Marine Rotifer Research Articles

Differential modes of response to zinc chloride in the marine rotifers Brachionus plicatilis and Brachionus rotundiformis: Reproductive flexibility and stress-defensive activity

Zinc is an essential trace metal used extensively as a dietary supplement in the cultivation of aquatic organisms. This practice can expose species such as rotifers, which are essential live food sources for rearing larvae in aquaculture, to zinc overexposure, which can inhibit rotifer reproduction. However, rotifers with distinct ecological features may respond differently to exposure. This study investigates the tolerance, reproduction, behavior, and mitochondria-mediated stress and energy defenses of two species of rotifers, the temperate and relatively large Brachionus plicatilis and the tropical and smaller Brachionus rotundiformis, following acute exposure (0–72 mg/L) and seven days of chronic exposure (0–2 mg/L) to zinc chloride. The 24 h and 48 h median lethal concentrations of ZnCl2 for B. plicatilis and B. rotundiformis were 29.9 and 9.0 mg/L and 13.3 and 3.6 mg/L, respectively. Long-term exposure to ZnCl2 at concentrations of 0.0125–0.1 mg/L had no adverse effects on survival and fecundity in either species. However, higher levels of ZnCl2 induced different reproductive phenomena, particularly in sexual reproduction. In B. plicatilis, ZnCl2 at concentrations ≥1 mg/L accelerated maturation, shortened life expectancy, and inhibited mixis induction and resting egg production, while similar ZnCl2 treatments stimulated sexual reproduction in B. rotundiformis. Subsequently, we detected different metabolic patterns between the two rotifers: decreased lipid storage and sperm viability and overcompensated antioxidant reactions (e.g., copper‑zinc superoxide dismutase, catalase, and glutathione S-transferase) with significantly low reactive oxygen species (ROS) levels in B. plicatilis and enhanced copper‑zinc superoxide dismutase activity, ATP generation, and sperm viability in B. rotundiformis. In behavioral tests, ZnCl2 exposure enhanced the swimming speeds of males and females of both species, potentially affecting the energy available for reproduction and male-female encounter rates. In conclusion, chronic exposure to ZnCl2 (≥1 mg/L) caused reductive stress with low ROS levels in B. plicatilis, possibly inhibiting sexual reproduction. However, the positive effects on reproduction in tropical B. rotundiformis revealed a potential requirement for nutritional zinc. Species-specific reproductive sensitivity to zinc in temperate and tropical rotifers may reflect ecological adaptations.

Metabolism deficiency and oxidative stress induced by plastic particles in the rotifer Brachionus plicatilis: Common and distinct phenotypic and transcriptomic responses to nano- and microplastics

Growing experimental data on the adverse effects of microplastic pollution on marine biota indicate that the size of the plastic particles is a key determinant of toxicity. Here, we investigated size-dependent toxicity at different levels of biological organizations in the marine rotifer Brachionus plicatilis, from bioaccumulation as an initiating event to adverse in-vivo outcomes, with ecotoxicogenomic approach to elucidate the size-dependent toxicity of microplastics. Nanoplastics strongly retarded the reproduction and population growth of B. plicatilis, while microplastics were associated with moderate effects. This size dependency could be attributed to the selective induction of oxidative stress by nanoplastic exposure in addition to a metabolic deficiency, which was a common toxicity mechanism with both nano- and microplastic exposure as predicted by transcriptomic analysis. Our findings suggested that metabolic deficiency is a shared toxicity mechanism of nano- and microplastics, while oxidative stress might be responsible for the stronger toxicity of nanoplastics.

Oxidative stress–mediated synergistic deleterious effects of nano- and microplastics in the hypoxia-conditioned marine rotifer Brachionus plicatilis

