Accumulation and detoxification dynamic of cyanotoxins in the freshwater shrimp Palaemonetes argentinus

The uptake and accumulation of microcystin-LR (MC-LR) in the shrimp Palaemonetes argentinus was investigated using both laboratory and field assays. Shrimps were exposed in aquarium during 1, 2, 3 and 7 days to 1, 10 and 50 μg L⁻¹ MCLR. Accumulation (0.7 ± 0.2 μg MC-LR g⁻¹) was observed after three days exposures to 50 μg L⁻¹ toxin. Then, shrimps were relocated in fresh water (free of MCLR) to verify the detoxification dynamic, showing a drop to 0.18 ± 0.01 μg MCLR g⁻¹ after three days. The activity of glutathione-S-transferase, measured in the microsomal fraction (mGST), was significantly increased during the exposure period, with further increment during the detoxification period. Furthermore, cytosolic GST (sGST) and glutathione reductase (GR) increased their activities during detoxification, while inhibition was observed for catalase (CAT) with no significant changes for glutathione peroxidase (GPx). Current results suggest that GSH conjugation could be an important MC detoxification mechanism in P. argentinus and that MCLR induce oxidative stress in this shrimp.Field exposures were carried out in San Roque Reservoir (Córdoba, Argentina) after a cyanobacteria bloom. Nodularin (Nod) presence was measured for the first time in this waterbody (0.24 ± 0.04 μg L⁻¹), being the first report of Nod in South America freshwaters. Nod was also detected in Palaemonetes argentinus (0.16 ± 0.03 μg g⁻¹) after three weeks of exposure in this reservoir, with the concomitant activation of mGST, sGST and CAT.Although internal doses of Nod were low throughout the exposure, they were enough to cause biochemical disturbances in Palaemonetes argentinus.Further laboratory studies on Nod accumulation and antioxidant responses in Palaemonetes argentinus are necessary to fully understand these field results. P. argentinus should be considered a potential vector for transferring cyanotoxins to higher trophic levels in aquatic environments.     

Optimisation and scale-up of α-glucuronidase production by recombinant Saccharomyces cerevisiae in aerobic fed-batch culture with constant growth rate

α-Glucuronidase (EC 3.2.1.139) of family GH 115 from Scheffersomyces stipitis is a valuable enzyme for the modification of water-soluble xylan into insoluble biopolymers, due to its unique ability to act on polymeric xylans. The influence of growth rate on the production of α-glucuronidase by recombinant Saccharomyces cerevisiae MH1000pbk10D-glu in glucose-limited fed-batch culture was studied at 14 and 100 L scale. At and below the critical specific growth rate (μ_crit) of 0.12 h⁻¹ at 14 L scale, the biomass yield coefficient (Y_x/s) remained constant at 0.4 g g⁻¹ with no ethanol production, whereas ethanol yields relative to biomass (k_eth/x) of up to 0.54 g g⁻¹ and a steady decrease in Y_x/s were observed at μ > 0.12 h⁻¹. Production of α-glucuronidase was growth associated at a product yield (k_α-glu/x) of 0.45 mg g⁻¹, with the highest biomass (37.35 g/L) and α-glucuronidase (14.03 mg/L) concentrations, were recorded during fed-batch culture at or near to μ_crit. Scale-up with constant k_La from 14 to 100 L resulted in ethanol concentrations of up to 2.5 g/L at μ = 0.12 h⁻¹. At this scale, α-glucuronidase yield could be maximised at growth rates below μ_crit, to prevent localised high glucose concentration pockets at the feed entry zone that would induce oxido-reductive metabolism. This is the first report where recombinant production of α-glucuronidase (EC 3.2.1.139) by S. cerevisiae was optimised for application at pilot scale.     

