Changes in photosynthetic rate and pigment content of blue-green algae in Lake Mendota.

Blue-green algal blooms were present in Lake Mendota (Dane County, Wis.) from June to November 1976. Concentrations of total algal biomass and of particular algal species were monitored and compared with the pigment contents (chlorophyll a and phycocyanin) and photosynthetic rate of the algal populations. The specific photosynthetic rate (micrograms of C fixed per microgram of chlorophyll a per hour) was a good measure of the physiological state of the algae because this quantity increased just before each population increase and decreased before algal densities diminished. Since the quantity of light in the epilimnion which was available for photosynthesis by algal cells decreased in summer when the high algal densities attenuated incoming radiation, we investigated the possibility that the organisms would utilize lower light intensities more efficiently by increasing their pigment contents. Although some evidence of enhanced utilization of low light levels was found in the period from July to October, this result was not due to increasing chlorophyll and phycocyanin contents. There was a decrease in the phycocyanin content of the algae during this period, perhaps related to the availability of inorganic nitrogen.     

Structure, Growth, and Decomposition of Laminated Algal-Bacterial Mats in Alkaline Hot Springs

Laminated mats of unique character in siliceous alkaline hot springs of Yellowstone Park are formed predominantly by two organisms, a unicellular blue-green alga, Synechococcus lividus, and a filamentous, gliding, photosynthetic bacterium, Chloroflexus aurantiacus. The mats can be divided approximately into two major zones: an upper, aerobic zone in which sufficient light penetrates for net photosynthesis, and a lower, anaerobic zone, where photosynthesis does not occur and decomposition is the dominant process. Growth of the mat was followed by marking the mat surface with silicon carbide particles. The motile Chloroflexus migrates vertically at night, due to positive aerotaxis, responding to reduced O₂ levels induced by dark respiration. The growth rates of mats were estimated at about 50 μm/day. Observations of a single mat at Octopus Spring showed that despite the rapid growth rate, the thickness of the mat remained essentially constant, and silicon carbide layers placed on the surface gradually moved to the bottom of the mat, showing that decomposition was taking place. There was a rapid initial rate of decomposition, with an apparent half-time of about 1 month, followed by a slower period of decomposition with a half-time of about 12 months. Within a year, complete decomposition of a mat of about 2-cm thickness can occur. Also, the region in which decomposition occurs is strictly anaerobic, showing that complete decomposition of organic matter from these organisms can occur in the absence of O₂.     

The role of transferrin and citrate in cellular uptake of aluminium

Summary The ability of human erythroleukaemia K562 cells to take up aluminium from Al-transferrin and Al-citrate has been examined. Uptake from Al-transferrin was dose-dependent over the range 68–544 ng/ml of aluminium, and increased over a 12-day period. In contrast, uptake from Al-citrate was low even at an aluminium concentration of 6800 ng/ml and did not increase over time. Neither form of aluminium greatly affected cell growth. It is concluded that Al-transferrin, rather than Al-citrate, is the physiologically relevant form of this metal with respect to cellular uptake, but that any metabolic abnormalities induced by aluminium do not affect proliferation of this cell line.     

Genetic Analysis of the Additional Sex Combs Locus of Drosophila Melanogaster

Additional sex combs (Asx) is a member of the Polycomb group of genes, which are thought to be required for maintenance of chromatin structure. To better understand the function of Asx, we have isolated nine new alleles, each of which acts like a gain of function mutation. Asx is required for normal determination of segment identity. AsxP1 shows an unusual phenotype in that anterior and posterior homeotic transformations are seen in the same individuals, suggesting that AsxP1 might upset chromatin structure in a way that makes both activation and repression of homeotic genes more difficult. Analysis of embryonic and adult phenotypes of Asx alleles suggests that Asx is required zygotically for determination of segment number and polarity. The expression pattern of even-skipped is altered in Asx mutant embryos, suggesting that Asx is required for normal expression of this gene. We have transposon-tagged the Asx gene, and can thus begin molecular analysis of its function.     