While pollution due to nano- and micro-sized plastics (NMPs) and hypoxic conditions both occur in coastal areas, the deleterious potential of co-exposure to hypoxia and NMPs (hypoxia and micro-sized plastics, HMPs; hypoxia and nano-sized plastics, HNPs) is largely unclear. Here, we provide evidence for multigenerational effects of HMP and HNP in the marine rotifer Brachionus plicatilis by investigating changes in its life traits, antioxidant system, and hypoxia-inducible factor (HIF) pathway using an orthogonal experimental design, with nanoscale and microscale particles measuring 0.05 μm and 6.0 μm in diameter, respectively, and hypoxic conditions of 0.5 mg/L for six generations. Combined exposure to NMPs and hypoxia caused a significant decrease in fecundity and overproduction of reactive oxygen species (ROS). The HIF pathway and circadian clock genes were also significantly upregulated in response to HMP and HNP exposure. In particular, synergistic deleterious effects of HNP were evident, suggesting that size-dependent toxicity can be a major driver of the effects of hypoxia and NMP co-exposure. After several generations of exposure, ROS levels returned to basal levels and transcriptomic resilience was observed, although rotifer reproduction remained suppressed. These findings help eluciating the underlying molecular mechanisms involved in responses to plastic pollution in hypoxic conditions.

Automated system of tubular filtration for rotifer production

AbstractThis study developed an automated filtration system for a selected rotifer, Brachionus ibericus. This system is controlled by a programmable logic controller, and it enables the high‐density cultivation of marine rotifers and the selection of rotifers for palatability. We tested seven mesh sizes (300, 200, 100, 50, 20, 5, and 1 μm) for commercial 10‐inch (25.4‐cm) stainless steel tubular filters in the proposed system, after which we selected the optimal mesh size for filtering impurities, separating rotifers, eliminating wastewater, and minimizing the rotifer loss rate. The results indicated that a combination of the 5‐ and 200‐μm meshes produced optimal filtration efficiency. After every 120 s of filtration followed by a 30‐s flushing process, a rotifer density of 3170 ± 101 individuals/ml, a mesh blocking loss rate of 4.95 ± 3.62%, and impurity‐free rotifer volume of 45.18 ± 1.2 L were obtained. Our study verified that tubular filters can be used in commercial aquaculture.

Toxicity of triphenyl phosphate toward the marine rotifer Brachionus plicatilis: Changes in key life-history traits, rotifer-algae population dynamics and the metabolomic response

Triphenyl phosphate (TPhP) is used as a flame retardant that gradually leaks from products into the marine environment and thus may threaten low-trophic-level marine organisms, such as zooplankton. To assess the effect of TPhP on these taxa, we treated the marine rotifer Brachionus plicatilis as a target and examined the changes in key life history parameters and the metabolome after exposure to TPhP at 0.02, 1 and 5 mg/L. Additionally, the rotifer-Phaeocystis population dynamics (a simulation of the prey-predator relationship) were studied under TPhP stress. Our results showed that TPhP at 1 and 5 mg/L reduced the average lifespan and the total offspring number and prolonged the prereproductive time, suggesting damage to survival and fecundity. In the 0.02 mg/L group, no obvious damage occurred in the overall condition of rotifers, but the volume of parental rotifers after the first brood decreased. This implied that rotifers sacrificed somatic growth to reproduction in the initial period of TPhP exposure at the low concentration. All the tested TPhP concentrations altered the rotifer-Phaeocystis population dynamic changes, especially that 1 mg/L TPhP reduced the ability of rotifers to remove this harmful alga, as evidenced by the decrease in the maximum population density of rotifers and the extended time to P. globosa extinction. At the molecular level, metabolomics identified 84 and 206 differentially expressed metabolites, most of which were enriched in glycerophospholipid metabolism, steroid biosynthesis and sphingolipid metabolism. Nile red staining showed a decrease in neutral lipids in rotifers, further indicating a disorder of lipid metabolism induced by TPhP. Moreover, the balance between ROS production and the defense system was disrupted by TPhP, which contributed to its toxicity. This finding will promote the understanding of the ecological risk and mode of action of TPhP in aquatic environments.

