Bacteria into Plowshares

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Science  14 Nov 2003:
Vol. 302, Issue 5648, pp. 1117
DOI: 10.1126/science.302.5648.1117a

Crops can be grown successfully in untilled soil by taking advantage of resident microorganisms. Mycorrhizal fungi are important for the healthy growth of most plants, including crop species. Their interaction is not always a simple one, however, and may require the presence of “helper bacteria” for root-fungus recognition, plant colonization, nutrition, and perhaps even to stimulate germination of fungal propagules.

Artursson and Jansson, recognizing the problems of culturing such specialized soil organisms, made use of an ingenious technique to identify a mycorrhizae-associated bacterium. After the thymidine analog bromodeoxyuridine was added to soil samples (gathered outside Uppsala), newly synthesized DNA containing bromodeoxyuridine was isolated by immunocapture. The DNA was then used as a source of ribosomal RNA genes, which led to the identification of actively growing bacterial species in the soil. Eleven distinct sequences were discerned, but the dominant organism was a Bacillus cereus strain. This was extracted, grown, and labeled with green fluorescent protein, and its behavior in the presence of mycorrhizae was observed. Of several tested, this strain of B. cereus preferentially attached to the surface of mycorrhizae, possibly by polar flagella. — CA

Appl. Environ. Microbiol. 69, 6208 (2003).

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