BACTERIAL EFFECTS AND ALGAL BIOREMEDIATION BY CHLORELLA ELLIPSOIDEA GERNECK OF THE BERKELEY PIT LAKE SYSTEM

Mitman, G. G. Department of Biological Sciences, Montana Tech of The University of Montana, Butte, MT 59701 The Berkeley Pit Lake System is one of the largest contaminated sites in North America and is located near the headwaters of the largest superfund site in the U.S. It is filling at a rate of about 28.7 million liters per day with metal laden, acidic (pH 2.7) water. Chlorella ellipsoidea is one of the first autochthonous species of algae from the Berkeley Pit Lake System to be tested for its bioremediative potential. An experimental matrix was designed for this experiment using a completely randomized design (CRD). The matrix was set up with tissue culture flasks having the following treatments: Na2HPO4 at 0, 25, 50, 75, 100 mg/l, inoculated vs. no- inoculated with algae (187,500 algae/ml final), and filtered (0.2Fm) vs. non filtered pit water as variables, NaNO₃ amount was fixed at 53 mg/ml. Three replicates were made of each and the experiment lasted 60 days. The results of this experiment demonstrated significant remediation of most metals. These results will be presented. In addition, filtering seemed to negatively impact the bioremediative potential of the cultures. As a result, axenic cultures of Chlorella ellipsoidea will be tested in Berkeley pit water to determine if it is bacteria or filtration that caused these results.     

9 Beyond biogeography: large-scale patterns of distribution and abundance of intertidal marine algae along the us west coast

This research was directed to gather a better understanding about the unicellular alga Chlamydomonas acidophila, one of the 6 algal species found in the Berkeley Pit Lake. Berkeley Pit Lake is a flodded, abandoned pit mine with a pH of 2.7 and high metal concentrations. It has been found that the effective concentrations of metals that limit the growth of C. acidophila by 50% were 9.024 mg/L for Cu2+ and 75.4 mg/L for Zn 2+. We have been able to grow C. acidophila from Berkeley Pit samples at high densities in medium containing 15.36 mg/L Cu2+ and 83.65 mg/L Zn2+. Moreover, this species is able to grow in nutrified Berkeley Pit water, which contains approximately 110 mg/L Cu2+ and 323 mg/L of Zn2+. The hypothesis is that the species found in Berkeley Pit Lake represents a genetic strain adapted to high metal concentrations environments. A comparison between the American Type Culture Collection strain of C. acidophila and the strain collected from Berkeley Pit was made. Growth rate of the two strains in Bold Basil Medium, Modified Acid Medium and Berkeley Pit nutrified water were calculated and compared. Moreover, preliminary investigations of the genome of C.acidophila from the Berkeley Pit Lake were initiated.     

10 Chlamydomonas acidophila from the berkeley pit lake – a strain adapted to an extreme environment

This research was directed to gather a better understanding about the unicellular alga Chlamydomonas acidophila, one of the 6 algal species found in the Berkeley Pit Lake. Berkeley Pit Lake is a flodded, abandoned pit mine with a pH of 2.7 and high metal concentrations. It has been found that the effective concentrations of metals that limit the growth of C. acidophila by 50% were 9.024 mg/L for Cu2+ and 75.4 mg/L for Zn 2+. We have been able to grow C. acidophila from Berkeley Pit samples at high densities in medium containing 15.36 mg/L Cu2+ and 83.65 mg/L Zn2+. Moreover, this species is able to grow in nutrified Berkeley Pit water, which contains approximately 110 mg/L Cu2+ and 323 mg/L of Zn2+. The hypothesis is that the species found in Berkeley Pit Lake represents a genetic strain adapted to high metal concentrations environments. A comparison between the American Type Culture Collection strain of C. acidophila and the strain collected from Berkeley Pit was made. Growth rate of the two strains in Bold Basil Medium, Modified Acid Medium and Berkeley Pit nutrified water were calculated and compared. Moreover, preliminary investigations of the genome of C.acidophila from the Berkeley Pit Lake were initiated.     

