Physiological Responses of Microcystis aeruginosa PCC7806 to Nonanoic Acid Stress

A recent study has shown that nonanoic acid (NA) is one of the strongest allelochemicals to a cyanobacterium Microcystis aeruginosa, but the physiological responses of M. aeruginosa to NA stress remain unknown. In this study, physiological characters such as the growth rate, photosynthetic processes, phosphorus and nitrogen uptake kinetics, and the contents of intracellular microcystin of M. aeruginosa PCC7806 were studied under the NA stress. The results showed that the growth rates of M. aeruginosa PCC 7806 were significantly inhibited in all NA stress treatments during first 3 days after exposure, and the growth rate was recovered after 5-day exposure. After 2-day exposure, the contents of both phycocyanin and allophycocyanin per cell decreased at NA concentration of 4 mg L-1, and oxygen evolution was inhibited even at the concentration of 0.5 mg L-1, but carotenoid content per cell was slightly boosted in NA stress. Physiological recovery of M. aeruginosa PCC7806 was observed after 7-day exposure to NA. It was shown that NA stress had no effect on uptake of nitrogen, but could stimulate the uptake of phosphorus. The contents of intracellular microcystin have not been affected in all NA treatments in contrast with the control. (C) 2008 Wiley Periodicals, Inc. Environ Toxicol 24: 610-617, 2009.

EFFECTS OF IRON ON PHYSIOLOGICAL AND BIOCHEMICAL CHARACTERISTICS OF Microcystis wesenbergii (Kom.) Kom. (Cyanobacterium)

Iron is an essential trace element for biological requirements of phytoplankton. Effects of iron on physiological and biochemical characteristics of Microcystis wesenbergii were conducted in this study. Results showed that 0.01 mu M [Fe3+] seriously inhibited growth and chlorophyll synthesis of M. wesenbergii, and induced temporary increase of ATPase activities, however, NR. ACP and ALP activities were restrained by iron limitation. Interestingly, iron addition on day 8 resulted in the gradual restoration of structures and functions of above enzymes and resisted a variety of stresses from iron limitation. M. wesenbergii in 10 mu M [Fe3+] treatment group grew normally. enzymes maintained normal levels, and residual phosphate contents in cultures first sharply decreased, then smoothly as M. wesenbergii has a characteristic of luxury consumption of phosphorus. Above parameters in 100 mu M [Fe3+] treatment group were almost same with those in 10 mu M [Fe3+] treatment group except for NR, ACP and ALP activities. In 100 mu M [Fe3+] treatment group, activities of ACP and ALP had temporary increase because phosphate and ferric iron could form insoluble compound - ferric phosphate (Fe3PO4) through adsorption effect. resulting in lack of bioavailable phosphate in culture media. The experiment suggested that too low or too high iron can affect obviously physiological and biochemical characteristics of M. wesenbergii.

Physiological Stress of High NH (4) (+) Concentration in Water Column on the Submersed Macrophyte Vallisneria Natans L.

The submersed macrophyte, Vallisneria natans L., was cultured in laboratory with NH (4) (+) -enriched tap water (1 mg L-1 NH4-N) for 2 months and the stressful effects of high ammonium (NH (4) (+) ) concentrations in the water column on this species was evaluated. The plant growth was severely inhibited by the NH (4) (+) supplement in the water column. The plant carbon and nitrogen metabolisms were disturbed by the NH (4) (+) supplement as indicated by the accumulation of free amino acids and the depletion of soluble carbohydrates in the plant tissues. The results suggested that high NH (4) (+) concentrations in the water column may hamper the restoration of submersed vegetation in eutrophic lakes.

