PCR and the Arrival of Tuberculosis in America

In the early 1600s, soon after Europeans arrived in the New World, devastating epidemics of tuberculosis ravaged many tribes of Native Americans. Anthropologists long argued that this disease was absent from the New World before 1492 and that Europeans first transmitted tuberculosis to the Native Americans. With no prior exposure to the disease and little natural immunity, the indigenous people would, it was argued, have been highly susceptible to tuberculosis.

A few anthropologists challenged this conventional view. On the basis of tuberculosis-like lesions found in a few skeletons and mummified remains that pre-date European contact, they suggested that the disease was present in Native Americans before European contact. On the other hand, many diseases and even bacteria that gain access to the body after death can produce similar marks, and the origin of tuberculosis in America remained controversial.

In 1994, pathologist Arthur C. Aufderheide and molecular biologist Wilmar Salo teamed up to resolve this controversy. Aufderheide obtained access to the remains of a woman who died and was naturally mummified in Peru about 1000 years ago, hundreds of years before Europeans arrived in South America. He removed samples of the woman's right lung and a lymph node and sent them to Salo, who used the newly developed polymerase chain reaction (PCR, which selectively amplifies sequences of DNA) to search the samples for DNA from Mycobacterium tuberculosis, the bacterium that causes tuberculosis. When applied to DNA from modern-day Mycobacterium tuberculosis, this technique produces copies of a 97-bp fragment of DNA. Salo detected an identical 97-bp piece of DNA by applying PCR to DNA samples from the ancient lung and lymph tissue, demonstrating unambiguously the presence of tuberculosis in the tissue of this 1000-year-old woman.

Although Europeans were not the first to transmit tuberculosis to Native Americans, they were still the most likely cause of the tuberculosis epidemics that accompanied their arrival in the Americas. European settlement was highly disruptive to many indigenous societies, often causing mass displacements of people and radically altering their traditional life styles. Stressful conditions, accompanied by crowding and malnutrition on reservations, probably lowered the resistance of many Native Americans and contributed to the spread of tuberculosis.

This story of the discovery of tuberculosis in the remains of a 1000-year-old woman illustrates the power of PCR, one of the techniques of molecular biology discussed in this chapter. We begin the chapter with a discussion of recombinant DNA technology and some of its effects. We then examine a number of methods used to isolate, study, alter, and recombine DNA sequences and place them back into cells. Finally, we explore some of the applications of recombinant DNA technology.

In reading this chapter, it will be helpful to understand two things. First, working at the molecular level is quite different from working with whole organisms: different approaches are needed, because the molecular objects of study cannot be seen directly. Second, there are a number of different approaches for isolating DNA sequences, amplifying them, and inserting them into bacteria, each approach with its own strengths and weaknesses. The optimal method depends on the starting materials, how much is known about the sequences to be isolated, and what the final objective is.

www.whfreeman.com/pierce More information about tuberculosis

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