Search

An inducible enzyme, catalyzing the formation of 3-ketosugars, has been isolated in a pure state from Agrobacterium tumefaciens, grown on lactose. It occurs in the cytoplasm. It is a FAD-protein with a sedimentation coefficient of 5.1 S and a molecular weight of 85,000 ± 7,700. The pH optimum varies with the nature of the electron acceptor: with cytochrome c it is 7.0, with 2,6-dichlorophenolindophenol 6.0 and with 5-methylphenazinium methyl sulphate 7.9. p-Chloromercuribenzoate, and to some extent atabrine, have an inhibitory effect. In view of its lability, the enzyme is best preserved in a nitrogen atmosphere at pit 7 and 0°. The substrate specificity as studied with a variety of sugars, justifies the name of hexopyranoside: cytochrome c oxidoreductase for the enzyme. As a rule, disaccharides are more easily oxidized than monosaccharides. The highest affirnity is observed with cellobiose and lactobionic acid (Km=2.0 × 10-4 M). Most of the 3-ulose endproducts were detected by thin layer and/or polarography. The minimal structural requirements of a substrate sugar allow the proposal of a molecular model for the active centre of the enzyme. The oxidation-reduction potential at pH 7 and 25° of the system lactose/3-ketolactose is calculated to be E0=+0.16 V. [ABSTRACT FROM AUTHOR]

Beardsley, Robert E. (Manhattan College, New York, N. Y.). Glycine resistance in Agrobacterium tumefaciens. J. Bacteriol. 83:6-13. 1962.-The application of the fluctuation test of Luria and Delbrück to the distribution of glycine-resistant bacteria among cultures of Agrobacterium tumefaciens strain B6 indicates that resistance arises by mutation in the absence of glycine. On glycine-supplemented medium, additional resistant colonies arise during prolonged periods of incubation. Their appearance is proceded by L-form growth. In general, the number of generations over which glycine resistance is inherited in the absence of glycine is increased by serial transfers on the selection medium. In liquid medium containing glycine, sensitive bacteria form spheroplasts. Resistant bacteria continue to grow as rod forms. In the medium employed, spheroplasts are unstable.

Beardsley, Robert E. (Manhattan College, New York, N. Y.). Amino acid cross resistance in Agrobacterium tumefaciens. J. Bacteriol. 84:1237-1240. 1962.-Resistant clones selected on medium supplemented with glycine were also resistant to d-methionine, d-valine, dl-norleucine, and dl-serine. Cross resistance was similarly exhibited by clones selected on d-methionine, d-valine, or dl-norleucine. Two types of resistant organisms were observed. One produced colonies containing normal rods on selection medium. The other produced translucent colonies containing L forms. Both grew as typical rods in unsupplemented medium. Some resistant clones did not produce a temperate phage carried by the parental strain, but these retained immunity to homologous phage. The toxicity of d-methionine and d-valine for nonresistant bacteria is not reversed by the l isomers. The lethal effects of toxic amino acids are additive.

Heberlein, Gary T. (Northwestern University, Evanston, Ill.), and James A. Lippincott. Photoreversible ultraviolet enhancement of infectivity in Agrobacterium tumefaciens. J. Bacteriol. 89:1511-1514. 1965.-Irradiation of a virulent strain of Agrobacterium tumefaciens with short-wavelength ultraviolet light, which reduces viability 50 to 90%, increases its infectivity as measured by the number of tumors initiated per viable bacterial cell on primary pinto bean leaves. A dark treatment of 1.5 to 2 hr between irradiation and inoculation results in a further increase in specific infectivity of as much as fourfold. This increase in infectivity is inhibited by white fluorescent light and light of 402 mmu, but only slightly by 549- or 619-mmu light. These results imply that some change in the deoxyribonucleic acid of the bacterium is responsible for this effect.