Biological control of predatory fungi inhabiting activated sludge in wastewater treatment.

The unfavorable phenomenon of activated sludge bulking that occurs in sewage treatment plants (WWTPs) is caused by the over-proliferation of filamentous bacteria that should be limited by the Lecane rotifers that feed on them; however, predatory, rotiferovorous fungi that often inhabit WWTPs pose a real threat to these organisms. To solve this problem, we investigated the interaction of the fungus Clonostachys rosea, which is a known Biological Control Agent (BCA) and the predacious Zoophagus sp. in simplified laboratory culture conditions. The presence of C. rosea in the cultures reduced the number of active traps, thus translating into a much smaller number of rotifers being caught. The mycelium of C. rosea was labeled with a red fluorescent protein (RFP). The life cycle of C. rosea that were attacking Zoophagus sp. (hunting for rotifers) is described. C. rosea spores germinate into single-celled forms and penetrate the interior of the Zoophagus mycelium where they feed on the cytoplasm. Then is the mycelium produced abundantly and forms conidiophores. This type of life strategy has not been known before. The obtained results demonstrated the potential of C. rosea as a BCA that can be used to protect rotifers in the event of an infection of activated sludge by the predatory fungi that threaten the rotifer population.

A free and user-friendly software protocol for the quantification of microfauna swimming behavior.

Characterizing swimming behavior can provide a holistic assessment of the health, physiology and ecology of microfaunal species when done in conjunction with measuring other biological parameters. However, tracking and quantifying microfauna swimming behavior using existing automated tools is often difficult due to the animals' small size or transparency, or because of the high cost, expertise, or labor needed for the analysis. To address these issues, we created a cost-effective, user-friendly protocol for behavior analysis that employs the free software packages HitFilm and ToxTrac along with the R package 'trajr' and used the method to quantify the behavior of rotifers. This protocol can be used for other microfaunal species for which investigators may face similar issues in obtaining measurements of swimming behavior.

Hexabromocyclododecane-induced reproductive toxicity in Brachionus plicatilis: Impacts and assessment.

Hexabromocyclododecane (HBCD), third-generation brominated flame retardants (BRFs), has aroused worldwide concern because of its wide application and potentially negative impacts on marine ecosystems, but an information gap still exists regarding marine low-trophic organisms. Brachionus plicatilis, the model marine zooplankton, was used in the present study, and its reproductive responses were used as the endpoint to indicate HBCD-induced toxicity. HBCD was suggested to be extremely highly toxic compounds regarding the 96 h-LC50 of 0.58 mg L-1. The sublethal exposure of HBCD injured the reproduction of B. plicatilis: The total number of offspring per female and the key population index calculated from the life table, including the intrinsic rate of population increase (rm) and net reproductive rate (R0), were significantly influenced in a concentration-dependent manner. The reproductive process was also altered, as indicated by the first spawning time, first hatching time and oocyst development time. At the same time, individual survival and growth (body length) were also negatively affected by HBCD. Reactive oxygen species (ROS) were suggested to be responsible for reproductive toxicity mainly because the total ROS contents as well as the main components of •OH and H2O2 greatly increased and resulted in the oxidative imbalance that presented as malondialdehyde (MDA) elevation. Simultaneous activation of the glutathione antioxidant system was accompanied by the apoptosis marker enzymes Caspase-3 and 9, as well as the correlation between ROS content, physiological alteration and cell apoptosis, providing further evidence for this. The integrated biomarker response (IBR) and adverse outcome pathway (AOP) showed that HBCD had a significant toxic effect on B. plicatilis near the concentration range of 96 h-LC50. The establishment of this concentration range will provide a reliable reference for future environmental concentration warning of HBCD in marine.

Detrimental effects of hull cleaning wastewater on oxidative status, life cycle parameters, and population growth of the monogonont rotifer Brachionus manjavacas.

While wastewater discharged from in-water cleaning process of ship hulls on rotifer consistently released into aquatic ecosystem, its detrimental effects on non-target animals are largely unclear. In this study, we provide evidence on detrimental effects of hull cleaning wastewater in the monogonont rotifer Brachionus manjavacas by analyzing biochemical and physiological parameters in its oxidative status, survival, lifespan, growth, fecundity, and population. The wastewater contained high concentrations of metals (Zn and Cu) and metal-based antifoulants (CuPT and ZnPT). Significant oxidative stress was observed in response to two wastewater samples [1) raw wastewater (RW) and 2) mechanical filtrated in the cleaning system (MF)]. Higher detrimental effects in survival, lifespan, fecundity, and population growth for 10 days were measured in the RW-exposed rotifers than those results analyzed in the MF-exposed rotifers. Two growth parameters, lorica length and width were also significantly modulated by both wastewater samples. These results indicate that even filtered hull cleaning wastewater would have deleterious effects on the maintenance of the rotifer population when they exposed constantly.

