Field Study Comparing Growth and Viability of a Population of Phototrophic Bacteria

The growth and viability of an anoxygenic, phototrophic bacterial community in the hypolimnion of Zaca Lake, Calif., were compared throughout the summer. The community is dominated by a single species, “Thiopedia rosea,” that inhabits the entire hypolimnion (6 to 8 m) for approximately 11 months. Suboptimal conditions in the hypolimnion (extremely low light intensity, high or low H₂S levels) result in zero or extremely low growth rates (doubling times > 1 month) for most of the population, most of the time, yet cells remain viable and capable of high specific growth rates (doubling times of 1 to 10 days) when placed under favorable conditions (higher light intensities and temperatures). We first conclude that phototrophic bacterial populations in situ may frequently exist in a viable yet nongrowing state. Second, the viability of cells is likely to be reduced with depth owing to higher concentrations of potentially toxic chemicals and to changes in the physiological state associated with the prolonged periods of darkness commonly found at the bottom of bacterial plates.     

The breeding biology of the WheatearOenanthe oenanthe in South Sweden during three contrasting years

Summary The breeding phenology, territory size, egg dimensions, clutch size, nestling growth and reproductive success of a dense population of WheatearsOenanthe oenanthe was studied on the island of Öland, S. Sweden during the years 1985–1987. The 1987 season was exceptionally cold and rainy, 1986 had the warmest and driest conditions, while 1985 was intermediate with respect to weather. Cold, windy and rainy weather was associated to prolonged incubation, greater intervals between first and replacement clutches, prolonged nestling growth, lower fledging condition, increased starvation and increased predation. Large clutches were laid earlier in the season and contained relatively larger eggs than small clutches. Incubation periods decreased with clutch size. Female size was positively correlated with egg size and with clutch size. The last egg laid in a clutch had a tendency to be heavier than eggs laid previously, especially in large clutches. Nestling starvation increased with brood size in 2 years.

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Zusammenfassung 1985–1987 wurden Phänologie, Siedlungsdichte, Eimaße, Gelegegröße, Jungenwachstum und Bruterfolg einer Population des Steinschmätzers auf der südschwedischen Insel Öland untersucht. 1987 waren die Lufttemperaturen besonders niedrig und die Niederschläge sehr hoch. Der Sommer 1986 wies dagegen die höchsten Temperaturen und niedrigsten Niederschläge der 3 Jahre auf. Kaltes, windiges und regnerisches Wetter war mit längerer Brütezeit, längeren Intervallen zwischen Erst- und Ersatzbruten, langsamerem Jungenwachstum, schlechterer Kondition der ausfliegenden Jungen und höheren Verlusten durch Verhungern und Beutefeinde korreliert. Die Gelegegröße nahm mit dem Legedatum ab; die größten Gelege hatten im Mittel größere Eier. Die Bebrütungszeit nahm mit der Gelegegröße ab. Größere Weibchen legten größere Eier und zeigten Tendenz, größere Gelege zu produzieren. Die zuletzt gelegten Eier waren meist die schwersten, besonders in großen Gelegen. Ausfälle durch Verhungern stiegen in 2 Jahren mit der Brutgröße.

     

The chemical modification of cysteine-69 of rat liver fatty acid-binding protein (FABP): a fluorescence approach to FABP structure and function

Summary Hepatic-FABP was labelled at cysteine-69 with the fluorescent environmentally sensitive reporter group AEDANS. The labelled protein had an emission maximum at 465 nm indicating that cysteine-69 was buried in a non-polar environment. The modified protein was still able to bind ligands such as oleic acid, oleoyl CoA and haem. The affinity of AEDANS-FABP for haem was unaltered as compared with the native protein indicating that cysteine-69 must be remote from the ligand binding site. The binding of oleic acid did not significantly perturb the fluorescence emission spectrum of the fluorescent reporter group suggesting that there are not large conformational changes in the region of cysteine-69 on fatty acid binding. The binding of stoichiometric amounts of oleoyl CoA was accompanied by a small fluorescence enhancement which suggests that fatty acyl CoAs may interact with other regions of the FABP molecule not involved in fatty acid binding.Abbreviations FABP Fatty Acid-Binding Protein - AEDANS 5-[2-(Acetyl)aminoEthyl]Aminonaphthalene-1-Sulphonic Acid - AAEDANS 5-[2-(Iodoacetyl-AminolEthyl] aminonaphthalene-1-Sulphonic Acid - DTNB 5,5Dithiobis-(2-Nitrobenzoic acid)     

