Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Histochemical staining of McCall soybean nodule occupied by wild-type Sinorhizobium fredii USDA191 and its myo-inositol dehydrogenase (idhA) mutant. The nodule shows sectors of distinct blue (occupied by the idhA mutant) and white zones (occupied by the wild type). A functional idhA gene is required for competitive nodulation of soybean by S. fredii USDA191. (See related article on page 2595.)