Chronic toxicity of methylparathion to the rotifer Brachionus calyciflorus fed on Nannochloris oculata and Chlorella pyrenoidosa

The effect of sublethal levels of methylparathion (0, 1, 3, 5, 7 mg l^–1) on the freshwater rotifer, Brachionus calyciflorus, during their entire life cycle was studied. Rotifers were fed on two species of unicellular algae: Nannochloris oculata and Chlorella pyrenoidosa; both algal concentrations were 5 × 10⁵ cell ml^–1.The parameters used to determine the toxicity of this compound were survival, fecundity, net reproductive rate (R)_o, generation time (T), intrinsic rate of natural increase (r), reproductive value (V _x/V_o) and life expectancy at hatching (eo). All the demographic parameters studied were affected by methyl-parathion exposure on rotifers fed on both species of algae, but the toxic effect was larger when animals were fed on Chlorella pyrenoidosa; in this case, animals showed a decreased in fertility and also a delayed first reproduction. Sublethal methylparathion levels produced a reduction in most of the parameters selected, especially after exposure to 7 mg l^–1, where the animals died before reproducing.     

THE EFFECT OF CULTURE CONDITIONS ON THE HYDROCARBON CONTENT OF CHLORELLA VULGARIS12

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.     

Phytoplankton community structure and environment in the Kenyan waters of Lake Victoria

• 1 Phytoplankton species composition, numerical abundance, spatial distribution and total biomass measured as chlorophyll a concentration were studied in relation to environmental factors in September 1994 (dry season) and March 1995 (rainy season), respectively, in the Kenyan waters of Lake Victoria; 103 species were recorded.
• 2 Blue‐green algae (Cyanophyceae) were most diverse, followed by diatoms (Bacillariophyceae), green algae (Chlorophyceae) and dinoflagellates (Dinophyceae).
• 3 Twinspan separated the phytoplankton communities in the Nyanza Gulf and those in the open lake during both seasons. During the dry season, the Nyanza Gulf was strongly dominated by blue‐greens, while diatoms dominated in the open lake. During the rainy season, blue‐greens remained dominant in the Nyanza Gulf although the number of species found was lower than during the dry season; in the open lake, blue‐greens replaced diatoms as the dominant group and there were more species than in the dry season.
• 4 Canonical correspondence analysis indicated that the phytoplankton species distribution was significantly correlated with turbidity during the dry season and with SiO₂ during the rainy season. Chlorophyll a concentrations ranging from 2.0 to 71.5 mg m^‐3 in the dry season and 2.0–17.2 mg m^‐3 in the rainy season confirm earlier reports of increasing phytoplankton biomass in Lake Victoria since the 1960s.

     

Phosphate uptake and utilization by bacteria and algae

Bacterial uptake of inorganic phosphate (closely investigated in Escherichia coli) is maintained by two different uptake systems. One (Pst system) is P_i-repressible and used in situations of phosphorus deficiency. The other system (Pit system) is constitutive. The Pit system also takes part in the phosphate exchange process where orthophosphate is continuously exchanged between the cell and the surrounding medium.Algal uptake mechanisms are less known. The uptake capacity increases during starvation but no clearly defined transport systems have been described. Uptake capacity seems to be regulated by internal phosphorus pools, e.g., polyphosphates. In mixed algal and bacterial populations, bacteria generally seem to be more efficient in utilizing low phosphate concentrations. The second half of this paper discusses how bacteria and algae can share limiting amounts of phosphate provided that the bacteria have pronouncedly higher affinity for phosphate. Part of the solution to this problem may be that bacteria are energy-limited rather than phosphate-limited and dependent on algal organic exudates for their energy supply.The possible phosphate exchange mechanism so convincingly demonstrated in Escherichia coli is here suggested to play a key role for the flux of phosphorus between bacteria and algae. Such a mechanism can also be used to explain the rapid phosphate exchange between the particulate and the dissolved phase which always occurs in short-term ³²P-uptake experiments in lake waters.     