Effects of phosphorus and nitrogen amendments on the growth of Egeria najas

The effect of nutrient addition on the growth of E. najas was evaluated in a dose response experiment using sand amended with phosphorus (P) and nitrogen (N), and in enrichment trials with N and P amendments to natural sediments. Plants, water and sediment came from lagoons of the Upper Paraná River Floodplain and from Itaipu Reservoir (Brazil). Relative growth rates (RGRs) of E. najas shoots, based on dry mass (DM), varied from 0.03 to 0.060 d⁻¹ for both nutrients. Root:shoot biomass ratios were related to sediment exchangeable P (r = −0.419; P = 0.03) and N (r = −0.54; P = 0.006), however root RGR was not related to sediment nutrient concentrations. When natural sediments were amended with N and P, neither shoot nor root RGRs differed among treatments for substrata from either the reservoir or the floodplain lagoons (P > 0.05). Comparison of nutrient concentrations measured in natural sediments collected from several sites in both the Upper Paraná River Floodplain (range 49–213 μg P g⁻¹ DM; 36–373 μg N g⁻¹ DM) and Itaipu Reservoir (range 43–402 μg P g⁻¹ DM; 7.9–238 μg N g⁻¹ DM) showed that sediment N and P from these systems usually exceeded minimum requirements necessary for E. najas growth, as measured in the dose response experiment. Together, these results indicate that E. najas, at least in early stages of development, responds to sediment nutrient amendments and relies upon bottom sediments to meet its N and P requirements and that for at least two Brazilian ecosystems, growth of this species is not limited by insufficient sediment N or P. Thus, reducing N and P in water is not enough to control E. najas growth in short time periods in these ecosystems.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

Accumulation of phycocyanin in heterotrophic and mixotrophic cultures of the acidophilic red alga Galdieria sulphuraria

The relationship between light intensity, nitrogen availability and pigmentation was investigated in mixotrophic and heterotrophic cultures of the unicellular red alga Galdieria sulphuraria 074G, a potential host for production of the blue pigment, phycocyanin (PC). During the exponential growth phase of batch cultures, G. sulphuraria 074G contained 2–4 mg phycocyanin per g dry weight. In carbon-limited and nitrogen-sufficient batch cultures grown in darkness, this value increased to 8–12 mg g⁻¹ dry weight during the stationary phase, whereas the phycocyanin content in nitrogen-deficient cells decreased to values below 1 mg g⁻¹ dry weight during stationary phase. Light intensities between 0 and 100 μmol photons m⁻² s⁻¹ had no influence on phycocyanin accumulation in mixotrophic cultures grown on glucose or fructose, while light stimulated phycocyanin synthesis in cultures grown on glycerol, in which the phycocyanin content in stationary phase was increased from 10 mg g⁻¹ dry weight in darkness to 20 mg g⁻¹ dry weight at a light intensity of 80 μmol photons m⁻² s⁻¹. At higher light intensities, less phycocyanin accumulated than at lower intensities, irrespective of the carbon substrate used. In carbon-limited continuous flow cultures grown on glucose or glycerol at a dilution rate of 0.63 day⁻¹, corresponding to 50% of the maximum specific growth rate, the highest steady-state phycocyanin content of 15–28 mg g⁻¹ dry weight was found at 65 μmol photons m⁻² s⁻¹. In contrast to the apparent glucose repression of light-induced PC synthesis observed in batch cultures, no glucose repression of the light stimulation was observed in continuous flow cultures because the glucose concentration in the culture supernatant always remained at limiting levels. Despite the fact that G. sulphuraria 074G contains less phycocyanin than some other microalgae and cyanobacteria, the ability of G. sulphuraria 074G to grow and synthesize phycocyanin in heterotrophic or mixotrophic cultures makes it an interesting alternative to the cyanobacterium, Spirulina platensis presently used for synthesis of phycocyanin.     

Differences in the photoacclimation and photoprotection exhibited by two species of the ciguatera causing dinoflagellate genus,Gambierdiscus

In culture, Gambierdiscus spp. have been shown to prefer irradiances that are relatively low (≤250 μmol photons m⁻² s⁻¹) versus those to which they are frequently exposed to in their natural environment (>500 μmol photons m⁻² s⁻¹). Although several behavioral strategies for coping with such irradiances have been suggested, it is unclear as to how these dinoflagellates do so on a physiological level. More specifically, how do long term exposures (30 days) affect cell size and cellular chlorophyll content, and what is the photosynthetic response to short term, high irradiance exposures (up to 1464 μmol photons m⁻² s⁻¹)? The results of this study reveal that cell size and chlorophyll content exhibited by G. carolinianus increased with acclimation to increasing photon flux density. Additionally, both G. carolinianus and G. silvae exhibited reduced photosynthetic efficiency when acclimated to increased photon flux density. Photosynthetic yield exhibited by G. silvae was greater than that for G. carolinianus across all acclimation irradiances. Although such differences were evident, both G. carolinianus and G. silvae appear to have adequate biochemical mechanisms to withstand exposure to irradiances exceeding 250 μmol photons m⁻² s⁻¹ for at least short periods of time following acclimation to irradiances of up to 150 μmol photons m⁻² s⁻¹.     

