MICROBIOLOGY: Life in a Melting Pot

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Science  04 Jan 2002:
Vol. 295, Issue 5552, pp. 17b
DOI: 10.1126/science.295.5552.17b

The pathogen Helicobacter pylori resides in the human stomach and can induce lifelong infections that cause gastric irritation, ulcers, and cancer. The long-term character of its tenancy enables a resident strain to benefit from genetic exchange with recent arrivals. Falush et al. have collected 22 paired isolates taken an average of 2 years apart from patients in New Orleans and the Colombian Andes. Approximately 5 kilobases of sequence from each isolate were analyzed with a mathematical model in order to estimate the frequency and extent of recombination. The average size of the acquired DNA was relatively small, about 400 base pairs, and raises the possibility that H. pylori may be nonspecifically importing fragments of partially digested DNA, unlike bacterial recipients that discriminate between related and unrelated donors. Each pair of isolates was found to differ as a consequence of about 100 recombination events, or by about 3% of the genome. From the mutation rate, they calculate that H. pylori has colonized humans for 2500 to 11,000 years. The age of the human malaria parasite Plasmodium falciparum, as estimated by Tiskoff et al. and Volkman et al. (Reports, 20 July 2001, p. 455 and 482), lies within this range, as does the date for the origin of agriculture. — GJC

Proc. Natl. Acad. Sci. U.S.A. 98, 15056 (2001).

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