In vivo biosynthesis of long-chain polyunsaturated fatty acids by the euryhaline rotifer (Brachionus plicatilis)

In order to increase omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA) availability and to improve the design of rotifer's enrichment protocols for marine larvae production, the endogenous fatty acid (FA) metabolism of the marine rotifer, Brachionus plicatilis was determined. To this purpose, the in vivo ability of this species to incorporate, esterify into the different lipid classes and to elongate/desaturate unsaturated FAs was investigated. Rotifers were incubated in 75 cm2 tissue culture flasks, at a density of 75,000 rotifers per incubation, for 4 h. Incubations (n = 4) were performed at 21 °C, with 0.3 μCi of [1-14C]FAs including C18 FAs (18:1n-9, OA; 18:2n-6, LA; 18:3n-3, ALA) and LC-PUFA (20:4n-6, ARA; 20:5n-3, EPA; 22:6n-3, DHA). The present study demonstrates that rotifers possess an active metabolism over dietary FAs, being this species able to produce LC-PUFA from its C18 FA precursors. Interestingly, the action of a Δ12 desaturase that converts OA to LA and of a Δ15 desaturase over LA to produce ALA, seems to be also present, in agreement with previously reported functional characterization of ωx desaturases genes in this species. However, a globally low transformation rate was obtained, in addition to a lower incorporation of DHA into rotifer tissues compared to the other incubated substrates. The aforementioned factors, together with a competitive esterification pattern of DHA, LA and ALA into phosphatidylcholine (PC) or of EPA and ARA into phosphatidylinositol (PI), may give rise to rotifers with inadequate essential FA ratios for marine larvae nutrition, if ignored or incorrectly handled in the lipid enrichment process of this live prey species.

Comparative genome analysis of the monogonont marine rotifer Brachionus manjavacas Australian strain: Potential application for ecotoxicology and environmental genomics

This is the first study to analyze the whole-genome sequence of B. manjavacas Australian (Aus.) strain through combination of Oxford Nanopore long-read seq, resulting in a total length of 108.1 Mb and 75 contigs. Genome-wide detoxification related gene families in B. manjavacas Aus. strain were comparatively analyzed with those previously identified in other Brachionus spp., including B. manjavacas German (Ger.) strain. Most of the subfamilies in detoxification related families (CYPs, GSTs, and ABCs) were highly conserved and confirmed orthologous relationship with Brachionus spp., and with accumulation of genome data, clear differences between genomic repertoires were demonstrated the marine and the freshwater species. Furthermore, strain-specific genetic variations were present between the Aus. and Ger. strains of B. manjavacas. This whole-genome analysis provides in-depth review on the genomic structural differences for detoxification-related gene families and further provides useful information for comparative ecotoxicological studies and evolution of detoxification mechanisms in Brachionus spp.

Iron reproductive toxicity of marine rotifer sibling species: Adaptation to temperate and tropical habitats.

Iron (Fe), a trace metal in coastal waters has increased significantly due to anthropogenic activities, however, few studies have examined its toxicity to marine organism reproduction and associated mechanisms. We employed two marine rotifers, the temperate Brachionus plicatilis, and tropical B. rotundiformis to investigate the toxicity of iron (FeSO4•7H2O) and its deleterious effects on reproductive features in females (sexual fecundity, abnormal resting eggs, and swimming speed) and males (lifespan, swimming speed, and spermatozoa quality) under lethal and sub-lethal exposure. The 24h median lethal concentration (LC50) of iron was determined as 0.9 and 1.7μg/mL per ng of dry weight for B. plicatilis and B. rotundiformis, respectively. During sub-lethal iron (20-75μg/mL) exposure, higher iron (≥ 20μg/mL for B. plicatilis and ≥ 45μg/mL for B. rotundiformis) induced rotifer sexual toxicity especially in normal resting egg development and production. These were supported by the data of male shorter lifespan, poor sperm vitality, and rotifer behavioral changes as the iron concentration increased. Iron effects on swimming behavior, slower males and faster females, should reduce male/female encounter rates associated with inactive fertilized egg (resting egg) production. Two rotifer species exhibited different iron-response patterns in genetic and enzymatic activities including iron homeostasis-maintaining related Fe-S protein, and oxidative/antioxidant related lipid peroxidation product (MDA), superoxidase dismutase/SOD, catalase/CAT, and cytochrome P450 under acute iron exposure. Antioxidant activities were vulnerable in B. plicatilis but kept activities in B. rotundiformis, which may attribute to their temperate and tropical habitat adaptations.

Alleviation of Tris(2-chloroethyl) Phosphate Toxicity on the Marine Rotifer Brachionus plicatilis by Polystyrene Microplastics: Features and Molecular Evidence.

