Aptamer selections against bacterial toxins and cells

In vitro selection of functional RNA molecules has formed the basis for a new class of molecules termed “aptamers.” Aptamers have been selected against a wide range of molecules, ranging from simple chemical compounds to multi-cellular living organisms. The majority of selections are carried out against targets, such as proteins, that are typically composed of one type of molecule. Targets composed of multiple types of molecules (lipids, proteins, carbohydrates, etc.) are termed “complex,” and examples of successful selections against them include parasites, virions, and red blood cell ghosts. Through various properties inherent in their composition, aptamers have the potential to play a role in everything from therapeutics to broad based detection platforms. Bacterial toxins are a means by which pathogenic bacteria are able to exert an effect on a host organism. Although there are a few aptamer selections that have been carried out against toxins, there have not been any successful selections against whole bacterial cells. As some bacteria are easily grown in laboratory conditions, the possibility of their use as a biological threat agent is relatively high. Therefore, there is a need develop rapid and reliable technologies for the detection of such threats. This work details two aptamer selections carried out against both a bacterial toxin, Bacillus. anthracis protective antigen (PA), and a Bacillus subtilis vegetative cell. The selection against PA resulted in a high affinity aptamer that is capable of inhibiting the cleavage of PA. This cleavage step is the first in the pathway whereby anthrax toxin is able to exert its effect. The selection against B. subtilis vegetative cells is a proof of principle selection. B. subtilis is meant to be a surrogate for B. anthracis, which has long been regarded as a potential bio-weapon. Aptamers selected against these vegetative cells are shown to discriminate between bacterial vegetative cells of the same genus, bacteria of a different genus, and also spores produced by B. subtilis. With these selections as examples, it is hoped that the role of aptamers can continue to be expanded into viable detection systems for biological threat agents.