Monogonont Rotifer Brachionus Koreanus Research Articles

Effects of low temperature on longevity and lipid metabolism in the marine rotifer Brachionus koreanus

Low-temperature exposure prolongs lifespans and changes lipid metabolism but the relationship between longevity and lipids is largely unknown. Here, we examine the relationship between longevity and lipid metabolism at low temperatures (20 °C and 15 °C) compared with a 25 °C control. Life parameters, fatty acid composition, and transcriptome changes were analyzed in the monogonont rotifer Brachionus koreanus. In vivo life-parameter data indicate that lifespan and fecundity exhibit opposite correlations at low temperatures. The amount of total fatty acids decreased significantly at low temperatures but areas stained with Nile red increased at 15 °C compared with the control. From RNA-seq–based transcriptional analysis, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway-enrichment analysis were conducted. GO analysis shows that telomeres were positively regulated at low temperatures. KEGG pathway-enrichment results indicate that gene expression involved in lipid metabolism was activated with increased glycerol and/or choline synthesis at low temperatures. We suggest that reduced reproductive rates are associated with a decrease of lecithin, which is involved in the conversion of glycerol to triacylglycerol in response to low temperatures by lowering the temperature of body fluid.

The genome of the marine rotifer Brachionus koreanus sheds light on the antioxidative defense system in response to 2-ethyl-phenanthrene and piperonyl butoxide

Brachionusspp. (Rotifera: Monogononta) have been introduced as ecotoxicological model-organisms that are widely distributed in aquatic environments. Among the Brachionus spp., the monogonont rotifer Brachionus koreanus has been widely used for ecology, ecotoxicology, and evolution, thus, providing the whole genome data of B. koreanus is important for further understandings of in-depth molecular mechanisms. In this study, the completed assembly and characterization of the B. koreanus genome resulted in a total length of 85.7 Mb with 14,975 annotated genes. The final number of scaffolds was 567 with an N50 value and a GC content of 1.86 Mb and 24.35 %, respectively. Based on the fully constructed genome database, a total of 24 CYPs, 23 GSTs, two SODs, and a single CAT genes were identified and analyzed antioxidant activities (CAT, SOD, and GST), and transcriptional regulation of the entire CYPs, GSTs, SODs, and CAT in response to 2-ethyl-phenanthrene (2-ethyl-PHE) and piperonyl butoxide (PBO), to demonstrate the usefulness of the whole genome library of B. koreanus in response xenobiotic-induced oxidative stress. The assembled B. koreanus genome will provide a better understanding on the molecular ecotoxicology in the view of molecular mechanisms underlying toxicological responses, particularly on xenobiotic detoxification processes in the rotifer B. koreanus.

Aging extension and modifications of lipid metabolism in the monogonont rotifer Brachionus koreanus under chronic caloric restriction

To examine the interrelationship of aging extension and modification of lipid metabolism under chronic caloric restriction (CCR; reduced concentration of the green algae Tetraselmis suecica) in the monogonont rotifer Brachionus koreanus, we assessed life cycle parameters, fatty acid composition, and expression of sirtuin and genes related to lipid metabolism. B. koreanus in the 5% T. suecica group showed an increased life span but decreased reproduction. Based on this finding, we chose 5% T. suecica for further experiments and compared the data with those for 100% T. suecica. Upregulation of sirtuin gene expression was observed under CCR. In addition, despite the reduction in the amount of total fatty acid (FA) and the area of triacylglycerol, increases in the ratios of saturated fatty acid and monounsaturated fatty acid (MUFA) to total FA in 5%-exposed B. koreanus were observed. Furthermore, mRNA expression analysis confirmed that CCR promoted the synthesis of MUFA through Δ9 desaturase. Moreover, expression of the docosahexaenoic acid (DHA) synthesizing gene Δ4 desaturase was also upregulated, together with DHA content. These data suggest that CCR modified protein acetylation and lipid metabolism, leading to a decrease in reproduction and consequently resulting in life span extension.

