Effects of antibiotics on metabolism of peptidoglycan, protein, and lipids in Bifidobacterium bifidum subsp. pennsylvanicus

Dietary Magnesium Alleviates Experimental Murine Colitis through Modulation of Gut Microbiota

Nutritional deficiencies are common in inflammatory bowel diseases (IBD). In patients, magnesium (Mg) deficiency is associated with disease severity, while in murine models, dietary Mg supplementation contributes to restoring mucosal function. Since Mg availability modulates key bacterial functions, including growth and virulence, we investigated whether the beneficial effects of Mg supplementation during colitis might be mediated by gut microbiota. The effects of dietary Mg modulation were assessed in a murine model of dextran sodium sulfate (DSS)-induced colitis by monitoring magnesemia, weight, and fecal consistency. Gut microbiota were analyzed by 16S-rRNA based profiling on fecal samples. Mg supplementation improved microbiota richness in colitic mice, increased abundance of Bifidobacterium and reduced Enterobacteriaceae. KEEG pathway analysis predicted an increase in biosynthetic metabolism, DNA repair and translation pathways during Mg supplementation and in the presence of colitis, while low Mg conditions favored catabolic processes. Thus, dietary Mg supplementation increases bacteria involved in intestinal health and metabolic homeostasis, and reduces bacteria involved in inflammation and associated with human diseases, such as IBD. These findings suggest that Mg supplementation may be a safe and cost-effective strategy to ameliorate disease symptoms and restore a beneficial intestinal flora in IBD patients.

A How-To Guide for Mode of Action Analysis of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are a promising alternative to classical antibiotics in the fight against multi-resistant bacteria. They are produced by organisms from all domains of life and constitute a nearly universal defense mechanism against infectious agents. No drug can be approved without information about its mechanism of action. In order to use them in a clinical setting, it is pivotal to understand how AMPs work. While many pore-forming AMPs are well-characterized in model membrane systems, non-pore-forming peptides are often poorly understood. Moreover, there is evidence that pore formation may not happen or not play a role in vivo. It is therefore imperative to study how AMPs interact with their targets in vivo and consequently kill microorganisms. This has been difficult in the past, since established methods did not provide much mechanistic detail. Especially, methods to study membrane-active compounds have been scarce. Recent advances, in particular in microscopy technology and cell biological labeling techniques, now allow studying mechanisms of AMPs in unprecedented detail. This review gives an overview of available in vivo methods to investigate the antibacterial mechanisms of AMPs. In addition to classical mode of action classification assays, we discuss global profiling techniques, such as genomic and proteomic approaches, as well as bacterial cytological profiling and other cell biological assays. We cover approaches to determine the effects of AMPs on cell morphology, outer membrane, cell wall, and inner membrane properties, cellular macromolecules, and protein targets. We particularly expand on methods to examine cytoplasmic membrane parameters, such as composition, thickness, organization, fluidity, potential, and the functionality of membrane-associated processes. This review aims to provide a guide for researchers, who seek a broad overview of the available methodology to study the mechanisms of AMPs in living bacteria.

The Bacillus subtilis cannibalism toxin SDP collapses the proton motive force and induces autolysis

Bacillus subtilis SDP is a peptide toxin that kills cells outside the biofilm to support continued growth. We show that purified SDP acts like endogenously produced SDP; it delays sporulation, and the SdpI immunity protein confers SDP resistance. SDP kills a variety of Gram-positive bacteria in the phylum Firmicutes, as well as Escherichia coli with a compromised outer membrane, suggesting it participates in defence of the B. subtilis biofilm against Gram-positive bacteria as well as cannibalism. Fluorescence microscopy reveals that the effect of SDP on cells differs from that of nisin, nigericin, valinomycin and vancomycin-KCl, but resembles that of CCCP, DNP and azide. Indeed, SDP rapidly collapses the PMF as measured by fluorometry and flow cytometry, which triggers the slower process of autolysis. This secondary consequence of SDP treatment is not required for cell death since the autolysin-defective lytC, lytD, lytE, lytF strain fails to be lysed but is nevertheless killed by SDP. Collapsing the PMF is an ideal mechanism for a toxin involved in cannibalism and biofilm defence, since this would incapacitate neighbouring cells by inhibiting motility and secretion of proteins and toxins. It would also induce autolysis in many Gram-positive species, thereby releasing nutrients that promote biofilm growth.

