Keeping the Fix In

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Science  03 Nov 2006:
Vol. 314, Issue 5800, pp. 729
DOI: 10.1126/science.314.5800.729a

The endophyte Azoarcus sp. strain BH72 resides within the roots of rice and other grasses. In return for supplying the plant with fixed nitrogen (diatomic nitrogen that has been converted into biochemically tractable forms such as ammonia), it is presumed to benefit from a sheltered and predictable habitat. Krause et al. have sequenced its genome and compared it to that of a free-living relative, the strain EbN1. They find the expected suite of nitrogen-fixing and -metabolizing enzymes along with a large set of transporters for dicarboxylic acids (though not of sugars) and chelated iron. On the other hand, the low-stress lifestyle appears to have led to the loss (or non-acquisition) of type III and IV secretion systems as well as a paucity of virulence and pathogenic components. Similarly, there are only a small number of mobile elements, in comparison to its independent cousin. How these characteristics might be harnessed in agronomic efforts to enhance rice cultivation, and perhaps that of other cereals, is not yet clear, but it's a start. — GJC

Nat. Biotechnol. 24, 10.1038/nbt1243 (2006).

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