As emerging pollutants, microplastics (MPs) and organophosphorus esters (OPEs) coexist in the aquatic environment, posing a potential threat to organisms. Although toxicological studies have been conducted individually, the effects of combined exposure are unknown since MPs can interact with OPEs acting as carriers. In this study, we assessed the response of marine rotifer, Brachionus plicatilis, to co-exposure to polystyrene MPs and tris(2-chloroethyl) phosphate (TCEP) at different concentrations, including population growth, oxidative status, and transcriptomics. Results indicated that 0.1 μm and 1 μm MPs were accumulated in the digestive system, and, even at up to 2000 μg/L, they did not exert obvious damage to the stomach morphology, survival, and reproduction of B. plicatilis. The presence of 1 μm MPs reversed the low population growth rate and high oxidative stress induced by TCEP to the normal level. Some genes involved in metabolic detoxification and stress response were upregulated, such as ABC and Hsp. Subsequent validation showed that P-glycoprotein efflux ability was activated by combined exposure, indicating its important role in the reversal of population growth inhibition. Such results challenge the common perception that MPs aggravate the toxicity of coexisting pollutants and elucidate the molecular mechanism of the limited toxic effects induced by MPs and TCEP.

The Genome of the Marine Rotifer Brachionus manjavacas: Genome-Wide Identification of 310 G Protein-Coupled Receptor (GPCR) Genes

The marine rotifer Brachionus manjavacas is widely used in ecological, ecotoxicological, and ecophysiological studies. The reference genome of B. manjavacas is a good starting point to uncover the potential molecular mechanisms of responses to various environmental stressors. In this study, we assembled the whole-genome sequence (114.1Mb total, N50 = 6.36Mb) of B. manjavacas, consisting of 61 contigs with 18,527 annotated genes. To elucidate the potential ligand-receptor signaling pathways in marine Brachionus rotifers in response to environmental signals, we identified 310 G protein-coupled receptor (GPCR) genes in the B. manjavacas genome after comparing them with three other species, including the minute rotifer Proales similis, Drosophila melanogaster, and humans (Homo sapiens). The 310 full-length GPCR genes were categorized into five distinct classes: A (262), B (26), C (7), F (2), and other (13). Most GPCR gene families showed sporadic evolutionary processes, but some classes were highly conserved between species as shown in the minute rotifer P. similis. Overall, these results provide potential clues for in silico analysis of GPCR-based signaling pathways in the marine rotifer B. manjavacas and will expand our knowledge of ligand-receptor signaling pathways in response to various environmental signals in rotifers.

Genome-wide identification of seven superoxide dismutase genes in the marine rotifer Brachionusrotundiformis and modulated expression and enzymatic activity in response to microplastics and nutritional status.

Microplastics (MPs) pollution has attracted worldwide attention. Superoxide dismutase (SOD) is a sensitive indicator for assessing the toxic effects of MPs in aquatic organisms. However, few studies have been performed to identify all genes encoding SOD in aquatic invertebrates. Especially, effects of MPs on SOD activity and expression in aquatic organisms under starvation or a subsequent refeeding status are unclear. In the present study, all full-length genes encoding SOD were cloned and characterized from the marine rotifer Brachionus rotundiformis, including CuZnSOD1, CuZnSOD2, CuZnSOD3, CuZnSOD4, CuZnSOD5, MnSOD1, and MnSOD2. The CuZnSOD1, CuZnSOD2 and MnSOD2 are homologous to SODs from vertebrates and the other SOD proteins are rotifer-specific according to the results from the phylogenetic tree. The conserved signature sequences and binding sites of Cu2+, Zn2+and Mn2+ were also identified in the seven SOD proteins. Compared with feeding, starvation down-regulated SOD activity and mRNA expression of CuZnSOD2, CuZnSOD4, CuZnSOD5, MnSOD1 and MnSOD2 while refeeding maintained SOD activity comparable to the feeding level and up-regulated CuZnSOD5 and MnSOD2. Intake of MPs by B. rotundiformis was observed by examining fluorescence signals from the fluorescently-labeled microplastics under different nutritional status. Exposure to MPs reduced rotifer density and increased malondialdehyde (MDA) content and SOD activity in the rotifers under the refeeding condition, but did not affect these indicators under the feeding and starvation conditions. However, mRNA expression of some tested genes was responsive to MPs in the fed, starved and refed rotifers. The present study for the first time demonstrated a nutritional status-dependent effect of MPs on oxidative stress response, and provided more sensitive molecular biomarkers for assessing the toxicity of MPs using B. rotundiformis as a model animal.

