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Four mutants of Rhizobium leguminosarum biovar viciae VF39 altered in lipopolysaccharide (LPS) synthesis were isolated upon random TnS mutagenesis. These mutants produced matt colonies on TY medium and showed autoagglutination and loss of motility. On sodium dodecyl sulfate-polyacrylamide gels, they lacked a slow-migrating carbohydrate band, corresponding to the complete LPS (LPSI). All four mutants formed small white nodules on Vicia hirsuta. These nodules were infected but showed no nitrogen-fixing activity and senesced prematurely. Three of the mutants were complemented by a wild-type cosmid to synthesis of normal LPS and induction of nitrogen-fixing nodules. By hybridization and in vivo cloning experiments, the mutations were mapped within different EcoRI fragments which could be localized on the VF39 chromosome. Crosscomplementation analyses revealed that the three mutants were affected in different transcriptional units. The results indicate that a cluster of genes necessary for LPSI production and symbiotic efficiency is located within a defined region of 20 kilobases on the R. keguminosarum bv. viciae chromosome.The establishment of nitrogen-fixing nodules in the Rhizobium-legume symbiosis is a complex multistep interaction between microsymbiont and its specific host plant (for a review, see reference 2). Early events involve recognition and deformation or curling of root hair cells. Cortical cell division, leading to the formation of a unique organ, the nodule, is induced probably by diffusible bacterial substances. Invasion of the nodule by the bacteria is initiated by penetration of the root hair cell wall and the formation of an infection thread, in which the bacteria are carried towards the dividing root cortex cells. Bacteria are eventually released from the infection thread into the plant cells. They remain separated from the host cytoplasm by peribacteroid membranes and differentiate into bacteroids able to reduce atmospheric nitrogen.This complex developmental process obviously requires continuous signal exchange between plant and bacterial cells. Undoubtedly, bacterial cell surface components play an important role in this specific interaction; particularly extracellular polysaccharides (EPSs) and lipopolysaccharides (LPSs) have been hypothesized to be involved in the symbiotic process (for reviews see references 5 and 15).The LPS of gram-negative bacteria consists of lipid A, a core oligosaccharide and an 0-antigenic side chain. The Rhizobium LPSs are very heterogenous molecules and vary greatly among different species as among strains of a single species (6, 49). Therefore, rhizobial LPS has been suggested to be involved in specific recognition and attachment of bacteria to the root hair cells of compatible host plants, mediated by the binding of lectins (47). While recent work (12) supports an essential function of lectins in host-plant specificity, a role of LPS in host-specific nodulation remains unclear.Differences in LPS composition were described between nodulating and nonnodulating str...

The degradation of radiolabeled 4(3',5'-dimethyl-3'-heptyl)-phenol [nonylphenol (NP)] was tested with resting cells of Sphingomonas sp. strain TTNP3. Concomitantly to the degradation of NP, a metabolite identified as hydroquinone transiently accumulated and short-chain organic acids were then produced at the expense of hydroquinone. Two other radiolabeled isomers of NP, 4(2',6'-dimethyl-2'-heptyl)-phenol and 4(3',6'-dimethyl-3'-heptyl)-phenol, were synthesized. In parallel experiments, the 4(2',6'-dimethyl-2'-heptyl)-phenol was degraded more slowly than the other isomers of NP by strain TTNP3, possibly because of effects of the side-chain structure on the kinetics of degradation. Alkylbenzenediol and alkoxyphenol derivatives identified as metabolites during previous studies were synthesized and tested as substrates. The derivatives were not degraded, which indicated that the mineralization of NP does not proceed via alkoxyphenol as the principal intermediate. The results obtained led to the elucidation of the degradation pathway of NP isomers with a quaternary alpha-carbon. The proposed mechanism is a type II ipso substitution, leading to hydroquinone and nonanol as the main metabolites and to the dead-end metabolites alkylbenzenediol or alkoxyphenol, depending on the substitution at the alpha-carbon of the carbocationic intermediate formed.