Active formation of 'chaos terrain' over shallow subsurface water on Europa.

Europa, the innermost icy satellite of Jupiter, has a tortured young surface and sustains a liquid water ocean below an ice shell of highly debated thickness. Quasi-circular areas of ice disruption called chaos terrains are unique to Europa, and both their formation and the ice-shell thickness depend on Europa's thermal state. No model so far has been able to explain why features such as Conamara Chaos stand above surrounding terrain and contain matrix domes. Melt-through of a thin (few-kilometre) shell is thermodynamically improbable and cannot raise the ice. The buoyancy of material rising as either plumes of warm, pure ice called diapirs or convective cells in a thick (>10 kilometres) shell is insufficient to produce the observed chaos heights, and no single plume can create matrix domes. Here we report an analysis of archival data from Europa, guided by processes observed within Earth's subglacial volcanoes and ice shelves. The data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres. Our results suggest that ice-water interactions and freeze-out give rise to the diverse morphologies and topography of chaos terrains. The sunken topography of Thera Macula indicates that Europa is actively resurfacing over a lens comparable in volume to the Great Lakes in North America.

Effect of light intensity upon lipid composition ofNitzschia closterium (Cylindrotheca fusiformis).

Total fatty acid, total sterol, fatty acids of specific lipid classes, and unsaturated fatty acids produced inNitzschia closterium were compared qualitatively and quantitatively as a function of changes in light intensity. Increased levels of total fatty acids were observed in cells grown at high light intensity when compared to cells grown at low light intensity. However, the percentage of unsaturated fatty acid decreased under high light conditions. Fatty acid analysis of triglyceride and 1,3 diglyceride fractions indicated an increase in levels of fatty acid at high light intensity when compared to low light intensity, while levels of polar lipid fatty acids increased at low light intensity. These analyses can be taken to indicate an increase in triglyceride and diglyceride at high light and a decrease in polar lipid at high light. Levels of free fatty acids did not differ significantly with light intensity. The levels of total sterol also were unaffected by changes in light intensity. However, levels of sterol isolated as free sterol and sterol associated in a yet unknown manner in the polar lipid fraction varied with changes in light intensity. Levels of polar lipid sterol increased at high light intensity compared to low light intensity, while the opposite was true for free sterol. The greatest percentage of total sterol was found in the polar lipid class regardless of light intensity.

Effects of cyclopropenoid fatty acids on fungal growth and lipid composition.

Cyclopropenoid fatty acids (CPE) isolated from Sterculia foetida oil by urea clathration and reverse phase high performance liquid chromatography (HPLC) were introduced into fungal cultures. Stearate levels in phospholipids and triacylglycerols from Ustilago maydis sporidia rose considerably in response to 30 microM CPE. In addition, CPE themselves were incorporated into glycerolipid fractions. Sterol composition was unaffected. Changes in lipid composition were accompanied by inhibition of dry weight accumulation and sporidial number. Treated sporidia showed irregular wall deposition and a branched morphology. Oleate alleviated CPE effects on growth and morphology. Hyphal extension by Rhizoctonia solani was inhibited somewhat by 30 microM sterculate, while Fusarium oxysporum showed no appreciable response. Although CPE appeared to inhibit fatty acid desaturation by F. oxysporum, gross increases in the proportion of stearate were limited to the triacylglycerol fraction during 30 microM treatments. The possibility that the CPE synthesized by plants serve as antifungal agents is discussed.

Metabolism of 2,4-3H-14alpha-methyl-5alpha-ergost-8-enol and 2,4-3H-5alpha-ergosta-8,14-dienol in Ochromonas malhamensis.

Tritium-labeled 14alpha-methyl-5alpha-ergost-8-enol and 5alpha-ergosta-8,14-dienol were converted to brassicasterol and poriferasterol in Ochromonas malhamensis. This indicates that the organism can rearrange these sterol structures so that they contain the naturally occurring 5(6) double bond, and suggests that O. malhamensis is able to introduce a 24(28) double bond into a nine-carbon saturated side chain which is alkylated to produce a C-29 sterol.

Use of an improved internal-standard method in the quantitative sterol analyses of phytoplankton and oysters.

Most work reporting the sterol composition of living organisms has not been done quantitatively, although good quantitative data are available for fatty acids and many other cellular components using an internal-standard method that compensates for errors during gas chromatographic analysis. In this paper, we report on the use of 7-stigmastenyl acetate as an internal standard for sterol analysis in two species of phytoplankton and oysters produced with two different diets. This internal-standard method provides an internal standard for this entire process of analysis, not just the gas chromatographic analysis. When analyzing 50-microgram samples of cholesterol acetate after hydrolysis and acetylation, about 30% of the sample was lost, resulting in a 30% error using the older external-standard method. Using the internal-standard method, the analysis error was less than 2%. Losses of sterol during analysis apparently are greater with plant and animal samples than with pure sterol standards. This internal-standard method was shown to be extremely useful, especially for samples with less than 500 micrograms of sterol. Finally, the standard error in sterol analysis is much lower when the internal-standard method is used, allowing statistical distinctions that are not possible otherwise. Use of 7-stigmastenyl acetate as an internal standard offers several advantages over the use of cholestane.