Impacts of nanoplastics on life-history traits of marine rotifer (Brachionus plicatilis) are recovered after being transferred to clean seawater

Impacts of nanoplastics on life-history traits of marine rotifer (Brachionus plicatilis) are recovered after being transferred to clean seawater

Reproductive toxicity of environmental levels of triphenyltin to the marine rotifer, Brachionus plicatilis

Triphenyltin (TPT) is a representative organotin often used in marine antifouling coatings, herbicides, and pesticides. However, leaching of TPT into water may be toxic to aquatic life. In this study, environmental concentrations of TPT were used to explore reproductive toxicity of TPT to Brachionus plicatilis, a representative marine rotifer. Toxicity was examined at individual, biochemical, and molecular levels and via phenotypic traits. Rotifers exposed to 10 ng/L TPT group showed increased population size, improved reproductive rate, and a higher weekly growth rate. At 100 ng/L TPT group, the greatest degree of oxidative damage was seen. Exposure to 200 ng/L TPT group shorten generation time, delayed reproduction, and obscured the reproductive peak. Expression of the Vasa gene associated with reproduction was increased after exposure to 10 and 200 ng/L TPT group and decreased at 100 ng/L TPT group. High concentrations of TPT reduced rotifer body length and width and slowed swimming speed. Findings provide a better understanding of the adverse effects of changing TPT concentrations on marine rotifer, by the life cycle parameters, oxidative stress defense mechanisms, expression of a gene related to reproduction, and phenotypic traits. This paper firstly analyzed the reproductive toxicity of environmental levels of organotin compounds to zooplankton, which provided new data support for the comprehensive evaluation of its marine ecological toxicity.

Multi-Label Classification and Deep Image Analysis Methods on Marine Microalgae and Rotifer Identification Using Transfer Learning and Two-Dimensional Convolutional Neural Networks

Multi-Label Classification and Deep Image Analysis Methods on Marine Microalgae and Rotifer Identification Using Transfer Learning and Two-Dimensional Convolutional Neural Networks

Species-specific ammonia tolerance in the marine rotifers Brachionus plicatilis and Brachionus rotundiformis: Reproductive characteristics and its mechanisms

High unionized ammonia (NH3−N) is a major stress factor for rearing aquatic animals that can collapse the mass culture of rotifers in aquaculture facilities. In rotifer mass culture, concentrations of NH3-N are elevated when reaching maximum density. As NH3-N toxicity has temperature-dependent characteristics, tropical and temperate rotifers should be subjected to different levels of habitat-resource NH3-N, which could affect their physiological adaptations. To investigate the NH3-N tolerance of rotifers associated with reproductive adaptations to different habitats, two rotifer species in the Brachionus plicatilis species complex were studied: temperate B. plicatilis and tropical B. rotundiformis. Survival, life history parameters, and reproductive patterns were assessed under acute (lethal) and chronic (sub-lethal) NH3-N exposure. These rotifer species were not treated with NH3-N or exposed to 1.1 and 8.5 mg/L NH3-N for 7 days to define the biochemical (i.e., oxidative and lipid metabolism) and behavioral (swimming speed) mechanisms of ammonia species sensitivity. High concentrations of NH3-N (≥8.5 mg/L) suppressed rotifer growth and reproduction, resulting in substantial maturation retardation and fecundity reduction in both species. Nevertheless, the tropical B. rotundiformis was more tolerant to acute and chronic NH3-N exposure than the temperate B. plicatilis, with 1.5 and 1.7 fold higher LC50 and EC50 (for intrinsic growth rate) values at 25 °C, respectively. Furthermore, B. rotundiformis showed stronger ammonia tolerance in sexual reproductive parameters, including mixis, fertilization, and resting egg production. High sexual reproduction tolerance is important for improving rotifer stress resistance and maintaining the population under harsh environments. The two species exhibited different modulations of lipid and stress defense activities under NH3-N exposure. Temperate B. plicatilis showed reduced neutral lipid accumulation in the reproductive organs (vitellarium/ovary), stimulated lipid peroxidation with a high level of malondialdehyde (MDA), and disrupted antioxidant activities. In contrast, the tropical B. rotundiformis exhibited active defense responses, with enhanced antioxidant activity and lipid synthesis. These findings with molecular evidence indicate the specific ammonia sensitivity between tropical and temperate rotifers, and more active anti-stress strategies of the tropical species than the temperate species, contributing to high ammonia tolerance. The higher ammonia tolerance of tropical B. rotundiformis species may support their high-density endurance during mass culture.