Patterns of [13N]ammonium uptake and assimilation by Frankia HFPArl3

Nitrogen-starved cells of Frankia strain HFPArl3 incorporated [¹³N]-labeled ammonium into glutamine serine (glutamate, alanine, aspartate), after five-minute radioisotope exposures. High initial endogenous pools of glutamate were reduced, while total glutamine increased, during short term NH _inf4 ^sup+ incubation. Preincubation of cells in methionine sulfoximine (MSX) resulted in [¹³N]glutamine reduced by more than 80%, while [¹³N]glutamate and [¹³N]alanine levels increased. The results suggest that glutamine synthetase is the primary enzyme of ammonium assimilation, and that glutamate dehydrogenase and alanine dehydrogenase may also function in ammonium assimilation at low levels. Efflux of [¹³N]serine and lesser amounts of [¹³N]glutamine was detected from the Frankia cells. The identity of both Ser and Gln in the extracellular compartment was confirmed with gas chromatography/mass spectrometry. Serine efflux may be of significance in nitrogen transfer in Frankia.Abbreviations Pthr phosphothreonine - Aad -amino-adipate - MSX methionine sulfoximine     

Cloning and expression of the toxin B gene ofClostridium difficile

Results from our cloning studies on toxin A indicated that the gene for toxin B resided approximately 1 kb upstream of the toxin A gene. Clone pCD19, which contains the 5-end of the toxin A gene and a small open reading frame, was found to contain 1.2 kb of DNA which, when subcloned, expressed a nontoxic peptide that reacted with toxin B antibodies. The rest of the toxin B gene was located on the 6.8 kb cloned fragment of plasmid pCD19L. The two fragments overlapped 0.8 kb. Lysates containing protein expressed by the 6.8 fragment were cytotoxic and lethal, and were neutralized by toxin B antibody. The two fragments were ligated to give the complete toxin B gene. The protein expressed by the complete gene was cytotoxic and lethal, and showed complete immunological identity with toxin B. Further analysis of the expressed protein and the toxin B gene confirmed our earlier findings showing that toxin B has a molecular weight of 240,000 or greater.     

Polyamines and basic proteins stimulate activation by cAMP and catalytic activity of Mucor rouxii cAMP-dependent protein kinase

Partial activation of Mucor rouxii cAMP-dependent protein kinase by cAMP was obtained when kemptide was used as substrate, but complete activation was attained with cAMP plus protamine or histone. Full activation could not be achieved by increasing kemptide or cAMP concentration. Complete activation by cAMP could be obtained by addition of 10 microM polylysine, 10 microM lysine-rich histone or 0.5 mM spermine plus spermidine. The degree of stimulation could be up to 5-fold, depending on the amount of enzyme in the assay. The same concentrations of polycations increased 1.5-2.3-fold the Vmax of kemptide phosphorylation by the free catalytic subunits of both Mucor and bovine heart protein kinases; 10 microM polyarginine inhibited completely the activity of both enzymes.     

Seed Germination Biology of the Narrowly Endemic Species Lesquerella stonensis (Brassicaceae)

Abstract Lesquerella stonensis (Brassicaceae) is an obligate winter annual endemic to a small portion of Rutherford County in the Central Basin of Tennessee, where it grows in disturbed habitats. This species forms a persistent seed bank, and seeds remain viable in the soil for at least 6 years. Seeds are dormant at maturity in May and are dispersed as soon as they ripen. Some of the seeds produced in the current year, as well as some of those in the persistent seed bank, afterripen during late spring and summer; others do not afterripen and thus remain dormant. Seeds require actual or simulated spring/summer temperatures to come out of dormancy. Germination occurs in September and October. Fully afterripened seeds germinate over a wide range of thermoperiods (15/6–35/20°C) and to a much higher percentage in light (14 h photoperiod) than in darkness. The optimum daily thermoperiod for germination was 30/15°C. Nondormant seeds that do not germinate in autumn are induced back into dormancy (secondary dormancy) by low temperatures (e.g., 5°C) during winter, and those that are dormant do not afterripen; thus seeds cannot germinate in spring. These seed dormancy/ germination characteristics of L. stonensis do not differ from those reported for some geographically widespread, weedy species of winter annuals and thus do not help account for the narrow endemism of this species.     

