Photosynthetic productivity of conical helical tubular photobioreactor incorporating Chlorella sorokiniana under field conditions.

The photosynthetic performance of a conical, helical tubular photobioreactor (HTP) incorporating Chlorella sorokiniana was investigated under conditions of high temperature and light intensity during midsummer in an outdoor environment. Although the culture medium temperature exceeded 40 degrees C for approximately 5 h each day, peaking at 47.5 degrees C under sunny conditions, a photosynthetic productivity of 30.0 g x m(-2) (installation area) x day(-1) and a photosynthetic efficiency of 8.66% [photosynthetically active radiation (PAR), 400-700 nm] were achieved. A maximum photosynthetic productivity of 33.2 g x m(-2) x day(-1) was achieved on a sunny day, when solar energy input was also maximal (11.5 MJ x m(-2) x day(-1) [PAR]). On the other hand, a maximum photosynthetic efficiency of 9.54% was obtained on a day that was rainy in the morning and cloudy in the afternoon, and there was relatively little solar energy input. The average daily photosynthetic efficiency over the two culture periods (August 4 to 7 and August 10 to 13, 1999) was 7.25%. Thus, a high level of photosynthetic performance was achieved in the conical HTP incorporating Chlorella sorokiniana despite the fact that culture medium temperature was not controlled. The use of Chlorella sorokiniana in the conical HTP should be a good choice to produce microalgal biomass during the summer under field conditions.     

Oxygen-tolerant Strain of Chlorella sorokiniana

An oxygen-tolerant strain (OTS) of Chlorella sorokiniana was isolated by growing and continuously subculturing the oxygen-sensitive strain (OSS) in growth medium bubbled continuously with 95% O(2)-5% CO(2). Under these conditions, 6 to 8 hr were required before the OSS began to grow. The growth rates of the OTS and the OSS were the same when grown in an atmosphere of air-5% CO(2), and the growth rate of the OTS was the same when aerated with 95% O(2)-5% CO(2) and air-5% CO(2). The adaptive process was irreversible since serial transfers of the OTS grown with air-5% CO(2) did not alter the ability of the OTS to grow with 95% O(2)-5% CO(2). Inasmuch as photosynthesis in the OTS and the OSS was inhibited to a similar extent by oxygen and the adaptive process occurred heterotrophically in the absence of photosynthesis, it was concluded that the adaptive process was independent of photosynthesis. Morphological differences between the OTS and the OSS are presented and discussed with respect to the adaptive process.     

Oxygen-tolerant Strain of Chlorella sorokiniana

[This corrects the article on p. 140 in vol. 17.].     

Operation Everest II: neuromuscular performance under conditions of extreme simulated altitude

The force output of the ankle dorsiflexors was studied during a 40-day simulated ascent of Mt. Everest in a hypobaric chamber; both electrically activated and maximal voluntary contractions (MVCs) were employed. The purpose of this study was to establish whether, under conditions of progressive chronic hypoxia, there was a decrease in muscle force output and/or increased fatigability. We also attempted to identify the main site of any failure, i.e., central nervous system, neuromuscular junction, or muscle fiber. Muscle twitch torque (Pt), tetanic torque (Po), MVC torque, and evoked muscle compound action potential (M wave) were monitored during 205-s exercise periods in five subjects at three simulated altitudes (760, 335, and 282 Torr). All three types of torque measurement were well preserved at the three altitudes. In some subjects, the responses to stimuli interpolated during repeated MVCs provided evidence of "central" fatigue at altitude. In addition, the rate of fatigue during 20-Hz electrical stimulation was greater (P less than 0.01) at altitude and there was increased fatigability of the twitch (P less than 0.025); however, the M wave amplitude was maintained. We conclude that central motor drive becomes more precarious at altitude and is associated with increased muscle fatigue at low excitation frequencies; the latter is the result, in part, of chronic hypoxia and occurs in the muscle fiber interior because no impairment in neuromuscular transmission could be demonstrated.     

Ozone Inhibition of Photosynthesis in Chlorella sorokiniana

Exposure of Chlorella sorokiniana (07-11-05) to ozone inhibits photosynthesis. In this study, the effects of ozone on O₂ evolution and fluorescence yields are used to characterize this inhibition. At an ozone dose of about 3 micromoles delivered to 2 × 10⁹ cells, the photosynthetic rate of the cells is inhibited 50%, as indicated by a decrease in bicarbonate-stimulated O₂ evolution (control rate, 1.4 ± 0.3 × 10⁻¹⁵ moles per cell per minute).     