Evaluation of distant carbon sources in biosurfactant production by a gamma ray-induced Pseudomonas putida mutant

Pseudomonas putida 33 wild strain, subjected to gamma ray mutagenesis and designated as P. putida 300-B mutant was used as microbial rhamnolipid-producer by using distant carbon sources (viz. hydrocarbons, waste frying oils ‘WFOs’, vegetable oil refinery wastes and molasses) in the minimal media under shake flask conditions. The behavior of glucose as co-substrate and growth initiator was examined. The 300-B mutant strain showed its ability to grow on all the substrates tested and produced rhamnolipid surfactants to different extents however; soybean and corn WFOs were observed to be preferred carbon sources followed by kerosene and paraffin oils, respectively. The best cell biomass (3.5 g l⁻¹) and rhamnolipids yield (4.1 g l⁻¹) were obtained with soybean WFO as carbon source and glucose as growth initiator under fed-batch cultivation showing an optimum specific growth rate (μ) of 0.272 h⁻¹, specific product yield (q_p) of 0.318 g g⁻¹ h and volumetric productivity (P_V) of 0.024 g l⁻¹ h. The critical micelle concentration of its culture supernatant was observed to be 91 mg rhamnolipids l⁻¹ and surface tension as 31.2 mN m⁻¹.     

Consumption of benthic cyanobacterial mats and nodularin-R accumulation in freshwater crayfish (Paranephrops planifrons) in Lake Tikitapu (Rotorua,New Zealand)

Recent surveys of periphyton in Lake Tikitapu revealed widespread benthic mats dominated by cyanobacteria. All mats tested positive for the cyanobacterial toxin nodularin-R. The New Zealand native freshwater crayfish or kōura (Paranephrops planifrons) are benthic-dwelling, opportunistic omnivores that are common in Lake Tikitapu. Benthic mats constitute a potential food source for this species. In this study an in-lake feeding experiment with isotopically labeled ¹³C benthic mats confirmed they were consumed by kōura. Consumption was variable amongst individuals, suggesting the benthic mats are an optional rather than primary food source. Nine kōura were also tested using liquid chromatography–mass spectrometry to determine if nodularin-R bioaccumulated in the hepatopancreas and tail tissue. The hepatopancreas of all kōura were positive for nodularin-R (9.7–225.3 μg kg⁻¹ ww) and nodularin-R was detected in low concentrations in the tail tissue of two individuals (0.5–0.7 μg kg⁻¹ ww). The detection of nodularin-R in kōura is the first in a freshwater organism in a freshwater system, and the first to show the accumulation of nodularin-R from freshwater benthic cyanobacterial mats. Benthic mats may need to be considered as a potential source of cyanotoxins in future freshwater food-web studies.     

Optimization of biomass production with enhanced glucan and dietary fibres content by Pleurotus ostreatus ATHUM 4438 under submerged culture

This work was aimed at optimizing biomass production by the edible basidiomycete Pleurotus ostreatus ATHUM 4438 in a submerged process with enhanced glucan and dietary fibres content. β-Glucan from Pleurotus sp. (pleuran) has been used as food supplements due to its immunosuppressive activity. Like other dietary fibre components, oyster mushroom polysaccharides can stimulate the growth of colon microorganisms (probiotics), i.e. act as prebiotics. We used the FF MicroPlate for substrate utilization and growth monitoring. The pattern of substrate catabolism forms a substrate assimilation fingerprint which is useful in selecting media components for media optimization of maximum biomass production. Different carbon sources (95) were used and then 8 of them were tested in shake flask cultures. The effect of various organic and complex nitrogen sources on biomass production was also examined and response surface methodology based on central composite design was applied to explore the optimal medium composition. When the optimized culture medium was tested in a 20-L stirred tank bioreactor, using 57 g L⁻¹ xylose and 37 g L⁻¹ corn steep liquor, high yields (39.2 g L⁻¹) of dry biomass was obtained. The yield coefficients for total glucan and dietary fibres on mycelial biomass formed were 140 ± 4 and 625 ± 9 mg g⁻¹ mycelium dry weight, respectively.     