Group B Streptococcus, phospholipids and pulmonary hypertension

OBJECTIVE

Group B Streptococcus is the most common cause of bacterial infection in the newborn. Our aim was to purify and identify molecules produced by the bacterium, which cause pulmonary hypertension.

STUDY DESIGN

Guided by bioassays performed in neonatal lambs, we utilized standard biochemical techniques for the purification of these bioactive compounds. The compounds were identified by mass spectrometry. Fully synthetic compounds were then tested using the bioassay to confirm their ability to induce pulmonary hypertension.

RESULT

The purified bacterial components causing pulmonary hypertension were the phospholipids cardiolipin and phosphatidylglycerol. Synthetic cardiolipin or phosphatidylglycerol also induced pulmonary hypertension in lambs.

CONCLUSION

Bacterial phospholipids are capable of causing pulmonary hypertension. This finding opens new avenues for therapeutic intervention in persistent pulmonary hypertension of the newborn and generates hypotheses regarding the etiology of respiratory distress in the newborn and the possible effect of antibiotic therapy.

Changes in intestinal bifidobacteria levels are associated with the inflammatory response in magnesium-deficient mice

Magnesium (Mg) deficiency is a common nutritional disorder that is linked to an inflammatory state characterized by increased plasma acute phase protein and proinflammatory cytokine concentrations. Recent studies have shown that changes in the composition of gut microbiota composition participate in systemic inflammation. In this study, therefore, we assessed the potential role of gut microbiota in intestinal and systemic inflammation associated with Mg deficiency in mice. For this purpose, mice were fed a control or Mg-deficient diet (500 mg vs. 70 mg Mg/kg) for 4 or 21 d. Compared with the mice fed the control diet, mice fed the Mg-deficient diet for 4 d had a lower gut bifidobacteria content (-1.5 log), a 36-50% lower mRNA content of factors controlling gut barrier function in the ileum (zonula occludens-1, occludin, proglucagon), and a higher mRNA content (by approximately 2-fold) in the liver and/or intestine of tumor necrosis factor-alpha, interleukin-6, CCAAT/enhancer binding protein homologous protein, and activating transcription factor 4, reflecting inflammatory and cellular stress. In contrast, mice fed the Mg-deficient diet for 21 d had a higher cecal bifidobacteria content compared with the control group, a phenomenon accompanied by restoration of the intestinal barrier and the absence of inflammation. In conclusion, we show that Mg deficiency, independently of any other changes in nutrient intake, modulates the concentration of bifidobacteria in the gut, a phenomenon that may time-dependently affect inflammation and metabolic disorders in mice.

Phosphatidylglycerol as biosynthetic precursor for the poly(glycerol phosphate) backbone of bifidobacterial lipoteichoic acid

Phosphatidylglycerol functions as donor of the sn-glycerol 1-phosphate units in the synthesis in vitro of the 1,2-phosphodiester-linked glycerol phosphate backbone of the lipoteichoic acids of Bifidobacterium bifidum subsp. pennsylvanicum. The incorporation was catalysed by a membrane-bound enzyme system. After addition of chloroform/methanol the product formed coprecipitated with protein. The material was phenol-extractable and was co-eluted with purified lipoteichoic acid on Sepharose 6B. The reaction was stimulated by Triton X-100, UDP-glucose and UDP-galactose, but Mg2+ ions had no effect. The apparent values for Km and Vmax. of the phosphatidylglycerol incorporation were 1.4 mM and 3.1 nmol/h per mg of membrane protein, respectively. Labelled UDP-glucose and UDP-galactose were not incorporated into the lipoteichoic acid fraction by the particulate membrane preparation.