Tris-induced K+-efflux from Chlorella sorokiniana

Tris induces K⁺ leakage from Chlorella sorokiniana under conditions of high pH and low osmolarity, in the absence of external K⁺. Using a cation specific electrode, two phases of K⁺ efflux were observed, an initial exponential leakage rate (0–30 min) and a steady-state leakage rate (30–200 min). The initial exponential efflux of K⁺ was inhibited by 0.6 M mannitol or 10 mM CaCl₂ and did not obey Michaelis-Menten kinetics with respect to Tris concentration. The steady-state efflux was not inhibited by mannitol, CO, or N₂, required only 3 mM CaCl₂ for inhibition, and obeyed Michaelis-Menten kinetics with an apparent half-saturation constant of 6 mM.     

Antioxidants from carbon dioxide fixing Chlorella sorokiniana

Chlorella sorokiniana H-84, which has toleranceto high temperatures and high concentrations ofCO₂, has been isolated from a hot spring inJapan. Large-scale culturing of C. sorokinianawas carried out in air containing 10% CO₂.Analysis of the biomass shows that protein, carbohydrate and lipids comprised 68.5, 11.9 and10.0% of dry matter, respectively. The totalcarotenoids comprised 0.69% dry matter. The luteinand -carotene contents were 4300 and 600 gg^-1 dry weight, respectively. The-tocopherol content was 112 g g^-1 dry weight. These carotenoids and -tocopherolare known to possess radical scavenging activity.Two fractions with radical scavenging activity wereisolated from the aqueous extract of C.sorokiniana H-84. The extract showed several singlepeaks by reversed phase HPLC analysis and two of themhad molecular weights of 710 and 1286, respectively.     

Growth of Chlorella sorokiniana at Hyperbaric Oxygen Pressures

The growth rate of Chlorella sorokiniana decreased in a linear fashion as the partial pressure of oxygen was increased from 711 to 1,478 mm of Hg. Under two atmospheres of oxygen pressure, growth ceased after 10 to 12 hr. This cessation of growth was not due to any permanent injury, as growth resumed when oxygen partial pressure was reduced to ambient levels. The inhibition occurred under both autotrophic and heterotrophic growth conditions and was not accompanied by an increase in cell size. The results indicated that the tolerance of Chlorella cells to elevated oxygen pressures was not an absolute immunity, and that inhibition of growth at very high oxygen pressures cannot be accounted for by an inhibition of photosynthesis alone.     

Proteins under extreme physical conditions

Life on earth is ubiquitous within the limits from -5 to 110 degrees C for temperature, 0.1 to 120 MPa for hydrostatic pressure, 1.0 to 0.6 for water activity and pH 1 to 12. In general, mutative adaptation of proteins to changing environmental conditions tends to maintain 'corresponding states' regarding overall topology, flexibility and hydration. Due to the minute changes in the free energy of stabilization responsible for enhanced stability, nature provides a wide variety of different adaptative strategies. In the case of thermophilic proteins, improved packing densities are crucial. In halophilic proteins, decreased hydrophobicity and clustered surface charges serve to increase water and salt binding required for solubilization at high salt concentration. In the case of barophiles, high-pressure adaptation is expected to be less important than adaptation to low temperatures governing the deep sea. Nothing is known with respect to the mechanisms underlying psychrophilic and acidophilic/alkalophilic adaptation.     

Ozone-induced Loss of Intracellular Potassium Ion from Chlorella sorokiniana

The unicellular algae Chlorella sorokiniana was used as a model system to investigate the interaction of ozone with plant cell membranes. Ozone induces K⁺ leakage from Chlorella sorokiniana similar to the electrolytic loss observed from many higher plants under stressful conditions. The kinetics of this leakage indicate that ozone initially interacts reversibly (within sec) with sites on membranes allowing a passive efflux of K⁺. This efflux ceases within minutes after the ozone stress is removed. This return to normal efflux is very temperature dependent. High intracellular osmolarity seems to be an important criterion of susceptibility to ozone injury in this model system, since rates of ozone-induced K⁺ leakage are less when the external osmotic potential is decreased by suspension of the cells in mannitol. Cell interaction with ozone is further complicated by a saturating-type dependence of the K⁺ efflux upon ozone concentration within the medium.     

Characterization of Nitrate Reductase Deficient Mutants of Chlorella sorokiniana

After x-ray irradiation, 13 mutants of Chlorella sorokiniana incapable of using NO₃⁻ as N source were isolated using a pinpoint method. Using immunoprecipitation and Western blot assays, no nitrate reductase was found in five strains while in eight mutants the enzyme was detected. The latter strains contained different patterns of nitrate reductase partial reactions. All isolates were of the nia-type as indicated by the inducibility of purine hydroxylase I and by complementation of nitrate reductase activity in the Neurospora crassa mutant Nit-1. A restoration of NADP-nitrate reductase in Nit-1 was also obtained with NH₄⁺-grown cells indicating that Mo-cofactor is constitutive in Chlorella. Complementation experiments among the Chlorella mutants resulted in restoration of NADH-nitrate reductase activity. The characteristics of some of the Chlorella mutants are discussed in view of an improper orientation of Mo-cofactor in the residual nitrate reductase protein.     