Interrelationship of salinity shift with oxidative stress and lipid metabolism in the monogonont rotifer Brachionus koreanus

Salinity is a critical key abiotic factor affecting biological processes such as lipid metabolism, yet the relationship between salinity and lipid metabolism has not been studied in the rotifer. To understand the effects of salinity on the monogonont rotifer B. koreanus, we examined high saline (25 and 35psu) conditions compared to the control (15psu). In vivo life cycle parameters (e.g. cumulative offspring and life span) were observed in response to 25 and 35psu compared to 15psu. In addition, to investigate whether high salinity induces oxidative stress, the level of reactive oxygen species (ROS) and glutathione S-transferase activity (GST) were measured in a salinity- (15, 25, and 35psu; 24h) and time-dependent manner (3, 6, 12, 24h; 35psu). Furthermore composition of fatty acid (FA) and lipid metabolism-related genes (e.g. elongases and desaturases) were examined in response to different salinity conditions. As a result, retardation in cumulative offspring and significant increase in life span were demonstrated in the 35psu treatment group compared to the control (15psu). Furthermore, ROS level and GST activity have both demonstrated a significant increase (P<0.05) in the 35psu treatment. In general, the quantity of FA and mRNA expression of the lipid metabolism-related genes was significantly decreased (P<0.05) in response to high saline condition with exceptions for both GST-S4 and S5 demonstrated a significant increase in their mRNA expression. This study demonstrates that high salinity induces oxidative stress, leading to a negative impact on lipid metabolism in the monogonont rotifer, B. koreanus.

Adverse effects of BDE-47 on life cycle parameters, antioxidant system, and activation of MAPK signaling pathway in the rotifer Brachionus koreanus

2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47) is widely dispersed endocrine disrupting chemicals (EDCs) in the aquatic ecosystem. Due to its devastating effect on marine organisms and insufficient database on toxicology, we investigated the adverse effects of BDE-47 on life parameters and antioxidant defense system following the reactive oxygen species (ROS) production in the monogonont rotifer Brachionus koreanus. In B. koreanus, the reduction in life cycle, fecundity, and population growth were observed in response to BDE-47. 50μg/L BDE-47 significantly reduced (P<0.05) life expectancy and net reproductive rate. In response to 10–50μg/L BDE-47 exposure, the oxidative stress was elicited via the generation of ROS, while the antioxidant related enzymes (e.g. glutathione S-transferase [GST] and glutathione reductase [GR]) have demonstrated significant activity levels (P<0.05) to further alleviate the oxidative stress in a concentration dependent manner. Furthermore, transcript profiles of antioxidant function (GST-A, -O, and -S1–S8)-related genes have shown the significant increase over 24h in response to BDE-47 (0, 10, 25, and 50μg/L). As for MAPK signaling pathway analysis, up-regulation of their activities was observed at 25μg/L BDE-47 but their activities have reduced at adult NOEC concentration of 50μg/L. This study provides a better understanding of the effects of BDE-47 on life parameters, molecular defense system, and activation of MAPK signaling pathway against generated oxidants in the rotifer.

Genome-wide identification of ATP-binding cassette (ABC) transporters and conservation of their xenobiotic transporter function in the monogonont rotifer (Brachionus koreanus)

The ATP-binding cassette (ABC) transporter family is one of the largest gene family in animals, and members of this family are known to be involved in various biological processes due to their ability to transport a wide range of substrates across membranes using ATP cleavage-derived energy. We identified 61 ABC transporters in the genome of the monogonont rotifer Brachionus koreanus, and classified these into eight distinct subfamilies (A–H) by phylogenetic analysis. ABC transporters in the rotifer B. koreanus are comprised of 11 ABCA genes, 19 ABCB genes, 14 ABCC genes, 3 ABCD genes, 1 ABCE gene, 3 ABCF genes, 8 ABCG genes, and 2 ABCH genes. Extensive gene duplication and loss events in synteny were observed in several subfamilies. In particular, massive gene duplications of P-glycoproteins (P-gps), multidrug resistance proteins (MRPs), and Bk-Abcg-like proteins were observed. The ability of these B. koreanus proteins to function as multixenobiotic resistance (MXR) ABC transporters was validated using specific fluorescence substrates/inhibitors. The ABC transporter superfamily members identified in this study will be useful in future toxicological studies, and will facilitate comparative studies of the evolution of the ABC transporter superfamily in invertebrates.