The effect of penicillin on fatty acid synthesis and excretion in Streptococcus mutans BHT

Treatment of exponentially growing cultures of Streptococcus mutans BHT with growth-inhibitory concentrations (0.2 microgram/ml) of benzylpenicillin stimulates the incorporation of [2-14C] acetate into lipids excreted by the cells by as much as 69-fold, but does not change the amount of 14C incorporated into intracellular lipids. At this concentration of penicillin cellular lysis does not occur. The radioactive label is incorporated exclusively into the fatty acid moieties of the glycerolipids. The increase in the radioactive content of the extracellular lipids reflects an actual net increase in the total fatty acid content as determined by a chemical assay. During a 4-hr incubation in the presence of penicillin, the extracellular fatty acid ester concentration (per mg cell dry weight) increases 1.5 fold, even though there is no growth or cellular lysis. No change is observed in the intracellular fatty acid ester content. An indication of the relative rate of fatty acid synthesis was most readily obtained by placing S. mutans BHT in a buffer containing 14C-acetate. Under these nongrowing conditions free fatty acids are the only lipids labeled, a factor which simplifies the assay. The addition of glycerol to the buffer causes all of the nonesterified fatty acids to be incorporated into glycerolipid. The cells excrete much of the lipid whether glycerol is present or not. Addition of penicillin to the nongrowth supporting buffer system does not stimulate the incorporation of [14C]-acetate into fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and ultrastructural changes in Staphylococcus aureus treated with staphylococcin 1580

Incorporation of precursors into macromolecules is immediately arrested upon treatment of Staphylococcus aureus cells with staphylococcin 1580. Except for a degradation of RNA, induced after about 40 min, no degradation of macromolecules is observed, and no trichloroacetic acid-insoluble components are released from the cells. The protein composition and content of membranes are not affected by staphylococcin 1580 treatment. The fatty acid pattern of cells is not significantly altered. Protoplasts do not lyse apparently upon treatment with staphylococcin 1580, but undergo morphological alterations. Thin sections of cells treated with the bacteriocin for 30 min show extensive mesosome-like structures, mostly arranged in honeycomb arrays connected to the plasma membrane, and alterations in the nucleoid area. Freeze-etched preparations taken after that time reveal alterations in the plasma membrane, presumably in relation to the formation of the mesosomal structures. No alterations were observed after bacteriocin treatment for 5 min, although at that time the permeability of the membrane is strongly affected. The implications of the observed changes with the development of irreversible lesions in the cells are discussed.

Effects of growth conditions on the ion composition of Bifidobacterium bifidum subsp. pennsylvanicum

The cation content of Bifidobacterium bifidum subsp. pennsylvanicum was markedly influenced by the washing procedure of the cells, by the growth phase and the temperature, and by the composition of the culture medium. Optimal retention of cations was achieved by washing with 0.25 M MgCl2 at 20C. The intracellular Na+ concentration rose during growth in normal medium to a constant value in the stationary phase, the K+ concentration rose in the exponential phase, but fell in the stationary phase. Cells from 29-C cultures contained more Na+ and less K+ in the stationary phase than did cells from 37-C cultures, but the total cation content was the same at 29 and 37C. Intracellular Na+ and K+ concentrations were dependent on the concentrations in the medium and on its osmolarity. The intracellular Na+/K+ ratio varied from 0.04 to 2.3. The concentrations of Na+,K+ and phosphate in the medium hardly affected growth. Mg2+-deficiency of the medium markedly decreased the concentration of Mg2+ within the cell; its concentration in the cell sap was greatly affected, but the amount of sedimentable, bound Mg2+ only slightly. The content of K+ within the cell decreased in Mg2+-deficient medium, but the concentration of Na+ did not. Omission of Tween 80 as well as its substitution by Tween 20 caused a decrease of intracellular K+. Cells from Tween 40 and Tween 60 cultures additionally contained markedly less Na+.

Biochemical changes in Bifidobacterium bifidum var. pennsylvanicus after cell wall inhibition. IX. Metabolism and release of cellular lipids in the presence of antibiotics

Inhibiton of cell wall synthesis caused simultaneously an increase in cellular phospho-and glycolipids and a marked release of these compounds to the medium. The composition of the cellular and the released glyco-and phospholipids was almost the same. Antibiotics, which inhibit cell wall synthesis, did not influence glycolipid composition, but increased the relative and absolute amounts of disphosphatidylglycerol and its lysoderivatives. Incorporation and chase experiments demonstrated a considerable stimulation of phospholipid metabolism, and of diphosphatidylglycerol synthesis especially. Release of lipids was not accompanied by loss of cellular protein. Omission of Tween 80 from the medium decreased the release by about 50% and increased the relative amounts of the phosphogalactolipids in the cells and in the culture fluid. Inhibitors of protein synthesis and valinomycin caused a decrease in cellular lipidphosphorus content, and a relative increase of the phosphogalactolipids. No release of lipids was observed under these conditions.