Effect of anaerobiosis on photosynthetic reactions and nitrogen metabolism of algae with and without hydrogenase

Summary The effect of anaerobic (N₂+CO₂) pre-incubation in the dark on photosynthetic reactions (O₂ evolution, measured manometrically and with the oxygraph; fluorescence; and photoproduction of H₂, measured with the mass spectrometer) was studied in algae with hydrogenase (strains of Chlorella fusca, C. kessleri, C. vulgaris f. tertia, and Ankistrodesmus braunii) and in algae without hydrogenase (strains of Chlorella vulgaris, C. saccharophila, and C. minutissima).The inhibition by anaerobic incubation of photosynthetic O₂ evolution is much stronger in algae without hydrogenase than it is in algae with hydrogenase. The effect of anaerobiosis is most pronounced at rather low light intensity (about 1000 lux), in acid medium (pH 4), and after prolonged anaerobic incubation in the dark (about 20 h). These results indicate that the presence of hydrogenase might be ecologically advantageous for algae under certain conditions.Chlorophyll fluorescence showed the fastest response to anaerobic incubation, and the most pronounced difference between algae with and without hydrogenase. After only 30 min under N₂+CO₂, fluorescence in algae with hydrogenase starts with a peak and decreases within 10 to 20 sec to a rather low steady-state level which is only slightly higher than that found under aerobic conditions. In algae without hydrogenase, fluorescence is rather low during the first 1 to 2 sec and then rises to a higher steady-state level which is much higher than that of the aerobic controls. This indicates an inhibition due to anaerobiosis of photosystem II in algae without hydrogenase.Algae with hydrogenase can react in different ways during the first minutes of illumination. In some cases there is an immediate photoproduction of H₂, which is followed after a few minutes by photosynthetic O₂ evolution; in other algae there is a simultaneous production of H₂ and O₂ from the very beginning; in a few experiments there was no photoproduction of H₂ at all, and in this case there was no photosynthetic O₂ evolution either. Thus, photoproduction of H₂ seems to be the process which normally enables algae with hydrogenase to oxidise and thereby activate their photosynthetic electron transport system after anaerobic incubation.A mass spectrometric search for nitrogen fixation (using N₂ and acetylene) in eucaryotic green algae gave negative results, even with species containing hydrogenase and under anaerobic conditions.     

THE INFLUENCE OF pH ON ALGAL CELL MEMBRANE PERMEABILITY AND ITS IMPLICATIONS FOR THE UPTAKE OF LIPOPHILIC METAL COMPLEXES1

Uptake of lipophilic metal complexes by freshwater algae has recently been shown to be pH dependent. Here we look at different physiological aspects that could influence the diffusion of the lipophilic Cd complex, Cd(diethyldithiocarbamate)₂⁰ (Cd(DDC)₂⁰), into algal cells at different exposure pH values. Changes in cell membrane permeability were assessed as a function of pH for three species of green algae [Chlamydomonas reinhardtii P. A. Dang., Pseudokirchneriella subcapitata (Korshikov) Hindák, and Chlorella fusca var. vacuolata Shihira et R. W. Kraus] using two neutral, nonionic probes, fluorescein diacetate (FDA) and D‐sorbitol. In parallel experiments, we exposed algae to inorganic Cd or to Cd(DDC)₂⁰ and monitored Cd intracellular metal distribution, together with phytochelatin synthesis. For the three algal species acclimated at pH 5.5 (w/wo DDC 1 μM) and exposed at this pH, their permeability to FDA and D‐sorbitol was consistently lower than for algae growing at pH 7.0 and exposed at this pH (P < 0.001). The ratio of the FDA hydrolysis rate measured at pH 7.0 with respect to the rate measured at pH 5.5 (both in the presence of DDC) correlated with the ratio of the Cd(DDC)₂⁰ initial internalization rate constant obtained at pH 7.0 versus that obtained at pH 5.5 (three algae species, n = 9, r = 0.85, P = 0.004). Our results strongly suggest that acidification affects metal availability to algae not only by proton inhibition of facilitated metal uptake but also by affecting membrane permeability.     

