Effects of stock enhancement on the macrobenthic community and ecological health in the intertidal zone of the estuarine wetland in Nanhui, China.

Nanhui Dongtan Wetland is an important part of Yangtze Estuary Wetland, and its species diversity has been affected by reclamation in recent years. To increase the diversity of species in reclamation areas, stock enhancement was implemented in the Nanhui Dongtan Wetland in May 2020 as a method of ecological restoration. We investigated macrobenthos before and after release, analysed changes in the macrobenthos and evaluated the ecological health of the sampled area. The diversity index showed species were more abundant and community structure were more diversified after release. Functional groups and redundancy analysis showed that the effects of stock enhancement on macrobenthos in Nanhui Dongtan wetland may be based on changes in secondary productivity. Stock enhancement may promote the resistance of macrobenthic communities to organic pollution without negatively affecting ecological health. As a method of ecological restoration, stock enhancement will play a positive role in the restoration of macrobenthic communities.

Comparative metabolomics analysis investigating the impact of melatonin-enriched diet on energy metabolism in the crayfish, Cherax destructor.

Melatonin is a multifunctional bioactive molecule present in almost all organisms and has been gradually used in the aquaculture industry in recent years. Energy metabolism is an essential process for individuals to maintain their life activities; however, the process through which melatonin regulates energy metabolism in aquatic animals remains unclear. The present study aimed to conduct a comprehensive analysis of the regulatory mechanism of melatonin for energy metabolism in Cherax destructor by combining metabolomics analysis with the detection of the key substance content, enzymatic activity, and gene expression levels in the energy metabolism process after culturing with dietary melatonin supplementation for 8 weeks. Our results showed that dietary melatonin increased the content of glycogen, triglycerides, and free fatty acids; decreased lactate levels; and promoted the enzymatic activity of pyruvate kinase (PK), malate dehydrogenase (MDH), and acetyl-CoA carboxylase. The results of gene expression analysis showed that dietary melatonin also increased the expression levels of hexokinase, PK, MDH, lactate dehydrogenase, lipase, and fatty acid synthase genes. The results of metabolomics analysis showed that differentially expressed metabolites were significantly enriched in lysine degradation and glycerophospholipid metabolism. In conclusion, our study demonstrates that dietary melatonin increased oxidative phosphorylation, improved glucose utilization, and promoted storage of glycogen and lipids in C. destructor. These lipids are used not only for energy storage but also to maintain the structure and function of cell membranes. Our results further add to the understanding of the mechanisms of energy regulation by melatonin in crustaceans.

Effects of ß-1,3-glucan on growth, immune responses, and intestinal microflora of the river prawn (Macrobrachium nipponense) and its resistance against Vibrio parahaemolyticus.

In this study, we investigated the impact of ß-1,3-glucan on the immune responses and gut microbiota of the river prawn (Macrobrachium nipponense) in the presence of Vibrio parahaemolyticus stress. Shrimps were fed one of the following diets: control (G1), 0.2% curdlan (G2), 0.1% ß-1,3-glucan (G3), 0.2% ß-1,3-glucan (G4), or 1.0% ß-1,3-glucan (G5) for 6 weeks and then challenged with V. parahaemolyticus for 96 h. Under Vibrio stress, shrimps in G4 exhibited the highest length gain rate, weight gain rate, and survival rate. They also showed increased intestinal muscle thickness and villus thickness compared to the control and 0.2% curdlan groups. The apoptosis rate was lower in G4 than in the control group, and the digestive enzyme activities (pepsin, trypsin, amylase, and lipase), immune enzyme activities (acid phosphatase, alkaline phosphatase, lysozyme, and phenoxidase), and energy metabolism (triglyceride, cholesterol, glycogen, and lactate dehydrogenase) were enhanced. Expression levels of growth-related genes (ecdysone receptor, calmodulin-dependent protein kinase I, chitin synthase, and retinoid X receptor) and immune-related genes (toll-like receptor 3, myeloid differentiation primary response 88, mitogen-activated protein kinase 7, and mitogen-activated protein kinase 14) were higher in G4 than in the control. Microbiota analysis indicated higher bacterial abundance in shrimps fed ß-1,3-glucan, as evidenced by Sob, Chao1, and ACE indices. Moreover, 0.2% ß-1,3-glucan increased the relative abundances of Bacteroidota and Firmicutes while reducing those of Corynebacteriales and Lactobacillales. In summary, ß-1,3-glucan enhances immune enzyme activities, alters immune-related gene expression, and impacts gut microbial diversity in shrimp. These findings provide valuable insights into the mechanisms underlying ß-1,3 glucan's immune-enhancing effects.