Salinity-dependent top-down effect of rotifer Brachionus plicatilis on removing harmful alga Phaeocystis globosa.

Using appropriate zooplankton to transfer the primary productivity of harmful algae to higher trophic levels through food chain is an eco-friendly mode to remove harmful algae. To assess the top-down efficiency of rotifer removing Phaeocystis and the salinity effect, we adopted a series of salinities to carry out Phaeocystis-rotifer population dynamics and rotifer life-history experiments. Results showed that the time for rotifers to remove Phaeocystis population was the shortest when the salinity was ≤20 ‰. With salinity rising to above 25 ‰, although the clearance time of Phaeocystis population by rotifer was significantly prolonged, ultimately the Phaeocystis population were almost completely eliminated at all salinities. Additionally, rotifer matured and reproduced earlier at low salinity, while high salinity significantly delayed first reproductive time and decreased the total offspring. The above findings are helpful to assess the impacts of external environmental factors on the application of zooplankton to control harmful algae.

Effects of nanoplastics exposure on ingestion, life history traits, and dimethyl sulfide production in rotifer Brachionus plicatilis.

Microplastics (MPs) and nanoplastics (NPs) have gained global concern due to their detrimental effects on marine organisms. We investigated the effects of 80 nm polystyrene (PS) NPs on life history traits, ingestion, and dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) production in the rotifer Brachionus plicatilis. Fluorescently labeled 80 nm PS NPs were ingested by the rotifer B. plicatilis and accumulated in the digestive tract. The lethal rates of B. plicatilis exposed to NPs were dose-dependent. High concentrations of PS NPs exposure had negative effects on developmental duration, leading to prolonged embryonic development and pre-reproductive periods, shortened reproductive period, post-reproductive period, and lifespan in B. plicatilis. High concentrations of PS NPs exposure inhibited life table demographic parameters such as age-specific survivorship and fecundity, generation time, net reproductive rate, and life expectancy. Consequently, the population of B. plicatilis was adversely impacted. Furthermore, exposure to PS NPs resulted in a reduced ingestion rate in B. plicatilis, as well as a decreased in DMS, particulate DMSP (DMSPp) concentration, and DMSP lyase activity (DLA), which exhibited a dose-response relationship. B. plicatilis grazing promoted DLA and therefore increased DMS production. PS NPs exposure caused a decline in the increased DMS induced by rotifer grazing. Our results help to understand the ecotoxicity of NPs on rotifer and their impact on the biogeochemical cycle of dimethylated sulfur compounds.

A transcriptomic examination of encased rotifer embryos reveals the developmental trajectory leading to long-term dormancy; are they "animal seeds"?

BACKGROUND: Organisms from many distinct evolutionary lineages acquired the capacity to enter a dormant state in response to environmental conditions incompatible with maintaining normal life activities. Most studied organisms exhibit seasonal or annual episodes of dormancy, but numerous less studied organisms enter long-term dormancy, lasting decades or even centuries. Intriguingly, many planktonic animals produce encased embryos known as resting eggs or cysts that, like plant seeds, may remain dormant for decades. Herein, we studied a rotifer Brachionus plicatilis as a model planktonic species that forms encased dormant embryos via sexual reproduction and non-dormant embryos via asexual reproduction and raised the following questions: Which genes are expressed at which time points during embryogenesis? How do temporal transcript abundance profiles differ between the two types of embryos? When does the cell cycle arrest? How do dormant embryos manage energy? RESULTS: As the molecular developmental kinetics of encased embryos remain unknown, we employed single embryo RNA sequencing (CEL-seq) of samples collected during dormant and non-dormant embryogenesis. We identified comprehensive and temporal transcript abundance patterns of genes and their associated enriched functional pathways. Striking differences were uncovered between dormant and non-dormant embryos. In early development, the cell cycle-associated pathways were enriched in both embryo types but terminated with fewer nuclei in dormant embryos. As development progressed, the gene transcript abundance profiles became increasingly divergent between dormant and non-dormant embryos. Organogenesis was suspended in dormant embryos, concomitant with low transcript abundance of homeobox genes, and was replaced with an ATP-poor preparatory phase characterized by very high transcript abundance of genes encoding for hallmark dormancy proteins (e.g., LEA proteins, sHSP, and anti-ROS proteins, also found in plant seeds) and proteins involved in dormancy exit. Surprisingly, this period appeared analogous to the late maturation phase of plant seeds. CONCLUSIONS: The study highlights novel divergent temporal transcript abundance patterns between dormant and non-dormant embryos. Remarkably, several convergent functional solutions appear during the development of resting eggs and plant seeds, suggesting a similar preparatory phase for long-term dormancy. This study accentuated the broad novel molecular features of long-term dormancy in encased animal embryos that behave like "animal seeds".

