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Research has been conducted on the Rhizobium leguminosarum bv. viciae VF39 gabT gene which encodes 2-oxoglutarate-dependent gamma-aminobutyrate aminotransferase. The identification, cloning and characterization of gabT have been carried out and the results indicate the importance of this gene in bacteroid metabolism.

The influence of DctA and DctB on the regulation of the dctA, dctB and dctD promoters was analyzed. LacZ fusion analysis was used to determine transcription in dctB and dctD. The result showed that both have only one promoter. Nitrogen limitation which induces the dctA promoter requires DctB-DctD and NtrC. DctA controls signal detection by DctB, thus the ligand specificity of DctB is wider when there is a lack of DctA. This suggests that DctA has an important role in the signal specificity of DctB-DctD.

A comparative analysis was made between the MCP-independent systems in enteric bacteria and the chemotactic systems in Rhodobacter sphaeroides. In this study, chemotaxis was mediated through transport and phosphorylation via phosphoenolpyruvate-dependent phosphotransferase system or through chemotaxis pathway. Results show that chemotactic signal in R. sphaeroides will most likely be created through activities of the electron-transport chain or metabolic intermediates.

The regulation of the uptake activity of the amino acid permease (Aap) in Rhizobium leguminosarum by the TCA cycle via the synthesis of the amino acids was demonstrated. The 2-oxoglutarate dehydrogenase was found to be the main enzyme. Results reveal that the TCA cycle in R. leguminosorum is regulated by the amino acid excretion and polyhydroxybutyrate biosynthesis which act as overflow pathways for excess carbon and reductant.

Amino acid uptake by the general amino acid permease (Aap) of Rhizobium leguminosarum strain 3841 was greatly reduced by the presence of aspartate in the growth medium when glucose was the carbon source. This was due to the prevention of uptake and not by transcriptional repression. However, the Ntr-regulated gene glnII was repressed by aspartate. The negative regulatory effect on both the Aap and glnII was prevented by mutation of any component of the dicarboxylate transport system or by the inclusion of a C4-dicarboxylate in the growth medium, including the non-metabolizable analogue 2-methylsuccinate.

Insertion of a nodC-phoA reporter plasmid with nodD into a symbiotic plasmid-absent Rhizobium leguminosarum strain that is chemically mutagenized helps delineate the host genes that affect nod gene expression in R. leguminosarum. The mutant resulting from insertion of the symbiotic plasmid pRL1Jl after curing the nodC-phoA plasmid exhibits normal nodule formation with 80% symbiotic nitrogen fixation. Introduction of the nodC-phoA allele on PRL1Jl leads to low level nod gene activation. Genetic analysis reveals the presence of IS 50 in the mutant regulatory gene dctB, leading to reduced nod gene expression is not affected by other mutations in dctB, indicating that the effect is allele-specific.

Enzyme assays suggest the involvement of 2-keto-myo-inositol and D-2,3-diketo-4-deoxy epi-inositol in the myo-inositol catabolism of Rhizobium leguminosarum bv. viciae. Growth of R. leguminosarum on myo-inositol increases the enzyme's myo-inositol dehydrogenase and 2-keto-myo-inositol dehydratase. Examination of the growth in glucose as carbon source and resuspension studies in myo-inositol show that O2 consumption is an inducible route. Mutation studies reveal the necessity of intra-cellular dicarboxylation for the repression of these enzymes. Isolation and studies of three transposon mutants that do not induce both enzymes suggest that myo-inositol is not vital as an energy source in bacteriods.

A Tn5 mutant (RU301) of R. leguminosarum that lacks the O-antigen, and which has rough colony morphology and is unable to swarm in TY agar, produces only lipopolysaccharide layer (LPS II). RU301 fails to grow on organic acids but high concentration of calcium or magnesium restores the growth. Southern blotting shows the location at transposon insertion in RU301 in a 3 kb EcoRI fragment. There is a separation of 10 kb between dctD and the region mutated in strain RU301. Additional calcium is not necessary for all LPS rough mutants, and gene mutation in RU301 is essential for nitrogen fixation.

A study of the behavior of a hetero-nipi all-optical reflection modulator using a numerical model reveals refractive index alterations to cause modulation. The quantum-confined stark effect causes optically stimulated electric field modifications, which alter the quantum well refractive index. This model indicates a 53% reflectivity modulation in device structures.

The chemotactic behavior, transport and metabolism of alanine and 2-aminoisobutyrate, a nonmetabolizable alanine analog, in Rhodobacter sphaeroides were investigated. The results showed that R. sphaeroides had a chemotactic response toward alanine but not to 2-aminoisobutyrate. Structurally unrelated compounds could inhibit chemotaxis toward alanine, suggesting that the chemotactic response involves a common metabolic intermediate or process.