Recovery of freshwater algal assemblage from copper and zinc toxicity in a semi-continuous culture system.

Viral infections are a major factor in diatom cell death. However, the effects of viruses on diatom dynamics remain unclear. Based on laboratory studies, it is hypothesized that virus-induced diatom mortality is dependent on the diatom growth rate. The present study aimed to elucidate the relationship between the diatom growth rate and virus-induced mortality using model systems of the marine planktonic diatom, Chaetoceros tenuissimus and its infectious viruses. We also examined the fate of diatom populations in a semi-continuous dilution culture system, in which host growth rates were controlled at 0.69, 2.08, and 3.47 day–1. Diatom populations gradually decreased following the viral inoculation of each culture system, and virus-induced mortality inversely correlated with the diatom growth rate. Furthermore, the viral burst size was slightly higher in lower growth rate cultures. These results suggested that the host physiological status related to the growth rate affected viral infection and proliferation. Diatom populations were not completely lysed or washed out in any of the dilution systems; they showed steady growth in the presence of infectious viruses. This may be partially explained by defective interference particles from viruses and cell debris. The present results indicate that diatoms in dilution environments maintain their populations, even under viral pressure. Moreover, diatom populations with a low growth rate may partially sustain higher growth populations through nutrient recycling following virus-induced cell death. The results of the present study provide insights into diatom dynamics in natural environments in the presence of infectious viruses.

Effects of Alternating High and Medium Concentrate Diets on Fermentation in a Semi-Continuous Rumen Culture System

The relationship between zinc and copper toxicity in Hyalella azteca and accumulation from metal-spiked sediments was determined for future use in identifying sites where these metals contribute to sediment toxicity. Both zinc and copper accumulation increased rapidly with increasing sediment concentrations, showing no evidence of saturation as seen in waterborne exposures. Zinc accumulation from zinc spiked sediments was substantial, even at concentrations below those causing chronic toxicity, and body concentrations can readily be used to infer chronic toxicity. Chronic toxicity in spiked sediment exposures occurred at excess (above background) body concentrations twice as high as in waterborne exposures, possibly as a result of zinc in gut contents. In contrast, chronic copper toxicity occurred at body concentrations lower than those observed in waterborne exposures. Furthermore, body copper at low sediment exposures was independent of copper in sediment. Body copper concentrations can be used to infer short-term (1-week) toxicity but not chronic toxicity. Copper, but not zinc, caused a reduction in growth, even at concentrations below the 4-week LC25. Reduced growth can, therefore, be used to differentiate between chronic copper and zinc toxicity in sediments.

Interactive toxic effects of heavy metals and humic acids on Vibrio fischeri

The effect of humic acids (HA) on the toxicity of copper, zinc and lead was investigated in this study, using the photobacterium Vibrio fischeri (Microtox test) as a test organism. The metal species and the complexation capacity of HA were predicted using model WinHumicV for speciation modeling. The toxicities of copper and lead were generally comparable, while the toxicity of zinc was lower than the ones of the other two method. The toxicity of copper decreased with the addition of HA, while the toxicity of zinc remained almost constant. The complexation of Zn with HA was low. Thus the presence of HA did not significantly influence the toxicity of Zn. For Cu and Zn, the free metal ion species showed to be basically responsible for the toxicity of these metals, while for Pb the chlorocomplexes and Pb-HA complexes contributed to the toxicity of Pb, indicating that the toxicity of heavy metals depends not only on the free metal ion species concentration but on different metal species that may be bioavailable.

The amyloid precursor protein (APP) of Alzheimer's disease can reduce copper (II) to copper (I) in a cell-free system potentially leading to increased oxidative stress in neurons. We used neuronal cultures derived from APP knock-out (APP(-/-)) and wild-type (WT) mice to examine the role of APP in copper neurotoxicity. WT cortical, cerebellar, and hippocampal neurons were significantly more susceptible than their respective APP(-/-) neurons to toxicity induced by physiological concentrations of copper but not by zinc or iron. There was no difference in copper toxicity between APLP2(-/-) and WT neurons, demonstrating specificity for APP-associated copper toxicity. Copper uptake was the same in WT and APP(-/-) neurons, suggesting APP may interact with copper to induce a localized increase in oxidative stress through copper (I) production. This was supported by significantly higher levels of copper-induced lipid peroxidation in WT neurons. Treatment of neuronal cultures with a peptide corresponding to the human APP copper-binding domain (APP142-166) potentiated copper but not iron or zinc toxicity. Incubation of APP142-166 with low-density lipoprotein (LDL) and copper resulted in significantly increased lipid peroxidation compared to copper and LDL alone. Substitution of the copper coordinating histidine residues with asparagines (APP142-166(H147N, H149N, H151N)) abrogated the toxic effects. A peptide corresponding to the zinc-binding domain (APP181-208) failed to induce copper or zinc toxicity in neuronal cultures. These data support a role for the APP copper-binding domain in APP-mediated copper (I) generation and toxicity in primary neurons, a process that has important implications for Alzheimer's disease and other neurodegenerative disorders.

Under autotrophic conditions, highly productive biodiesel production was achieved using a semi-continuous culture system in Neochloris oleoabundans. In particular, the flue gas generated by combustion of liquefied natural gas and natural solar radiation were used for cost-effective microalgal culture system. In semi-continuous culture, the greater part (~80%) of the culture volume containing vegetative cells grown under nitrogen-replete conditions in a first photobioreactor (PBR) was directly transferred to a second PBR and cultured sequentially under nitrogen-deplete conditions for accelerating oil accumulation. As a result, in semi-continuous culture, the productivities of biomass and biodiesel in the cells were increased by 58% (growth phase) and 51% (induction phase) compared to the cells in batch culture, respectively. The semi-continuous culture system using two stage photobioreactors is a very efficient strategy to further improve biodiesel production from microalgae under photoautotrophic conditions.