Microplastic Size-Dependent Toxicity, Oxidative Stress Induction, and p-JNK and p-p38 Activation in the Monogonont Rotifer (Brachionus koreanus).

In this study, we evaluated accumulation and adverse effects of ingestion of microplastics in the monogonont rotifer (Brachionus koreanus). The dependence of microplastic toxicity on particle size was investigated by measuring several in vivo end points and studying the ingestion and egestion using 0.05-, 0.5-, and 6-μm nonfunctionalized polystyrene microbeads. To identify the defense mechanisms activated in response to microplastic exposure, the activities of several antioxidant-related enzymes and the phosphorylation status of mitogen-activated protein kinases (MAPKs) were determined. Exposure to polystyrene microbeads of all sizes led to significant size-dependent effects, including reduced growth rate, reduced fecundity, decreased lifespan and longer reproduction time. Rotifers exposed to 6-μm fluorescently labeled microbeads exhibited almost no fluorescence after 24 h, while rotifers exposed to 0.05- and 0.5-μm fluorescently labeled microbeads displayed fluorescence until 48 h, suggesting that 6-μm microbeads are more effectively egested from B. koreanus than 0.05- or 0.5-μm microbeads. This observation provides a potential explanation for our findings that microbead toxicity was size-dependent and smaller microbeads were more toxic. In vitro tests revealed that antioxidant-related enzymes and MAPK signaling pathways were significantly activated in response to microplastic exposure in a size-dependent manner.

Acute Toxicity of Gamma Radiation to the Monogonont Rotifer Brachionus koreanus.

We examined the tolerance of the monogonont rotifer Brachionus koreanus in response to gamma radiation. In order to determine the median lethal dose (LD50) of rotifers against gamma radiation, we irradiated B. koreanus with gamma rays from 0 to 7000 grays (Gy). The LD50s were 2900 and 2300Gy at 24h (LD50-24h) and 96h (LD50-96h) after irradiation, respectively. In addition, the no observed effect levels (NOEL) were 1500 and 1000Gy at 24 and 96h, respectively. This is the first determination of lethal doses of gamma radiation for B. koreanus, which could be useful in ecological assessment of gamma radiation toward aquatic life and could be useful for understanding toxic mechanisms over sublethal doses.

Adverse Effects, Expression of the Bk-CYP3045C1 Gene, and Activation of the ERK Signaling Pathway in the Water Accommodated Fraction-Exposed Rotifer.

To examine the deleterious effects of the water accommodated fraction (WAF) of crude oil, the growth curve, fecundity, and lifespan of the monogonont rotifer (Brachionus koreanus) were measured for 24 h in response to three different doses (0.2×, 0.4×, and 0.8×) of WAFs. A higher dose of WAFs significantly reduced the fecundity and lifespan. A rotifer 32K microarray chip showed that the Bk-CYP3045C1 gene had the highest expression. Of the 25 entire CYP genes, the Bk-CYP3045C1 gene showed a significant expression for different doses and times in response to WAFs and chemical components of WAFs (naphthalene and phenanthrene); also, glutathione S-transferase genes, ABC transporter, and other genes showed dose responses upon exposure to 80% WAF over time. Different doses of WAFs increased the oxidative stress with an induction of reactive oxygen species (ROS) and a depletion of glutathione (GSH). Exposure to WAFs did not show toxic effects on survivability in B. koreanus; however, toxicity to WAFs was shown when piperonyl butoxide, a potent inhibitor of cytochrome P450 (CYP) enzymes, was added. This toxicity was dose-dependent. After WAFs exposure, p-ERK was activated over time in response to WAFs, which suggests that WAFs can be activated by the p-ERK signaling pathway.