Uptake and allocation of 13C by Enhalus acoroides at sites differing in light availability

Carbon fixation and allocation were studied using ¹³C incubation and leaf marking techniques in mature monospecific stands of Enhalus acoroides L.f. Royle in August 1998 and January 1999 in Banten Bay, Indonesia. The highest rate of ¹³C uptake (>0.008 g ¹³C g C⁻¹ d⁻¹) was found in the middle to distal parts of leaves of E. acoroides. Young and senescing leaves numbers had lower ¹³C incorporation compared to mature leaves. The incorporation of ¹³C by epiphytes on the leaves was higher than that of the leaves themselves (>0.01 g ¹³C g C⁻¹ d⁻¹). The results showed that turbidity of the water influenced the leaf growth, productivity and Relative Growth Rate of E. acoroides, which were lower at Kepuh Island, the more turbid site. However, at Kepuh Island, where the water column was turbid, the plant could still harvest sufficient light for an uptake rate of ¹³C, higher than the uptake rates at Kubur and Panjang Islands, stations with a much more transparent water column (on average 0.0047 g ¹³C g C⁻¹ d⁻¹ at Kepuh Island, versus 0.0045 g ¹³C g C⁻¹ d⁻¹ at Panjang Island and 0.0034 g ¹³C g C⁻¹ d⁻¹ at Kubur Island). There was evidence that ¹³C was exported from the incubated shoots to the roots and rhizomes and to neighboring shoots of E. acoroides in clear water, but not in turbid water. We suggest that single shoots of E. acoroides are able to grow in turbid water under low light conditions. They assimilate sufficient carbon for their own maintenance but are not able to export to neighboring plant parts.     

The relationship between Pseudo-nitzschia (Peragallo) and domoic acid in Scottish shellfish

The diatom genus Pseudo-nitzschia (Peragallo) associated with the production of domoic acid (DA), the toxin reposnsible for amnesic shellfish poisoning, is abundant in Scottish waters. A two year study examined the relationship between Pseudo-nitzschia cells in the water column and DA concentration in blue mussels (Mytilus edulis) at two sites, and king scallops (Pecten maximus) at one site. The rate of DA uptake and depuration differed greatly between the two species with M. edulis whole tissue accumulating and depurating 7 μg g⁻¹ (now expressed as mg kg⁻¹) per week. In contrast, it took 12 weeks for DA to depurate from P. maximus gonad tissue from a concentration of 68 μg g⁻¹ (now mg kg⁻¹) to <20 μg g⁻¹ (now mg kg^‐1). The DA depuration rate from P. maximus whole tissue was <5% per week during both years of the study. Correlations between the Pseudo-nitzschia cell densities and toxin concentrations were weak to moderate for M. edulis and weak for P. maximus. Seasonal diversity on a species level was observed within the Pseudo-nitzschia genus at both sites with more DA toxicity associated with summer/autumn Pseudo-nitzschia blooms when P. australis was observed in phytoplankton samples. This study reveals the marked difference in DA uptake and depuration in two shellfish species of commercial importance in Scotland. The use of these shellfish species to act as a proxy for DA in the environment still requires investigation.     

Morphology and bloom dynamics of Cochlodinium geminatum (Schütt) Schütt in the Pearl River Estuary,South China Sea

An unarmored dinoflagellate bloom of Cochlodinium geminatum (Schütt) Schütt has been identified in the Pearl River Estuary, South China Sea during the severe dry season, from late October to early November, 2009, when temperature and salinity ranged between 20.0–27.2 °C and 10.6–33.4, respectively. Light and scanning electron microscopy were used to identify the characteristics of C. geminatum and provided the clear morphological structure for this species. The organism was primarily found in chains of two cells or single cell, and no longer chains were observed. Cells were irregularly spherical or slightly dorso-ventrally, with size ranged between 28 and 36 μm and longer than wide. A large nucleus in the center with numerous golden chloroplasts was present, and the cingulum made 1.5 turns around the cell. The concentration of C. geminatum ranged from 10² to greater than 10⁷ cells l⁻¹ during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00 μM NO₃, 0.14–12.14 μM NO₂, 0.21–6.29 μM NH₄, 0.23–6.26 μM PO₄ and 3.29–171.43 μM SiO₃, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45 μg l⁻¹, with an average 19.9 μg l⁻¹ in surface water throughout the PRE. Two main clusters corresponding to the water sectors were defined with multivariate analysis (cluster and nMDS). Based on the composition and abundance of phytoplankton, spatial variations were observed at a significant level (ANOSIM, R = 0.44, P < 0.01). Although the pairwise correlation analysis detected no significant effect of any single environmental variable on the abundance of C. geminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO₃, NO₂, NH₄, PO₄ and SiO₃) which showed a combined effect during the bloom of C. geminatum in the Pearl River Estuary (ρ_w = 0.477).     

Effects of feed sugar concentration on continuous ethanol fermentation of cheese whey powder solution (CWP)

Cheese whey powder (CWP) solution with different CWP or sugar concentrations was fermented to ethanol in a continuous fermenter using pure culture of Kluyveromyces marxianus (DSMZ 7239). Sugar concentration of the feed CWP solution varied between 55 and 200 g l⁻¹ while the hydraulic residence time (HRT) was kept constant at 54 h. Ethanol formation, sugar utilization and biomass formation were investigated as functions of the feed sugar concentration. Percent sugar utilization and biomass concentrations decreased and the effluent sugar concentration increased with increasing feed sugar concentrations especially for the feed sugar contents above 100 g l⁻¹. Ethanol concentration and productivity (DP) increased with increasing feed sugar up to 100 g l⁻¹ and then decreased with further increases in the feed sugar content. The highest ethanol concentration (3.7%, v v⁻¹) and productivity (0.54 gE l⁻¹ h⁻¹) were obtained with the feed sugar content of 100 g l⁻¹ or 125 g l⁻¹. The ethanol yield coefficient (Y_P/S) was also maximum (0.49 gE gS⁻¹) when the feed sugar was between 100 and 125 g l⁻¹. The growth yield coefficient (Y_X/S) decreased steadily from 0.123 to 0.063 gX gS⁻¹ when the feed sugar increased from 55 to 200 g l⁻¹ due to adverse effects of high sugar contents on yeast growth. The optimal feed sugar concentration maximizing the ethanol productivity and sugar utilization was between 100 and 125 g l⁻¹ under the specified experimental conditions.     

Effects of flooding on photosynthesis and root respiration in saltcedar (Tamarix ramosissima), an invasive riparian shrub

The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO₂, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500 μmol quanta m⁻² s⁻¹ (A₁₅₀₀) in flooded plants ranged from 2.3 to 6.2 μmol CO₂ m⁻² s⁻¹ during the first week, but A₁₅₀₀ increased to 6.4–12.7 μmol CO₂ m⁻² s⁻¹ by the third week of flooding. Stomatal conductance (g_s) at 1500 μmol quanta m⁻² s⁻¹ also decreased initially during flooding, where g_s was 0.018 to 0.099 mol H₂O m⁻² s⁻¹ during the first week, but g_s increased to 0.113–0.248 mol H₂O m⁻² s⁻¹ by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ¹³C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.     

Effect of Zinc nanoparticles on oxidative stress-related genes and antioxidant enzymes activity in the brain of Oreochromis niloticus and Tilapia zillii

This study was carried out to determine the median lethal concentrations (LC₅₀) of Zinc nanoparticles (ZnNPs) on Oreochromis niloticus and Tilapia zillii. The biochemical and molecular potential effects of ZnNPs (500 and 2000 μg L⁻¹) on the antioxidant system in the brain tissue of O. niloticus and T. zillii were investigated. Four hundred fish were used for acute and sub-acute studies. ZnNP LC₅₀ concentrations were investigated in O. niloticus and T. zillii. The effect of 500 and 2000 μg L⁻¹ ZnNPs on brain antioxidants of O. niloticus and T. zillii was investigated. The result indicated that 69 h LC₅₀ was 5.5 ± 0.6 and 5.6 ± 0.4 for O. nilotica and T. zillii, respectively. Fish exposed to 500 μg L⁻¹ ZnNPs showed a significant increase in reduced glutathione (GSH), total glutathione (tGSH) levels, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) activity and gene expression. On the contrary, malondialdehyde (MDA) levels significantly decreased. Meanwhile, fish exposed to 2000 μg L⁻¹ ZnNPs showed a significant decrease of GSH, tGSH levels, SOD, CAT, GR, GPx and GST activity and gene expression. On the contrary, MDA levels significantly increased. It was concluded that, the 96 h LC₅₀ of ZnNPs was 5.5 ± 0.6 and 5.6 ± 0.4 for O. nilotica and T. zillii, respectively. ZnNPs in exposure concentrations of 2000 μg/L induced a deleterious effect on the brain antioxidant system of O. nilotica and T. zillii. In contrast, ZnNPs in exposure concentrations of 500 μg L⁻¹ produced an inductive effect on the brain antioxidant system of O. nilotica and T. zillii.     

Comparative assessment of single and joint effects of diuron and Irgarol 1051 on Arctic and temperate microalgae using chlorophyll a fluorescence imaging

Ship groundings and ice-breakers can cause pollution of the polar environment with antifouling biocides such as diuron and Irgarol 1051. The present study used pulse amplitude modulated fluorometry to compare single and joint toxicities of diuron and Irgarol 1051 on two freshwater taxa of microalgae (Chlorella and Chlamydomonas) originating from Arctic and temperate regions. 30 min acute toxicity tests using chlorophyll a (Chl a) fluorescence revealed that Arctic strains of microalgae were more sensitive to herbicides than their temperate counterparts. Diuron and Irgarol 1051 had equal toxicities in the Arctic species, while Irgarol 1051 was more toxic (EC₅₀ = 5.55–14.70 μg L⁻¹) than diuron (EC₅₀ = 12.90–>40 μg L⁻¹) in the temperate species. Toxicity assessment of various mixtures of diuron and Irgarol 1051 revealed antagonistic, additive, and synergistic effects. Our data suggest that herbicides can adversely affect photosynthesis in Arctic microalgae at relatively low levels, and their impact can increase under complex mixture conditions.     

Selenium accumulation in the floral tissues of two Brassicaceae species and its impact on floral traits and plant performance

Selenium (Se) is a metalloid that can occur naturally in soils from the Cretaceous shale deposits of a prehistoric inland sea in the western United States. Agricultural irrigation and runoff solubilizes Se from these shales, causing buildups of toxic levels of selenate (SeO₄²⁻) in water and soil. Our main objective was to investigate the accumulation of Se in two Brassicaceae species chosen for their potential as phytoremediators of Se contaminated soils. We tested the hypothesis that Se will accumulate in the pollen and nectar of two plant species and negatively affect floral traits and plant reproduction. Certain species of Brassicaceae can accumulate high concentrations of Se in their leaf tissues. In this study Se accumulation in plant tissues was investigated under greenhouse conditions. Se accumulator (Brassica juncea) and Se hyperaccumulator (Stanleya pinnata) plants were irrigated in sand culture with 0 μM selenate (control), 8 μM selenate, and 13 μM selenate.Nectar and pollen in S. pinnata contained up to 150 μg Se mL⁻¹ wet weight and 12900 μg Se g⁻¹ dry weight when irrigated with 8 μM selenate. Se levels in nectar (110 μg Se mL⁻¹ wet weight) and pollen (1700 μg Se g⁻¹ dry weight) were not as high in B. juncea. Floral display width, petal area and seed pod length were significantly reduced in the 13 μM selenate Se treatment in B. juncea. S. pinnata floral traits and seeds were unaffected by the Se treatments.This study provides crucial information about where some of the highest concentrations of Se are found in two phytoremediators, and may shed light on the potential risks pollinators may face when foraging upon these accumulating plants. In the field, duration of the plant's exposure, Se soil and water concentrations as well as other environmental factors may also play important roles in determining how much Se is accumulated into the leaf and floral tissues. Our greenhouse study shed light on two species’ ability to accumulate Se, as well as determined the specific plant tissues where Se concentrations are highest.     

Allelopathic inhibition of phytoplankton by exudates from Stratiotes aloides

The allelopathic potential of exudates from the aquatic macrophyte Stratiotes aloides on the growth of phytoplankton was investigated. A selection of phytoplankton species, occurring in habitats similar to that of Stratiotes, was used: two cyanobacterial strains (toxic and non-toxic Microcystis aeruginosa), one green alga (Scenedesmus obliquus) and one eustigmatophyte (Nannochloropsis limnetica). The results indicate allelopathic effects of Stratiotes on phytoplankton in six of the eight cases, expressed in an extended duration of the initial biovolume doubling time. The overall inhibitory effect (8–51%) was strain-specific for the two cyanobacteria. We also studied the effect of irradiance on the allelopathic potential of exudates from Stratiotes. Irradiance influenced the response of Scenedesmus only. The inhibitory effect of Stratiotes exudates on the growth of this green alga was stronger at 35 μmol m⁻² s⁻¹ than at 105 μmol m⁻² s⁻¹. We conclude that Stratiotes has allelopathic effects on phytoplankton, and that irradiance can, but does not always determine the extent of the allelopathic inhibition. In our experiments, the sensitivity of cyanobacteria to Stratiotes exudates was not higher than for other phytoplankton strains, but within cyanobacteria, the toxic strain was more sensitive than the non-toxic one.     

Bioconversion of spent coffee grounds into carotenoids and other valuable metabolites by selected red yeast strains

Spent coffee grounds (SCG) represent the main coffee industry residues with a great potential to be reutilized in various biotechnological processes. In this study, several carotenogenic yeasts strains were exploited for the production of vitamin-enriched biomass, cultivating in SCG-based media. The fermentation was firstly carried out in Erlenmeyer flasks in order to select the best biomass and pigment producer. Among four tested strains, Sporobolomyces roseus showed the highest potential for the accumulation of carotenoids. Maximum pigment concentration and yield was obtained when cultivating in SCG-based media, 12.59 mg l⁻¹ and 1.26 mg g⁻¹, respectively. Comparing both, the batch and the fed-batch cultivation modes, the strategy of sequential addition of pre-concentrated SCG media in the bioreactor gave higher biomass yield (maximum 41 g l⁻¹ during 41–48 h after the beginning of fermentation). Thus, SCG can be considered as potentially promising industrial waste stream for economically feasible production of enriched yeasts biomass.     

Estimation of the nutrient consumption by various cell sizes of the diatom Eucampia zodiacus: A representative organism causing bleaching of aquacultured nori

The diatom Eucampia zodiacus is a harmful species that indirectly causes bleaching to nori (Pyropia) cultivation through competitive utilization of nutrients during its bloom, however cellular storage and changes in physiology by asexual reproduction remains unclear. In the present study, we experimentally investigated the nitrate (N), phosphate (P) and silicic acid (Si) consumption by various cell sizes of E. zodiacus strains, the apical axis length of which ranged from 10.2 to 77.3 μm. Nutrient cell quotas of E. zodiacus ranged from 2.7 to 8.4 pM cell⁻¹ for N, 0.34–0.76 pM cell⁻¹ for P and 1.7–7.3 pM cell⁻¹ for Si, and they increased with cell size, in which there is a significant correlation between these two elements. The N and P quotas were estimated to be several times higher than the minimum cell quotas. In contrast, the Si cell quotas were approximately equal to those of the minimum values. Based on the present cell quotas, total nitrate consumption by E. zodiacus population when the blooms reached maximum cell density (=1000 cells ml⁻¹) were estimated to be 6.5 μM. Monthly mean concentrations of dissolved inorganic nitrogen (DIN) range from 3.5 to 8.2 μM during the period of late nori harvest season when E. zodiacus blooms occur, and nori bleaching is reported at the condition of DIN concentration of less than 3 μM in Harima-Nada, eastern Seto Inland Sea, Japan. Therefore, the present results suggest that E. zodiacus causes serious damage to nori cultivation due to high levels of nutrient consumption.