Marine Rotifer Brachionus Research Articles

Tributyltin Affects Retinoid X Receptor-Mediated Lipid Metabolism in the Marine Rotifer Brachionus koreanus.

To examine how tributyltin (TBT), a model obesogen, affects the lipid metabolism in the marine rotifer Brachionus koreanus, we carried out life-cycle studies and determined the in vitro and in silico interactions of retinoid X receptor (RXR) with TBT, the transcriptional levels of RXR and lipid metabolic genes, and the fatty acid content. The lethal concentration 10% (LC10) was determined to be 5.12 μg/L TBT, and negative effects on ecologically relevant end points (e.g., decreased lifespan and fecundity) were detected at 5 μg/L TBT. On the basis of these findings, subsequent experiments were conducted below 1 μg/L TBT, which did not show any negative effects on ecologically relevant end points in B. koreanus. Nile red staining analysis showed that after exposure to 1 μg/L TBT, B. koreanus stored neutral lipids and had significantly increased transcriptional levels of RXR and lipid metabolism-related genes compared to the control. However, the content of total fatty acids did not significantly change at any exposure level. In the single fatty acids profile, a significant increase in saturated fatty acids (SFAs) 14:0 and 20:0 was observed, but the contents of omega-3 and omega-6 fatty acids were significantly decreased. Also, a transactivation assay of TBT with RXR showed that TBT is an agonist of Bk-RXR with a similar fold-induction to the positive control. Taken together, these results demonstrate that TBT-modulated RXR signaling leads to increase in transcriptional levels of lipid metabolism-related genes and the synthesis of SFAs but decreases the content of polyunsaturated fatty acids (PUFAs). Our findings support a wider taxonomic scope of lipid perturbation due to xenobiotic exposure that occurs via NRs in aquatic animals.

Genome-wide characterization and expression of the elongation of very long chain fatty acid (Elovl) genes and fatty acid profiles in the alga (Tetraselmis suecica) fed marine rotifer Brachionus koreanus

To understand the lipid metabolism in invertebrate species, identification of the fatty acid (FA) synthesis gene families in invertebrate species is important, since some FA are unable to be synthesized in the organisms by themselves. In the study, to identify the elongation of very long chain fatty acid (Elovl) genes in the marine rotifer Brachionus koreanus, the genome-wide identification and phylogenetic analysis of Elovl genes have been conducted with the expression profile of Elovl genes on the alga Tetraslemis suecica-fed B. koreanus. A total 10 Elovl genes have been identified from the genome of B. koreanus, with conserved HXXHH motif. Synteny analysis showed that tandem duplication event has occurred (Elovl3/6a and b, Elovl9a and b, and Elovl9c and d) in the ancestor. Phylogenetic analysis have clearly revealed that Brachionus spp. has only 2/5 and 3/6 subfamilies, and two novel Elovl classes have been revealed, namely Elovl9 and 10. Transcriptional data showed that the 10 Elovl genes were differently expressed and their expression could be regulated by feeding the alga T. suecica. From fatty acid (FA) profile data of the alga Tetraslemis suecica-fed B. koreanus, we revealed that the marine rotifer B. koreanus may synthesize very long chain fatty acid (VLCFA; >22 carbons) by themselves, as VLCFA was hardly detected in the alga T. suecica. The study provides a better understanding of FA metabolism of the marine rotifer B. koreanus after feeding the T. suecica.

Effect of probiotic Pediococcus acidilactici on growth, reproductive and bacterial count of marine rotifer Brachionus plicatilis

