Expanding the diversity of mycobacteriophages: insights into genome architecture and evolution

Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists.

Benign smooth muscle tumors of the gastrointestinal tract. A 24-year experience

Between 1963 and 1987, 131 patients with benign gastrointestinal stromal tumors, primarily leiomyomas, were treated at the Massachusetts General Hospital. Eighty per cent of tumors were located in stomach or small intestine. Two thirds of the tumors were discovered in symptomatic patients before operation by a variety of diagnostic studies. A mitotic index (MI) was determined for each tumor, defined as the number of mitoses per 50 high-power microscopic fields. Only gastric and small intestine tumors had MIs more than 2. Tumors were treated by conservative excision in 67% and radical excision in 33%. At a median follow-up of 6 years there were no local recurrences. No patient with a tumor discovered incidentally has recurred. Three symptomatic patients have died of metastatic liver disease. Each patient with recurrence had a tumor with MI of 2 or more, which represents a recurrence rate of 16% in this group. We conclude that symptomatic gastric and small intestine tumors having two or more mitoses per 50 high-power fields carry a significant risk for recurrence, and that routine pathologic assessment of MI may identify a subset of patients who would potentially benefit from close follow-up and consideration for further therapy.

New Kerr cell for low-temperature measurements

A Kerr cell has been constructed which can be used to study the Kerr effect in liquids from room temperature down to 77 K. At low temperatures, the cell windows are free of moisture. The cell has been tested and measurements on liquid carbon disulfide, between 170 and 300 K, are discussed.