Triclosan (TCS) and Triclocarban (TCC) cause lifespan reduction and reproductive impairment through oxidative stress-mediated expression of the defensome in the monogonont rotifer (Brachionus koreanus)

Triclosan (TCS) and Triclocarban (TCC) are used as antimicrobial agents and have been widely dispersed and detected in the marine environment. However, the toxicities of TCS and TCC have been poorly investigated in marine invertebrates. In this study, the effects of TCS and TCC on mortality, population growth, lifespan, and fecundity were examined in the monogonont rotifer (Brachionus koreanus) using cellular ROS levels, GST enzymatic activity, and gene expression of defensomes. The median lethal concentration (LC50) of TCS (393.1μg/L) and TCC (388.1μg/L) was also determined in the same species. In TCS- and TCC-exposed B. koreanus, growth retardation and reduced fecundity were observed and were shown to have a potentially deleterious effect on the life cycle of B. koreanus. In addition, time-dependent increases in ROS content (%) and GST enzymatic activity were shown in response to TCS and TCC exposure. Additionally, transcript levels of detoxification proteins (e.g., CYPs), antioxidant proteins (e.g., GST-sigma, Cu/ZnSOD, CAT), and heat shock proteins (Hsps) were modulated in response to TCS and TCC exposure over a 24h period. Our results indicate that TCS and TCC induce oxidative stress and transcriptional regulation of detoxification, antioxidant, and heat shock proteins, resulting in changes in lifespan and fecundity.

Effects of chlorpyrifos on life cycle parameters, cytochrome P450S expression, and antioxidant systems in the monogonont rotifer Brachionus koreanus.

Chlorpyrifos is a widely used organophosphorus insecticide for controlling diverse insect pests of crops. In the monogonont rotifer Brachionus koreanus, population growth retardation with the inhibition of lifespan, fecundity, and individual body size of ovigerous females was shown over 10 d in response to chlorpyrifos exposure. At the molecular and biochemical levels, the rotifer B. koreanus defensome, composed of cytochrome P450 complements, heat shock protein 70, and antioxidant enzymatic systems (i.e., glutathione, glutathione peroxidase, glutathione reductase, and glutathione S-transferase), was significantly induced in response to different concentrations of chlorpyrifos. Thus, chlorpyrifos strongly induced a defensome system to mitigate the deleterious effects of chlorpyrifos at in vivo and in vitro levels as a trade-off in fitness costs. Environ Toxicol Chem 2016;35:1449-1457. © 2015 SETAC.

Multi-walled carbon nanotubes (MWCNTs) lead to growth retardation, antioxidant depletion, and activation of the ERK signaling pathway but decrease copper bioavailability in the monogonont rotifer (Brachionus koreanus)

To examine the toxic effects of multi-walled carbon nanotubes (MWCNTs) in the marine environment, we first exposed the monogonont rotifer (Brachionus koreanus) to MWCNTs in the presence of copper. The acute toxicity of copper decreased significantly with a decrease in copper bioavailability resulting from MWCNT exposure. Furthermore, we examined the effects of MWCNT exposure on reproductive capacity, population growth rate, growth patterns, antioxidant systems, and mitogen-activated protein kinase (MAPK) activation. Reproductive capacity, population growth rate, and body growth rate were significantly suppressed in B. koreanus in response to 1.3–4mg/L MWCNT exposure. Furthermore, MWCNTs induced the generation of reactive oxygen species (ROS) and decreased the antioxidant enzymatic activities of catalase (CAT) and glutathione reductase (GR). However, the enzymatic activity of glutathione S-transferase (GST) was up-regulated after a 24 h-exposure to 100mg/L MWCNTs. Exposure to 100mg/L MCWNTs induced extracellular signal-regulated kinase (ERK) activation in B. koreanus, suggesting that p-ERK may mediate the adverse effects of MWCNTs in B. koreanus via the MAPK signaling pathway. Our results provide insight into the mechanistic basis of the ecotoxicological effects of MWCNTs in the marine environment.

