Insights into the mode of action of the two-peptide lantibiotic haloduracin.
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ABSTRACT:
SUBMITTER: Oman TJ
PROVIDER: S-EPMC2812937 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:1,4-Dioxane (1,4-DX) is an environmental contaminant found in drinking water throughout the United States (US). While it is a suspected liver carcinogen, there is no federal or state maximum contaminant level for 1,4-DX in drinking water. Very little is known about the mechanisms by which this chemical elicits liver carcinogenicity. In the present study, we performed chronic and short-term dosing studies in female BDF-1 mice to explore the toxic effects of 1,4-DX. Histopathology studies and a multi-omics approach (transcriptomics and metabolomics) were performed to investigate potential mechanisms of toxicity. Mice were exposed to various concentrations of 1,4-DX (0, 50, 500 and 5,000 mg/L) in their drinking water for one or four weeks. Immunohistochemical analysis of the liver revealed an increase in the number of H2AXγ-positive hepatocytes (a marker of DNA double strand breaks) in mice exposed to 5,000 mg/L 1,4-DX for one and four weeks. In addition, an expansion of precholangiocytes was observed after four weeks of 5,000 mg/L 1,4-DX exposure, as reflected by CK-7 immunostaining. An increase in these markers reflect both DNA damage and repair mechanisms. Liver transcriptomics profiling showed that exposure to 5,000 mg/L 1,4-DX for four weeks resulted in the differential expression of 65 genes compared to controls. Pathway analysis of the transcriptomic data revealed 1,4-DX-induced perturbations in multiple signaling pathways in the liver, including those involved in xenobiotic metabolism, nicotine degradation and glutathione-mediated detoxification. Changes to these pathways as a result of 1,4-DX exposure reflect would be predicted to impact the oxidative stress response, detoxification, and DNA damage. Liver, kidney, stool and urine metabolomics profiling revealed no effect of 5,000 mg/L 1,4-DX exposure for one or four weeks on metabolites. We speculate that this may be reflective of DNA damage being counterbalanced by the repair response, with the net result being a null overall effect on the systemic biochemistry of the exposed mice. Our results show a novel approach for the investigation of environmental chemicals that do not elicit cell death, but have activated the repair systems in response to 1,4-DX exposure
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Project description:BackgroundLantibiotics are small microbial peptide antibiotics that are characterized by the presence of the thioether amino acids lanthionine and methyllanthionine. Lantibiotics possess structural genes which encode inactive prepeptides. During maturation, the prepeptide undergoes posttranslational modifications including the introduction of rare amino acids as lanthionine and methyllanthione as well as the proteolytic removal of the leader. The structural gene (lanA) as well as the other genes which are involved in lantibiotic modification (lanM, lanB, lanC, lanP), regulation (lanR, lanK), export (lanT(P)) and immunity (lanEFG) are organized in biosynthetic gene clusters.Methodology/principal findingsSequence comparisons in the NCBI database showed that Bacillus licheniformis DSM 13 harbours a putative lantibiotic gene cluster which comprises two structural genes (licA1, licA2) and two modification enzymes (licM1, licM2) in addition to 10 ORFs that show sequence similarities to proteins involved in lantibiotic production. A heat labile antimicrobial activity was detected in the culture supernatant and a heat stabile activity was present in the isopropanol cell wash extract of this strain. In agar well diffusion assays both fractions exhibited slightly different activity spectra against Gram-positive bacteria. In order to demonstrate the connection between the lantibiotic gene cluster and one of the antibacterial activities, two Bacillus licheniformis DSM 13 mutant strains harbouring insertions in the structural genes of the modification enzymes licM1 and licM2 were constructed. These strains were characterized by a loss of activity in the isopropanol extract and substractive MALDI-TOF predicted masses of 3020.6 Da and 3250.6 Da for the active peptides.Conclusions/significanceIn conclusion, B. licheniformis DSM 13 produces an antimicrobial substance that represents the two-peptide lantibiotic lichenicidin and that shows activity against a wide range of Gram-positive bacteria including methicillin resistant Staphylococcus aureus strains.
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