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This Week in PNAS: Jul 13, 2010

In the PNAS Early Edition this week, researchers at the University of Victoria and the National Institute of Allergy and Infectious Diseases report that they've inserted nine "essential genes" from Arctic bacteria into mammalian pathogenic bacteria "to construct stable, temperature-sensitive bacterial vaccines." One ligA gene, the team writes, "was shown to render Francisella tularensis, Salmonella enterica, and Mycobacterium smegmatis temperature-sensitive." Three temperature-sensitive strains of F. tularenis "were shown to induce protective immunity after vaccination at a cool body site," the authors write.

A European research team this week reports their reconstruction of the Candidatus Nitrospira defluvii genome, and suggest that its metagenome "illuminates the physiology and evolution of globally important nitrite-oxidizing bacteria." The researchers suggest their study shows that Nitrospira evolved from microaerophillic — or even anaerobic — ancestors, based on the "reverse tricarboxylic acid cycle as the pathway for CO2 fixation and the lack of most classical defense mechanisms against oxidative stress."

Walter Reisner at McGill University and his international colleagues describe the "power of denaturation mapping as a single-molecule technique" in PNAS this week. "By partially denaturing YOYO-1-labeled DNA in nanofluidic channels with a combination of formamide and local heating, we obtain a sequence-dependent 'barcode' corresponding to a series of local dips and peaks in the intensity trace along the extended molecule," the authors write, adding that this is an effect of the physics of local denaturation. Reisner et al. suggest that their technique is cognizant of sequence variation "without requiring enzymatic labeling or a restriction step."

Also in this week's PNAS, researchers at the Duke University Medical Center show that DNA mismatch repair protein PMS2 "endonuclease activity has distinct biological functions and is essential for genome maintenance and tumor suppression," a finding they've determined using endonuclease-deficient Pms2E702K knock-in mice. These murine models showed increased mutation rates and a strong predisposition for cancer, the authors write, adding that class-switch recombination was hindered in Pms2EK/EK B cells, "indicating a specific role in Ig diversity."

The Scan

Pig Organ Transplants Considered

The Wall Street Journal reports that the US Food and Drug Administration may soon allow clinical trials that involve transplanting pig organs into humans.

'Poo-Bank' Proposal

Harvard Medical School researchers suggest people should bank stool samples when they are young to transplant when they later develop age-related diseases.

Spurred to Develop Again

New Scientist reports that researchers may have uncovered why about 60 percent of in vitro fertilization embryos stop developing.

Science Papers Examine Breast Milk Cell Populations, Cerebral Cortex Cellular Diversity, Micronesia Population History

In Science this week: unique cell populations found within breast milk, 100 transcriptionally distinct cell populations uncovered in the cerebral cortex, and more.