Microcystin-RR induces physiological stress and cell death in the cyanobacterium Aphanizomenon sp DC01 isolated from Lake Dianchi, China

The phytoplankton community in Lake Dianchi (Yunnan Province, Southwestern China) is dominated in April by a bloom of Aphanizomenon, that disappears Suddenly and is displaced by a Microcystis bloom in May. The reasons for the rapid bloom disappearance phenomenon and the temporal variability in the composition of phytoplankton assemblages are poorly understood. Cell growth, ultrastructure and physiological changes were examined in cultures of Aphanizomenon sp. DC01 isolated from Lake Dianchi exposed to different closes of rnicrocystin-RR (MC-RR) produced by the Microcystis bloom. MC-RR concentrations above 100 mu g L-1 markedly inhibited the pigment (chlorophyll-a, phycocyanin) synthesis and caused an increase of soluble carbohydrate and protein contents and nitrate reductase activity of toxin-treated blue-green algae. A drastic. reduction in photochemical efficiency of PSII (Fv/Fm) was also found. Morphological examinationn showed that the Aphanizomenon filaments disintegrated and file cells lysed gradually after 48 h Of toxin exposure. Transmission electron microscopy revealed that cellular inclusions of stressed cells almost leaked out completely and the cell membranes were grossly damaged. These findings demonstrate the allelopathic activity of Microcystis aeruginosa inducing physiological stress and cell death of Aphanizomenon sp. DC01 Although the active concentrations of microcystin were rather high, we propose that microcystin may function as allelopathic Substance due to inhomogeneous toxin concentrations close to Microcystis cells. Hence, it may play a role in species Succession of Aphanizomenon and Microcystis in Lake Dianchi.

Colony development and physiological characterization of the edible blue-green alga, Nostoc sphaeroides (Nostocaceae, Cyanophyta)

The edible blue-green alga, Nostoc sphaeroides Kutzing, is able to form microcolonies and spherical macrocolonies. It has been used as a potent herbal medicine and dietary supplement for centuries because of its nutraceutical and pharmacological benefits. However, limited information is available on the development of the spherical macrocolonies and the environmental factors that affect their structure. This report described the morphogenesis of N. sphaeroides from single trichomes to macrocolonies. During the process, most structural features of macrocolonies of various sizes were dense maculas, rings, the compact core and the formation of liquid core; and the. laments within the macrocolonies showed different lengths and arrays depending on the sizes of macrocolonies. Meanwhile temperature and light intensity also strongly affected the internal structure of macrocolonies. As microcolonies further increased in size to form 30 mm macrocolonies, the colonies differentiated into distinct outer, middle and inner layers. The. laments of the outer layer showed higher maximum photosynthetic rates, higher light saturation point, and higher photosynthetic effciency than those of the inner layer; whereas the. laments of the inner layer had a higher content of chlorophyll a and phycobiliproteins than those of the outer layer. The results obtained in this study were important for the mass cultivation of N. sphaeroides as a nutraceutical product. (c) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Diel isotopic fluctuation in surface seston and its physiological and ecological implications

We reported diet fluctuation in isotopic composition of surface seston from two connected lakes in China, oligotrophic Lake Fuxian and eutrophic Lake Xingyun. The decrease in nighttime and the increase in daytime of isotope signatures of seston might be attributed to the light-dependent balance between the photosynthesis and the respiration of phytoplankton and to the changes in the species composition and the relative abundance of phytoplankton functional groups at the water's surface in diel growth. The relatively high isotopic signatures and the large-extent diel fluctuation of phytoplankton in the eutrophic lake could be due to utilization of heavy-isotope-enriched inorganic sources and the high primary productivity. Extent of diel fluctuation in delta C-13 and delta N-15 of phytoplankton were relatively small compared with the isotopic enrichment per trophic transfer and thus might have negligible effect on the source identification and the trophic evaluation of consumers.

Physiological advantages may contribute to successful invasion of the exotic Cyprinus carpio into the Xingyun Lake, China

Feeding and growth traits of Cyprinus carpio and Cyprinus pellegrini (both at age-0) were compared in three experiment, in an attempt to analyze potential causes for the displacement of the native C. pellegrini in the Xingyun Lake, Yuxi, Yunan, China. Experiment I was conducted in water which fluctuated between 15 and 20 degrees C. Experiment II and III were conducted in a laboratory and water temperature was maintained between 20 degrees C and 25 degrees C, respectively. Three common trends were noted for all three experiments: (1) feeding rate of C. carpio was lower than that of C. pellegrini, and this difference was found to be significant in experiment I; (2) growth rate of C. carpio was higher than C. pellegrini, and the difference was found to be significant in experiment II; (3) food conversion efficiency and energy retention efficiency for C. carpio were higher than those of C. pellegrini, and significant differences were noted in experiment I and II. Since the growth period for fish in the Xingyun Lake generally occurs when water temperatures are between 15 and 25 degrees C, it can be suggested that C. carpio has advantages over C. pellegrini in growth and food utilization efficiency, and lower food consumption than C. pellegrini. These physiological traits of C. carpio might allow this species to be more resistant to food shortage and predation, and may be partially responsible for the displacement of C. pellegrini by C. carpio.

