Ultrastructural analysis of ineffective alfalfa nodules formed by nif::Tn5 mutants of Rhizobium meliloti.

Ineffective alfalfa nodules formed by Rhizobium meliloti nif::Tn5 mutants were examined by light and electron microscopy. R. meliloti nifH::Tn5 mutants formed nodules that were similar in structure to wild-type nodules except that nifH- bacteroids accumulated a compact, electron-dense body. In contrast to nodules induced by wild type and nifH mutants, nifDK- R. meliloti mutants induced nodules which contained numerous starch grains and prematurely senescent bacteroids. In addition, meristematic activity in nifDK- nodules ceased significantly earlier than in nifH- nodules. All mutant nodules exhibited elevated levels of rough endoplasmic reticulum and Golgi membranes compared to wild-type nodule cells. These elevated levels may reflect either a response to nitrogen starvation in the ineffective nodules or an abnormal synthesis and export of nodule-specific proteins during later developmental stages.     

In vitro and in vivo effects on brain GABA metabolism of (S)-4-amino-5-fluoropentanoic acid,a mechanism-based inactivator of γ-aminobutyric acid transaminase

The effects of intraperitoneal administration of (S)-4-amino-5-fluoropentanoic acid, a mechanism-based covalent inactivator of γ-aminobutyric acid transaminase (GABA-T), on whole brain GABA metabolism in mice were investigated. A dose-dependent and time-dependent irreversible inactivation of GABA-T was observed with a concomitant increase in whole brain GABA levels. The compound exhibited no $\text{in vitro}$ nor $\text{in vivo}$ time-dependent inhibition of glutamate decarboxylase (GAD), alanine transaminase, or aspartate transaminase (Asp-T). It was, however, a potent competitive reversible inhibitor of GAD and a weak competitive inhibitor of Asp-T. The chloro analogue, (S)-4-amino-5-chloropentanoic acid, was ineffective.     

Down's syndrome in twins with discordant HL-A phenotypes

Summary A male twin pair discordant in morphological characteristics and HL-A phenotype but concordant in trisomy 21 and the blood group markers is reported.The coincidental occurrence of two rare conditions (nondisjunction and dizygotic twinning) and a high probability of monozygosity (inferred from the blood group findings) gave rise to the question of whether the boys might represent intermediates between dizygotic and monzygotic twins. Postcleavage fertilization can be excluded as a circumstance leading to intermediates since the twins have different maternal HL-A haplotypes.

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Zusammenfassung Ein männliches Zwillingspaar wird vorgestellt, das in einigen morphologischen Merkmalen und im HL-A-Phänotypus diskordant, hinsichtlich einer Trisomie 21 und der Blutgruppenmerkmale aber konkordant ist.Auf Grund des Zusammentreffens zweier seltener Ereignisse (nondisjunction und Zweieiigkeit), insbesondere aber auch wegen starker blutgruppenserologischer Hinweiswahrscheinlichkeiten für Eineiigkeit, wird die Frage gestellt, ob die Knaben möglicherweise eine intermediäre Position zwischen Eineiigkeit und Zweieiigkeit einnehmen. Von den Möglichkeiten, die zu einer solchen Zwischenstellung führen könnten, scheidet die einer Befruchtung des Eies erst nach der Furchung aus, da beide Zwillingspartner unterschiedliche mütterliche HI-A-Haplotypen aufweisen.

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Supported by the Deutsche Forschungsgemeinschaft.     

Biology of budding bacteria

Summary Budding bacteria from aquatic or terrestrial habitats were found to accumulate ferric oxide hydrate (ferric hydroxide) on their cell surfaces. Metal paper clips served as the source of oxidizable iron. Pure cultures deposited ferric hydroxide during growth on sea water medium at a pH of 7.8, but not in a mineral salts medium of normal ionic strength, of pH 7.2, and without NaCl, although some active strains came from fresh water or soil.Ferric iron deposition was found to be initiated at primary active sites on the cell surface; the hyphae and rods eventually become completely encased by the heavy coat.The presence of iron depositing, budding bacteria in fresh water, brackish water or sea water indicates an ubiquitous distribution of these microorganisms.Actively depositing isolates from marine environments are more closely related to Pedomicrobium than to Hyphomicrobium spp. because of their multiple formation of hyphae from rod-shaped swarmer cells. A taxonomic and cultural study of these new forms is in progress.     

Differential Dialysis Culture for Separation and Concentration of a Macromolecular Product

A differential dialysis flask, constructed with three chambers and two membranes of different porosity, was used to effect the separation and concentration of enterotoxin B produced extracellularly by a culture of Staphylococcus aureus. Variables were examined that affected the diffusion of glucose, as measured by half-equilibration time and permeability coefficient; the relative chamber volume, type of membrane, membrane masking, and mixing all exerted a substantial influence on diffusion rates. A number of membrane filters were tested for usefulness; one type, made with vinylidene fluoride, had desirable physical and diffusional properties, but neither it nor others consistently withheld the bacteria for more than a marginally useful period of about 50 hr. In ordinary two-chambered dialysis culture, the amount of enterotoxin reached 10 times that in control culture; in differential, three-chambered dialysis culture the comparable factor of increase was about 7, with about two-thirds of this amount being separated from cells in the product chamber of the flask.