Short‐term enrichment of microalgae with inorganic selenium and zinc and their effects on the mineral composition of microalgae and marine rotifer Brachionus plicatilis

Rotifers are widely used as a live prey for finfish larvae, although their content in minerals such as selenium and zinc is lower than in fish. In the present study, mixed microalgae (i.e., Isochrysis aff. galbana and Nannochloropsis oculata) were enriched with different amounts of Se and Zn either alone (45, 90, and 135 mg L−1 of Zn, 60, 120, and 180 mg L−1 of Se) or mixed (22.5, 45, and 90 mg Zn L−1 and 30, 60, and 120 mg Se L−1). The content of minerals in the microalgae was analysed after 1 and 3 h enrichment and their effect on the growth and mineral composition of the rotifer. Based on the results, 1 h enrichment time and 90 and 120 mg L−1 of Zn and Se, respectively, resulted in the highest amount of Se and Zn in enriched microalgae. The maximum Zn content was detected in the rotifers fed 90 mg L−1 Zn and 90 mg L−1 Zn +120 mg L−1 of Se, but the maximum Se was observed in rotifers fed with 120 and 180 mg L−1 Se. Thus, Se- and Zn-enriched rotifers can be used as a mineral delivery method to cover marine fish larvae nutritional requirements.

Abiotic and Biotic Damage of Microalgae Generate Different Volatile Organic Compounds (VOCs) for Early Diagnosis of Algal Cultures for Biofuel Production.

Open microalgal ponds used in industrial biomass production are susceptible to a number of biotic and abiotic environmental stressors (e.g., grazers, pathogens, pH, temperature, etc.) resulting in pond crashes with high economic costs. Identification of signature chemicals to aid in rapid, non-invasive, and accurate identification of the stressors would facilitate targeted and effective treatment to save the algal crop from a catastrophic crash. Specifically, we were interested in identifying volatile organic compounds (VOCs) that can be used to as an early diagnostic for algal crop damage. Cultures of Microchloropsis gaditana were subjected to two forms of algal crop damage: (1) active grazing by the marine rotifer, Brachionus plicatilis, or (2) repeated freeze–thaw cycles. VOCs emitted above the headspace of these algal cultures were collected using fieldable solid phase microextraction (SPME) fibers. An untargeted analysis and identification of VOCs was conducted using gas chromatography-mass spectrometry (GC-MS). Diagnostic VOCs unique to each algal crop damage mechanism were identified. Active rotifer grazing of M. gaditana was characterized by the appearance of carotenoid degradation products, including β-cyclocitral and various alkenes. Freeze–thaw algae produced a different set of VOCs, including palmitoleic acid. Both rotifer grazing and freeze–thawed algae produced β-ionone as a VOC, possibly suggesting a common stress-induced cellular mechanism. Importantly, these identified VOCs were all absent from healthy algal cultures of M. gaditana. Early detection of biotic or abiotic environmental stressors will facilitate early diagnosis and application of targeted treatments to prevent algal pond crashes. Thus, our work further supports the use of VOCs for monitoring the health of algal ponds to ultimately enhance algal crop yields for production of biofuel.