Physiological comparison between colonial and unicellular forms of Microcystis aeruginosa Kutz. (Cyanobacteria)

In order to gain insight into the bloom sustainment of colonial Microcystis aeruginosa Katz., physiological characterizations were undertaken in this study. Compared with unicellular Microcystis, colonial Microcystis phenotypes exhibited a higher maximum photosynthetic rate (Pm), a higher maximum electron transfer rate (ETRmax), higher phycocyanin content, and a higher affinity for inorganic carbon (K-0.5 DIC <= 8.4 +/- 0.7 mu M) during the growth period monitored in this study. This suggests that photosynthetic efficiency is a dominant physiological adaptation found in colonial Microcystis, thus promoting bloom sustainment. In addition, the high content of soluble and total carbohydrates in colonial Microcystis suggests that this phenotype may possess a higher ability to tolerate enhanced stress conditions when compared to unicellular (noncolonial) phenotypes. Therefore, high photosynthetic activities and high tolerance abilities may explain the bloom sustainment of colonial Microcystis in eutrophic lakes.

Physiological and biochemical responses of Scytonema javanicum (cyanobacterium) to salt stress

Scytonema javanicum (Kutz.) Born et Flah (cyanobacterium) is one of the species distributed widely in the crust of desert soils regularly subjected to severe water stress. To investigate the response of the species to salt stress, many physiological and biochemical parameters, including growth rate, ratio of variable fluorescence to maximum fluorescence (Fv/Fm), reactive oxidative species (ROS), malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD), were determined in culture. The results showed that 50 mM NaCl inhibited growth and Fv/Fm in the medium BG-110, and that the inhibition was maximum after 1-2 days' exposure to salt stress; 50 mM NaCl also increased the contents of ROS and MDA in treated cells, which suggests that salt stress may lead to oxidative damage and lipid peroxidation in the alga. Further, changes in the antioxidative enzymes SOD and CAT in the treated alga were consistent with changes in ROS and MDA at certain extent. These observations suggest that oxidative stress resulting from salt stress in S. javanicum could result in the production of antioxidative enzymes to counteract the oxidative damage, and the enzymes may contribute to the ability of S. javanicum to survive the adverse desert environment. (c) 2007 Elsevier Ltd. All rights reserved.

In situ studies on physiological and biochemical responses of four fishes with different trophic levels to toxic cyanobacterial blooms in a large Chinese lake

Physiological and biochemical responses of four fishes with different trophic levels to toxic cyanobacterial blooms were studied in a large net cage in Meiliang Bay, a hypereutrophic region of Lake Taihu. We sampled four fishes: the phytoplanktivorous Hypophthalmichthys molitrix and Aristichthys nobilis, the omnivorous Carassius auratus, and the carnivorous Culter ilishaeformis. Alterations of the antioxidant (GSH) and the major antioxidant enzymes (CAT, SOD, GPx, GST) in livers were monitored monthly, and the ultrastructures of livers were compared between the bloom and post-bloom periods. During the cyanobacterial blooms, the phytoplanktivorous fishes displayed only slight ultrastructural changes in liver, while the carnivorous fish presented the most serious injury as swollen endomembrane system and morphologically altered nuclei in hepatocytes. Biochemically, the phytoplanktivorous fishes possessed higher basal GSH concentrations and better correlations between the major antioxidant enzymes in liver, which might be responsible for their powerful resistance to MCs. This article provided physiological and toxicological evidences for the possible succession of fish communities following occurrence of toxic cyanobacterial blooms and also for the applicability of using phytoplanktivorous fish to counteract toxic cyanobacterial blooms in natural waters. (C) 2007 Elsevier Ltd. All rights reserved.

