Effect of Nutrient Starvation under High Irradiance on Lipid and Starch Accumulation in Chlorella fusca (Chlorophyta).

The effect of nitrogen and sulphur limitation under high irradiance (PAR) was studied in the green microalga Chlorella fusca (Chlorophyta) in order to follow lipid and/or starch accumulation. Growth, biomass composition and the changes in photosynthetic activity (in vivo chlorophyll a fluorescence) were followed in the trials. The full nutrient culture showed high biomass production and starch accumulation at Day 1, when photosynthetic activity was high. Gradual deprivation (no nutrients added) became evident when photosynthesis was significantly suppressed (Day 3 onwards), which entailed a decrease of maximum relative electron transport rate (rETRmax) and increase of non-photochemical quenching (NPQ), accompanied by the onset of lipid accumulation and decline in starch content. In N- and S-starved cultures, rETRmax significantly decreased by Day 3, which caused a substantial drop in biomass production, cell number, biovolume and induction of lipid and starch accumulation. High starch content (45-50 % of DW) was found at the initial stage in full nutrient culture and at the stationary phase in nutrient-starved cultures. By the end of the trial, all treatments showed high lipid content (~30 % of DW). The full nutrient culture had higher biomass yield than starved treatments although starch (~0.2 g L(-1) day(-1)) and lipid (~0.15 g L(-1) day(-1) productivities were fairly similar in all the cultures. Our results showed that we could enrich biomass of C. fusca (% DW) in lipids using a two-stage strategy (a nutrient replete stage followed by gradual nutrient limitation) while under either procedure, N- or S-starvation, both high lipid and starch contents could be achieved.

Resistance of common carp (Cyprinus carpio L.) to oxidative stress after chloramine-T treatment is increased by microalgae carotenoid-rich diet.

OBJECTIVES: In fish aquaculture, disinfectants are used against bacterial and protozoal infections. These compounds cause oxidative stress that may stimulate the generation of reactive oxygen species, and subsequently the alteration in antioxidant systems of exposed organisms. Antioxidants like carotenoids present in microalgae increase carp resistance to oxidative stress after chemical treatment. DESIGN: The aim of these experiments was to prove increased resistance of common carp (Cyprinus carpio L.) juveniles fed on experimental diets with microalgae biomass supplement (Algadiets) to oxidative stress caused by a disinfectant chloramine-T. In indoor experiments fish were fed on laboratory-prepared extruded diets containing supplement of Chlorella spp. (cf. C. vulgaris Beijerinck) biomass which contains antioxidants (carotenoids) like lutein. The young-of-the-year-old fish were acclimatized and fed on basal diet (control group) and the on diets containing 1, 2, 5 and 10% (w/w) of spray-dried Chlorella biomass (Algadiet 1, 2, 5 and 10) for 14 days followed by 6 weeks. Consequently, fish were treated daily with chloramine-T (Chl-T) at concentration of 10 mg x l(-1) for 1 h in three consecutive days. After this treatment, the indices of oxidative stress and antioxidant enzyme activity were assayed in fish gill, muscle and hepatopancreas. RESULTS: The fish fed on different Algadiets had increased antioxidant enzyme activities of glutathione peroxidase, glutathione reductase and catalase in flesh after the exposure to Chl-T. Higher activities of superoxide dismutase, glutathione peroxidase and glutathione reductase were also observed in the hepatopancreas in all tested concentrations compared to the control group fed on the basal diet. The increased production and activity of antioxidant enzymes confirmed improved protection ability of fish tissues against oxidative damage when microalgae biomass was supplemented to the fish diet which was more pronounced by higher microalgae supplement in Algadiet 5 and 10 where the content of carotenoids was 105 mg and 214 mg per kilogram of fed, respectively. CONCLUSION: The results show the positive effect of carotenoids from microalgae biomass to maintain the antioxidant capacity which increases resistance of fish to oxidative stress.

Trichloroethylene (TCE) removal in a single pulse suspension bioreactor.

This work describes TCE biotic removal in a single-pulse bioreactor under aerobic conditions. Activated sludge from a wastewater-treatment plant was used for inoculation of the cultivator. The experiment focused on a more detailed verification of microbial composition of mixed heterotrophic culture during pulsed phenol dosage. Attention was given to suppressing eucaryotic organisms, particularly yeasts and fungi, by the addition of cycloheximide. The TCE-removal capacity of the heterotrophic culture, described by kinetic tests, was dependent on pulsed phenol injection and on cyclic addition of phenol and TCE. Maximum TCE degradation was determined in a batch test. It was found that the addition of cycloheximide (an antibiotic against propagation and growth of fungi and yeast) increased the TCE degradation activity of the mixed microbial suspension. A certain residual amount of TCE remained in some of the experiments.