Dietary melatonin positively impacts the immune system of crayfish, Cherax destructor, as revealed by comparative proteomics analysis.

Melatonin, an indoleamine with various biological activities, is being used increasingly in the aquaculture industry for its broad immune effects. Cherax destructor is an emerging economically cultured crayfish that faces many problems in the breeding process. Previous work found that dietary melatonin has positive effects on the growth and immunity of C. destructor, but the specific mechanism involved remained unclear. In this study, proteomics was used to determine the mechanism of action of melatonin in C. destructor. Results showed that dietary melatonin resulted in decreased levels of hydrogen peroxide, alanine aminotransferase, and aspartate aminotransferase, but increased levels of glutathione peroxidase, acid phosphatase, and glutathione S-transferases. In total, 608 proteins were differentially expressed (418 upregulated and 190 downregulated), and were enriched in three main categories: innate immunity (B cell receptor signaling pathway and natural killer cell-mediated cytotoxicity), glucose metabolism (pentose phosphate pathway, pentose and glucuronate interconversions, and propionate metabolism), and amino acid metabolism (valine, leucine, and isoleucine degradation, and cysteine and methionine metabolism). In addition, dietary melatonin was also involved in the regulation of the mTOR signaling pathway, and upregulated the expression of genes encoding key factors, such as Ras-related GTP-binding protein A/B, eukaryotic initiation factor 4E, eukaryotic initiation factor 4E-binding protein, and p70 ribosomal S6 kinase. Overall, this study demonstrates the role of melatonin in the physiological regulation of C. destructor, laying the foundation for the development of melatonin as a feed additive in the aquaculture of this species.

Comparison of Growth Performance and Biochemical Components between Low-Salinity-Tolerant Hybrid and Normal Variety of Pacific White Shrimp (Penaeus vannamei).

Penaeus vannamei, a high-yield economical shrimp, is confronting germplasm degradation in the culture environments found in China, which results in a sharp drop in production. Genetic improvement by hybridization is an effective way to solve this problem. In this study, we selected the hybrid species adapted to low-salinity culture obtained by intraspecific crossing as the experimental group. The control group consisted of normal variety from the Hainan Lutai Company. The two groups of shrimps were cultured for three months under salinities of 1 PSU, 5 PSU, and 15 PSU. Growth-performance-related indicators, biochemical composition, and molting-related gene expression were examined. The results showed that at salinities of 1 PSU and 5 PSU, the survival rate and growth performance of the low-salt breeding group were better than those of the normal variety population. The digestive enzyme activity in the low-salt breeding group was higher, which was consistent with its better growth performance, and was also associated with higher triglyceride, total cholesterol, and glycogen content. Lower levels of lactic acid indicated less anaerobic metabolism and better adaptability to the environment. The amino acid and fatty acids analysis showed that levels of essential amino acids and high unsaturated fatty acids were both higher in the low-salt breeding group than in the normal variety shrimp cultured in a low-salinity environment. The expression levels of genes associated with molting (CHS, CaMKI, RXR, EcR, HSP60, and HSP70) were also higher in the low-salt breeding group than in the control group. The results indicated that the hybrid shrimp showed better growth performance and nutritional advantages compared with the normal shrimp under salinities of 1 PSU and 5 PSU. This research provides a valuable reference for subsequent genetic breeding and shrimp culture.