Correlation between the DNA methyltransferase (Dnmt) gene family and genome-wide 5-methylcytosine (5mC) in rotifer, copepod, and fish

DNA methyltransferases (DNMTs) are an enzyme family that catalyzes the transfer of a methyl group to DNA for a wide variety of biological functions. To determine whether the number and composition of the Dnmt gene family affects the 5-methylcytosine (5mc) ratio at the genome level, genome-wide 5mc ratios from three marine animals, the mangrove killifish (Kryptolebias marmoratus), an intertidal copepod (Tigriopus japonicus), and a monogonont rotifer (Brachionus koreanus), were analyzed in each organism after the cloning of Dnmt genes. Lineage- and teleost-specific gene evolution was observed in the vertebrate Dnmt3 gene family, while unique gene expansion was found in the T. japonicus Dnmt1 gene family. However, the rotifer did not have any apparent homologue of Dnmt1 or Dnmt3 in its genome. This gene information was highly supportive of genome-wide 5mc levels in the three marine animals. Therefore, the absence or presence of the Dnmt gene family could be an important evolutionary parameter of how this could affect genome-wide epigenetic metabolism.

Early expansion and expression of the lipopolysaccharide (LPS)-induced TNF-α factor (LITAF) gene family in the LPS-exposed monogonont rotifer Brachionus koreanus.

To date, a single lipopolysaccharide-induced TNF-α factor (LITAF) homologue, mediating the expression of inflammatory cytokines including TNF-α in terms of host defense was identified in vertebrates and most invertebrates such as insects, mollusks, and crustaceans. However, LITAF gene family members have recently been characterized in only two mollusks, Crassostrea gigas and Mytilus galloprovincialis. Although a large gene family expansion of LITAF homologues was observed in the nematode Caenorhabditis elegans, the amino acid sequences encoded by the C. elegans LITAF homologue have low similarities to other LITAF gene family members. In this study, three LITAF genes were identified in the monogonont rotifer Brachionus koreanus. In silico analyses of B. koreanus LITAF genes of conserved domains and phylogenetic relationships supported gene annotations that indicated that LITAF is involved in innate immunity in primitive rotifers. To examine transcriptional sensitivity of B. koreanus LITAF genes, the rotifers were exposed to different concentrations of lipopolysaccharide (LPS). Transcriptional levels of LITAF1 and LITAF2 gene were significantly upregulated dose- and time-dependently in response to LPS exposure for 24 h. LPS exposure induced glutathione (GSH) depletion and antioxidant enzyme activity levels for 24 h in B. koreanus. These results suggested that the B. koreanus LITAF gene family has potential sensitivities directly and/or indirectly to immune stimulator-triggered oxidative stress.

Modulated expression and enzymatic activity of the monogonont rotifer Brachionus koreanus Cu/Zn- and Mn-superoxide dismutase (SOD) in response to environmental biocides

