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This Week in PLOS: Jul 8, 2013

In PLOS Biology, researchers from Japan report on their study examining the boundaries of heterochromatic regions in yeast, particularly focusing on HMR, HML, and telomere regions. Using fluorescently labeled proteins to track gene expression changes that occur over generations of a single cell, they found that epigenetic gene expression is reversible and is regulated by the histone acetylation state. "Future work," the researchers add, "will identify connections between variation in boundary positioning and novel transcription control systems."

A study of the Verigene Gram-Positive Blood Culture Test by researchers in Wisconsin shows that it can detect most gram-positive bacteria behind blood infections and genetic markers indicating their resistance to methicillin or vancomycin. Researchers led by Medical College of Wisconsin's Nathan Ledeboer collected 1,252 blood cultures containing Gram-positive bacteria and 387 contrived blood cultures containing more uncommon targets. From this, they report that the Verigene test had 92.6 percent to 100 percent sensitivity and 95.4 percent to 100 percent specificity for its 12 genus or species targets and that it could identify many resistance genes. "One weakness of the BC-GP test is the inability to assign mecA positivity to a specific organism in a mixed culture," Ledeboer and colleagues note in PLOS Medicine. "In the case of a culture positive for 'S. aureus,' 'S. epidermidis,' and 'mecA,' the laboratory would have to wait for solid media-based isolation of each organism and susceptibility testing to determine which organism was methicillin resistant."

In PLOS Pathogens, Harvard School of Public Health's Sarah Fortune and her colleagues report that a certain DNA methyltransferase influences gene expression in Mycobacterium tuberculosis and affects its fitness under hypoxic conditions. Strains that lack the DNA methyltransferase, dubbed MamA, grow normally in vitro, but are attenuated during hypoxia. "Our findings identify a novel mechanism by which M. tuberculosis modulates gene expression in response to stress," the researchers write.