Spatial distribution of phytoplankton in Lake Baikal, Spring 1991

• 1 Studies carried out in Lake Baikal in late spring (late May-early June) 1991 showed marked differences in the species composition and abundance of phytoplankton in different regions of the lake. The south and north basins were characterized by small forms of algae. The middle basin, Maloe More and the shallow waters of the Selenga had species with large cells including Aulacoseira islandica subsp. helvetica, Dinobryon cylindricum and D. divergens.
• 2 Areas of high biomass were correlated with shallow waters and river inputs. This was especially apparent in the region of the Selenga delta. The vertical distribution of phytoplankton indicated the non-synchronous start of the spring homothermy throughout the lake. Phytoplankton were concentrated in the upper 100 m layer with subsurface maxima resulting from the sinking of large algae.
• 3 The concentration of phytoplankton biomass in general at this time characterized the lake as moderately productive.

     

Photosynthesis,photooxidation of chlorophyll and fluorescence of normal and manganese-deficient Chlorella with and without hydrogenase

Summary Growth, chlorophyll content, chloroplast structure, photosynthesis, photooxidation of chlorophyll and fluorescence were studied in normal and manganese-deficient, closely related Chlorella strains with hydrogenase (Chlorella vulgaris f. tertia 211-8k) and without hydrogenase (Chlorella vulgaris 211-8m).Under Mn-deficient conditions, algae with hydrogenase grow slowly for several weeks without becoming chlorotic and without any major change in thylakoid structure, whereas those without hydrogenase show a rapid loss of most of their chlorophyll, followed by a breakdown of thylakoid structure. In algae without hydrogenase, the inhibition of photosynthesis by Mn deficiency is much less pronounced when photosynthesis is determined on a chlorophyll rather than on a cell-volume or dry-weight basis. Thus the little remaining chlorophyll of these algae is photosynthetically much more active than the chlorophyll of the Mn-deficient, non-chlorotic algae with hydrogenase.Photooxidation of chlorophyll under pure O₂ in very strong light is always accelerated by Mn deficiency.Only in algae containing hydrogenase is there under aerobic conditions a pronounced peak of fluorescence at the beginning of illumination. This is indicative of a high degree of reduction of Q, the primary electron acceptor of System II of photosynthesis. The fluorescence peak can be eliminated by either 1 min preillumination with far red (=717 nm) or by treatment in the dark for 1 hr with pure O₂. In algae without hydrogenase, in contrast, fluorescence intensity at the onset of illumination is lower than the steady-state level, indicating an oxidized state of Q. In these algae a high start of fluorescence can only be produced by prolonged anaerobic incubation. These results indicate that even under aerobic conditions algal hydrogenase, or a biochemical system very closely associated with it, has some residual activity which enables it to feed electrons into System II of photosynthesis, thereby keeping Q in a reduced state with correspondingly high fluorescence at the beginning of illumination. In organisms without hydrogenase, in contrast, this can only be achieved by prolonged anaerobiosis. In addition, the presence of hydrogenase seems to protect the chlorophyll against photooxidative destruction when the cells are under Mn deficiency.This paper is dedicated to Professor A. Pirson on the occasion of his 60th birthday.     

Studies on the hormonal relationships of algae in pure culture

Summary Indole-3-acetic acid (IAA) stimulated the growth (increase in dry weight) of the blue-green algae Anacystis nidulans, Chlorogloea fritschii, Phormidium foveolarum, Nostoc muscorum, Anabaena cylindrica, and Tolypothrix tenuis and the green algae Chlorella pyrenoidosa, Ankistrodesmus falcatus and Scenedesmus obliquus growing under as sterile conditions as possible. The optimum concentration varied from species to species; in the blue-green algae it ranged from 10^-5 to 10^-9 M and in the green algae it was 10^-3 M. These results are discussed in the light of present studies in this field.     