Superoxide dismutases (SODs) are important antioxidant enzymes whose expression levels are often used as biomarkers for oxidative stress. To investigate the biomarker potential of the monogonont rotifer Brachionus koreanus SOD genes, the full-length Cu/Zn-SOD (Bk-Cu/Zn-SOD) and Mn-SOD (Bk-Mn-SOD) genes were cloned from genomic DNA and characterized. All amino acid residues involved in the formation of tertiary structure and metal binding in Bk-Cu/Zn-SOD and Bk-Mn-SOD were highly conserved across species. Phylogenetic analysis revealed that Bk-Mn-SOD, in particular, was closely clustered with mitochondrial Mn-SOD. Transcript analysis after exposure to six different biocides (alachlor, chlorpyrifos, dimethoate, endosulfan, lindane, and molinate) revealed that the transcriptional level of Bk-Cu/Zn-SOD was significantly increased in a dose-dependent manner. In contrast, the level of Bk-Mn-SOD transcript was significantly increased compared with control cells in response to chlorpyrifos, endosulfan, and molinate at their no observed effect concentrations (NOECs). However, exposure to alachlor, chlorpyrifos, and molinate significantly reduced the enzymatic activity of total SOD protein, while a decreased pattern was observed in all biocide treatments. Taken together, these results indicate that exposure to waterborne environmental biocides induces the transcription of Bk-Cu/Zn-SOD and Bk-Mn-SOD, but inhibits the enzymatic activity of Bk-SODs. These results contribute to our understanding of the modes of action of oxidative stress-mediating biocides on rotifer.

Sublethal gamma irradiation affects reproductive impairment and elevates antioxidant enzyme and DNA repair activities in the monogonont rotifer Brachionus koreanus

To examine the effects of gamma radiation on marine organisms, we irradiated several doses of gamma ray to the microzooplankton Brachionus koreanus, and measured in vivo and in vitro endpoints including the survival rate, lifespan, fecundity, population growth, gamma ray-induced oxidative stress, and modulated patterns of enzyme activities and gene expressions after DNA damage. After gamma radiation, no individuals showed any mortality within 96h even at a high intensity (1200Gy). However, a reduced fecundity (e.g. cumulated number of offspring) of B. koreanus at over 150Gy was observed along with a slight decrease in lifespan. At 150Gy and 200Gy, the reduced fecundity of the rotifers led to a significant decrease in population growth, although in the second generation the population growth pattern was not affected even at 200Gy when compared to the control group. At sub-lethal doses, reactive oxygen species (ROS) levels dose-dependently increased with GST enzyme activity. In addition, up-regulations of the antioxidant and chaperoning genes in response to gamma radiation were able to recover cellular damages, and life table parameters were significantly influenced, particularly with regard to fecundity. DNA repair-associated genes showed significantly up-regulated expression patterns in response to sublethal doses (150 and 200Gy), as shown in the expression of the gamma-irradiated B. koreanus p53 gene, suggesting that these sublethal doses were not significantly fatal to B. koreanus but induced DNA damages leading to a decrease of the population size.

Identification of three doublesex genes in the monogonont rotifer Brachionus koreanus and their transcriptional responses to environmental stressor-triggered population growth retardation.

Doublesex and Mab-3-related transcription factor (Dmrt) gene family members have rarely been identified or characterized in aquatic invertebrates. In this study, we identified and characterized three DMdomain-containing genes - Dmrt11E, Dmrt93B, and Dmrt99B - in the monogonont rotifer, Brachionus koreanus. DMdomains of the proteins encoded by the B.koreanus Dmrt (Bk-Dmrt) genes had high similarities to DM domains of other invertebrate species. To understand the potential effects of environmental stressors on the transcriptional expression of Dmrt genes in rotifers, we exposed B.koreanus to a wide range of UV-B radiation and different concentrations of benzo[a]pyrene (B[a]P) over different time courses. Transcript levels of all Bk-Dmrt genes decreased significantly in response to relatively high doses of UV-B irradiation, and were also downregulated in response to exposure to UV-B radiation over time. Transcript levels of all Bk-Dmrt genes were downregulated in response to B[a]P exposure for 24h. This decrease in expression of all Bk-Dmrt genes was concomitant with the growth retardation induced by UV-B and B[a]P exposure. We concluded that both environmental stressors have detrimental effects on transcriptional regulation of all Bk-Dmrt genes, especially relatively high doses of these stressors, leading to growth retardation. However, further studies are required to better understand the potential role of Dmrt genes in environmental stressor-triggered growth retardation in the rotifer B.koreanus.