Biofertilizing Effect of Chlorella sorokiniana Suspensions on Wheat Growth

Journal of Plant Growth Regulation - The potential of microalgae as a biofertilizer in agriculture is increasingly recognized. We studied the effect of applications of Chlorella on growth of wheat...     

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-3β-ol, and ergosterol that occur in control culture, pollinastanol, 14α-methyl-5α-ergost-8-en-3β-ol, 5α-ergosta-8, 14, 22-trien-3β-ol, 5α-ergosta-8(14), 22-dien-3β-ol, 5α-ergosta-8(9), 22-dien-3β-ol, 5α-ergosta-8, 14-dien-3β-ol, 5α-ergost-8(9)-3n-3β-ol, 5α-ergost-8(14)-en-3β-ol, 5α-ergosta-7, 22-dien-3β-ol, and 5α-ergost-7-en-3β-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, 5α-ergosta-8, 14, 22-trien-3β-ol, 5α-ergosta-8(14), 22-dien-3β-ol and 5α-ergost-8(14)-en-3β-ol.     

Penetration of Mannitol into the Intracellular Space of Chlorella sorokiniana

It was found that in the alga, Chlorella sorokiniana, mannitol penetrated the plasmalemma (normally thought to be impermeable to mannitol) into the intracellular space. The rate of penetration is exponential and relatively slow, having a half-time of 6 to 12 minutes and requiring over 60 minutes for complete penetration. This penetration was demonstrated both by the Millipore filtration of cells incubated with ¹⁴C-mannitol and by centrifugation of the cells through a silicon oil layer after incubation with tritiated water and ¹⁴C-mannitol. Further, mannitol caused an inhibition of both autotrophic (on CO₂) and heterotrophic (on glucose) growth. A low rate of mannitol metabolism was demonstrated, although this rate could not support heterotrophic growth.     

Crenarchaeal biofilm formation under extreme conditions

Background

Biofilm formation has been studied in much detail for a variety of bacterial species, as it plays a major role in the pathogenicity of bacteria. However, only limited information is available for the development of archaeal communities that are frequently found in many natural environments.

Methodology

We have analyzed biofilm formation in three closely related hyperthermophilic crenarchaeotes: Sulfolobus acidocaldarius, S. solfataricus and S. tokodaii. We established a microtitre plate assay adapted to high temperatures to determine how pH and temperature influence biofilm formation in these organisms. Biofilm analysis by confocal laser scanning microscopy demonstrated that the three strains form very different communities ranging from simple carpet-like structures in S. solfataricus to high density tower-like structures in S. acidocaldarius in static systems. Lectin staining indicated that all three strains produced extracellular polysaccharides containing glucose, galactose, mannose and N-acetylglucosamine once biofilm formation was initiated. While flagella mutants had no phenotype in two days old static biofilms of S. solfataricus, a UV-induced pili deletion mutant showed decreased attachment of cells.

Conclusion

The study gives first insights into formation and development of crenarchaeal biofilms in extreme environments.     

Homocysteine biosynthesis in green plants. Physiological importance of the transsulfuration pathway in Chlorella sorokiniana growing under steady state conditions with limiting sulfate

The physiological roles of the transsulfuration and direct sulfhydration pathways in Chlorella sorokiniana growing under steady state photoautotrophic conditions with limiting sulfate were studied by following the patterns of assimilation of 35SO4(2-) into sulfur amino acids. The labeling patterns expected of each pathway were defined by means of models based on the rates of net synthesis of the terminal pools of GSH, protein cysteine, and protein methionine. The labeling patterns observed are entirely consistent with the transsulfuration pathway and inconsistent with the direct sulfhydration pathway. By analysis of the amounts of radioactivity present in key intermediates at labeling times as short as 1 s, it was demonstrated that direct sulfhydration makes no detectable contribution to homocysteine biosynthesis, and if operative contributes no more than approximately 3% of the total homocysteine biosynthesized. From the combined determinations of the initial rates of labeling and net rates of synthesis of the various sulfur amino acids, a tentative working model is presented that summarizes our best current estimates of the major fluxes of sulfur in the experimental system. The labeling data further showed that soluble cysteine consists of at least two pools. One pool, termed "rapidly turning over" cysteine comprises less than 1% of the total soluble cysteine, and is the precursor of GSH, protein cysteine, and, almost certainly, cystathionine. The other pool, "slowly turning over" cysteine, appears to be in equilibrium with "rapidly turning over" cysteine, but not to be further metabolized.