Sterol composition during the life cycle of the soybean and the squash.

Sterol analyses were performed on soybeans and squash at intervals throughout the life cycle from seed to mature seed-bearing plant. The sterols of the soybean (24-methyl-cholesterol, stigmasterol and sitosterol) increased in quantity from that in the seed in each stage examined except for a pause or decrease prior to flowering and a decrease at senescence. Individual sterols remained in the same proportion to each other and changes in content were similar in roots and shoots. In the squash a much more complicated sterol mixture was found, composed primarily of C-7 unsaturated sterols characteristic of Cucurbitaceae. Sterol composition also increased during the life cycle except for approximately two wk in the preflowering to early flowering period. The data indicate low synthesis or high turnover of sterols (or both) in these plants in the weeks at or just prior to flowering.

Techniques for the isolation and identification of steroids in insects and algae.

Analytical techniques, methods and instrumentation employed for the extraction, isolation separation, purification and identification of steroids from algae and insects are presented. The techniques include adsorption and argentation column chromatography and counter-current distribution for separating the individual steroids, and thin layer chromatography and gas liquid chromatography for monitoring the purification process. Double bond, steric and alkyl substituent separation factors and relative retention times are reported for a large number of sterols on 4 different column systems. Their use permits the tentative structural assignment of sterols. Ultraviolet, infrared, nuclear magnetic resonance (NMR) and mass spectral analyses are discussed in light of their significance in the isolation and identification of steroids from insects and algae. Numerous examples are presented, including the use of 220 MHz NMR spectrometry, which permits the differentiation and characterization of C-24 epimetric sterols and allows for a semiquantitative estimate of the 24α- and 24ß-epimers present in a mixture.

Sterols of eustigmatophytes.

The oyster cannot synthesize sterols from smaller molecules but must obtain them from its diet, which consists of detritus and small organisms, i.e., mostly single-celled algae. Algae differ widely in their effectiveness as oyster food. Small (< 5 microns) algae which are abundant in sterols and polyunsaturated fatty acids appear to be most effective. Recent studies have shown the occurrence of cholesterol in strains of the unicellular algae Tetraselmis, Chaetoceros and Skeletonema, sometimes in large quantities. In the study reported here, six isolates of a recently constructed algal class, the Eustigmatophyceae, have been examined for sterols and fatty acids by gas chromatography and gas chromatography/mass spectrometry. All strains were shown to contain cholesterol as the principal sterol. Two isolates contained large amounts of total sterol (400-1000 fg/cell), and one (Sticho 0-18) also contained large amounts of eicosapentaenoic acid (20:5n-3). These biochemical characteristics are desirable in a potential food source for oysters.

Science potential from a Europa lander.

The prospect of a future soft landing on the surface of Europa is enticing, as it would create science opportunities that could not be achieved through flyby or orbital remote sensing, with direct relevance to Europa's potential habitability. Here, we summarize the science of a Europa lander concept, as developed by our NASA-commissioned Science Definition Team. The science concept concentrates on observations that can best be achieved by in situ examination of Europa from its surface. We discuss the suggested science objectives and investigations for a Europa lander mission, along with a model planning payload of instruments that could address these objectives. The highest priority is active sampling of Europa's non-ice material from at least two different depths (0.5-2 cm and 5-10 cm) to understand its detailed composition and chemistry and the specific nature of salts, any organic materials, and other contaminants. A secondary focus is geophysical prospecting of Europa, through seismology and magnetometry, to probe the satellite's ice shell and ocean. Finally, the surface geology can be characterized in situ at a human scale. A Europa lander could take advantage of the complex radiation environment of the satellite, landing where modeling suggests that radiation is about an order of magnitude less intense than in other regions. However, to choose a landing site that is safe and would yield the maximum science return, thorough reconnaissance of Europa would be required prior to selecting a scientifically optimized landing site.

THE EFFECT OF CULTURE CONDITIONS ON THE HYDROCARBON CONTENT OF CHLORELLA VULGARIS(1) (2).

Cultures of Chlorella vulgaris were grown aulo-trophically under fluorescent light and heterotrophically on glucose and inorganic salts. Hydrocarbons were extracted and analyzed by gas-liquid chromatography, molecular sieve separations, and silicic acid-AgNO3 chromatography. Chlorella vulgaris grown under both culture conditions contained a series of saturated n-paraffins ranging from 17 to 36 carbon atoms in length. This is in contrast to reports in the early literature which indicated that the hydrocarbon fraction of algae was composed of only 1 or 2 specific hydrocarbons. Only under heterotrophic conditions, however, did C. vulgaris produce 1-penta-cosene and 1-heptacosene as the primary components of the hydrocarbon mixture. Other Chlorella species were examined, but only C. vulgaris produced significant quantities of these compounds.