This study investigated the effects of different concentrations of probiotic Pediococcus acidilactici on the total number, specific growth rate, attached egg number and microbial count (lactic acid and total aerobic bacteria) in culture water and body of marine rotifer Brachionus plicatilis . The experiment was conducted as a completely randomized design in four groups: first group fed probiotic at 0.5×10 6 CFU ml -1 (P1), the second group fed probiotic at 1×10 6 CFU ml -1 (P2), the third group fed probiotic at 1.5×10 6 CFU ml -1 (P3), and the last group fed without probiotic (NP, control) . Rotifers were cultured in standard conditions at an initial density of 30 ind.ml -1 using a 2.5×10 6 cell mL -1 of Nanochloropsis oculta . Based on the results, the maximum number (215±4.91 ind.ml -1 ) of rotifers were significantly obtained after ten days in the third group in comparison to other treatments ( P 0.05). Moreover, it was revealed that the total aerobic bacteria was significantly related to the 3rd group that found be 1.80×10 3 CFU rotifer -1 and 34.0×10 4 CFU ml -1 in rotifer body and culture water,respectively ( P <0.05). Nonetheless, lactic acid bacteria of rotifer body and culture water was not concentration-dependent and the highest number of lactic acid bacteria in rotifer body (50.58±6.08 CFU rotifer -1 ) and rotifer culture water (4.43±3.28×10 3 CFU ml -1 ) was obtained in the treatments of P1 and P2, respectively. In conclusion, the present study showed that the bacteria P. acidilactici with N. oculta algae provide a higher growth rate and total aerobic bacteria in rotifer B. plicatilis.

Using Proales similis (Rotifera) for toxicity assessment in marine waters.

There is a need to develop more animal species for assessing toxicity in marine environments. Cyst‐based toxicity tests using invertebrates are especially fast, technically simple, cost‐effective, and sensitive to a variety of toxicants. Over the past 30 years, a variety of toxicity endpoints have been measured using the marine rotifer Brachionus plicatilis hatched from cysts, including mortality, reproduction, ingestion, swimming, enzyme activity, and gene expression. A consensus has developed that the most ecologically relevant toxicity measurements should be made using more than one species. Furthermore, it has been noted that the rotifer species toxicant sensitivity distribution is much broader than which endpoint is measured. This implies that toxicity should be measured with the simplest, fastest, least expensive test available on as many species as feasible. If a battery of test species is to be used to estimate toxicity, diapause egg‐based toxicity tests that do not require culturing of test animals will be key. In this paper, we describe how diapause eggs of a new marine rotifer, Proales similis, can be produced, stored and hatched under controlled conditions to produce animals for toxicity tests. Methods are described for quantifying the toxicity of copper, mercury and cadmium based on mortality, ingestion, reproduction, and diapause egg hatching endpoints. We found that reproduction and ingestion endpoints were generally more sensitive to the metals than mortality or diapause egg hatching. When the copper sensitivity of P. similis was compared to Brachionus manjavacas and B. plicatilis using an ingestion test, similar EC50s were observed. In contrast, the B. rotundiformis ingestion EC50 for copper was about 4× more sensitive. Although diapause egg hatching was not the most sensitive endpoint, it is the most ecologically relevant for assessing sediment toxicity. Our discovery of diapausing eggs in the P. similis life cycle has created a conundrum. We have not observed males or sex in P. similis populations, which is a direct contradiction to the orthodox view of the monogonont rotifer life cycle. Work is needed to clarify how diapause egg production is accomplished by P. similis and whether sexual reproduction is involved.

Genome-wide identification and expression of eight fatty acid desaturase genes, and the fatty acid profile, in the marine rotifer Brachionus koreanus fed the alga Tetraselmis suecica

Fatty acid desaturases catalyze the formation of a C=C double bond from a C–C single bond in fatty acids, leading to diversification of the fatty acid pool. In this study, we identified the fatty acid desaturase genes in the monogonont marine rotifer Brachionus koreanus, measured the messenger RNA (mRNA) expression, and quantified fatty acid composition under feeding with the alga Tetraselmis suecica. Eight fatty acid desaturase genes were identified and classified by phylogenetic analysis. Fatty acid desaturases in the rotifer B. koreanus were categorized into two Δ4 desaturases, five Δ5/6 desaturases, and one Δ9 desaturase. mRNA expression of B. koreanus under the alga T. suecica-fed condition clearly indicated that transcriptional levels of desaturase genes were increased compared to the non-T. suecica-fed group. Also, the distribution of fatty acids of B. koreanus fed T. suecica was more balanced compared to that of T. suecica. These results provide a better understanding of the role of fatty acid desaturases in B. koreanus fed the alga T. suecica.