Intracellular alkalinization leads to Ca2+ mobilization from agonist-sensitive pools in bovine aortic endothelial cells

Receptor-stimulated phosphoinositide turnover leads to activation of Na+/H+ exchange and subsequent intracellular alkalinization. To probe the effect of increased intracellular pH (pHi) on Ca2+ homeostasis in cultured bovine aortic endothelial cells (BAEC), we studied the effect of weak bases, ammonium chloride (NH4Cl) and methylamine (agents which increase pHi by direct passive diffusion), on resting and ATP (purinergic receptor agonist)-induced Ca2+ fluxes. Changes in cytosolic free Ca2+ ([Ca2+]i) or pHi were monitored in BAEC monolayers using the fluorescent dyes, fura-2 or 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, respectively. NH4Cl-induced, dose-dependent (5-20 mM) increases in [Ca2+]i (maximum change = 195 +/- 26 nM) which were temporally similar to the NH4Cl-induced pHi increases. Methylamine (20 mM) induced a more sustained pHi increase and also stimulated a prolonged [Ca2+]i increase. When BAEC were bathed in HCO3- buffer, removal of extracellular CO2/bicarbonate caused pHi to increase and also induced [Ca2+]i to increase transiently. Extracellular Ca2+ removal did not abolish the rapid NH4Cl-induced rise in [Ca2+]i, although the response was blunted and more transient. NH4Cl addition to BAEC cultures resulted in an increase in 45Ca efflux and decrease in total cell 45Ca content. BAEC treatment with ATP (100 microM) to deplete inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ pools completely blocked the NH4Cl (20 mM)-induced rise in [Ca2+]i. Likewise, prior NH4Cl addition partially inhibited ATP-induced increases in [Ca2+]i, as well as slowed the frequency of repetitive [Ca2+]i spikes in single endothelial cells due to agonist. NH4Cl augmented the rate of [Ca2+]i increase that occurs in response to the depletion of agonist-sensitive intracellular Ca2+ pools. However, the internal Ca2+ store remained depleted during the continued presence of NH4Cl, as indicated by a decreased [Ca2+]i response to ATP in Ca2(+)-free medium. Finally, NH4Cl exerted these actions without affecting basal or ATP-stimulated IP3 formation. These observations provide direct evidence that increased pHi leads to Ca2+ mobilization from an agonist-sensitive pool and impairs Ca2+ pool(s) refilling mechanisms without altering cellular IP3 levels.     

The effects of light quality on the growth of phototrophic bacteria in lakes

The effects of light quality (color) on the ¹⁴CO₂ fixation rates of natural population of photosynthetic sulfur bacteria were tested. The phototrophic bacteria were collected from the sulfide containing waters of 3 stratified lakes. The populations sampled survive in environments where light intensities are very low. Not only are the light intensities low but, due to the light filtering characteristics of the lake water, the light is of specific color. It was determined that the spectral properties of the three lakes differed, hence the quality of light reaching the phototrophic bacteria in each lake differed. It was also observed that only green sulfur bacteria were present in the study lake which transmits mainly red light and both purple and green sulfur bacteria were present in the two study lakes which transmit predominantly green light. Enrichment cultures were set up with phototrophic bacteria from two of the lakes serving as the inocula. Enrichment culture studies and photosynthetic responses of the natural populations indicate that light quality is a major factor in determining the composition of phototrophic bacterial population in some lakes.Non-Common Abbreviations Bchl Bacteriochlorophyll - DPM Disintegrations per minute     

Quantitative in situ hybridization reveals extent of sequence homology between related DNA sequences in Drosophila melanogaster

Cloned DNA from the larval serum protein one (LSP-1) genes was hybridized to polytene chromosomes of D. melanogaster. The ratio of grains deposited over any two of the three LSP-1 genes with any one LSP-1 subunit probe was constant. Varying the gene dose of any one LSP-1 subunit relative to the others by up to six fold gave a linear relationship of grain ratios to gene ratios. We show that these constant ratios closely reflect the extent of sequence homology between the genes as determined by heteroduplex mapping (Smith et al., 1981) and thermal denaturation studies. The results obtained demonstrate that the LSP-1 subunit genes are present in equal copies in the genome.     

