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Abstract
Carbohydrate mutants were isolated from Rhizobium meliloti L5-30 using the translocatable drug-resistance element Tn5. Enzyme assays with cell-free extracts of four mutants showed that they lacked mannitol dehydrogenase, ribose kinase, xylose isomerase and fructose kinase, respectively. An l-arabinose mutant was also isolated. Uptake studies showed that the ribose, xylose and fructose mutants still utilized the sugars on which they were unable to grow, possibly indicating that R. meliloti possesses alternative metabolic routes which do not result in growth. All the mutants were able to nodulate alfalfa plants, but the fructose kinase mutant was unable to fix nitrogen and the l-arabinose mutant showed either late or no nitrogen-fixing ability.
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