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Unique E. coli Protein May Be Not After All

A bacterial protein recently thought to be a unique mechanism for utilizing iron may not be after all. Researchers from the University of Georgia, the Fellowship for Interpretation of Genomes, the University of Oklahoma and the University of Utah School of Medicine report their findings in the latest issue of the online journal mBio.

The ability to acquire iron from their host is an important factor in the ability of bacteria to establish an infection. The major source of host iron in infections is heme, a component of hemoglobin and disease-causing bacteria have evolved complex mechanisms to acquire the heme and extract the iron. In the case of E. coli bacteria recent research has reported that the bacterial protein YfeX is able to remove iron from heme using a process called dechelation and leave an intact tetrapyrrole. This is totally unlike any other described biological system for iron removal from heme and, thus, would represent a dramatically new feature with potentially profound implications for understanding how bacteria cause disease.

Based on the gene sequences responsible for its production, this compound appears to be a dye-decolorizing peroxidase (DyP), a relatively recently recognized superfamily of heme-containing peroxidases that are found in fungi and bacteria.

"Given the diversity of organisms that possess DyP-type proteins, the identification of this class of proteins as heme dechelatases would have profound physiological and environmental implications. Because of this and our interest in heme metabolism, we undertook to examine in more detail the protein YfeX," write the researchers.

In the study, they propose and demonstrate that YfeX is a typical DyP with no ability to dechelate iron from heme.

"The data presented herein demonstrate that recombinant YfeX is a typical DyP-type peroxidase and does not possess the catalytic ability to dechelate iron from heme in vitro," write the researchers. "In vivo experiments with YfeX in E. coli and its homolog in Vibrio fischeri revealed no evidence that YfeX either is involved in iron acquisition from heme or generates prophyrin from exogenously supplied heme."

Promiscuity of Resistance Plasmid Unprecedented

Genetic analysis of an outbreak of drug-resistant infections in one institution shows an unprecedented level of transference of resistance among strains and even species of bacteria. Researchers from the University of Virginia and the Centers for Disease Control and Prevention report their findings in the current issue of the journal mBio.

Carbapenem-resistant Enterobacteriaceae (CRE) have emerged as a major cause of health-care associated infections worldwide. The global spread of CRE has largely been attributed to dissemination of a dominant strain of Klebsiella pneumoniae which produces a compound called K. pneumoniae carbapenemase (KPC). The gene for KPC is often contained on a plasmid, a DNA molecule that the bacteria can transmit to other bacteria.

In August 2007 the researchers identified their first known case of CRE at their institution, prompting them to immediately screen all clinical isolates for KPC production and conduct a molecular genetic analysis. Of 11 unique strains of different bacteria isolated from patients, 9 contained the same DNA plasmid with a specific gene coding for KPC.

"Here we report an outbreak of KPC-producing CRE infections in which the degree of horizontal transmission between strains and species of a promiscuous plasmid is unprecedented," write the researchers. "The ease of horizontal transmission of carbapenem resistance observed in this study has serious public health and epidemiological implications."

The Private Nuclear Rooms of Herpesviruses

Researchers from Princeton University have discovered why, despite being bombarded by many different herpesviruses, infected cells produce only a limited number of those viruses. They report their findings in the current issue of the online journal mBio.

Herpes viruses are very effective at deploying a host's cellular machinery to do their bidding. Once they infect a cell they begin to replicate their DNA inside distinct foci within the cell's nucleus known as replication compartments.

In the study the researchers explain that it's because replication compartments are like little private rooms: each one only contains one kind of viral genome. Using mixtures of isogenic pseudorabies viruses that express three different fluorescent proteins, the authors determined that each replication compartment probably initiates from a single incoming viral genome. Only a few types of viruses come out of a lysed cell because only a few viruses create replication compartments.

"Previously we described a method to estimate the average number of virus genomes expressed in an infected cell," write the researchers. "We found that fewer than seven herpesvirus genomes can be expressed and replicated. Here we have expanded and improved upon our method and demonstrated that the phenomenon of limited genome expression is independent of the recombinants used. We correlated the small number of genomes expressed to the limited number of replication compartments by demonstrating that most replication compartments originate with a single genome."


Contact: Jim Sliwa
American Society for Microbiology

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