Inhibition of Sterol Biosynthesis in Chlorella sorokiniana by Triparanol.

When Chlorella sorokiniana was cultured in the presence of 1 mg/1 triparanol succinate, there was a 42% reduction in total sterol concentration. Algal biomass was reduced by approximately the same amount. In addition to the cycloartenol, cyclolaudenol, 24-methyl-pollinastanol, ergosta-5, 7-dien-3beta-ol, and ergosterol that occur in control culture, pollinastanol, 14alpha-methyl-5alpha-ergost-8-en-3beta-ol, 5alpha-ergosta-8, 14, 22-trien-3beta-ol, 5alpha-ergosta-8(14), 22-dien-3beta-ol, 5alpha-ergosta-8(9), 22-dien-3beta-ol, 5alpha-ergosta-8, 14-dien-3beta-ol, 5alpha-ergost-8(9)-3n-3beta-ol, 5alpha-ergost-8(14)-en-3beta-ol, 5alpha-ergosta-7, 22-dien-3beta-ol, and 5alpha-ergost-7-en-3beta-ol were isolated and identified from triparanol succinate-treated cells. A biosynthetic pathway for sterol biosynthesis in this organism is postulated based on all the sterols that were isolated and identified in triparanol-treated cultures of C. sorokiniana. Cyclolaudenol appears to be the product of the first alkylation at C-24 in this organism rather than the more common 24-methylene cycloartanol. Since 24-methylene sterols are needed for the second alkylation reaction, this would explain the absence of C-29 sterols in C. sorokiniana. Four of the sterols identified in C. sorokiniana are reported for the first time in a living organism. They are: 24-methyl pollinastanol, 5alpha-ergosta-8, 14, 22-trien-3beta-ol, 5alpha-ergosta-8(14), 22-dien-3beta-ol and 5alpha-ergost-8(14)-en-3beta-ol.

Effects of cation levels of the nutrient medium on the biochemistry of chlorella: I. Concentration series.

The effects of variations in nutrient cation levels on the growth and biochemistry of Chlorella were investigated. This study involved concentration-series experiments in which the levels of Mg(2+), K(+), and Ca(2+) varied from deficiency to toxicity levels for growth. The nutrient sufficiency concentrations of Mg(2+) and K(+) were 0.08 and 0.10 meq/1, respectively. Deficiencies of Mg(2+) or K(+) reduced the growth rate, as well as cellular total nitrogen and unsaturated fatty acid levels. K(+) deficiency increased total lipid levels, while total fatty acids were unaffected. Increasing Mg(2+) or K(+) concentrations in the nutrient media were accompanied by corresponding increases in growth rate and certain biochemical fractions. Calcium was without effect except at a toxicity level. Cellular sufficiency concentrations for Mg(2+) and K(+) were 0.3 and 1.2% of the dry weight, respectively.

Effects of Cation Levels of the Nutrient Medium on the Biochemistry of Chlorella: II. Factorial Experiment.

A factorial experiment was designed to study the effects of Mg(2+), K(+), and Na(+) on the growth and biochemistry of Chlorella sorokiniana. Raising Mg(2+) or K(+) concentration in the nutrient medium increased growth rates as well as total N levels and Mg(2+) and K(+) accumulation by the cells. The total N effect was Mg(2+)-dependent-if Mg(2+) was below a certain level in the medium-increasing the K(+) concentration did not raise the total N level of cells. Low nutrient levels of K(+) decreased the levels of unsaturated fatty acids (especially 18:1 and 18:3), while increasing the levels of palmitic acid (16:0), total fatty acids, and total lipid. Increasing nutrient K(+) concentrations were accompanied by increases in levels of some unsaturated fatty acids, with a concomitant reduction in 16:0, total fatty acids and total lipid. Low Mg(2+) levels in the nutrient medium reduced the cellular levels of palmitic acid, total fatty acids, total lipid, and certain unsaturated fatty acids (though this last effect also depended on the nutrient level of K(+)). These relationships indicate that Mg(2+) may be important in the initial steps of fatty acid synthesis, whereas K(+) may be necessary for the formation of certain unsaturated fatty acids. Variations in Na(+) concentration did not have any significant effect on the growth and biochemistry of C. sorokiniana.

Triparanol Inhibition of Sterol Biosynthesis in Chlorella ellipsoidea.

The sterol composition of C. ellipsoidea was markedly changed when this alga was grown in the presence of 1 mug/g triparanol. Triparanol appears to inhibit the removal of 14alpha-methyl group, the second alkylation at C-24, Delta(7)-reductase, and Delta(8) --> Delta(7)-isomerase. The effect of triparanol in Chlorella is much more diversified than the specific effect originally assigned to it in animals.