively.ConclusionsThis study shows that integration of transcriptomics, 13C metabolic flux analysis and metabolomics analysis provides a comprehensive understanding of biosynthesized riboflavin's regulatory mechanisms in B. subtilis grown under different dissolved oxygen tension conditions. The two-component system, ResD-ResE, was considered as the signal receiver of DO tension and gene regulator that led to differences between biomass and riboflavin production after triggering the shifts in gene expression, metabolic flux distributions and metabolite pool sizes.

Project description:Iron (Fe) is one of the most important micronutrients for most life forms on earth. While abundant in soil, Fe bioavailability in oxic soil is very low. Under environmental conditions, bacteria need to acquire sufficient Fe to sustain growth while limiting the energy cost of siderophore synthesis. Biofilm formation might mitigate this Fe stress, since it was shown to accumulate Fe in certain Gram-negative bacteria and that this Fe could be mobilized for uptake. However, it is still unclear if, and to what extent, the amount of Fe accumulated in the biofilm can sustain growth and if the mobilization of this local Fe pool is modulated by the availability of environmental Fe (i.e., Fe outside the biofilm matrix). Here, we use a nondomesticated strain of the ubiquitous biofilm-forming soil bacterium Bacillus subtilis and stable Fe isotopes to precisely evaluate the origin of Fe during growth in the presence of tannic acid and hydroxides, used as proxies for different environmental conditions. We report that this B. subtilis strain can accumulate a large quantity of Fe in the biofilm, largely exceeding Fe associated with cells. We also report that only a fraction of biofilm-bound Fe is available for uptake in the absence of other sources of Fe in the vicinity of the biofilm. We observed that the availability of environmental Fe modulates the usage of this pool of biofilm-bound Fe. Finally, our data suggest that consumption of biofilm-bound Fe relates to the efficacy of B. subtilis to transport Fe from the environment to the biofilm, possibly through siderophores.IMPORTANCE Recent pieces of evidence suggest that Fe bound to the biofilm could assume at least two important functions, a local source of Fe for uptake and a support to extracellular metabolism, such as extracellular electron transfer. Our results show that B. subtilis can use biofilm-bound Fe for uptake only if it does not compromise Fe homeostasis of the biofilm, i.e., maintains a minimum Fe concentration in the biofilm for extracellular purposes. We propose a theoretical framework based on our results and recent literature to explain how B. subtilis manages biofilm-bound Fe and Fe uptake in response to environmental Fe availability. These results provide important insights into the management of biofilm-bound and environmental Fe by B. subtilis in response to Fe stress.

Project description:In Bacillus subtilis, the Spx transcription factor controls a large regulon in response to disulfide, heat, and cell wall stresses. The regulatory mechanisms that activate the Spx regulon are remarkably complex and involve changes in transcription, proteolysis, and posttranslational modifications. To identify genes involved in Spx regulation, we performed a transposon screen for mutations affecting expression of trxB, an Spx-dependent gene. Inactivation of ctsR, encoding the regulator of the Clp proteases, reduced trxB expression and lowered Spx levels. This effect required ClpP, but involved ClpC rather than the ClpX unfoldase. Moreover, cells lacking McsB, a dual function arginine kinase and ClpCP adaptor, largely reverted the ctsR phenotype and increased trxB expression. The role of McsB appears to involve its kinase activity, since loss of the YwlE phosphoarginine phosphatase also led to reduced trxB expression. Finally, we show that Spx is itself a regulator of the ctsR operon. Altogether, this work provides evidence for a role of CtsR regulon members ClpC, ClpP, and McsB in Spx regulation and identifies a new feedback pathway associated with Spx activity in B. subtilisIMPORTANCE In Bacillus subtilis, the Spx transcription factor is proteolytically unstable, and protein stabilization figures prominently in the induction of the Spx regulon in response to oxidative and cell envelope stresses. ClpXP is largely, but not entirely, responsible for Spx instability. Here, we identify ClpCP as the protease that degrades Spx under conditions that antagonize the ClpXP pathway. Spx itself contributes to activation of the ctsR operon, which encodes ClpC as well as the McsB arginine kinase and protease adaptor, thereby providing a negative feedback mechanism. Genetic studies reveal that dysregulation of the CtsR regulon or inactivation of the YwlE phosphoarginine phosphatase decreases Spx activity through mechanisms involving both protein degradation and posttranslational modification.

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Relationship between cardiolipin metabolism and oxygen availability in Bacillus subtilis.

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Relationship between cardiolipin metabolism and oxygen availability in Bacillus subtilis.

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