Haloxyfop-P-methyl induces immunotoxicity and glucose metabolism disorders and affects the Nrf2/ARE pathway mediated antioxidant system in Chiromantes dehaani.

Haloxyfop-P-methyl is used extensively in agricultural production, and its metabolites in soil have potentially toxic effects on aquatic ecosystems. In this study, we explored the toxicity of haloxyfop-P-methyl on Chiromantes dehaani. The results of the 21-day toxicity test showed that haloxyfop-P-methyl decreased the weight gain (WG), specific growth rate (SGR) and hepatosomatic index (HSI). In glucose metabolism, haloxyfop-P-methyl reduced pyruvate, lactate, lactate dehydrogenase and succinate dehydrogenase, but enhanced glucose-6-phosphate dehydrogenase and hexokinase. Furthermore, expression of glucose metabolism-related genes was upregulated. We cloned the full-length CdG6PDH gene, which contains a 1587 bp ORF that encoded a 528 amino acid polypeptide. In antioxidant system, haloxyfop-P-methyl increased glutathione, thioredoxin reductase and thioredoxin peroxidase activities and activated the Nrf2/ARE pathway through upregulation of ERK, JNK, PKC and Nrf2. In immunity, low concentrations haloxyfop-P-methyl, or short-term exposure, upregulated the expression of immune-related genes and enhanced immune-related enzymes activity, while high concentrations or long-term exposure inhibited immune function. In summary, haloxyfop-P-methyl inhibited the growth performance, disrupted glucose metabolism, activated the antioxidant system, and led to immunotoxicity. The results deepen our understanding of the toxicity mechanism of haloxyfop-P-methyl and provide basic biological data for the comprehensive assessment of the risk of haloxyfop-P-methyl to the environment and humans.

Effects of dietary melatonin on growth performance, antioxidant capacity, and nonspecific immunity in crayfish, Cherax destructor.

Melatonin (MT) is an indole hormone widely found in plants and animals. Many studies have shown that MT promotes the growth and immunity of mammals, fish, and crabs. However, the effect on commercial crayfish has not been demonstrated. The purpose of this study was to evaluate the effects of dietary MT on growth performance and innate immunity of Cherax destructor from three aspects of individual level, biochemical level, and molecular level after 8 weeks of culture. In this study, we found that MT supplementation increased weight gain rate, specific growth rate, and digestive enzyme activity in C. destructor compared to the control group. Dietary MT not only promoted the activity of T-AOC, SOD, and GR, increased the content of GSH, and decreased the content of MDA in the hepatopancreas, but also increased the content of hemocyanin and copper ions and AKP activity in hemolymph. Gene expression results showed that MT supplementation at appropriate doses increased the expression of cell cycle-regulated genes (CDK, CKI, IGF, and HGF) and non-specific immune genes (TRXR, HSP60, and HSP70). In conclusion, our study showed that adding MT to the diet improved growth performance, enhanced the antioxidant capacity of hepatopancreas, and immune parameters of hemolymph in C. destructor. In addition, our results showed that the optimal dietary supplementation dose of MT in C. destructor is 75-81 mg/kg.

Effects of dietary soluble ß-1,3-glucan on the growth performance, antioxidant status, and immune response of the river prawn (Macrobrachium nipponense).

