Initial Algal Density Research Articles

Gramine-induced growth inhibition, oxidative damage and antioxidant responses in freshwater cyanobacterium Microcystis aeruginosa

In recent years, the exploration and development of the effective methods of treatment and prevention to algal blooms, especially Microcystis aeruginosa blooms has been an important issue in the field of water environment protection. Allelochemicals (natural plant toxins) are considered promising sources of algicides to control algal blooms. The objective of this study is to determine the inhibitory effects and potential mechanisms of a well-known allelochemical gramine (N,N-dimethyl-3-amino-methylindole) on bloom-forming cyanobacterium M. aeruginosa. The results showed that this indole alkaloid effectively inhibited the growth of M. aeruginosa. The effective concentration causing a 50% inhibition at 3 d (EC 50, 3 d) increased with the initial algal density (IAD) increasing. When IAD increased from 5 × 10 4 to 5 × 10 5 cells mL −1, the values of EC 50, 3 d increased from 0.5 to 2.1 mg L −1. In the cells of M. aeruginosa, gramine caused an obvious increase in the level of reactive oxygen species (ROS). The lipid-peroxidation product malondialdehyde (MDA) increased significantly in gramine-treated cells. The effects of gramine on enzymatic and non-enzymatic antioxidants were in different manners. The activity of superoxide dismutase (SOD) was decreased after gramine exposure. The catalase (CAT) activity was increased after 4 h but decreased from 60 h. Both the contents and the regeneration rates of ascorbic acid (AsA) and reduced glutathione (GSH) were increased after 4 h of exposure to gramine. However, only GSH content was still increased after 40 h of exposure. These results suggested that the activation of antioxidants in M. aeruginosa played an important role to resist the stress from gramine at initial time, the inactivation of SOD is crucial to the growth inhibition of M. aeruginosa by gramine, and the phytotoxicity of gramine on M. aeruginosa may be due to oxidative damage via oxidation of ROS.

Growth and physiological responses of freshwater green alga Selenastrum capricornutum to allelochemical ethyl 2-methyl acetoacetate (EMA) under different initial algal densities

Most natural algicides including macrophytic allelochemicals are known to selectively inhibit algal growth. The investigations on the modes of action about the species-specific algicides are little. In this study, the effects of allelochemical ethyl 2-methyl acetoacetate (EMA) identified from reed ( Phragmites communis) on the growth, physiological, and biochemical processes of green alga Selenastrum capricornutum were investigated. The results showed that EMA had multiple effects on the growth of S. capricornutum under different initial algal densities (IADs). The algal growth was inhibited by EMA at low IADs, but stimulated at high IADs. Further, the potential modes of action of EMA on S. capricornutum were explored from ultrastructure, metabolic activity, reactive oxygen species level, and lipid peroxidation to trace the microenvironment changes in the algal cells. Damage in cell structure occurred at low IAD, but cells were well developed with increased metabolic activity at high IAD. The reactive oxygen species (ROS) levels were increased under both conditions. The increase of ROS level was acute at low IAD but slow at high IAD. EMA caused significant lipid peroxidation, i.e. oxidative damage on membrane lipids at low IAD but not at high IAD. Based on these results, the initial algal density is considered an important factor to influence algal growth and physiological and biochemical responses to EMA, the effects of EMA on S. capricornutum may be “hormesis-like”, and different ROS increase ratio may be directly related with different responses of S. capricornutum to EMA.

Allelopathic effects of the submerged macrophyte Potamogeton malaianus on Scenedesmus obliquus