Biotransformation of mercury in pH-stat cultures of eukaryotic freshwater algae

Eukaryotic algae were studied to determine their ability to biotransform Hg^II under aerated and pH controlled conditions. All algae converted Hg^II into β-HgS and Hg⁰ to varying degrees. When Hg^II was administered as HgCl₂ to the algae, biotransformation by species of Chlorophyceae (Selenastrum minutum and Chlorella fusca var. fusca) was initiated with β-HgS synthesis (K _1/2 of hours) and concomitant Hg° evolution occurred in the first hour. Hg° synthesis was impeded by the formation of β-HgS and this inhibition was released in C. fusca var. fusca when cellular thiols were oxidized by the addition of dimethylfumarate (DMF). The diatom, Navicula pelliculosa (Bacillariophyceae), converted a substantially greater proportion of the applied Hg^II into Hg⁰, whereas the thermophilic alga, Galdieria sulphuraria (Cyanidiophyceae), rapidly biotransformed as much as 90% of applied Hg^II into β-HgS (K _1/2 ≈ 20 min). This thermophile was also able to generate Hg⁰ even after all exogenously applied HgCl₂ had been biotransformed. The results suggest that β-HgS may be the major dietary mercurial for grazers of contaminated eukaryotic algae.     

<Emphasis Type="Italic">Utricularia</Emphasis>: a vegetarian carnivorous plant?

Aquatic carnivorous plants of the genus Utricularia capture and utilise a wide range of small aquatic organisms. Most of the literature focuses on animals as prey. In this study, we investigate the occurrence of algae inside the traps of four species of bladderwort. We observed that algae of 45 genera form up to 80% of the total prey; algae were found frequently in traps without animal prey. The majority are coccal and trichal algae of the families Desmidiaceae and Zygnemataceae. The percentage of algae increases significantly with decreasing electric conductivity of the water (r _S = −0.417; P = 0,000). Thus, algae are the most frequent prey in extremely soft waters. The percentage of algae did not differ significantly, not within the investigated Utricularia species or within the various study sites. However, the taxonomic composition of the algal prey showed highly significant differences between different sites. More than 90% of the trapped algae were killed and degraded by the bladders. The recent data allow for two alternative hypotheses: either algal prey supplements animal prey in oligotrophic waters, or the unprofitable trapping of algae is rather an additional stress factor for Utricularia and contributes to its limited distribution in some peat bogs.     

The effects of intervessel pit characteristics on xylem hydraulic efficiency and photosynthesis in hemiepiphytic and non‐hemiepiphytic Ficus species

Xylem vulnerability to cavitation and hydraulic efficiency are directly linked to fine‐scale bordered pit features in water‐conducting cells of vascular plants. However, it is unclear how pit characteristics influence water transport and carbon economy in tropical species. The primary aim of this study was to evaluate functional implications of changes in pit characteristics for water relations and photosynthetic traits in tropical Ficus species with different growth forms (i.e. hemiepiphytic and non‐hemiepiphytic) grown under common conditions. Intervessel pit characteristics were measured using scanning electron microscopy in five hemiepiphytic and five non‐hemiepiphytic Ficus species to determine whether these traits were related to hydraulics, leaf photosynthesis, stomatal conductance and wood density. Ficus species varied greatly in intervessel pit structure, hydraulic conductivity and leaf physiology, and clear differences were observed between the two growth forms. The area and diameter of pit aperture were negatively correlated with sapwood‐specific hydraulic conductivity, mass‐based net assimilation rate, stomatal conductance (g_s), intercellular CO₂ concentration (C_i) and the petiole vessel lumen diameters (D_v), but positively correlated with wood density. Pit morphology was only negatively correlated with sapwood‐ and leaf‐specific hydraulic conductivity and D_v. Pit density was positively correlated with g_s, C_i and D_v, but negatively with intrinsic leaf water‐use efficiency. Pit and pit aperture shape were not significantly correlated with any of the physiological traits. These findings indicate a significant role of pit characteristics in xylem water transport, carbon assimilation and ecophysiological adaptation of Ficus species in tropical rain forests.     