Effects of polluted seawater on oxidative stress, mortality, and reproductive parameters in the marine rotifer Brachionus koreanus and the marine copepod Tigriopus japonicus

Although many efforts have been made to understand the toxic effects of metals in aquatic invertebrates, there are limited data regarding metal toxicity in natural ecosystems, as most previous studies were conducted under controlled laboratory conditions. To address this data gap, we analyzed toxic effects and molecular responses in the marine rotifer Brachionus koreanus and the marine copepod Tigriopus japonicus following in vivo exposure to a seawater sample collected from a polluted region in South Korea. Inductively coupled plasma-mass spectrometry (ICP-MS) analysis of the field seawater sample found a variety of metals. Exposure to several dilutions of the field seawater sample impacted several endpoints in both species, including mortality and reproduction. Interestingly, the rotifer and copepod test species exhibited different patterns of effects on reactive oxygen species (ROS) and antioxidant enzymatic activities, suggesting that different regulatory mechanisms may be activated in the two species in response to exposure to toxic chemicals. Our study helps to better understand the defense mechanisms activated in aquatic invertebrates in response to metal-induced oxidative stress induced by contaminated seawater.

Lipid metabolism modulation by five different food types in the monogonont marine rotifer Brachionus koreanus

To investigate the effects of five different foods on fatty acid metabolism in the monogonont marine rotifer Brachionus koreanus, we measured life cycle parameters, analyzed the area of Nile red staining, fatty acid composition, and mRNA expression of fatty acid desaturase (Fads) and elongation of very long chain fatty acid (Elovl) genes. Among the five different foods (Tetraselmis suecica, Chlorella sp., Isochrysis galbana, Chaetoceros sp., and Nannochloropsis oculata), life span of I. galbana-fed group was significantly increased compared to the other groups. However, the reproduction parameters (cumulative offspring and daily reproduction) were the highest in T. suecica-fed group, and the lowest in Chlorella sp.-fed group. The area of Nile red staining analysis showed similar trends, in respect to the content of total fatty acid. The single fatty acid analysis result clearly indicated that not only the most of the content of fatty acid was highly dependent on the food types, especially in omega-6 fatty acids group, but also, B. koreanus could newly synthesize some specific fatty acids by themselves (e.g. omega-3 and -9 families). Lastly, the mRNA expression of Elovl and Fads genes were modulated by food types indicating the lipid metabolism could be controlled by food in B. koreanus and probably very small amount of 18:3n-3 fatty acids was utilized and synthesized omega-3 fatty acids through the increase in Elovl and Fads gene expression in Chaetoceros sp. and N. oculata-fed groups. In conclusion, this study revealed that although B. koreanus could modulate fatty acid metabolism by itself, some nutrient values (e.g. omega-6 fatty acids) should be considered, therefore, it is important to understand the essential nutrient through both the molecular and quantitative analysis.

Targeted cytochrome P450 3045C1 (CYP3045C1) gene mutation via CRISPR-Cas9 ribonucleoproteins in the marine rotifer Brachionus koreanus

The CRISPR-Cas9 system has revolutionized genetic engineering and has been applied in numerous model organisms to date. To examine the capacity of the CRISPR-Cas9 system for generation of mutants in the marine rotifer Brachionus koreanus, we electroporated purified Cas9 proteins fused with GFP (Cas9-GFP) into rotifers. A dose-dependent increase in green fluorescent signal was highly detected in ovary and eggs. The purified Cas9-GFP proteins showed sustained fluorescence signals in rotifers at 24 h after electroporation, which also suggests stability of Cas9 ribonucleoproteins (RNPs) and the possibility of Cas9-mediated gene editing in rotifers. We electroporated B. koreanus with the wild-type Cas9 and single-guide RNAs targeting the endogenous Bk-CYP3045C1 gene and observed different insertion and deletion (indel) mutation profiles near the DNA cleavage sites using targeted deep sequencing. Although the indel rates were low in several salinity conditions (0.30% in 1 psu and 0.20% in 2 psu), these results confirm successful Cas9 RNP-induced mutations. Our results confirm that CRISPR-Cas9 can be applied to generate diverse mutants to demonstrate the functional roles of genes in rotifers.