Comparison of the Effect of Different pH Buffering Techniques on the Toxicity of Copper and Zinc to Daphnia Magna and Pseudokirchneriella Subcapitata

This study determined the influence of key water chemistry parameters (pH, alkalinity, dissolved organic carbon [DOC], and hardness) on the aqueous speciation of copper and zinc and its relationship to the acute toxicity of these metals to the cladoceran Ceriodaphnia cf dubia. Immobilization tests were performed for 48-h in synthetic or natural waters buffered at various pH values from 5.5 to 8.4 (other chemical parameters held constant). The toxicity of copper to C. cf dubia decreased fivefold with increasing pH, whereas the toxicity of zinc increased fivefold with increasing pH. The effect of DOC on copper and zinc toxicity to C. cf dubia was determined using natural fulvic acid in the synthetic water. Increasing DOC was found to decrease linearly the toxicity of copper, with the mean effect concentration of copper that immobilized 50% of the cladocerans (EC50) value 45 times higher at 10 mg/L, relative to 0.1 mg/L DOC at pH 6.5. In contrast, the addition of 10 mg/L DOC only resulted in a very small (1.3-fold) reduction in the toxicity of zinc to C. cf dubia. Copper toxicity to C. cf dubia generally did not vary as a function of hardness, whereas zinc toxicity was reduced by a factor of only two, with an increase in water hardness from 44 to 374 mg CaCO3/L. Increasing bicarbonate alkalinity of synthetic waters (30-125 mg/L as CaCO3) decreased the toxicity of copper up to fivefold, which mainly could be attributed to the formation of copper-carbonate complexes, in addition to a pH effect. The toxicity of copper added to a range of natural waters with varying DOC content, pH, and hardness was consistent with the toxicity predicted using the data obtained from the synthetic waters.

High production of β-thujaplicin with Thuja dolabrata var. hondai cells in a semi-continuous culture system

Effects of EDTA, peat soil extracts (PSE) and humic acid (HA) on toxicity of copper and zinc to goldfish, Carassius auratus were studied in toxicity tests. Data obtained indicated that the toxicity of Zn was effectively reduced in the presence of EDTA because of complexation of Zn to EDTA. Toxicity of Cu in the presence of EDTA, PSE and HA, however, was less predictable on the basis of complexation/speciation theory because at high concentrations of added Cu, mortality of test organisms occurred despite the fact that free Cu2+ was low (pCu < 7) and could not be detected by Cu ion-selective electrode (Cu-ISE). All complexants tested managed to suppress the toxic effects of Cu at the lowest concentration of Cu used (0.25 mg L-1), while higher Cu concentrations tested resulted in mortality indicating that the Cu complexes formed could have been toxic to goldfish. Cu-EDTA complex seem to be the most toxic, followed by Cu-PSE and Cu-HA which were of similar toxicity.

Toxicity of copper and zinc to Puntius parrah (Day, 1865)

The effect of culture medium on metal toxicity to the marine diatom Nitzschia closterium and the freshwater green alga Chlorella pyrenoidosa

The acute toxicity of copper, zinc and manganese and copper‐zinc and copper‐manganese mixtures were determined for juvenile longfin dace, Agosia chrysogaster in hard water bioassays (mean=218 mg 1−1 CaCO3). Copper‐zinc was the most lethal toxicant (96‐h L.c.50= 0.21 mg 1−1 copper and 0.28 mg 1−1 zinc) and exhibited a more than additive toxicity which was in contrast to the additive toxicity of copper‐manganese mixtures (96‐h L.c.50= 0.45 mg 1−1 copper and 64.0 mg 1−1 manganese). The toxicity of copper (96‐h L.c.50= 0.86 mg 1−1) and zinc (96‐h L.c.50= 0.79 mg 1−1) to the fish was similar but both were considerably more lethal than manganese (96‐h L.c.50= 130 mg 1−1).

To overcome the problems associated with high concentrations of nutrient and test chemicals in laboratory Lemna gibba bioassays, a semi-continuous culture system was adopted, and specific equipment was designed and constructed to simulate steady-state conditions of the most natural aquatic systems. The equipment for Lemna semicontinuous culture consists of a growth chamber and a circulation control unit. Lemna gibba is kept in the growth chamber in a growth pot (with 1 mm diameter perforation at about 10 cm above the bottom), which retains the plant but allows an efficient exchange of the growth medium. Flow rate and composition of the medium is therefore varied independently of the L. gibba population density. The media are kept in circulation, and recharges or discharge of the media are controlled. The system took into consideration chemical processes such as O2 and CO2 exchange and maintained a degree of turbulence through continuous shaking of the growth chambers. It is also possible to investigate growth under different supply of O2 and CO2, and pH control with dissolved CO2 or reducing conditions with N2 gases. Theoretical analysis of growth in the steady state shows that integrated activation time of the dilution pump is proportional to the growth rate of L. gibba. Theoretical analysis was also used to determine the minimum flow-rate and nutrient concentration of the medium to cover the requirements of L. gibba. Experiments were carried out that demonstrated that the steady state growth could be attained and be controlled by the nutrient concentration, flow rate, and recharge intervals. The cultures could be kept at steady state over 21 days of the Lemna test period. Keywords. Lemna gibba, steady state, semicontinuous culture, batch culture, nutrient media