Stress plays an important role in the development of affective disorders. Women show a higher prevalence for these disorders than men. The course of a depression is thought to be positively influenced by social support. We have used a chronic stress model in which rats received foot-shocks daily for 3 weeks. Since rats are social animals we hypothesised that 'social support' might reduce the adverse effects of chronic stress. To test this hypothesis, male and female rats were housed individually or socially in unisex groups of four rats. The proliferation marker bromodeoxyuridine (BrdU) was injected 2 weeks before the sacrifice to investigate if stress and social housing influenced the survival of proliferating cells in the dentate gyrus (DG). To investigate changes in proliferation, another group of rats was sacrificed the day after the last BrdU injection. Stress significantly decreased BrdU labelling in individually housed males and not significantly in socially housed males. In individually housed females stress increased BrdU labelling, which was prevented by social housing. The increase found in females is most likely caused by differences in survival rate, since cell proliferation was not affected by stress or housing conditions. These results indicate that social support can affect neurogenesis in both female and male rats, however in a different way.

A study was performed to gain insight into the mechanism of acid-tolerant, chemolithotrophic nitrification. Microorganisms that nitrified at pH 4 were enriched from two Dutch acid soils. Nitrate production in the enrichment cultures was indicated to be of a chemolithoautotrophic nature as it was (i) completely inhibited by acetylene at a concentration as low as 1 ,umol/liter and (ii) strongly retarded under conditions of carbon dioxide limitation. Electron microscopy of the enrichment cultures showed the presence of bacteria that were morphologically similar to strains of known chemolithotrophic nitrifying genera. Many of the enriched bacteria, in particular those that were identified as ammonium oxidizers, were aggregated. Filtration experiments indicated that aggregated cells were able to nitrify at low pH, whereas single cells were not. It is hypothesized that cells inside the aggregates are protected against the toxicity of nitrous acid. Nitrification by aggregated chemolithoautotrophic bacteria may be the dominating process of nitrate formation in many acid soils as it does not appear to depend on the existence of microsites of high pH (acid-sensitive autotrophic nitrification) or on the availability of organic carbon (heterotrophic nitrification).

A freshwater Spirillum sp., which apparently belongs to a niche of low nutritional status (Matin & Veldkamp, 1978), accumulated poly-P-hydroxybutyric acid (PHB) during lactate-limited growth in continuous culture. The PHB content varied in a complex manner with the dilution rate (D), but was greatest at the lowest D value examined: about 18 yo (w/w) at D = 0.025 h-l. It is not known what mechanism accounted for PHB accumulation during carbon-limited growth. The resistance of cultures of Spirillum sp. to starvation after growth at various D values was compared with that of a Pseudomonas sp. which appears to belong to relatively richer environments (Matin & Veldkamp, 1978) and does not accumulate PHB. In Spirillum sp., resistance correlated directly with the PHB content of the culture subjected to starvation, whereas in Pseudomonas sp. it increased with RNA content. Further, after growth at D = 0.03 to 0.05 h-l, the Spirillum sp. was much more resistant to starvation than was the Pseudomonas sp. Since the microflora of oligotrophic environments are probably often subjected to starvation conditions, PHB accumulation by Spirillurn sp. during growth in such environments may assist survival. PHB in Spirillum sp. was rapidly degraded during starvation but it had no sparing effect on RNA degradation. It is not known how PHB enhanced resistance to starvation. I N T R O D U C T I O NWe have previously described a Spirillum sp. and a Pseudomonas sp. which possess crossing substrate saturation curves. We found several physiological and morphological differences between these bacteria which are consistent with the different niches that they appear to occupy in nature: Spirillum sp. occupies those scarce in nutrients and Pseudomonas sp. occupies the richer ones capable of supporting rapid growth (Matin & Veldkamp, 1978).The studies described in this paper emanated from the observation of poly-P-hydroxybutyric acid (PHB)-like inclusions in electron micrographs of Spirillum sp., but not of Pseudomonas sp., grown under L-lactate limitation. Since PHB is believed to accumulate in bacteria primarily under conditions of carbon excess (Dawes, 1976;Dawes & Senior, 1973) and because Spirillum sp. represents a bacterial type hitherto little studied (Matin & Veldkamp, 1978; Harder et al., 1977), we investigated the influence of culture dilution rate ( D ) on PHB accumulation. We also compared the ability of cells of Spirillum sp. and Pseudomonas sp., grown at different D values, to withstand starvation stress. METHODSOrganisms andgrowth conditions. The freshwater Spirillum sp. DSM 1109 and Pseudomonas sp. DSM 11 10, isolated in our laboratory (Matin & Veldkamp, 1978), were used in these studies. These bacteria are in the Deutsche Sammlung von Mikroorganismen, Gottingen, West Germany. [The address previously given (Matin & Veldkamp, 1978) erroneously specified Munchen.] The medium and details of chemostat cultivation have been described previously Matin & Veldkamp, 1978). The chemostat had a working volume of 200 ml; the incubation temp...

MATERIALS AND METHODS B. subtilis W 23 was grown in a medium containing 0.8% Tryptone (Difco Laboratories, Detroit, Mich.) and 0.5% NaCl at 37 C with vigorous aeration. Cells were harvested at an absorbancy at 660 nm of 1.0 to 1.5, washed with 0.1 M potassium-phosphate, pH 7.3, and centrifuged (20 min at 14,000 x g). Cells were suspended in 0.1 M potassium-phosphate, pH 8.0, with 20% sucrose at 37 C at a concentration of 1 g (wet weight) per 80 ml. Lysozyme (E. Merck AG, Darmstadt, Germany) was added at a final concentration of 300 ,ug/ml. The mixture was incubated for 30 min, after which the protoplasts were harvested by centrifugation (30 min at 14,000 x g). Cells were suspended in 0.05 M potassium-phosphate, pH 8.0, at 37 C at a concentration of 4 g (wet weight) per liter. Lysozyme (E. Merck AG, Darmstadt, Germany), deoxyribonuclease-1 (DNase-1; bovine pancreas DNase, BDH Chemicals Ltd., Poole, England), and ribonuclease (RNase; pancreas, E. Merck AG, Darmstadt, Germany) were added at final concentrations of 300, 10, and 10 Mig per ml, respectively. The solution became gradually viscous due to the liberation of deoxyribonucleic acid (DNA). After 15 min of incubation. MgSO4 was added at a final concentration of 10 mM. Due to the action of RNase and DNase, the viscosity decreased. During this incubation the original turbid cell suspension became 1456

Hydrogenase and the adenosine 5'-triphosphate (ATP) synthetase complex, two enzymes essential in ATP generation in Methanobacterium thermoautotrophicum, were localized in internal membrane systems as shown by cytochemical techniques. Membrane vesicles from this organism possessed hydrogenase and adenosine triphosphatase (ATPase) activity and synthesized ATP driven by hydrogen oxidation or a potassium gradient. ATP synthesis depended on anaerobic conditions and could be inhibited in membrane vesicles by uncouplers, nigericin, or the ATPase inhibitor N,N'-dicyclohexylcarbodiimide. The presence of an adenosine 5'-diphosphate-ATP translocase was postulated. With fluorescent dyes, a membrane potential and pH gradient were demonstrated.