Expression Pattern of Entire Cytochrome P450 Genes and Response of Defensomes in the Benzo[a]pyrene-Exposed Monogonont Rotifer Brachionus koreanus

Cytochrome P450 (CYP) proteins are involved in the first line of detoxification mechanism against diverse polycyclic aromatic hydrocarbons (PAHs) including benzo[a]pyrene (B[a]P). In aquatic invertebrates, there is still a lack of knowledge on the CYP genes involved in the molecular response to B[a]P exposure due to limited gene information. In this study, we cloned the entire 25 CYP genes in the monogonont rotifer Brachionus koreanus with the aid of next generation sequencing (NGS) technologies and analyzed their transcript profiles with a real-time RT-PCR array to better understand B[a]P-triggered molecular response over different time courses. As a result, B[a]P exposure induced CYP2/3-involved detoxification mechanisms and defensome, including phase II detoxification and antioxidant systems with a modulation of the chaperone heat shock protein (hsp) expression but did not change expression of other CYP clans in B. koreanus . Therefore, we found that B[a]P induced a strong detoxification mechanism to overcome detrimental effects of B[a]P associated with B[a]P-induced growth retardation as a trade-off in fitness costs. Also, this approach revealed that the entire CYP profiling can be a way of providing a better understanding on the mode of action of B[a]P in B. koreanus with respect to molecular defense metabolism.

Effect of copper exposure on GST activity and on the expression of four GSTs under oxidative stress condition in the monogonont rotifer, Brachionus koreanus

Glutathione S-transferases (GSTs; EC 2.5.1.18) are major enzymes that function in Phase II detoxification reactions by catalyzing the conjugation of reduced glutathione through cysteine thiol. In this study, we cloned and sequenced four GST genes from the monogonont rotifer Brachionus koreanus. The domain regions of four Bk-GSTs showed a high similarity to those of other species. In addition, to evaluate the potential of GST genes as an early warning signal for oxidative stress, we exposed sublethal concentrations of copper (Cu) to B. koreanus and measured glutathione (GSH) contents and several antioxidant enzymes such as glutathione S-transferase (GST), glutathione peroxidase (GPx; EC 1.11.1.9), and glutathione reductase (GR; EC 1.8.1.7). The reactive oxygen species (ROS) at 12h and 24h after copper exposure increased significantly. GSH contents however did not increase significantly and even it decreased at 0.24mg/L at 12h. The activities of several antioxidant enzymes, particularly GPx and GR, showed a dramatic increase in 0.24mg/L of CuCl2. Messenger RNAs of each Bk-GST showed different patterns of modulations according to GST types, and particularly, Bk-GST-omega, Bk-GST-sigma, and Bk-GST zeta genes were highly sensitive to Cu. These results indicate that Bk-GSTs, functioning as one of the enzymatic defense mechanisms particularly in the early stage of oxidative stress response, were induced by Cu exposure. This also suggests that these genes and related enzymes have a potential as biomarkers for a more sensitive initial stress response.

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

The complete mitochondrial genome was obtained from the assembled genome data sequenced by next generation sequencing (NGS) technology from the monogonont rotifer Brachionus koreanus. The mitochondrial genome of B. koreanus was composed of two circular chromosomes designated as mtDNA-I (10,421 bp) and mtDNA-II (11,923 bp). The gene contents of B. koreanus were identical with previously reported B. plicatilis mitochondrial genomes. However, gene orders of B. koreanus showed one rearrangement between the two species. Of 12 protein-coding genes (PCGs), 3 genes (ATP6, ND1, and ND3) had an incomplete stop codon. The A + T base composition of B. koreanus mitochondrial genome was high (68.81%). They also showed anti-G bias (12.03% and 10.97%) on the second and third position of PCGs as well as slight anti-C bias (15.96% and 14.31%) on the first and third position of PCGs.