In vitro stimulation and inhibition of steroid hormone release from postovulatory follicles of the tilapia,Oreochromis mossambicus

Summary Postovulatory follicles of the tilapia, Oreochromis mossambicus, were incubated with graded doses of salmon gonadotropin to identify the steroid hormones released by this tissue. In addition, the effects of either cytochalasin B or colchicine on steroid hormone release were studied. After the incubation, the tissue was examined by electron microscopy. Postovulatory follicles released testosterone and estradiol-17B in a dose-dependent manner with gonadotropin. There was no detectable release of progesterone or 17a-OH-progesterone. When stimulated with high doses of gonadotropin, the steroidogenic cells showed an increase in smooth endoplasmic reticulum, Golgi complexes, and lipid droplets. Also, microfilaments became arranged in orderly bundles and were found close to the numerous secretory vesicles and lipid droplets. Upon incubation with gonadotropin and either colchicine or cytochalasin B, the cells still appeared steroidogenic, but the filaments were not organized nor associated with vesicles or lipid droplets. Release of steroid hormone decreased significantly. Also in these tissues, vesicles were no longer numerous in the apical region of the granulosa cells, but were located primarily near smooth endoplasmic reticulum and Golgi complexes. This suggests that disruption of the cytoskeleton results in reduced steroid hormone synthesis or release.     

Proteolysis of ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of Citrus explants throughout the annual cycle and its regulation by ethylene

Leaf senescence and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) degradation in orange [ Citrus sinensis (L.) Osbeck cv. Washington Navel] explants have been investigated. Explants consisted of a segment of stem (ca 15 cm) and 5 mature leaves. In vitro RuBP carboxylase degradation was determined by culturing the explants in water for different periods of time (3 days usually) and quantifying the two RuBP carboxylase subunits in the extracts following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In vitro RuBP carboxylase degradation was estimated by autodigestion of leaf extracts and SDS-PAGE. The extent of in vivo RuBP carboxylase degradation in explants cultured under 16 h light/8 h dark photoperiod varied throughout the year and showed a cyclic behaviour correlated with the growth cycle of Citrus. The highest proteolytic activity both in vivo and in vitro was found in explants made from April to August coinciding with the maximum vegetative growth period of the tree.
Leaf senescence and abscission could be retarded significantly at any time of the year by maintaining the explants continuously in the dark. Treatment of the explants in the dark with a continuous flow of ethylene enhanced both leaf abscission and rate of RuBP carboxylase degradation, proportionally to ethylene concentration (0.1-0.6 ppm). Ethylene-induced senescence of Citrus leaf explants in the dark appears to be a convenient model system to study the regulation of the proteolytic degradation of RuBP carboxylase.     

Response of aromatic-pathway enzymes to changing physiological states of growth in suspension cultures of Nicotiana silvestris

The activity levels of enzymes of aromatic amino acid biosynthesis respond to changing physiological states of growth, as illustrated by results obtained from suspension-cultured cells of Nicotiana silvestris Speg. et Comes line ANS 1 (2N=24). The experimental system provides a foundation for interpretations about overall regulation of enzyme levels in relationship to growth physiology. Levels of activity for shikimate dehydrogenase (EC 1.1.1.25), prephenate aminotransferase and arogenate dehydrogenase were followed throughout a growth cycle obtained by a conventional subculture protocol. Enzyme date were also obtained from cell cultures maintained in continuous exponential growth for greater than 10 generations (EE cells). Both shikimate dehydrogenase and prephenate aminotransferase exhibited elevated stationary-phase levels of enzyme, much of which was carried over into a subsequent subculture. At least 4 generations of exponential growth were required before diminution of the latter two enzymes to the levels characteristic of truly exponential-phase growth (EE cells) occurred. This is reminiscent of the overall behavior of 3-deoxy-D- arabino -heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15), specifically attributed to the properties of the cytosolic isozyme species (DAHP synthase-Co). Elevation of arogenate dehydrogenase also occurred in stationary-phase cells, but diminished rapidly during lag phase to reach the level characteristic of EE cells.