Carbon utilization by free-living and bacteroid forms of cowpea Rhizobium strain NGR234

Nitrogen Fixation Research Group, School of Environmental and Life Sciences, Murdoch University, Murdoch, Western Australia 6150 ABSTRACT Free-living cells of the fast-growing cowpea Rhizobium NGR234 were able to grow on a variety of carbon substrates at growth rates varying from 2.5 h on glucose or fumarate to 15.6 h on p-hydroxybenzoate. Free-living cells constitutively oxidized glucose, glutamate and aspartate but were inducible for all the other systems investigated. Bacteroids from root nodules of snake bean, however, were only capable of oxidizing C 4 -dicarboxylic acids and failed to oxidize any other carbon sources. Free-living cells of NGR234 possess inducible fructose and succinate uptake systems. These substrates are accumulated by active processes since accumulation is in hi bi ted by azide, 2,4-dini trop hen01 and carbonyl cyanide m-chlorophenyl hydrazone. Bacteroids failed to take up fructose although they actively accumulated succinate, suggesting that the latter substrate is significant in the development of an effective symbiosis.