Nutritional-status dependent effects of microplastics on activity and expression of alkaline phosphatase and alpha-amylase in Brachionus rotundiformis

Tissue-nonspecific alkaline phosphatase (ALPL) and alpha-amylase (AMY) are essential in the immune and digestive systems, respectively. Microplastics (MPs) pose a risk to zooplankton which may be in a state of feeding, starvation, or subsequent refeeding. However, molecular characterization of both enzymes and the regulated mechanisms affected by nutritional statuses and MPs remain unclear in zooplankton. In the present study, four full-length genes encoding ALPL and two genes encoding AMY were cloned and characterized from an isolated marine rotifer, Brachionus rotundiformis, including alplA, alplB, alplC, alplD, amy2a, and amy2al. AMY activity and expression of amy2a and amy2al were reduced by starvation and recovered after refeeding compared with feeding. ALPL activity remained unchanged among different statuses, while alplA, alplB and alplD were down-regulated by starvation and refeeding compared with feeding. ALPL activity was not affected by exposure to 10, 100 and 1000 μg/L MPs in rotifers subjected to feeding, starvation and refeeding, whereas AMY activity was significantly enhanced by 1000 μg/L MPs in rotifers subjected to refeeding. Gene expression of the tested genes, except amy2a, was significantly responsive to MPs, especially in the feeding rotifers, depending on MPs concentrations and nutritional statuses. Two-way ANOVA confirmed that these changes were strongly associated with the interaction between MPs concentrations and nutritional statuses. The present study is the first to demonstrate a nutritional status-dependent impact of MPs on immune and digestive responses, and provides more sensitive molecular biomarkers for assessing MPs toxicity using the species as model animals.

Potential Applications of Arthrospira platensis Lipid-Free Biomass in Bioremediation of Organic Dye from Industrial Textile Effluents and Its Influence on Marine Rotifer (Brachionus plicatilis).

Arthrospira platensis is one of the most important cultured microalgal species in the world. Arthrospira complete dry biomass (ACDB) has been reported as an interesting feedstock for many industries, including biodiesel production. The A. platensis by-product of biodiesel production (lipid-free biomass; LFB) is a source of proteins, functional molecules, and carbohydrates, and can also be reused in several applications. The current study investigated the efficiency of ACDB and LFB in bioremediation of dye (Ismate violet 2R, IV2R) from textile effluents. In addition, the potential of ACDB and LFB loaded by IV2R as a feed for Rotifer, Brachionus plicatilis, was examined. The surface of the adsorbents was characterized by SEM, FTIR, and Raman analysis to understand the adsorption mechanism. The batch sorption method was examined as a function of adsorbent dose (0.02–0.01 g L−1), solution initial concentration (10–100 mg L−1), pH (2–10), and contact time (15–180 min). The kinetic studies and adsorption isotherm models (Freundlich, Langmuir, Tempkin, and Halsey) were used to describe the interaction between dye and adsorbents. The results concluded that the adsorption process increased with increasing ACDB and LFB dose, contact time (120 min), initial IV2R concentration (10 mg L−1), and acidity pH (2 and 6, respectively). For the elimination of industrial textile wastewater, the ACDB and LFB sorbents have good elimination ability of a dye solution by 75.7% and 61.11%, respectively. The kinetic interaction between dye and adsorbents fitted well to Langmuir, Freundlish, and Halsey models for LFB, and Langmuir for ACDB at optimum conditions with R2 > 0.9. In addition, based on the bioassay study, the ACDB and LFB loaded by IV2R up to 0.02 g L−1 may be used as feed for the marine Rotifer B. plicatilis.

Effects of salinity and temperature on reproductivity and fatty acid synthesis in the marine rotifer Brachionus rotundiformis

To examine the effect of salinity and temperature in the marine tropical rotifer Brachionus rotundiformis, we analyzed various in vivo life cycle parameters, fatty acid (FA) composition, and transcriptional levels of elongation of very long-chain fatty acid (Elovl) and fatty acid desaturase (Fad) genes. In the case of life cycle parameters, the reproduction of B. rotundiformis showed the highest fecundity under 5 practical saline unit (PSU) and 30 °C conditions, while the concentrations of total FAs were the highest in 15 PSU and 25 °C-exposed groups, respectively. Besides, changes in culture condition (salinity and temperature) resulted in a decrease in n-3 FAs. Therefore, the correlation between nutrient components and the total yield should be considered to determine the optimal culture conditions for B. rotundiformis. The changes in the transcriptional level of Elovl and Fad genes appear to be involved in the compositional modulations of FA, and in particular, Elovl9b could be suggested as useful biomarker due to its temperature-dependent modulation.