Identification of the full 26 cytochrome P450 (CYP) genes and analysis of their expression in response to benzo[α]pyrene in the marine rotifer Brachionus rotundiformis

Cytochrome P450s (CYPs) are a large gene superfamily that are found in all living organisms. CYPs have a key role in detoxification of xenobiotics and endogenous chemicals. Although aquatic invertebrate CYPs and their detoxification mechanisms have been reported, little is known about interspecific comparison of CYPs and their detoxification mechanism in the rotifer Brachionus spp. The aim of this study was to identify the entire CYPs in the rotifer Brachionus rotundiformis (B. rotundiformis) and compare B. rotundiformis-CYPs to the previously reported CYPs in other model Brachionus spp. (B. koreanus, B. plicatilis, and B. calyciflorus). To validate the model, the rotifer, specifically Brachionus rotundiformis was exposed to various concentrations of B[α]P, which is widely used PAH xenobiotic, and analyzed gene expression in response to B[α]P. Here, in silico analysis results showed the total of 26 CYPs from the rotifer B. rotundiformis. Based on the phylogenetic analysis, the 26 B. rotundiformis-CYPs were separated into five different clans: 2, 3, 4, mitochondrial, and 46 clans in comparison to three rotifers species, B. koreanus, B. plicatilis, and B. calyciflorus. To understand the detoxification mechanisms of 26 B. rotundiformis-CYPs, we investigated transcriptional expression of 26 CYPs and found that five CYPs (CYP3045A2, CYP3045B4, CYP3045C10, CYP3049A5, and CYP3049E8) were significantly increased (P < 0.05) in response to 10 and 100 μg B[α]P. In addition, we identified the aryl hydrocarbon receptor (AhR) and aryl hydrocarbon receptor nuclear translocator (ARNT) and observed slight up-regulation of B. rotundiformis-AhR and -ARNT, indicating that these CYPs are likely associated with detoxification mechanism and could be used as potential molecular biomarkers of B[α]P in B. rotundiformis. Overall, this study will be helpful for expanding our knowledge of invertebrate CYPs on detoxification mechanisms associated with AhR signaling pathway in rotifers.

Body size-dependent interspecific tolerance to cadmium and their molecular responses in the marine rotifer Brachionus spp.

Although several studies have reported on different interspecific sensitivities in response to various toxicants, the response mechanisms are still poorly understood. Here, we investigate the interspecific toxicity of cadmium (Cd) and its mechanism using three marine rotifer Brachionus spp. that are distinguishable by body size, which is considered the most significant indicator of phenotypic difference. The body sizes of B. plicatilis, B. koreanus, and B. rotundiformis are significantly different throughout their life cycles (egg, neonate, and adult), with the smaller rotifer exhibiting higher sensitivity to Cd. To investigate the mechanisms that result in body size-dependent tolerance to Cd, metabolic and Cd bioaccumulation rates were investigated. Both rates have shown a significant correlation with body size, indicating that body size and its variables are important factors in determining Cd tolerance in Brachionus spp. In addition, similar patterns that further explain body size-dependent tolerance are shown in the phosphorylation status of mitogen-activated protein kinases, reactive oxygen species level, and antioxidant enzymatic activities. Our study provides valuable insight into size- and species-dependent toxicity mechanisms of species in the same genus.

Using the Marine Rotifer Brachionus plicatilis as an Endpoint to Evaluate Whether ROS-Dependent Hemolytic Toxicity Is Involved in the Allelopathy Induced by Karenia mikimotoi.