Temperature preferences and oxygen consumption of three species of sculpin (Cottus) from the Pit River drainage,California

Synopsis I examined the temperature preferences and routine metabolic rates of Pit sculpin, Cottius pitensis, marbled sculpin, C. klamathensis macrops, and rough sculpin, C. asperrimus, of the Pit River drainage of California to determine if the distributional patterns of these species can be explained on the basis of physiological or behavioral responses to temperature. The routine metabolic rates of these species did not increase significantly between 10 and 15°C, indicating an area of thermal compensation. Metabolic rates then rapidly increased between 15 and 20°C (Q₁₀ values>4.0) followed by little increase between 20 and 25°C (Q₁₀ values >2.0), indicating another area of thermal compensation. The final temperature preferenda of Pit, marbled and rough sculpin were 11.2, 12.1 and 13.5°C, respectively. Marbled and rough sculpin appear to be more stenothermal than Pit sculpin. At acclimation temperatures of 10, 15 and 20°C the acute preferred temperatures of marbled and rough sculpin ranged from 11.1 to 14.7° C and 13.3 to 14.4°C, respectively. Values for Pit sculpin ranged from 9.9 to 16.4°C at acclimation temperatures of 10, 15 and 20°C. The distributions of marbled and rough sculpin are consistent with their behavioral and metabolic responses to temperature. The widespread distribution of Pit sculpin is consistent with its greater tolerance of high temperatures and eurythermal behavior, but the absence of Pit sculpin from habitats dominated by marbled and rough sculpin is not consistent with a temperature related explanation.     

Über die Amine einzelliger Grünalgen

Zusammenfassung Die einzelligen Grünalgen Chlorella fusca und Scenedesmus acutus enthalten 10–11 Hauptamine, wovon die folgenden Verbindungen mit Hilfe dünnschichtchromatographischer Methoden identifiziert wurden: Äthanolamin, Methylamin, Dimethylamin, Putrescin und Spermidin. Cadaverin und Spermin fehlten. Der Spermidingehalt der beiden Algen wurde in seiner Abhängigkeit von Kulturalter, Kulturtemperatur, Lichtintensität und der N-Quelle des Nährmediums untersucht. Der mittlere Spermidingehalt bei 30°C kultivierter Algen lag bei 1,9 mg/g Trockenmasse (minimal 0,29 mg/g, maximal 2,24 mg/g). Mit abnehmender Kulturtemperatur und mit zunehmendem Kulturalter sank der Spermidingehalt der Zellen. Beim Einsatz von KNO₃ oder (NH₄)₂SO₄ als Stickstoffquelle war der Spermidingehalt signifikant höher als bei Verwendung von Harnstoff. Die Lichtintensität hatte keinen Einfluß auf die Höhe des Spermidingehalts der Algen.

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Amines in unicellular green algae1. Spermidine content of Scenedesmus acutus (276-3a) and Chlorella fusca (211-8b)

Summary From the 10 to 11 major amines which could be distinguished in the unicellular green algae Chlorella fusca and Scenedesmus acutus, by thin-layer chromatography, the following compounds were identified: Aethanolamine, methylamine, dimethylamine, putrescine and spermidine. Cadaverine and spermine were lacking. The spermidine content of both of the algae was quantitatively determined, and its dependence on age, temperature, light intensity and source of nitrogen was tested. The average spermidine content in algae cultivated at 30°C was 1.9 mg/g dry weight (minimum 0.29 mg/g, maximum 2.24 mg/g). The spermidine content decreased with decreasing temperature as well as with increasing age. With KNO₃ or (NH₄)₂SO₄ as the source of nitrogen, the spermidine content was significantly higher as compared to algae grown in urea. Light intensity had no effect on the spermidine content.

     