Homogenization of Functional Diversity of Rotifer Communities in Relation to Eutrophication in an Urban River of North China.

Rapid urbanization has triggered nutrient loading, which will inevitably lead to the eutrophication of water bodies and further affect the structure of aquatic populations. At present, eutrophication is a significant challenge for urban aquatic ecosystems. However, we still know little about the correlation between eutrophication in urban rivers and the composition of aquatic functional groups. The effects of urban river eutrophication on rotifer communities were investigated using an annual field survey of the Jinan section of the Xiaoqing River, a typical urban river in northern China. Using functional diversity (FD) and beta diversity, the spatiotemporal variation of the aquatic biological functional groups regime along stretches subject to different eutrophication was investigated. The functional evenness (FEve) and functional divergence (FDiv) decreased significantly with the increment of the trophic level index. Functional diversity exhibits an extremely low level across functional groups, with the richness difference (RichDiff) being an important component. The results indicate that eutrophication led to the homogenization of rotifer communities. This can be attributed to the functional homogenization of the rotifer community in the Jinan section of the Xiaoqing River. The observed homogenization may be due to widely distributed species complementing the ecological niche space. Our findings provide valuable information on the conservation of the urban river under the threat of eutrophication caused by high-intensity human activities.

Butyl benzyl phthalate induced reproductive toxicity in the endoplasmic reticulum and oxidative stress in Brachionus plicatilis Müller, 1786.

To study the adverse effects of butyl benzyl phthalate (BBP) on Brachionus plicatilis, rotifers were exposed to different BBP concentrations (0 [control], 0.001, 0.01, 0.1, and 1 mg/L). We measured the activities of the antioxidant enzymes superoxide dismutase, catalase, and reduced glutathione, which play a key role in detoxification, and the malondialdehyde content, which represents the level of lipid peroxidation. In addition, we investigated the effect of BBP on the submicroscopic structure and transcriptome of rotifer ovary cells. Our results showed that B. plicatilis exhibited a rapid oxidative stress response accompanied by a significant increase in superoxide dismutase enzyme activity. High BBP concentrations resulted in a significant decrease in malondialdehyde content, which indicated that BBP interferes with the lipid metabolism of rotifer cells. Our observations showed that the endoplasmic reticulum structure of rotifer ovary cells was severely damaged by BBP exposure. Transcriptomic data further demonstrated that oxidative stress and cellular sub-microstructural damage were associated with altered expression of functional genes related to rotifer redox regulation, biosynthetic processes, and cellular damage components. In conclusion, our study demonstrates that BBP triggers changes in antioxidant-related indicators in rotifers; this leads to activation of related genes and subsequent changes in intracellular signaling, which in turn triggers endoplasmic reticulum stress and ultimately leads to disruption of cell function and structure. These findings highlight the potential risks associated with BBP exposure and provide fundamental insights into its toxicological effects on marine invertebrates.

Rotifer distribution patterns in relation to dissolved organic matter in the middle reaches of Huai River Basin during the dry season.

Increased dissolved organic matter (DOM) may induce water browning and affect zooplankton communities by changing photochemical environment, microbial food web, and bioavailability of organic carbon supply. However, little is known about the relationship between DOM components and rotifers in natural rivers, relative to the cladocerans and copepods. Here, we investigated the spatial patterns of rotifer distribution in relation to DOM by collecting forty-four water samples from four areas in the middle reaches of Huai River Basin. Results revealed that DOM was described by two humic-like and two protein-like components. There were significant differences in the composition and diversity of rotifer communities among areas, which might be related to autochthonous and allochthonous DOM as well as geographical distances. Specifically, rotifer communities were mainly related to molecular weight, substituents on the aromatic ring, humification level, and protein-like materials. Autochthonous and fresh DOM was positively associated with rotifer abundance and richness, and terrigenous humic-like substances were positively associated with rotifer diversity and evenness. There was a reciprocal effect between rotifer and DOM. Our findings will contribute to the understanding of the possible effects of water browning on rotifer communities, providing new insights into the key role of DOM and rotifer in the energy transfer of aquatic systems.

