November 1998
Links to Other ASM Pages:
Journal Highlights
Tetrachloroethene Dehalogenase Cloned and Sequenced: Bioremediation May Benefit
Polychlorinated compounds are major environmental contaminants of human origin. Many have proven very difficult to remediate.
Gabriele Diekert and colleagues, of the Institut für Mikrobiologie der Universitat Stuttgart, Germany, have cloned and sequenced the genes that encode tetrachloroethene dehalogenase from Dehalospirillum multivorans and have expressed the pceA gene in Escherichia coli. This enzyme is potentially very useful for bioremediation, because it allows cells to generate biological energy by using this polychlorinated compound as an anaerobic electron acceptor. It also is novel, containing a vitamin B12 cofactor, as well as several iron sulfur centers and other metals. Identification and cloning of the gene opens the possibility of engineering the ability to reduce tetrachloroethene into other bacteria that might be more suitable than D. multivorans for use in bioremediation, as well as of modifying this enzyme to act upon other recalcitrant pollutant molecules.
(A. Neumann, G. Wohlfarth, and G. Diekert. 1998. Tetrachloroethene dehalogenase from Dehalospirillum multivorans: cloning, sequencing of the encoding genes, and expression of the pceA gene in Escherichia coli. J. Bacteriol. 180:4140-4145.)
Anaerobic Escherichia coli Responsible for Chronic Infection of Prosthetic Hip
About 5% of hip-replacement patients end up with persistent chronic prosthetic hip infections. Andreas Roggenkamp and colleagues of Ludwig Maximilians University, Munich, Germany, isolated abscess material from a patient with a chronically infected prosthetic hip and found that the infection was caused by an anaerobic, "small colony variant" (SCV) of E coli. "This is the first characterization of a non-Staphylococcus aureus SCV [in a clinical infection]," says Roggenkamp. Anaerobiasis was caused by a deletion of all or part of the hemB gene, which is involved in biosynthesis of hemin.
"Fluoroquinolones exhibit the highest activity against slow-growing and nongrowing bacteria," but had uncertain results in this patient, the authors write.
The researchers' current task is to find ways to eradicate these infections, says coauthor Heeseman. "Until now, clinicians were not aware of small-colony variant E. coli in chronic infections."
(A. Roggenkamp, A. Sing, M. Horneff, U. Brunner, 1. B. Autenrieth, and J. Heesemann. 1998. Chronic prosthetic hip infection caused by a small-colony variant of Escherichia coli. J. Clin. Microbiol. 36:2530-2534.)
New Role for "Guardian of the Genome"
p53 has been called the guardian of the genome. In the presence of certain mutagens, It induces cell cycle arrest or apoptosis, depending on the degree of DNA damage. Mutations in p53 can contribute to cancer and other genetic defects. p53 forms complexes with proteins involved in DNA repair and recombination.
Lisa Wiesmüller and colleagues of the University of Hamburg, Hamburg, Germany, demonstrated that wild-type p53 inhibits homologous recombination of mismatched regions. "Our data imply that p53 monitors homologous recombination immediately after strand exchange by binding to and scanning heteroduplexes for certain mispairings," says Wiesmüller. "These data for the first time provide a mechanistic explanation for the genome-stabilizing function of p53 via recombination control." This data could lead to development of more specific therapeutics. Wiesmüller currently is testing the hypothesis that p53 works in concert with mismatch repair factor hMSH2.
(C. Dudenhoffer, G. Rohaly, K. Will, W. Deppert, and L. Wiesmüller. 1998. Specific mismatch recognition in heteroduplex intermediates by p53 suggests a role in fidelity control of homologous recombination. Mol. Cell. Biol. 18:5332-5342.)
Massive Mitochondrial Migration during Swine Fever Virus Infection
African swine fever virus (ASFV) is a large, very complex DNA virus that causes severe disease in domestic pigs.
Jose Salas of the Universidad Autonoma de Madrid, Madrid, Spain, and colleagues used electron microscopy to show that in infected cells, there is a massive migration of mitochondria to the periphery of the cytoplasmic viral factories, but not to factories containing precursor membranes. This suggests that ASFV induces this migration. The mitochondria also take on characteristics of those seen in actively respiring organelles. Salas also found that the microtubule component of the cellular cytoskeleton was responsible for the mitochondrial migration to the virus assembly factories. "We plan to further investigate the mechanisms by which ASFV activates the transport of mitochondria," says Salas. "Certain microtubule-associated proteins may act as motors for the movement of mitochondria along microtubule tracks." Such research might lead to identification of potential targets for drug intervention in the virus' life cycle.
(G. Rojo, M. Chamorro, M. L. Salas, E. Vinuela, J. M. Cuezva, and J. Salas. 1998. Migration of mitochondria to viral assembly sites in African swine fever virus-infected cells. J. Virol. 72:7583-7588.)
Insights Into Evolution of Vancomycin Resistance Genes
Vancomycin-resistant enterococci are a major clinical hazard in the United States and in Europe.
Gerry Wright of McMaster University, Hamilton, Ontario, Canada, and colleagues at McMaster and the Harvard Medical School, Boston, Mass., have shown that organisms which produce glycopeptide antibiotics such as vancomycin have three resistance genes, which encode proteins that are very similar to those found in vancomycin-resistant enterococci. The three proteins are necessary and sufficient for synthesis of the structures in the cell walls of gram-positive organisms that cause vancomycin resistance. "It is very likely that the vancomycin resistance gene cluster found in VRE originated either in a producing organism or that VRE and producing organisms have obtained the genes from a common source," says Wright. "We are planning to investigate the genes' structure and mechanism."
(C. G. Marshall, I. A. D. Lessard, I.-S. Park, and G. D. Wright. 1998. Glycopeptide antibiotic resistance genes in glycopeptide-producing organisms. Antimicrob. Agents Chemother. 42:2216-2220.)
Helicobacter pylori Vaccine Shows Promise in Monkeys
Helicobacter pylori colonizes the stomachs of most humans throughout the world, causing various gastrointestinal ills in 10-20% of cases. Eradicating H. pylori is frequently difficult, and antibiotic resistance is an emerging problem.
Andre Dubois of the Uniformed Services University of the Health Sciences, Bethesda, Md., and others had previously documented in a rhesus monkey colony an incidence and prevalence of H. pylori similar to that in human populations. They tested an oral vaccine, consisting of recombinant H. pylori urease combined with a mucosal adjuvant, in 55 nine-month-old animals from this colony and found a significant reduction in infection rates as compared to controls, without adverse side effects, says Dubois. "Ongoing clinical studies carried out by OraVax, Inc., in partnership with Pasteur Merieux Connaught, will attempt to determine the most efficacious vaccine formulation in humans," says Dubois.
(A. Dubois, C. K. Lee, N. Fiala, H. Kleanthous, R T. Mehlman, and T Monath. 1998. Immunization against natural Helicobacter pylori infection in nonhuman primates. Infect. Immun. 66:4340-4346.)
Email: webmaster@asmusa.org