The toxic effects of the typically noxious bloom-forming dinoflagellate Karenia mikimotoi were studied using the allelopathic experimental system under controlled laboratory conditions. The potency of intact cell suspensions with whole cells, cell-free culture filtrate in different growth phases, and lysed cells with ultrasonication were compared, and the growth and reproduction of the marine rotifer Brachionus plicatilis were used as endpoints to evaluate toxic differences. The intact cell suspension resulted the most significant growth inhibition, including lethality, on the growth of B. plicatilis (p < 0.05). Lysed culture medium treated with ultrasonication and the cell-free culture filtrates at either the exponential or stationary phase exhibited limited negative impacts compared to the control according to changes in the population growth rate (r) and survival rate (p > 0.05). Reproduction presented a similar tendency to change, and the number of eggs produced per individual, as well as spawning period decreased in the whole cell and lysed cell suspensions. The key parameters in the lift table include the net reproductive rate (R0) and the intrinsic rate of increase (rm), which were more sensitive to treatment and were significantly suppressed compared to that of the control. The addition of the ROS inhibitor N-acetylcysteine (NAC) could not change the growth or reproduction patterns. Moreover, substantial hemolytic toxicity was found in the treatment of the intact cell suspension (p < 0.05), while limited toxicity was found in other treatments compared to that of the control. K. mikimotoi was speculated to secrete allelopathic substances onto the cell surface, and direct cell contact was necessary for allelopathic toxicity in B. plicatilis. Reactive oxygen species (ROS)-independent hemolytic toxicity was assumed to be the explanation for what was observed.

Nanoplastic Ingestion Enhances Toxicity of Persistent Organic Pollutants (POPs) in the Monogonont Rotifer Brachionus koreanus via Multixenobiotic Resistance (MXR) Disruption.

Among the various materials found inside microplastic pollution, nanosized microplastics are of particular concern due to difficulties in quantification and detection; moreover, they are predicted to be abundant in aquatic environments with stronger toxicity than microsized microplastics. Here, we demonstrated a stronger accumulation of nanosized microbeads in the marine rotifer Brachionus koreanus compared to microsized ones, which was associated with oxidative stress-induced damages on lipid membranes. In addition, multixenobiotic resistance conferred by P-glycoproteins and multidrug resistance proteins, as a first line of membrane defense, was inhibited by nanoplastic pre-exposure, leading to enhanced toxicity of 2,2',4,4'-tetrabromodiphenyl ether and triclosan in B. koreanus. Our study provides a molecular mechanistic insight into the toxicity of nanosized microplastics toward aquatic invertebrates and further implies the significance of synergetic effects of microplastics with other environmental persistent organic pollutants.

Adverse effects of two pharmaceuticals acetaminophen and oxytetracycline on life cycle parameters, oxidative stress, and defensome system in the marine rotifer Brachionus rotundiformis

To investigate the adverse effect of two widely used pharmaceuticals, paracetamol (acetaminophen [APAP]) and oxytetracycline (OTC) on the marine rotifer Brachionus rotundiformis (B. rotundiformis), the animals were exposed to various environmentally-relevant concentrations. Up to date, acetaminophen and oxytetracycline have been considered as toxic, if used above threshold concentration, i.e. overdosed. However, this study demonstrated these two pharmaceuticals even at low concentration (i.e., μg/L scale) elicited oxidative stress through the generation of reactive oxygen species (ROS) along with the increased glutathione S-transferase activity, despite no-observed effect in in-vivo population growth. To validate the adverse effects of the two pharmaceuticals at relatively low concentrations, mRNA expression analysis was performed of the entire set of genes encoding 26 cytochrome P450s (CYPs) of phase I and 19 glutathione S-transferases (GSTs) of phase II of the rotifer B. rotundiformis. The mRNA expression analysis suggested specific genes CYP3045A2 and GSTσ1, GSTσ4, and GSTω1 take part in detoxification of APAP and OTC, resulting in no significant changes in the population growth and undetermined no observed effect concentration (NOEC) in the marine rotifer B. rotundiformis.

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.

Comparison of resting egg gene expression with different hatchability related to salinity variations in the marine rotifer Brachionus manjavacas

Salinity is a significant factor in affecting resting egg hatching in the euryhaline rotifers. In order to clarify the effects of salinity on resting egg hatchability, this study investigated gene expressions of resting eggs subjected to two different incubation salinities (at 17 and 33 ppt) in the rotifer Brachionus manjavacas. The resting eggs formed at 17 ppt showed a higher hatching rate at 17 ppt incubation salinity, compared to those at 33 ppt. Related to these circumstances, the resting eggs incubated at 17 ppt expressed genes which have putative functions implying cellular differentiation and embryonic development: late embryogenesis abundant protein (LEAs-1), α-amylase, and deaminase. The resting eggs incubated at 33 ppt highly expressed the genes related to the environmental stresses: AP2 transcription factors (AP2TF), and ATP decomposition: ABC transporter permease (ABC-TP), NAD + synthase, copper-translocating P-type ATPase (CTP-ATPase). It is expected that the resting eggs incubated at 33 ppt may need more energy (ATP) to endure saline stress during incubation. The obtained results indicated that the resting eggs regulate their hatching by allocating energy between embryo development and self-defense against environmental conditions like salinity stresses.