Allelopathic effects of the submerged macrophyte Potamogeton malaianus on Scenedesmus obliquus were assessed using a twophase approach under controlled laboratory conditions. In the co- culture experiment ( phase I), the growth of S. obliquus at two different initial cell densities was significantly inhibited by P. malaianus. Moreover, the growth inhibition was dependent on the biomass density of P. malaianus. Antioxidant enzymes ( SOD, CAT and POD), MDA, APA, total soluble protein, protein electrophoretic pattern and morphology of S. obliquus were determined after the coculture experiment was terminated. The activities of SOD, CAT, POD and APA at the low initial cell density were stimulated, the contents of MDA and total soluble protein were increased, and some special protein bands disappeared in P. malaianus treatments. The macrophyte had no effect on the activities of SOD and APA at the high initial cell density, but significantly influenced other physiological parameters of S. obliquus with the increase of biomass density. The morphology of S. obliquus showed no difference in the macrophyte treatments and the controls, and the cultures were dominated by 4- celled coenobia. The results indicated P. malaianus had significant allelopathic effects on the growth and physiological processes of S. obliquus. Moreover, the allelopathic effects depended on initial algal cell density, biomass density of the macrophyte, and their interaction. In the experiment of P. malaianus culture filtrates ( phase II), filtrates from combined culture of plant and S. obliquus at the low initial cell density exhibited no apparent growth inhibitory effect on S. obliquus. The result showed that initial addition of growth- inhibiting plant filtrates had no allelopathic effect on S. obliquus. We concluded that the allelopathic effects on S. obliquus were found in the presence of P. malaianus, but not in P. malaianus filtrates. However, the absence of allelopathic effect on S. obliquus might be due to the very low concentrations of allelochemicals in the filtrates.

Isolation and algae-lysing characteristics of the algicidal bacterium B5

Water blooms have become a worldwide environmental problem. Recently, algicidal bacteria have attracted wide attention as possible agents for inhibiting algal water blooms. In this study, one strain of algicidal bacterium B5 was isolated from activated sludge. On the basis of analysis of its physiological characteristics and 16S rDNA gene sequence, it was identified as Bacillus fusiformis. Its algaelysing characteristics on Microcystis aeruginosa, Chlorella and Scenedesmus were tested. The results showed that: (1) the algicidal bacterium B5 is a Gram-negative bacterium. The 16S rDNA nucleotide sequence homology of strain B5 with 2 strains of B. fusiformis reached 99.86%, so B5 was identified as B. fusiformis; (2) the algal-lysing effects of the algicidal bacterium B5 on M. aeruginosa, Chlorella and Scenedesmus were pronounced. The initial bacterial and algal cell densities strongly influence the removal rates of chlorophyll- a. The greater the initial bacterial cell density, the faster the degradation of chlorophyll- a. The greater the initial algal cell density, the slower the degradation of chlorophyll- a. When the bacterial cell density was 3.6 fi 10 7 cells/ml, nearly 90% of chlorophyll- a was removed. When the chlorophyll- a concentration was less than 550 μg/L, about 70% was removed; (3) the strain B5 lysed algae by secreting metabolites and these metabolites could bear heat treatment.

Herbivory under Different Flow Regimes: A Field Experiment and Test of a Model with a Benthic Stream Insect

An experiment was conducted in an open-canopy mountain stream to examine the effects of different densities of the grazing caddisfly Agapetus boulderensis (Trichoptera: Glossosomatidae) on algal biomass and assemblage structure at two current velocities. Unglazed ceramic tiles were colonized by algae in grazer-free troughs for 30 d at slow (∼ 20 cm s −1 ) and fast (∼ 40 cm s −1 ) velocities before transfer to open troughs of similar velocity, where they were exposed to grazer densities ranging from ca 0.7 to 2.7 times natural streambed densities. At low velocity, algal biomass (chl-a and particulate C) and absolute densities of bacillariophytes, chlorophytes and cyanophytes declined as grazer density increased. Grazers also significantly altered algal assemblage structure by reducing the relative abundance of cyanophytes (mostly Anabaena cf. affinis) and chlorophytes (Ulothrix zonata) and increasing the relative abundance of some bacillariophytes (Cocconeis placentula, Fragilaria pinnata, F. vaucheriae, Melosira italica). The algal assemblage was effectively converted from a «late-successional» to an «early-successional» stage by grazers. By contrast, at high velocity, initial algal density was relatively low and grazers were less effective in inducing changes. As grazer density increased, total algal cell abundance (mostly bacillariophytes) declined, although the relative abundances of individual diatom species remained unmodified under increasing grazer densities. Grazers essentially maintained the «early-successional» nature of the algal assemblage under high velocity conditions. Further, for both current velocities, we tested a model that predicts algal biomass as a function of grazer density and time. Independent estimates of current-dependent grazing rate and algal growth rate were used in the model to generate predictions of particulate C along a gradient of grazer density at two current velocities. Algal biomass predicted by the model compared favorably with an empirical fit of the data under low and high velocities. These results suggest that the role of grazers in structuring algal assemblages may vary spatially with local current velocity in heterogeneous stream systems