Cr3+和Cd2+对普通小球藻生长及抗氧化酶活性的影响

[目的] 为探究重金属对淡水绿藻生长的影响。[方法] 选取对水质检测具有明显指示作用的普通小球藻（Chlorella vulgaris）为实验材料,CdCl₂·2H₂O和CrCl₃·7H₂O提供重金属离子,探究不同浓度Cr³⁺和Cd²⁺在单一和复合胁迫下对藻细胞浓度、叶绿素a及相关抗氧化酶活性的影响。[结果] 随着Cr³⁺和Cd²⁺浓度不断增加,藻细胞浓度呈先增长后下降趋势;叶绿素a含量呈现先下降后升高再下降的现象,浓度为1 mg/L的单一和复合胁迫下有最大值,且毒性作用表现为Cr³⁺ < Cd²⁺ < Cr³⁺+Cd²⁺;与藻细胞膜相关的丙二醛（MDA）和过氧化氢（H₂O₂）含量随着重金属离子浓度的增大而增长;重金属离子浓度低于10 mg/L时对藻细胞内抗氧化酶系统中的超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和过氧化物酶（POD）表现为促进作用,而大于10 mg/L时具有抑制作用。[结论] 结果表明在单一或复合重金属胁迫下,普通小球藻会充分调动与抗逆性相关的酶来维持自身的正常生长。     

The Influence of CO2 Concentration and pH on Two Chlorella Species Grown in Continuous Light

Both Chlorella pyrenoidosa and Chlorella vulgaris grow equally well at 20°C aerated with ordinary air or mixtures of air with 5 or 12 per cent CO₂ (5 klux continuous light). Whereas C. vulgaris relatively rapidly adapts to a higher CO₂ tension, adaptation takes about 24 hours for C. pyrenoidosa. In Chlorella vulgaris pH in the range 3.6–7.6 has no apparent influence on the rate of photosynthesis in experiments having a duration of two hours. This is true both for algae grown aerated by ordinary air and for algae grown with a mixture of 5 per cent CO₂ in air. The adaptation time must be short. In Chlorella pyrenoidosa the same is found for algae in ordinary air, whereas an influence of pH is seen in some experiments where the aeration was by 5 per cent CO₂ in air. As is to be expected, the rate of photosynthesis in C. pyrenoidosa during the first two hours is very much influenced by the concentration of free CO₂. The highest rate is found at the CO₂ concentration at which the algae had been growing previously. The influence on the rate of photosynthesis in C. vulgaris is very much less, although in principle the same. The investigation of the corresponding influence on the rate of respiration is complicated by considerable variation from one series to another. In C. vulgaris this is particularly of importance. In C. pyrenoidosa, the highest rate of respiration is generally found at the CO₂-concentration at which the alga had been growing before the experiment. It seems probable that variations between similar series is due to the fact that the algae were grown in continuous light but with dilution with fresh culture medium when the optical density had reached a certain magnitude. Algae grown in this way are neither synchronized nor non-synchronized.Our thanks are due to the Danish State Research Foundation for financial support.     

Ecology of Dictyosphaerium pulchellum Wood (Chlorophyta, Chlorococcales) in a shallow, acid, forest lake

This study relates to the ecology of Dictyosphaerium pulchellum Wood in Delamere Lake in Cheshire, UK. Dictyosphaerium pulchellum is a cosmopolitan, green colonial phytoplankton species that occasionally forms dense, monospecific populations in lakes. Delamere Lake is a small, shallow, acid lake (mean pH, 4.5) with very high phytoplankton biomass (annual mean chlorophyll a, 290 μg l⁻¹) and devoid of any significant cladoceran population, the efficient grazers of phytoplankton. A predominantly unicellular form of D. pulchellum was the dominant species in Lake Delamere, and it comprised on average ca. 80% (maximum >99%) of the lake phytoplankton biovolume. Laboratory and lake experiments were conducted on this species showed that its pH tolerance varied between 2.4 and 10.7, and its optimum tolerance range between 3.3 and 8.5 depending on other environmental variables. Low pH was not responsible for the unicellular habit of this alga, but a very high nutrient regime could be an important factor. Bioassays revealed that in Delamere Lake this species was limited by nitrogen, but nitrogen did not hamper high growth in the lake. Dictyosphaerium pulchellum can persist at low light levels, tolerate CO₂-deficiency and can grow in polyhumic water with water colour around 300 mg Pt l⁻¹, but probably not in darker waters. The dominance of D. pulchellum in Delamere Lake is apparently due to a combination of several factors: its ability to tolerate both low pH and high turbidity, exploit high nutrient conditions, absence of effective grazing pressure by zooplankton and being a superior competitor.