Physiological effects and molecular response in the marine rotifer Brachionus plicatilis after combined exposure to nanoplastics and copper.

Because nanoplastics (NPs) can transport pollutants, the absorption of surrounding pollutants into NPs and their effects are important environmental issues. This study shows a combined effect of high concentrations of NPs and copper (Cu) in the marine rotifer Brachionus plicatilis. Co-exposure decreased the growth rate, reproduction, and lifespan. The highest level of NP ingestion was detected in the co-treated group, but the Cu concentration was higher in the Cu single-exposure group. ERK activation played a key role in the downstream cell signaling pathway activated by the interaction of NPs and Cu. The increased sensitivity of B. plicatilis to Cu could be due to the impairment of MXR function caused by a high concentration of NPs, which supports our in vivo experiment results. Our results show that exposure to NPs could induce the dysfunction of several critical molecular responses, weakening resistance to Cu and thereby increasing its physiological toxicity in B. plicatilis.

Biochemical and structural characterization of the first-discovered metazoan DNA cytosine-N4 methyltransferase from the bdelloid rotifer Adineta vaga.

Much is known about the generation, removal, and roles of 5-methylcytosine (5mC) in eukaryote DNA, and there is a growing body of evidence regarding N6-methyladenine, but very little is known about N4-methylcytosine (4mC) in the DNA of eukaryotes. The gene for the first metazoan DNA methyltransferase generating 4mC (N4CMT) was reported and characterized recently by others, in tiny freshwater invertebrates called bdelloid rotifers. Bdelloid rotifers are ancient, apparently asexual animals, and lack canonical 5mC DNA methyltransferases. Here, we characterize the kinetic properties and structural features of the catalytic domain of the N4CMT protein from the bdelloid rotifer Adineta vaga. We find that N4CMT generates high-level methylation at preferred sites, (a/c)CG(t/c/a), and low-level methylation at disfavored sites, exemplified by ACGG. Like the mammalian de novo 5mC DNA methyltransferase 3A/3B (DNMT3A/3B), N4CMT methylates CpG dinucleotides on both DNA strands, generating hemimethylated intermediates and eventually fully methylated CpG sites, particularly in the context of favored symmetric sites. In addition, like DNMT3A/3B, N4CMT methylates non-CpG sites, mainly CpA/TpG, though at a lower rate. Both N4CMT and DNMT3A/3B even prefer similar CpG-flanking sequences. Structurally, the catalytic domain of N4CMT closely resembles the Caulobacter crescentus cell cycle-regulated DNA methyltransferase. The symmetric methylation of CpG, and similarity to a cell cycle-regulated DNA methyltransferase, together suggest that N4CMT might also carry out DNA synthesis-dependent methylation following DNA replication.

Impact of invertebrates on water quality safety and their sheltering effect on bacteria in water supply systems.

Invertebrates in drinking water not only affect human health, but also provide migration and shelter for pathogenic microorganisms. Their residues and metabolites also produce DBPs (disinfection by-products), which have adverse effects on the health of residents. In this study, the contributions of the rotifers and nematodes to the BDOC (biodegradable dissolved organic carbon), BRP (bacterial regrowth potential) and DBPs in drinking water were explored, and the sheltering effects of chlorine-resistant invertebrates on indigenous bacteria and pathogenic bacteria were studied, and the health and safety risk of invertebrates in drinking water was also assessed. The contributions of rotifer BAPs (biomass-associated products), UAPs (utilization-associated products) of rotifer, and nematode BAPs to the BRP were 46, 1240, and 24 CFU/mL. Nematodes were found to have a sheltering effect on indigenous bacteria and pathogenic bacteria, allowing them to resist chlorine disinfection and UV (ultraviolet) disinfection. When subjected to a UV dose of 40 mJ/cm2, the inactivation rates of indigenous bacteria and three pathogenic bacteria decreased by 85% and 39-50% when bacteria were sheltered by the living nematodes; while decreased by 66% and 15-41% when they were sheltered by nematode residue. The safety risk posed by invertebrates in the drinking water was mainly due to their ability to promote bacterial regeneration and carry bacteria. This study aims to provide a theoretical basis and technical support for the risk control of invertebrates' pollution, and provides references for ensuring the safety of drinking water and formulating standards for the levels of invertebrates in drinking water.

Toxicological effects of tire rubber-derived 6PPD-quinone, a species-specific toxicant, and dithiobisbenzanilide (DTBBA) in the marine rotifer Brachionus koreanus.

The ingredients of tire-rubber products include a complex range of chemicals additives, most of which are leached into surrounding water as unmeasured toxicants with unexplored ecotoxicological impacts. The present study summarizes the reported species-specific acute toxicity of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), the ozonation product of anti-oxidant 6PPD used in tire rubber. Also, chronic toxicity and oxidative response of 6PPD-Q and another tire-rubber derivative, 2',2'''-dithiobisbenzanilide (DTBBA), in rotifer Brachionus koreanus were investigated. Although 6PPD-Q has been reported to be highly toxic to several species of salmonids, only moderate chronic toxicity was observed in B. koreanus. In contrast, DTBBA significantly retarded the population growth and fecundity. The varying toxicity of 6PPD-Q and DTBBA was linked to the level of reactive oxygen species in which DTBBA exposure caused a significant concentration-dependent increase. Our results imply unanticipated risks to aquatic species posed by chemical additives in tire-rubber which may be considered emerging contaminants of toxicological concern.

How do rotifer communities respond to floating photovoltaic systems in the subsidence wetlands created by underground coal mining in China?

Along with the increasing demand for energy and pressure to reduce carbon emissions, floating photovoltaic (FPV) systems are increasingly built on the surface of water bodies with the aim to produce clean energy. However, little is known about how FPV systems influence freshwater ecosystems, e.g., their zooplankton communities. We investigated how rotifer communities responded to FPV systems in subsidence wetlands created by underground coal mining in the North China Plain. Diversity metrics of the rotifer communities were compared between wetlands with and without FPV systems. The density of rotifers was higher in wetlands without FPV systems. In contrast, rotifer diversity as represented by Shannon-Weiner and Pielou evenness indices was higher in the FPV-covered wetlands, while there was no difference in species richness between the two types of wetlands. Furthermore, community structures differed between the two types of wetlands, in large part reflecting differences in the relative abundance of five dominant species found in both types of wetlands. These differences in rotifer assemblages were in large part explainable from environmental changes caused by the FPV panels, notably reduced light availability and water temperature, leading to reduced phytoplankton production. These findings show that FPV systems cause major changes to rotifer communities in these subsidence wetlands and likely in wetlands more generally, and monitoring of the longer-term effects is recommended given the fundamental role of zooplankton in freshwater ecosystems.

Maternal exposure to nanoplastic induces transgenerational toxicity in the offspring of rotifer Brachionus koreanus.

Nanoplastics have received a great deal of attention as evidence of their potential harmful effects on aquatic biota. In zooplankton, ingestion is known as a major uptake route of nanoplastics due to the low feeding selectivity of filter-feeding organisms. In this study, we propose maternal transfer as an alternative uptake route of nanoplastic in the rotifer Brachionus koreanus. Exposure to nanoplastics in parental rotifers induced maternal transfer in offspring, as revealed by fluorescence in rotifer eggs. We further verified that egg shells are not permeable to nanoplastics, and the observed fluorescence was associated with nanoplastic particles, not leached fluorescent dye, supporting the idea that nanoplastics can be transferred through an intrinsic maternal transfer route. This maternal transfer induced adverse effects on life-cycle parameters, including development and reproduction, in offspring rotifers, and was associated with oxidative stress. The results of this study shed light on the ecological impacts of nanoplastics in marine environments.

Swimming behaviour as an alternative endpoint to assess differences in abiotic stress sensitivities between strains of Brachionus koreanus (Rotifera: Monogononta).

Brachionus plicatilis is a cosmopolitan rotifer used as a model organism in several research areas and as live food in aquaculture. Being a species complex, responses to stressors vary even among strains of the same species and, thus, the responses of one species are not representative of the whole complex. This study aimed to address the effects of extreme salinity ranges, and different concentrations of hydrogen peroxide, copper, cadmium, and chloramphenicol, in two strains of B. koreanus (MRS10 and IBA3) from B. plicatilis species complex, by assessing effects on their survival and swimming capacity. Neonates (0-4 h old) were exposed to the stressors in 48 well-microplates, for 24 and 6 h, to evaluate lethal and behavioural effects, respectively. Tested conditions of chloramphenicol did not show any effects on rotifers. The behavioural endpoint showed to be particularly sensitive to assess the effects of high salinity, hydrogen peroxide, and copper sulfate, as swimming capacity impairment was observed for both strains in the lowest concentrations used in lethal tests. Overall, results showed that IBA3 was more tolerant to the majority of stressors, comparing to MRS10, which may be due to differences in physiological characteristics, highlighting the importance of performing multiclonal experiments. Also, swimming capacity inhibition proved to be a good alternative to the classical lethality tests, being sensitive to lower concentrations and with shorter exposure periods.

m6A-mediated nonhomologous end joining (NHEJ) pathway regulates senescence in Brachionus plicatilis (Rotifera).

Epigenetic modifications play an important role in the regulation of senescence. N6-methyladenosine (m6A) is the most abundant modification of mRNA. However, the impact of m6A on senescence remains largely unknown at the animal individual level. Standard model organisms Caenorhabditis elegans and Drosophila melanogaster lack many gene homologs of vertebrate m6A system that are present in other invertebrates. In this study, we employed a small aquatic invertebrate Brachionus plicatilis which has been used in aging studies for nearly 100 years to study how m6A affects aging. Phylogenetic analysis confirmed that rotifers' m6A pathway has a conserved methyltransferase complex but no demethylases and the m6A reading system was more akin to that of vertebrates than that of D. melanogaster. m6A methyltransferases are highly expressed during development but reduces dramatically during aging. Knockdown of METTL3 results in decreased fecundity and premature senescence of rotifers. Furthermore, RT-qPCR analysis indicates a role for m6A in the nonhomologous end joining (NHEJ) pathway of DNA double-strand breaks (DSBs) repair. Altogether, our work reveals a senescence regulatory model for the rotifer METTL3-m6A-NHEJ pathway.

An LRR domain-containing membrane protein gene in rotifer Brachionus plicatilis: Sequence feature, expression pattern, and ligands binding activity.

Leucine-rich repeat (LRR) domains mediate multiple innate immune responses via protein-ligand and protein-protein interactions, but their exact roles in invertebrates are poorly understood. Herein, an LRR domain-containing transmembrane protein (BpLRRm) was identified in the rotifer Brachionus plicatilis. The 1069 bp BpLRRm nucleotide sequence contains a 942 bp open reading frame (ORF) encoding a 313 amino acid polypeptide with four LRR motifs harbouring the LXXLXXLXLXXNXLXXL motif, and a transmembrane domain. Treatment with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) decreased BpLRRm mRNA levels at 3 h, but they increased thereafter and peaked at 12 h. Lipopolysaccharide (LPS) treatment first increased BpLRRm mRNA levels at 3 h, but levels returned to normal at 12 h, then increased and peaked at 24 h. Recombinant BpLRRm protein bound pathogen-related molecular patterns (PAMPs), including LPS, peptidoglycan (PGN), glucan (GLU) and polyinosinic-polycytidylic acid (poly IC), in a dose-dependent manner. Thus, BpLRRm might function as a pattern recognition receptor (PRR) in the innate immunity of B. plicatilis, and mediate responses to environmental pollution.

Changes in key life-history traits and transcriptome regulations of marine rotifer Brachionus plicatilis in eliminating harmful algae Phaeocystis.

Rotifers have great potential in controlling the harmful algae Phaeocystis blooms that frequently occur in coastal waters. To evaluate the effects of harmful algae on the key life-history traits of rotifer in eliminating Phaeocystis and reveal the underlying mechanism of these effects, we fed Brachionus plicatilis with Chlorella vulgaris and Phaeocystis globosa respectively, recorded the key life-history traits, and conducted transcriptomic analysis. Results showed that the rotifers feeding on P. globosa significantly decreased total offspring but obviously prolonged lifespan compared to those feeding on C. vulgaris, indicating that there was a trade-off between the reproduction and lifespan of rotifers feeding on algae with different nutrient contents. Nevertheless, rotifers can completely eliminate the population of P. globosa. The changes in the reproduction and lifespan of rotifers are highly correlated with algal key nutrition and the expression of some related genes. Transcriptomic analysis showed that the changes in the key life history traits of rotifers feeding on harmful algae are determined by regulating the expression of some key genes involved in the pathways of carbohydrate digestion and absorption, glycolysis, gluconeogenesis, unsaturated fatty acid biosynthesis, and environmental stress. Understanding the trade-off of the key life history traits of zooplankton in eliminating harmful algae from the underlying mechanism helps improve their application for controlling harmful algae.