Effects of bisphenol A and its analogs bisphenol F and S on life parameters, antioxidant system, and response of defensome in the marine rotifer Brachionus koreanus

To understand the adverse outcome in response to bisphenol A and its analogs bisphenol F and S (BPA, BPF, and BPS), we examined acute toxicity, life parameter, and defensome in the marine rotifer Brachionus koreanus. Among the bisphenol analogs, BPA showed the highest acute toxicity and then BPF and BPS, accordingly in the view of descending magnitude of toxicity. In life parameters including life span and reproduction, BPA, BPF, and BPS were found to cause adverse effect. Both intracellular ROS level and GST activity were significantly increased (P < 0.05) in response to each dosage of bisphenol analogs exposures. In response to bisphenol analogs, defensomes of phase I, II, and III detoxification mechanism demonstrated inverse relationship between the lipophilicity of bisphenol analogs and the expression patterns of defensomes. BPA and BPF were found to have significant modulation (P < 0.05) in the expression of cytochrome P450 (CYP) and GST genes. In phase III, BPS with comparatively lower lipophilicity demonstrated highly diversified expressional pattern, suggesting that BPS is likely caused less toxicity compared to BPA and BPF. In this study, via phase I, II, and III detoxification mechanism, bisphenol A and its analogs F and S demonstrated specific detoxification mechanism in rotifer.

Effect of nutritional status and concentration of Nannochloropsis gaditana as enrichment diet for the marine rotifer Brachionus sp

The development of strategies to improve the quality and to optimize the costs of rotifer production for fish larval feeding, particularly those related to microalgal supply, are highly desirable. In the present work, three different rations (80,000, 130,000 or 200,000 cells rotifer−1) of Nannochloropsis gaditana were assessed as enrichment diets for the marine rotifer Brachionus sp. The microalga was cultured in semi-continuous regime with two different daily renewal rates, 10% and 40%, which provided nutrient-depleted or nutrient-sufficient conditions respectively and resulted in strong differences in biochemical composition. Protein and arachidonic acid (ARA) content were twice higher and eicosapentaenoic acid (EPA) was three times higher in N. gaditana from nutrient-sufficient cultures. After 24-h enrichment, rotifers fed N. gaditana cultured in nutrient-sufficient conditions showed higher dry weight, as well as higher contents of protein, lipids and carbohydrates. Total polyunsaturated fatty acids (PUFAs) and ARA contents increased >50%, whereas EPA content doubled in rotifers fed N. gaditana from nutrient-sufficient conditions. As for feed ration, the increase from 80,000 to 130,000 cells individual−1 enhanced the accumulation of protein, lipids, carbohydrates, total PUFAs, ARA and EPA, but a further increase to 200,000 cells individual−1 only enhanced the accumulation of lipid content. Our results show that the nutritional quality of microalgae, rather than concentration, is the most important factor influencing biomass productivity and biochemical composition of rotifer cultures. Since microalgal biomass is in general a limited resource for aquaculture, the improvement of its nutritional value through the optimization of culture conditions should be considered as an adequate and cost-efficient strategy to produce high-quality live feed.

Is it photosensitization or photodegradation when UV-B irradiation is combined with BDE-47? Evidence from the growth and reproduction changes of rotifer Brachionus plicatilis