Comparative studies on physiological responses to phosphorus in two phenotypes of bloom-forming Microcystis

Toxic Microcystis blooms frequently occur in eutrophic water bodies and exist in the form of colonial and unicellular cells. In order to understand the mechanism of Microcystis dominance in freshwater bodies, the physiological and biochemical responses of unicellular ( 4 strains) and colonial ( 4 strains) Microcystis strains to phosphorus ( P) were comparatively studied. The two phenotype strains exhibit physiological differences mainly in terms of their response to low P concentrations. The growth of four unicellular and one small colonial Microcystis strain was significantly inhibited at a P concentration of 0.2 mg l - 1; however, that of the large colonial Microcystis strains was not inhibited. The results of phosphate uptake experiments conducted using P- starved cells indicated that the colonial strains had a higher affinity for low levels of P. The unicellular strains consumed more P than the colonial strains. Alkaline phosphatase activity in the unicellular strains was significantly induced by low P concentrations. Under P- limited conditions, the oxygen evolution rate, Fv/ Fm, and ETRmax were lower in unicellular strains than in colonial strains. These findings may shed light on the mechanism by which colonial Microcystis strains have an advantage with regard to dominance and persistence in fluctuating P conditions.

Population growth and physiological characteristics of microalgae in a miniaturized bioreactor during space flight

A strain of microalgae (Anabaena siamensis) had been cultured in a miniaturized bioreactor during a retrievable satellite flight for 15 days. By means of remote sensing equipment installed in the satellite, we gained the growth curve of microalgae population in space every day in real time. The curve indicated that the growth of microalgae in space was slower than the control on ground. Inoculation of the retrieved microalgae culture showed that the growth rate was distinctively higher than ground control. But after several generations, both cultures indicated similar growth rates. Those data showed that algae, can adapt to space environment easily which may be valuable for designing more complex bioreactor and controlled ecological life support system in future experiment. (C) 2006 Elsevier Ltd. All rights reserved.

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.

Effects of heavy metals on plants and resistance mechanisms

Goal, Scope and Background. As one of the consequences of heavy metal pollution in soil, water and air, plants are contaminated by heavy metals in some parts of China. To understand the effects of heavy metals upon plants and the resistance mechanisms, would make it possible to use plants for cleaning and remediating heavy metal-polluted sites. Methods. The research results on the effects of heavy metals on plants and resistant mechanisms are compiled from Chinese publications from scientific journals and university journals, mostly published during the last decade. Results and Discussion. Effects of heavy metals on plants result in growth inhibition, structure damage, a decline of physiological and biochemical activities as well as of the function of plants. The effects and bioavailability of heavy metals depend on many factors, such as environmental conditions, pH, species of element, organic substances of the media and fertilization, plant species. But, there are also studies on plant resistance mechanisms to protect plants against the toxic effects of heavy metals such as combining heavy metals by proteins and expressing of detoxifying enzyme and nucleic acid, these mechanisms are integrated to protect the plants against injury by heavy metals. Conclusions. There are two aspects on the interaction of plants and heavy metals. On one hand, heavy metals show negative effects on plants. On the other hand, plants have their own resistance mechanisms against toxic effects and for detoxifying heavy metal pollution. Recommendations and Outlook. To study the effects of heavy metals on plants and mechanisms of resistance, one must select crop cultivars and/or plants for removing heavy metals from soil and water. More highly resistant plants can be selected especially for a remediation of the pollution site. The molecular mechanisms of resistance of plants to heavy metals should be studied further to develop the actual resistance of these plants to heavy metals. Understanding the bioavailability of heavy metals is advantageous for plant cultivation and phytoremediation. Decrease in the bioavailability to farmlands would reduce the accumulation of heavy metals in food. Alternatively, one could increase the bioavailability of plants to extract more heavy metals.

Effects of CO2 enrichment on the bloom-forming cyanobacterium Microcystis aeruginosa (Cyanophyceae): Physiological responses and relationships with the availability of dissolved inorganic carbon

Microcystis aeruginosa Kutz. 7820 was cultured at 350 and 700 muL.L-1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom-forming cyanobacterium. Doubling Of CO2 concentration in the airflow enhanced its growth by 52%-77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light-saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC-saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3- levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 muL.L-1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3- concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease.