Freshwater Rotifer Brachionus Calyciflorus Research Articles

Suitability of Different Live Feed for First Feeding of Freshwater Fish Larvae

First feeding of many fish larvae depends on live feed. A comparative investigation on the effectiveness of different types of live feed is not available to our knowledge. Hence, we conducted a study to examine the effect of different types and combinations of live feed on the performance (survival rate, total length, body width, body mass, malformation rate) of pikeperch, Sander lucioperca, larvae. From day 0 (onset of exogenous feeding) to day 10, the saltwater rotifer Brachionus plicatilis, the freshwater rotifer Brachionus calyciflorus, the ciliate Paramecium bursaria, copepods (nauplii and copepodites) from a lake population, and Artemia nauplii were tested. Feeding with B. plicatilis, B. calyciflorus, and P. bursaria resulted in high survival rates of 80% and a homogenous and significant growth (increase in total length of 50% and in body width of 20%). As follow-up feed, copepod nauplii and Artemia nauplii were tested from day 11 to day 20. Copepod nauplii were superior to Artemia nauplii, as larvae fed with copepods showed higher survival rates (67–70% versus 38–47%) and a more homogeneous growth. A switch from seawater live feed to freshwater live feed or vice versa resulted in decreased survival rates. Therefore, a feeding regime consisting of B. calyciflorus or P. bursaria followed by copepods is considered optimal as first feed of pikeperch. The malformation rate was not affected by the tested feeding regimes. To investigate the wider applicability and transferability of these findings, complementary investigations were performed on burbot, Lota lota, and the freshwater whitefish Coregonus atterensis. The feeding regimes used for S. lucioperca larvae were also suitable for Lota lota. Moreover, L. lota could be fed with lake copepods from the onset of exogenous feeding. For C. atterensis, initial feeding with B. plicatilis, B. calyciflorus, or P. bursaria had no positive effects. Feeding with copepods from the onset of exogenous feeding was optimal considering survival rate and growth. Therefore, optimal first feeding regimes are very species specific and should be established for each new species.

The Effect of Brachionus calyciflorus (Rotifera) on Larviculture and Fatty Acid Composition of Pikeperch (Sander lucioperca (L.)) Cultured under Pseudo-Green Water Conditions

A new cultivation system with the chlorophyte Monoraphidium contortum combined with a self-sustaining culture of the freshwater rotifer Brachionus calyciflorus was applied for Sander lucioperca (L.) larviculture. Survival, morphometrics, as well as fatty acid composition of pikeperch larvae were analyzed after a ten-day feeding period. By using the pseudo-green water technique with improved aeration and water movement at the surface, survival rates reached up to 94%, with a total larval length of 8.1 ± 0.3 mm and a specific length growth rate of up to 4.1% day−1 for S. lucioperca. The biochemical composition of B. calyciflorus and especially its contents in C18 PUFAs and suitable n-3/n-6 ratios met the nutritional requirements of pikeperch larvae. The high abundance of highly unsaturated fatty acids (HUFAs) in the diet appeared to be less important in the first feeding due to a possible retention of essential fatty acids, which originate from the yolk sac reserves, at adequate levels. Exponential growth of microalgae and zooplankton under the applied conditions was most effective when stocking M. contortum five days and B. calyciflorus three days before adding the fish larvae. Appropriate timing and sufficient live feed density allowed a successful integration of B. calyciflorus into pikeperch larviculture. We hypothesize that feeding pikeperch larvae with a self-sustaining Brachionus-culture under pseudo-green water conditions with minor disruptions during larviculture will improve survival and growth. This system is a first step towards pikeperch larviculture inside recirculated aquaculture systems (RAS) under continuous feed supply with live feed within the same aquaculture unit.

Individual and mixed effects of anticancer drugs on freshwater rotifers: A multigenerational approach

Human population growth has led to an increased release of chemical contaminants into aquatic environments. Emerging chemical contaminants (ECCs) are of increasing concern because they can affect non-target organisms in aquatic ecosystems. The application of anticancer drugs is increasing because of enhanced cancer rates and use of chemotherapy. We assessed the impacts of two widely used anticancer drugs known for their distinct modes of action, namely 5-fluorouracil (5-FU) and doxorubicin (DOX), on the freshwater rotifer Brachionus calyciflorus across generations. Rotifer mortality (24 h) and population growth (48 h) were assessed to determine initial lethal and sub-lethal effects. Exposure of rotifers to 5-FU (up to 200 mg L−1) did not cause mortality, while DOX caused mortality at high concentrations (EC50 = 15.6 mg L−1). Effects of 5-FU on population growth rate was higher than DOX (5-FU EC50 =10.49 µg L−1, DOX EC50 = 8.78 mg L−1). The effects of the drugs in binary mixture on population growth rates were dose dependent; significant antagonistic effects were found when 5-FU was present in the mixture at high concentrations. Finally, a transgenerational assay for five generations revealed that rotifers were able to recover their population growth rate after fourth generation when exposed to 5-FU; however, population became non-viable after the second generation of exposure to DOX. At the cellular level, accumulation of reactive oxygen species and plasma membrane damage were observed at EC10 and increased at EC50 for both drugs. After exposure of rotifers to 5-FU across generations, there were signs of oxidative stress recovery, as shown by a decrease in ROS accumulation and plasma membrane damage. Our results showed for the first time that the adverse effects of anticancer drugs on freshwater rotifer populations are drug and dose dependent and can persist or be attenuated along generations.

Expression variations of two retinoid signaling pathway receptors in the rotifer Brachionus calyciflorus exposed to three endocrine disruptors.

Endocrine disruption compounds (EDC) are known to affect reproduction, development, and growth of exposed organisms. Although in vertebrates, EDCs mainly act through steroid receptors (e.g. androgen and estrogen receptors), their absence in many invertebrates suggests the involvement of another biological pathway in endocrine disruption effects. As retinoid signaling pathway is present in almost all Metazoa and its involvement in the endocrine disruption of gastropods (i.e. imposex) has been demonstrated, the present work was devoted to investigating the relative mRNA variations of two retinoid receptors genes, retinoid X receptor (RXR) and retinoid acid receptor (RAR), in the freshwater rotifer Brachionus calyciflorus exposed for 6, 12 and 24 h to flutamide, fenitrothion and cyproterone acetate, three anti-androgens known to disrupt sexual reproduction of Brachionus sp. Results revealed that fenitrothion did not affect the relative mRNA levels RXR and RAR in B. calyciflorus, whereas RXR and RAR mRNA levels could be significantly increased by 2 to 4.5-fold and from 2 to 7-fold after exposure to flutamide and cyproterone acetate, respectively. Moreover, the effects of flutamide and cyproterone acetate were measured from 6 and 12 h of exposure, respectively. Cyproterone acetate caused the highest increase of RXR and RAR mRNA levels, probably due to its progestin activity in addition to its anti-androgenic activity and the potential presence of a membrane-associated progesterone receptor as reported in Brachionus manjavacas. Consequently, although it is still difficult to evaluate the hormonal pathways involved in the endocrine disruption in Brachionus sp., this work suggests that the retinoid signaling pathway appears to be a good starting point to try to elucidate the molecular mechanisms involved in sexual reproductive dysfunction in Brachionidae.

Effects of Temperature on Population Growth and Resting Egg Production of Freshwater Rotifer (Brachionus calyciflorus)Effects of Temperature on Population Growth and Resting Egg Production of Freshwater Rotifer (Brachionus calyciflorus)

Resting egg production of rotifers provides critical advantages in larviculture of most fish species due to the reduction in the costs of labour and algae production. The study was conducted to investigate the effects of temperature on population growth and resting egg production of a freshwater rotifer, Brachionus calyciflorus, collected in Northern Vietnam. The rotifer was pre-cultured at 27ºC before being transferred to the cultures at 15 and 35ºC while the control was maintained at 27ºC. One-liter beakers filled with 500mL culture medium were used with three replicates for each temperature group. Stock rotifers were inoculated at an initial density of 200 ind ml-1 and fed with concentrated fresh algae. The results indicated that population growth rate (r) of rotifers cultured at 27 and 35ºC were significantly higher than that of rotifers at 15ºC while the highest density was attained from the treatment of 27ºC, at 608.3 ind mL-1, compared to 468.3 and 360.5 ind mL-1 at 35 and 15ºC, respectively. Transferring the cultures from 27 to 35ºC significantly increased the rate of resting egg carrying females with the maximum rate of 31.5% compared to 21.2 and 13.5% of the rotifers at 27 and 15ºC, respectively. The resting egg densities of the cultures at 35ºC were also significantly higher than those at 15 and 27ºC. The resting egg carrying females appeared and increased their rates in concurrence with increases in the population density. The present results are important information for resting egg induction and production of rotifer in larviculture.

Biogenic Aggregation of Small Microplastics Alters Their Ingestion by a Common Freshwater Micro-Invertebrate

In recent years, increasing concerns have been raised about the environmental risk of microplastics in freshwater ecosystems. Small microplastics enter the water either directly or accumulate through disintegration of larger plastic particles. These particles might then be ingested by filter-feeding zooplankton, such as rotifers. Particles released into the water may also interact with the biota through the formation of aggregates, which might alter the uptake by zooplankton. In this study, we tested for size-specific aggregation of polystyrene microspheres and their ingestion by a common freshwater rotifer Brachionus calyciflorus. The ingestion of three sizes of polystyrene microspheres (MS) 1-, 3-, and 6-μm was investigated. Each MS size was tested in combination with three different treatments: MS as the sole food intake, MS in association with food algae and MS aggregated with biogenic matter. After 72 h incubation in pre-filtered natural river water, the majority of the 1-μm spheres occurred as aggregates. The larger the particles, the higher the relative number of single particles and the larger the aggregates. All particles were ingested by the rotifer following a Type-II functional response. The presence of algae did not influence the ingestion of the MS for all three sizes. The biogenic aggregation of microspheres led to a significant size-dependent alteration in their ingestion. Rotifers ingested more microspheres (MS) when exposed to aggregated 1- and 3-μm MS as compared to single spheres, whereas fewer aggregated 6-μm spheres were ingested. This indicates that the small particles when aggregated were in an effective size range for Brachionus, while the aggregated larger spheres became too large to be efficiently ingested. These observations provide the first evidence of a size- and aggregation-dependent feeding interaction between microplastics and rotifers. Microplastics when aggregated with biogenic particles in a natural environment can rapidly change their size-dependent availability. The aggregation properties of microplastics should be taken into account when performing experiments mimicking the natural environment.

Algal density affects the influences of polyethylene microplastics on the freshwater rotifer Brachionus calyciflorus

Most previous researches focused on the toxicity of polystyrene microplastics (MPs) to marine organisms, but less on polyethylene MPs and freshwater zooplanktons. The present study aims to elucidate the toxicity of polyethylene (PE) MPs (diameter = 10–22 μm) to the typical freshwater rotifer Brachionus calyciflorus. Firstly, fluorescent microscope observation showed that rotifers could ingest PE MPs and accumulate them in their digestive tracts. Life-table experiments revealed that exposure to 0.5 × 103, 2.5 × 103, and 1.25 × 104 particles/mL PE MPs significantly reduced net reproductive rate and intrinsic rate of pollution increase of rotifers under algal densities (Scenedesmus obliquus) of 0.1 × 106, and 0.5 × 106 cells/mL, but no significant effects were observed under 2.5 × 106 cells/mL algal density. These results showed that PE MPs suppressed the reproduction of rotifer and this negative effect could be alleviated by increasing food supply. The swimming linear speed of rotifers significantly decreased with increasing MP concentrations. The activities of superoxide dismutase and Na+-K+-ATPase significantly decreased in treatments with high concentration of PE MPs under 0.1 × 106 cells/mL algal density, but did not change significantly in MP treatments under 0.5 × 106 and 2.5 × 106 cells/mL, compared to the control. Glutathione peroxidase activity significantly increased in treatments with 1.25 × 104 particles/mL and 2.5 × 103 particles/mL under 0.1 × 106 and 0.5 × 106 cells/mL algal density, respectively, but did not change significantly in all MP treatments under 2.5 × 106 cells/mL. Exposure to PE MPs might lower the gathering capacity of algae, induce oxidative stress, trigger cell membrane damages and disturb energy metabolism in rotifers, which can explain the PE MPs toxicity to rotifer reproduction.

Effects of metal nanoparticles on freshwater rotifers may persist across generations

Nanotechnology has become one of the fastest growing industries in the current century because nanomaterials (NMs) are present in an ever-expanding range of consumer products increasing the chance of their release into natural environments. In this study, the impacts of two metal nanoparticles (Ag-NPs and CuO-NPs) and their equivalent ionic forms (Ag+ and Cu2+) were assessed on the lentic freshwater rotifer Brachionus calyciflorus and on its ability to adapt and recover through generations. In our study, Ag-NPs and CuO-NPs inhibited the rotifer population growth rate and caused mortality at low concentrations (< 100 μg L−1). Ag-NPs and CuO-NPs decreased in the medium when organisms were present (48 h exposure: 51.1 % and 66.9 %, respectively), similarly Ag+ and Cu2+ also decreased from medium in presence of the organisms (48 h: 35.2 % and 47.3 %, respectively); although the metal concentrations removed from the medium were higher for nanoparticles than metal ions, metal ions showed higher effects then their respective nanoparticle forms. Rotifer populations exposed for 4 generations to the toxicants were able to recover the population growth rate, but some rotifers showed developmental delay and inability to reproduce even after the removal of the toxicants. Intracellular accumulation of reactive oxygen species as well as plasma membrane damage were found in the rotifers at concentrations corresponding to EC10 (Ag-NPs = 1.7 μg L-1, Ag+ = 4.5 μg L-1, CuO-NPs = 46.9 μg L-1, Cu2+ = 35 μg L-1) of the population growth rate. Our results showed, for the first time, that effects of metal nanoparticles and metal ions on rotifer populations may persist along several generations. This should be taken into account when assessing risks of metal nanoparticles in freshwaters.

Complete mitochondrial genome of the freshwater monogonont rotifer Brachionus angularis (Rotifera, Brachionidae)

The two complete mitochondrial genomes were sequenced from the freshwater monogonont rotifer Brachionus angularis. The mitochondrial genome sequences were 10,764 bp (mitochondrial DNA I) and 12,238 bp (mitochondrial DNA II) in size, respectively. The gene structure and its orientation of 12 protein-coding genes (PCGs) of complete mitochondrial genomes of B. angularis was identical to those shown in other marine rotifers and the freshwater rotifer Brachionus rubens, but was different from the freshwater rotifer Brachionus calyciflorus. Of 12 PCGs, one gene (ND5) had incomplete stop codon. Furthermore, the start codon for CO1, ND4L, ND5, and CO2 was GTG, while the start codon for ND3 and other PCGs was ATA and ATG, respectively. The base composition of 12 PCGs in B. angularis mitogenome showed 20.4% for A, 47.3% for T, 17.5% for C, and 14.8% for G, respectively. The mitochondrial genome A + T base composition (67.7%) of 12 PCGs was higher than G + C (32.3%), while the complete mitochondrial genome A + T base composition (66.3%) was higher than G + C (33.7%).

Protective role of the freshwater rotifer Brachionus calyciflorus glutathione S-transferase zeta 3 recombinant protein in response to Hg and Cd.

Gluatathione S-transferases (GSTs) play a major role in phase II detoxification pathway to defend organisms in response to oxidative stress induced by xenobiotics and toxicants. To reveal the role of the recombinant GST zeta protein from the freshwater rotifer Brachionus calyciflorus, we isolated the zeta class GST in the freshwater rotifer B. calyciflorus. The recombinant B. calyciflorus GST zeta protein was highly expressed in the transformed Escherichia coli using pET28a vector. To determine its characteristics, effects of pH and temperature on B. calyciflorus GST zeta with enzymatic kinetics were also studied. In addition, a disk diffusion assay, uncovering the ability of transformed GST zeta in Escherichia coli, revealed that E. coli-transformed GST zeta significantly protected the transformed E. coli cells in response to oxidative stress induced by H2O2 and metals such as mercury and cadmium. These results suggest that B. calyciflorus GST zeta recombinant protein is likely playing an important role to defend in response to metal-induced oxidative stress, providing a better understanding on the possible antioxidant role of GST zeta class in B. calyciflorus.

Effects of TiO2 nanoparticles on the life-table parameters, antioxidant indices, and swimming speed of the freshwater rotifer Brachionus calyciflorus.

Titanium dioxide nanoparticles (nTiO2 ) have raised environmental concerns and display potential hazards to aquatic organisms and even humans. However, only a few reports tested the toxicity of nTiO2 to rotifers. In the present study, acute and chronic toxicity of nTiO2 to the freshwater rotifer Brachionus calyciflorus was investigated at different temperatures. At 25°C, the 24 and 48-hr LC50 was 117.14 and 60.11 mg/L, respectively. At 15°C, 20°C, 25°C, and 30°C, exposure to nTiO2 significantly decreased life expectancy at birth, net reproductive rate, generation time, average lifespan, and/or intrinsic rate of population increase of B. calyciflorus (p < .05). High temperature enhanced the toxicity of nTiO2 to rotifers. The swimming linear speed of rotifers significantly increased (p < .05) in treatments with 200 µg/L nTiO2 , compared with the control. In addition, treatments with 8 µg/L to 5 mg/L nTiO2 significantly increased superoxide dismutase activity (p < .05). Glutathione content and catalase activity increased significantly after exposure to 8 µg/L nTiO2 but decreased significantly in treatments with nTiO2 concentrations ranging from 40 µg/L to 5 mg/L (p < .05). There were no significant changes in malondialdehyde contents among nTiO2 treatments and control. Overall, the present study indicated that nTiO2 revealed high toxicity to rotifers, displaying high environmental risks to aquatic ecosystems.

Joint effects of predation risk and food nutrient on sexual and asexual reproductions, and morphological defenses of freshwater rotifer Brachionus calyciflorus

Ecological stoichiometry predicts that the extent to which herbivores are limited by nutrients depends on their metabolic demands. Nonconsumptive effects (NCEs) caused by predators have been demonstrated to trigger not only inducible defenses but also physiological stresses in prey. Stressed prey always exhibit increased metabolism and decreased nutrient deposition (e.g., nitrogen and phosphorus) as physiological stress responses to their predators. Consequently, prey exposed to predation risk should reduce demands for nutrients intake and become adaptive to nutrient limitations. In this study, results obtained from classic Brachionus–Asplanchna model revealed that Brachionus calyciflorus fed with full nutrient algal food showed energetic costs, e.g., reduced investment in asexual (lifetime fecundity) and sexual (mixis ratio) reproductions, in response to predation risk. However, reduction in sexual and asexual reproductions diminished when herbivorous Brachionus were supplied with nitrogen- or phosphorus-limited algal food. Moreover, long posterolateral spines and high posterolateral spine-body length ratio developed in either nitrogen- or phosphorus-deficient conditions containing Asplanchna kairomones, indicating an additive effect of nutrient limitation and predation risk on posterolateral spine development in Brachionus. The findings of this study highlighted predator-facilitated adaptation of prey to nutrient limitations of primary producers, which may have implications in understanding roles of NCEs in regulating trophic interactions.

Protective Role of Freshwater and Marine Rotifer Glutathione S-Transferase Sigma and Omega Isoforms Transformed into Heavy Metal-Exposed Escherichia coli.

Glutathione S-transferases (GSTs) play an important role in phase II of detoxification to protect cells in response to oxidative stress generated by exogenous toxicants. Despite their important role in defense, studies on invertebrate GSTs have mainly focused on identification and characterization. Here, we isolated omega and sigma classes of GSTs from the freshwater rotifer Brachionus calyciflorus and the marine rotifer Brachionus koreanus and explored their antioxidant function in response to metal-induced oxidative stress. The recombinant Bc- and Bk-GSTs were successfully transformed and expressed in Escherichia coli. Their antioxidant potential was characterized by measuring kinetic properties and enzymatic activity in response to pH, temperature, and chemical inhibitor. In addition, a disk diffusion assay, reactive oxygen species assay, and morphological analysis revealed that GST transformed into E. coli significantly protected cells from oxidative stress induced by H2O2 and metals (Hg, Cd, Cu, and Zn). Stronger antioxidant activity was exhibited by GST-S compared to GST-O in both rotifers, suggesting that GST-S plays a prominent function as an antioxidant defense mechanism in Brachionus spp. Overall, our study clearly shows the antioxidant role of Bk- and Bc-GSTs in E. coli and provides a greater understanding of GST class-specific and interspecific detoxification in rotifer Brachionus spp.

Food quantity–quality co‐limitation: Interactive effects of dietary carbon and essential lipid supply on population growth of a freshwater rotifer

Abstract Food quantity and quality are highly variable in natural systems. Therefore, their interplay and the associated effects on consumer population growth are important for predator–prey interactions and community dynamics. Experiments in which consumers were exposed to elemental nutrient limitations along food quantity gradients suggest that food quality effects on consumer performance are relevant only at high food quantities. However, elemental nutrients act differently on physiological processes than biochemical nutrients. So far, the interactive effects of food quantity and biochemical compounds on consumer performance have been insufficiently studied. We studied interactive effects of food quantity and biochemical food quality on population growth, including fecundity and survival, of the freshwater rotifer Brachionus calyciflorus. We hypothesised that these life history traits are differently affected by the availability of biochemical nutrients and that food quality effects gain importance with increasing food quantity. In a first experiment, we established food quantity and quality gradients by providing rotifers with different concentrations of a low‐quality food, the sterol‐free cyanobacterium Synechococcus elongatus, supplemented with increasing amounts of cholesterol. In a second experiment, food quantity and quality gradients were established by providing different proportions of two prey species differing in biochemical food quality, i.e. S. elongatus and the lipid‐rich alga Nannochloropsis limnetica, at different total food concentrations. We found that the effects of cholesterol supplementation on population growth increased with increasing food quantity. This interactive effect on population growth was mainly due to food quality effects on fecundity, as effects on survival remained constant along the food quantity gradient. In contrast, when feeding on the mixed algal diet, the food quality effect associated with increasing the proportion of the high‐quality alga did not change along the food quantity gradient. The data on survival and fecundity demonstrate the missing interactive effect of food quantity and quality on population growth, as both traits were oppositely affected. Survival was affected by food quality primarily at low food quantity, whereas food quality effects on fecundity were stronger at high food quantity. Our results highlight the significance of essential biochemicals in mediating the interactive effects of food quantity and quality on population growth. The interplay between food quantity and biochemical food quality limitation seems to influence resource allocation patterns in order to optimise survival or reproduction, which may strongly affect population dynamics in variable environments. As opposed to exploring the function of a single nutrient via supplementation, using algae mixtures allowed us to assess food quality effects on consumer performance in a more natural context by taking potential interactive effects of multiple co‐limiting nutrients into account.

Adverse effects of the insecticides chlordecone and fipronil on population growth and expression of the entire cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and the marine rotifer Brachionus plicatilis

Chlordecone and fipronil are used as an insecticide and have been widely detected in the aquatic environments. However, their toxicity is still poorly investigated in aquatic invertebrates. In this study, we examined effects of chlordecone and fipronil on population growth and transcriptional regulation of the entire cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and the marine rotifer B. plicatilis. In B. calyciflorus, a 24 h-no observed effect concentration (NOEC-24 h) and a 24 h-median lethal concentration (LC50-24 h) of chlordecone were determined as 100 μg/L and 193.8 μg/L, respectively, while NOEC-24 h and LC50-24 h of fipronil were determined as 1000 μg/L and 2033.0 μg/L, respectively. In B. plicatilis, NOEC-24 h and LC50-24 h of chlordecone were 100 μg/L and 291.0 μg/L, respectively, while NOEC-24 h and LC50-24 h of fipronil were determined as 1000 μg/L and 5735.0 μg/L, respectively. Moreover, retardation in the population growth were observed in response to chlordecone and fipronil in both rotifer species, suggesting that chlordecone and fipronil have a potential adverse effects on life cycle parameters of two rotifer species. Additionally, modulation in the expressions of the entire CYP genes were demonstrated in response to chlordecone and fipronil at 24 h period. These results provide the better understanding on how chlordecone and fipronil can affect in population growth of two rotifers and CYP gene expressions in chlordecone- and fipronil-exposed rotifers.

Genome-wide identification of 31 cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and analysis of their benzo[α]pyrene-induced expression patterns

While marine invertebrate cytochrome P450 (CYP) genes and their roles in detoxification mechanisms have been studied, little information is available regarding freshwater rotifer CYPs and their functions. Here, we used genomic sequences and RNA-seq databases to identify 31 CYP genes in the freshwater rotifer Brachionus calyciflorus. The 31 Bc-CYP genes with a few tandem duplications were clustered into CYP 2, 3, 4, mitochondrial, and 46 clans with two marine rotifers Brachionus plicatilis and Brachionus koreanus. To understand the molecular responses of these 31 Bc-CYP genes, we also examined their expression patterns in response to benzo[α]pyrene (B[α]P). Three Bc-CYP genes (Bc-CYP3044B3, Bc-CYP3049B4, Bc-CYP3049B6) were significantly upregulated (P<0.05) in response to B[α]P, suggesting that these CYP genes can be involved in detoxification in response to B[α]P exposure. These genes might be useful as biomarkers of B[α]P exposure in B. calyciflorus. Overall, our findings expand the repertoire of known CYPs and shed light on their potential roles in xenobiotic detoxification in rotifers.

Combined effects of microcystin and nitrite on the growth, lipid peroxidation, and antioxidant responses of the freshwater rotifer Brachionus calyciflorus

Toxicants released during the degradation of cyanobacterial blooms, such as microcystin-LR (MC-LR) and nitrite (NO2-N), affect the growth of aquatic organisms. The freshwater rotifer Brachionus calyciflorus was exposed to solutions with different combined concentrations of MC-LR (0, 10, 50, 100, and 200μgL−1) and NO2-N (0, 2, 4, 6, and 8mgL−1) to assess the combined effects of MC-LR and NO2-N on life cycle parameters and oxidative stress. Single solutions of MC-LR 200μgL−1 and NO2-N 8mgL−1 were toxic to rotifers. MC-LR combined with NO2-N decreased population growth rate (r), survival, and reproduction, but increased reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH) contents (p<0.01). Superoxide dismutase (SOD) and catalase (CAT) activities and mRNA expression levels of MnSOD, CuZnSOD, and CAT significantly decreased under high concentrations of MC-LR or NO2-N (p<0.05). ROS levels had negative correlations with antioxidant enzyme activities and expression levels of antioxidant genes (p<0.01). MC-LR and NO2-N had interactive effects on r, reproduction, ROS levels, MDA content, SOD activity, and expression levels of MnSOD and CAT (p<0.05). By contrast, these effects were antagonistic on survival, CAT activity, GSH content, and expression level of CuZnSOD (p>0.05). Results showed that cyanobacterial metabolites act synergistically and antagonistically to cause toxicity to B. calyciflorus. ROS-mediated toxicity was considered the mechanism by which MC-LR and NO2-N induce damage.

Development and validation of a chronic Pb bioavailability model for the freshwater rotifer Brachionus calyciflorus.

The univariate effects of Ca, pH, and dissolved organic carbon (DOC) on chronic (48-h) Pb toxicity to the freshwater rotifer Brachionus calyciflorus were investigated. High pH (8.2) and higher concentrations of DOC were protective against filtered Pb toxicity, whereas Ca was not. However, expressed as the free Pb2+ ion, Pb2+ toxicity increased with increasing DOC concentration, indicating that Pb-fulvic acid (FA) complexes may be bioavailable and may contribute to toxicity. Two different bioavailability models were developed. The pH effect was modeled as a single-site competition effect by H+ (log KHBL = 7.14). In the first model, only this H+ effect was considered; in a second model, a log-linear fulvic acid bioavailability effect (SFA = 0.602) was also incorporated. Both models predicted chronic Pb toxicity for most waters used for model development within a 2-fold error. To validate the predictive capacities of the models, chronic Pb toxicity to B. calyciflorus was tested in 5 natural waters and a reference water. Both models consistently underestimated Pb toxicity in the natural waters, as a result of a shift in rotifer sensitivity to Pb between the development and the validation test series. However, optimizing the intrinsic sensitivity in the models specific for the validation test series resulted in reasonable predictions of Pb toxicity in the natural waters. The second, more complex model predicted chronic Pb toxicity most accurately. The protective effects of water chemistry on Pb toxicity to Brachionus are comparable to those observed for Ceriodaphnia. However, the developed Brachionus models were not able to accurately predict chronic Pb toxicity to the rotifer Philodina rapida. It remains unclear why the influence of water chemistry on chronic Pb toxicity appears to be different between 2 rotifer species. Environ Toxicol Chem 2016;35:2977-2986. © 2016 SETAC.

Effects of Multi-metal (Cu, Zn, Cd, Cr, and Mn) Mixtures on the Reproduction of Freshwater Rotifer Brachionus calyciflorus.

In the field, organisms are usually exposed to mixtures of various metals. However, the effects of multi-metal mixtures on growth and reproduction of rotifers remain unknown. In the present study, effects of multi-metal mixtures (Cu, Zn, Cd, Cr, and Mn) on reproduction of the freshwater rotifer Brachionus calyciflorus were assessed by determining various endpoints, including the ratio of ovigerous females to nonovigerous females, the ratio of mictic to amictic females, the mictic rate, the fertilization rate, the population growth rate, and the resting eggs production. The results demonstrated that reproduction of rotifers was significantly affected by all multi-metal mixtures assessed. Moreover, the ratio of mictic to amictic females was the most sensitive endpoint and might be suitable to evaluate effects of multi-metal mixtures to rotifers.

Reduced expression of exocytotic proteins caused by anti-cholinesterase pesticides in Brachionus calyciflorus (Rotifera: Monogononta).

The organophosphate and carbamate pesticides methyl-parathion and carbaryl have a common action mechanism: they inhibit acetylcholinesterase enzyme by blocking the transmission of nerve impulses. However, they can alter the expression of exocytotic membrane proteins (SNARE), by modifying release of neurotransmitters and other substances. This study evaluated the adverse effects of the pesticides methyl-parathion and carbaryl on expression of SNARE proteins: Syntaxin-1, Syntaxin-4 and SNAP-23 in freshwater rotifer Brachionus calyciflorus. Protein expression of these three proteins was analyzed before and after exposure to these two pesticides by Western Blot. The expression of Syntaxin-1, Syntaxin-4 and SNAP-23 proteins in B. calyciflorussignificantly decreases with increasing concentration of either pesticides. This suggests that organophosphates and carbamates have adverse effects on expression of membrane proteins of exocytosis by altering the recognition, docking and fusion of presynaptic and vesicular membranes involved in exocytosis of neurotransmitters. Our results demonstrate that the neurotoxic effect of anticholinesterase pesticides influences the interaction of syntaxins and SNAP-25 and the proper assembly of the SNARE complex.