Ecotoxicological methods were applied in the present study, and the marine rotifer Brachionus plicatilis was used as the toxic endpoint to depict what occurred when 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was combined with solar ultraviolet-B radiation (UV-B). B. plicatilis was exposed to three different combination methods of BDE-47 and UV-B at an equal toxicity ratio, including normal rotifer co-cultured with UV-B-irradiated BDE-47 (known as Method I), UV-B-irradiated rotifer co-cultured with BDE-47 exposure (known as Method II) and normal rotifer co-cultured with the simultaneous addition of BDE-47 and UV-B irradiation (known as Method III). Acute and chronic experiments were preformed to determine the toxicity differentiation according to the growth and reproduction changes in the rotifer. Twenty-four-hour acute experiments showed that the modes of three combined methods changed from antagonism to additive, to synergistic with the concentration/dose increment, and the contribution rates of Method I and Method II to Method III were calculated by approximately 40.4% and 59.6%, respectively. Chronic exposure to either the single stressor or the combination of stressors inhibited the growth and reproduction of the rotifer, demonstrating the inhibition of the population growth rate and the decrease in the larvae production. Three combined groups presented more serious damages compared to groups with single stress exposure, and the ascending sequence of toxicity was Method I<Method II<Method III. A higher bioaccumulation of BDE-47 was found in all combined groups than BDE-47 single stress group, and bioconcentration factor (BCF) general ranked Method II<Method I<Method III. Moreover, BDE-28, photodegradation production of BDE-47, were found in groups preformed Method I and III. We thus speculated that the toxicity enhancement when BDE-47 was combined with UV-B was mainly due to photosensitization and photodegradation, and the photosensitization might be more noxious to the growth and reproduction of the rotifer.

Comparative ecotoxicity of polystyrene nanoparticles in natural seawater and reconstituted seawater using the rotifer Brachionus plicatilis

The impact of nanoplastics using model polystyrene nanoparticles (PS NPs), anionic (PS-COOH) and cationic (PS-NH2), has been investigated on the marine rotifer Brachionus plicatilis, a major component of marine zooplanktonic species. The role of different surface charges in affecting PS NP behaviour and toxicity has been considered in high ionic strength media. To this aim, the selected media were standardized reconstituted seawater (RSW) and natural sea water (NSW), the latter resembling more natural exposure scenarios. Hatched rotifer larvae were exposed for 24h and 48h to both PS NPs in the range of 0.5–50μg/ml using PS NP suspensions made in RSW and NSW. No effects on lethality upon exposure to anionic NPs were observed despite a clear gut retention was evident in all exposed rotifers. On the contrary, cationic NPs caused lethality to rotifer larvae but LC50 values resulted lower in rotifers exposed in RSW (LC50=2.75±0.67µg/ml) compared to those exposed in NSW (LC50=6.62±0.87µg/ml). PS NPs showed similar pattern of aggregation in both high ionic strength media (RSW and NSW) but while anionic NPs resulted in large microscale aggregates (Z-average 1109 ± 128nm and 998±67nm respectively), cationic NP aggregates were still in nano-size forms (93.99 ± 11.22nm and 108.3 ± 12.79nm). Both PDI and Z-potential of PS NPs slightly differed in the two media suggesting a role of their different surface charges in affecting their behaviour and stability. Our findings confirm the role of surface charges in nanoplastic behaviour in salt water media and provide a first evidence of a different toxicity in rotifers using artificial media (RSW) compared to natural one (NSW). Such evidence poses the question on how to select the best medium in standardized ecotoxicity assays in order to properly assess their hazard to marine life in natural environmental scenarios.

Identification of 28 cytochrome P450 genes from the transcriptome of the marine rotifer Brachionus plicatilis and analysis of their expression

Whole transcriptomes of the rotifer Brachionus plicatilis were analyzed using an Illumina sequencer. De novo assembly was performed with 49,122,780 raw reads using Trinity software. Among the assembled 42,820 contigs, 27,437 putative open reading frame contigs were identified (average length 1235bp; N50=1707bp). Functional gene annotation with Gene Ontology and InterProScan, in addition to Kyoto Encyclopedia of Genes and Genomes pathway analysis, highlighted the metabolism of xenobiotics by cytochrome P450 (CYP). In addition, 28 CYP genes were identified, and their transcriptional responses to benzo[α]pyrene (B[α]P) were investigated. Most of the CYPs were significantly upregulated or downregulated (P<0.05) in response to B[α]P, suggesting that Bp-CYP genes play a crucial role in detoxification mechanisms in response to xenobiotics. This study sheds light on the molecular defense mechanisms of the rotifer B. plicatilis in response to exposure to various chemicals.