Biology of Azospirillum-Sugarcane Association: Enhancement of Nitrogenase Activity

Azospirillum brasilense was reisolated from associations with callus tissue cultures of sugarcane and compared with stock cultures of the inoculated bacterium and related strains. Although the reisolate had a growth rate similar to stock cultures, it exhibited a severalfold increase in maximum specific activity of nitrogenase. The reisolate and the parent culture had similar ultrastructure. The general ultrastructure of Azospirillum is described. The bacterium was capsulated when grown on nitrogen-free nutrient agar plates and on callus, but was not capsulated when growing in a subsurface zone in N-free semisolid nutrient agar, except rarely in aging cultures. Capsulation may be a protective mechanism against unfavorable pO₂ under dinitrogen-fixing conditions. Pleomorphism occurred in capsulated forms, and the ultrastructure of these forms is described.     

Social status and season of birth: a study of a metropolitan area in the southeastern United States

An analysis of live birth statistics obtained from the Health Department of Fulton County, Georgia for 1967-1977 indicated that seasonal variation in birth was significantly related to maternal social status. Mothers were assigned to social status classification on the basis of whether they lived in an upper, upper middle, lower middle, or lower socioeconomic census tract. Periodic regression analysis and analysis of variance was applied to the data. Specific findings were 1) upper status groups showed no significant variation in births; 2) upper and lower middle classes showed a similar and a significant degree of seasonal variation with depressed birth levels from January-June and elevated levels from July-December; 3) lower class birth patterns showed more seasonal variation than the other classes; 4) the periodic curve accounted for 92.3% of the monthly variation in births for the lower class, 70.6% for the lower middle class, and 64.6% for the upper middle class; 5) the relationship between social status and seasonal variation in births held for both whites and non-whites; 6) seasonal variations were somewhat more marked for non-whites than for white in the lower and lower middle class; and 7) the observed relationship held throughout the 11 year period of observation. The results were of special concern given previous studies which found that children born in September-October entered school on the average earlier than other children and did less well in school than other students. Major findings were presented in graphic and tabular form.     

Foetal glutamate as a possible precursor of placental glutamine in the guinea pig.

The role of foetal glutamate as a source of placental glutamine was investigated in the near-term pregnant guinea-pig placenta perfused in situ through the umbilical vessels. With normal foetal amino acid concentrations there was a significant two-way exchange of glutamate between the placenta and foetal perfusate, but a net release of the amino acid from the placenta. Radioactively labelled glutamate carbon entering the placenta by this exchange was freely incorporated into intracellular glutamine, but only 1.5% of it was found in glutamine transported out into the foetal circulation. In the guinea pig, therefore, foetal glutamate does not appear to be a precursor of glutamine released from the placenta on the foetal side.     

The effect of AZT on in vitro lymphokine-activated killer (LAK) activity in human immunodeficiency virus type-1 (HIV-1) infected individuals

Human immunodeficiency virus type-1 (HIV-1)-infected individuals exhibit functional impairment in various forms of cell-mediated cytotoxicities (CMC) at all stages of disease. The purpose of this study was to determine (i) if peripheral blood mononuclear cells (PBMC) obtained from HIV-1-infected patients could be stimulated in vitro to yield lymphokine-activated killer (LAK) activity; (ii) if non-MHC-restricted gp120-specific CMC could be preserved; and (iii) what effect zidovudine (AZT) would have on LAK activity. Fourteen asymptomatic HIV-1 seropositive adults and five healthy seronegative adults (controls) were evaluated. PBMCs were isolated and incubated in media or supplemented with IL-2 for 4 or 72 hr. Lysis of the NK resistant target cell line, Daudi, was similar for the control and experimental group. The increase in activity after stimulation was elevated to a similar degree in both seronegative and seropositive groups (P less than 0.001). LAK activity was significantly decreased (P = 0.011) when AZT was added to LAK cultures. In addition, virus production may not have been completely inhibited by AZT in LAK cultures. Thus, PBMCs from asymptomatic HIV-1-infected patients could be stimulated to yield LAK activity. However, AZT can impair LAK generation. It is unclear if LAK activation results in virus production that cannot be inhibited by AZT in this system. Further definition in other patient populations is required prior to applying this information to clinical trials.     

Novobiocin-dependent topA deletion mutants of Escherichia coli.

Previous reports of the transduction of topA deletions in Escherichia coli suggested that delta top A transductants grow normally only if they acquire spontaneous mutations that compensate for the topoisomerase I defect. We show that P1-mediated transduction of delta topA in the presence of sublethal concentrations of novobiocin, an inhibitor of the DNA gyrase B subunit, yields uncompensated Top- isolates which are dependent on novobiocin for optimum growth. In the absence of novobiocin these delta topA strains grow slowly, indicating that topA deletions are deleterious but not lethal to the cell. We propose that inhibitors of DNA gyrase B, presumably by lowering intracellular levels of DNA supercoiling, can phenotypically suppress a topoisomerase I defect in E. coli.