Molecular cloning of the leuB gene from Bacteroides fragilis by functional complementation in Escherichia coli

Integrative Physiological and Transcriptome Analysis Reveals the Mechanism for the Repair of Sub-Lethally Injured Escherichia coli O157:H7 Induced by High Hydrostatic Pressure

The application of high hydrostatic pressure (HHP) technology in the food industry has generated potential safety hazards due to sub-lethally injured (SI) pathogenic bacteria in food products. To address these problems, this study explored the repair mechanisms of HHP-induced SI Escherichia coli O157:H7. First, the repair state of SI E. coli O157:H7 (400 MPa for 5 min) was identified, which was cultured for 2 h (37 °C) in a tryptose soya broth culture medium. We found that the intracellular protein content, adenosine triphosphate (ATP) content, and enzyme activities (superoxide dismutase, catalase, and ATPase) increased, and the morphology was repaired. The transcriptome was analyzed to investigate the molecular mechanisms of SI repair. Using cluster analysis, we identified 437 genes enriched in profile 1 (first down-regulated and then tending to be stable) and 731 genes in profile 2 (up-regulated after an initial down-regulation). KEGG analysis revealed that genes involved in cell membrane biosynthesis, oxidative phosphorylation, ribosome, and aminoacyl-tRNA biosynthesis pathways were enriched in profile 2, whereas cell-wall biosynthesis was enriched in profile 1. These findings provide insights into the repair process of SI E. coli O157:H7 induced by HHP.

Comparative evaluation of conventional and real-time PCR assays for detecting Bacteroides fragilis in clinical samples

A conventional PCR and a real-time PCR for detecting Bacteroides fragilis were evaluated against clinical specimens. Analytical sensitivities were 100 and 40 fg of DNA, respectively. Detection limits were 100 and 10 CFU/ml, respectively. A total of six culture-negative specimens were positive by PCR. Altering the gold standard from "positive culture" to "positive culture or both PCR assays positive" resulted in sensitivities of 91.7% and 100%, respectively, and in specificities of 100% and 98.6%, respectively.

Molecular biological access to the chemistry of unknown soil microbes: a new frontier for natural products

Cultured soil microorganisms have provided a rich source of natural-product chemistry. Because only a tiny fraction of soil microbes from soil are readily cultured, soil might be the greatest untapped resource for novel chemistry. The concept of cloning the metagenome to access the collective genomes and the biosynthetic machinery of soil microflora is explored here.

Nucleotide sequence of the gene encoding beta-isopropylmalate dehydrogenase (leuB) from Bacteroides fragilis

The complete nucleotide sequence of the gene (leuB) coding for beta-isopropylmalate dehydrogenase of Bacteroides fragilis was determined. An open reading frame of 1,061 nucleotides was detected that could encode a polypeptide of 353 amino acid residues with a calculated molecular mass of 39,179 Da. The deduced amino acid sequence of the beta-isopropylmalate dehydrogenase from B. fragilis showed substantial sequence similarity with the beta-isopropylmalate dehydrogenases from other bacteria.