Effect of Temperature on Blue-Green Algae (Cyanobacteria) in Lake Mendota

The temperature optimum for photosynthesis of natural populations of blue-green algae (cyanobacteria) from Lake Mendota was determined during the period of June to November 1976. In the spring, when temperatures ranged from 0 to 20°C, there were insignificant amounts of blue-green algae in the lake (less than 1% of the biomass). During the summer and fall, when the dominant phytoplankton was blue-green algae, the optimum temperature for photosynthesis was usually between 20 and 30°C, whereas the environmental temperatures during this period ranged from 24°C in August to 12°C in November. In general, the optimum temperature for photosynthesis was higher than the environmental temperature. More importantly, significant photosynthesis also occurred at low temperature in these samples, which suggests that the low temperature alone is not responsible for the absence of blue-green algae in Lake Mendota during the spring. Temperature optima for growth and photosynthesis of laboratory cultures of the three dominant blue-green algae in Lake Mendota were determined. The responses of the two parameters to changes in temperature were similar; thus, photosynthesis appears to be a valid index of growth. However, there was little photosynthesis by laboratory cultures at low temperatures, in contrast to the natural samples. Evidence for an interaction between temperature and low light intensities in their effect on photosynthesis of natural samples is presented.     

Environmental factors influencing the rate of hydrocarbon oxidation in temperate lakes.

Rates of hydrocarbon biodegradation were estimated by following oxygen uptake during mineral oil oxidation or oxidation of [1-14C]hexadecane to 14CO2, when these substrates were added to natural water samples from Wisconsin lakes. A lag phase preceded hydrocarbon oxidation, the length of which depended on population density or on factors influencing growth rate and on the presence of nonhydrocarbon organic compounds. Hydrocarbon oxidation was coincident with growth and presumably represented the development of indigenous hydrocarbon-degrading microorganisms in response to hydrocarbon additions. In detailed studies in Lake Mendota, it was found that, despite the continued presence of hydrocarbon-degrading microorganisms in water samples, seasonal variations in the rates of mineral oil and hexadecane oxidation occurred which correlated with seasonal changes in temperature and dissolved inorganic nitrogen and phosphorus. The temperature optimum for oil biodegradation remained at 20 to 25 C throughout the year, so that temperature was the main limiting factor during winter, spring, and fall. During summer, when temperatures were optimal, nutrient deficiencies limited oil biodegradation, and higher rates could be obtained by addition of nitrogen and phosphorus. The rates of hydrocarbon biodegradation were thus high only for about 1 month of the ice-free period, when temperature and nutrient supply were optimal. Nutrient limitation of oil biodegradation was also demonstrated in 25 nutrient-poor lakes of northern Wisconsin, although in almost every case oil-degrading bacteria were detected. Knowledge of temperature and nutrient limitations thus will help in predicting the fate of hydrocarbon pollutants in freshwater.     

Protein measurements in the early prenatal diagnosis of spina bifida.

Measurement of beta-lipoprotein concentration in amniotic fluid is introduced as a new parameter for the early prenatal diagnosis of spina bifida. It was successful in 15 cases of spinal bifida, but failed in 5 cases of open spina bifida and 2 cases of closed spina bifida. All assays were performed before the end of the second trimester and most between 15 and 20 weeks of pregnancy. beta-lipoprotein was compared with alpha-fetoprotein and alpha2-macroglobulin in its effectiveness in diagnosing spina bifida at an early enough date to allow a termination of pregnancy.