Effect of algal density on nutrient removal from primary settled wastewater

Laboratory scale batch experiments were employed to examine the effect of initial inoculum sizes of algae on their activities and reduction of nutrients form the primary settled municipal sewage. The microalgae, Chlorella vulgaris, with four initial inoculum sizes, namely ‘superconcentrated’ (1 × 10 7 cells ml −1) ‘concentrated’ (5 × 10 6 cells ml −1), ‘medium’ (1 × 10 6 cells ml −1) and ‘low’ (5 × 10 5 cells ml −1), were applied to primarily treated sewage. The cell number and chlorophyll content of all algal cultures increased gradually in the first week and the rates of increase were similar in all cultures. During the experimental period, even in the ‘superconcentrated’ cultures, the self-shading problem was not found probably due to good mixing. At the end of the 10 days study, over 90% NH 4 + —N and 80% PO 4 3—P were removed from wastewater in all cultures except the ‘low’ one. The residual concentrations of NH 4 +—N, PO 4 3—P, TKN and total P in wastewater were negatively correlated with the cell numbers and chlorophyll content of the cultures. These results indicated that the efficiency of reducing wastewater-borne nutrients by an algal system was directly related to the physiological activity and growth of the Chlorella cells which in turn were affected by the initial inoculum size. The super-concentrated culture with an initial algal density of 1 × 10 7 cells ml 1 seemed to be more beneficial as this treatment achieved satisfactory nutrient removal within 7 days instead of 10. The sharp initial reduction of COD (>50%) and total organic-N (>60%) was not related to the algal number or chlorophyll content, the performance in the control (without algal cells) was similar to that of the algal cultures. This suggests that the removal of COD and TON was mainly due to the metabolism of the indigenous bacteria. Under the open system, the interaction between algal and bacterial cells was significant which could enhance the simultaneous removal of N, P and organic matter from primary settled sewage.

Effects of initial algal density on community development in aquatic microcosms

Effects of initial algal density on community development in aquatic microcosms

Cadmium incorporation by the marine copepod Pseudodiaptomus coronatus1

Pseudodiaptomus coronatus, after exposure to phytoplankton and cadmium in concentrations like those in temperate, coastal environments, incorporated 109Cd at higher rates from ambient water than from phytoplankton food. When ambient stable cadmium concentrations were increased from 0.03 to 1.00 µg·liter−1, cadmium concentration by phytoplankton cells increased and the rate of cell ingestion by P. coronatus decreased. This inverse relation between the accumulation of cadmium in phytoplankton cells and the animal’s ingestion rate resulted in relatively small net increases in the cadmium accumulated from phytoplankton by copepods.Rates of stable cadmium ingestion for P. coronatus ranged from 0.18 to 0.38 ng·mg animal dry wt−1·h−1, depending on the initial algal cell density and the ambient cadmium concentration. For cadmium concentrations of 0.03 to 1.00 µg·liter−1, percentage assimilation efficiencies ranged from 13.20 to 68.40. Both rates of cadmium ingestion and assimilation efficiencies were higher than published values for carnivorous zooplankton.

The corrosion of metals by acids

In this study, three strains of microalgae, including Scenedesmus sp. LX1, Navicula pelliculosa and Cyclotella sp., were selected to investigate their treatment effects on black and odorous water and their growth potential, after which the optimal treatment conditions were obtained. All three strains, especially Navicula, have been shown to be effective at removing pollutants from black and odorous water samples. The removal rate of ammonia nitrogen (NH4+-N) and total phosphorus (TP) from the water samples treated by Navicula could reach up to 100%, and total nitrogen (TN) and chemical oxygen demand (COD) were cut by 66.67 ± 2.30% and 81.82 ± 2.10%, respectively. After treatment with Navicula, the dissolved oxygen (DO) and the oxidation-reduction potential (ORP) values of the water samples significantly improved, and the pH value was closest to neutrality. The samples treated with Navicula exhibited the best water quality. All three microalgae could grow in black and odorous water samples with different growth characteristics, among which Navicula, with more moderate growth characteristics, was considered to have greater application potential than the other two strains for the future treatment of black and odorous water. To promote the ability of Navicula to purify black and odorous water, the optimal conditions to allow Navicula to promote pollutant removal for water purification were determined to be an initial algal density of 2.50 × 105 cells mL−1, a temperature of 10.60 °C and a light intensity of 2437.5 lx using a Box-Behnken design of response surface methodology.