The effects of dietary ß-1,3-glucan on the growth performance, body composition, hepatopancreas tissue structure, antioxidant activities, and immune response of the river prawn (Macrobrachium nipponense) were investigated. In total, 900 juvenile prawns were fed one of five diets with different contents of ß-1,3-glucan (0%, 0.1%, 0.2%, and 1.0%) or 0.2% curdlan for 6 weeks. The growth rate, weight gain rate, specific growth rate, specific weight gain rate, condition factor, and hepatosomatic index of juvenile prawns fed 0.2% ß-1,3-glucan were significantly higher than those fed 0% ß-1,3-glucan and 0.2% curdlan (p < 0.05). The whole-body crude lipid content of prawns supplemented with curdlan and ß-1,3-glucan was significantly higher than that of the control group (p < 0.05). The antioxidant and immune enzyme activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), catalase (CAT), lysozyme (LZM), phenoloxidase (PO), acid phosphatase (ACP), and alkaline phosphatase (AKP) in the hepatopancreas of juvenile prawns fed 0.2% ß-1,3-glucan were significantly higher than those of the control and 0.2% curdlan groups (p < 0.05), and tended to increase and then decrease with increasing dietary ß-1,3-glucan. The highest malondialdehyde (MDA) content was observed in juvenile prawns without ß-1,3-glucan supplementation. The results of real-time quantitative PCR indicated that dietary ß-1,3-glucan promoted expression of antioxidant and immune-related genes. Binomial fit analysis of weight gain rate and specific weight gain rate showed that the optimum ß-1,3-glucan requirement of juvenile prawns was 0.550%-0.553%. We found that suitable dietary ß-1,3-glucan improved juvenile prawns growth performance, antioxidant capacity, and non-specific immunity, which provide reference for shrimp healthy culture.

Integrated physiological and transcriptome analysis reveals potential toxicity mechanism of haloxyfop-P-methyl to Chiromantes dehaani.

Haloxyfop-P-methyl is widely used in controlling gramineous weeds, including the invasive plant Spartina alterniflora. However, the mechanism of its toxicity to crustaceans is unclear. In this study, we adopted transcriptome analysis combined with physiologic changes to investigate the response of estuarine crab (Chiromantes dehaani) to haloxyfop-P-methyl. The results showed that the median lethal concentration (LC50) of C. dehaani to haloxyfop-P-methyl at 96 h was 12.886 mg/L. Antioxidant system analysis indicated that MDA, CAT, GR, T-GSH, and GSSG might be sensitive biomarkers that characterize the oxidative defense response of the crab. In total, 782 differentially expressed genes were identified, including 489 up-regulated and 293 down-regulated genes. Glutathione metabolism, detoxification response and energy metabolism were significantly enriched, revealing the potential toxic mechanism of haloxyfop-P-methyl to C. dehaani. These results provide a theoretical foundation for further research on haloxyfop-P-methyl toxicity to crustaceans.

Effects of Low Temperature on Antioxidant and Heat Shock Protein Expression Profiles and Transcriptomic Responses in Crayfish (Cherax destructor).

Low temperature is a critical factor restricting the growth and survival of aquatic animals, but research on the mechanism of response to low temperature in Cherax destructor is limited. C. destructor is one of the most important freshwater crustaceans with strong adaptability in Australia, and it has been commercialized gradually in recent years. Here, growth indicators, antioxidant parameters, anti-stress gene expression, and transcriptome sequencing were used on crayfish following 8 weeks of low-temperature acclimation. The results showed that weight gain, length gain, and molting rates decreased as the temperature decreased. The activity of antioxidant enzymes decreased, while the content of antioxidant substances and the expression of anti-stress genes increased. Transcriptome sequencing identified 589 differentially expressed genes, 279 of which were upregulated and 310 downregulated. The gene functions and pathways for endocrine disorders, glucose metabolism, antioxidant defense, and immune responses were identified. In conclusion, although low-temperature acclimation inhibited the basal metabolism and immune ability of crayfish, it also increased the antioxidant substance content and anti-stress-gene expression to protect the organism from low-temperature damage. This study provided molecular insights into the study of low-temperature responses of low-temperature-tolerant crustacean species.

Methionine biosynthesis pathway genes affect curdlan biosynthesis of Agrobacterium sp. CGMCC 11546 via energy regeneration.

Curdlan is a water-insoluble exopolysaccharide produced by Agrobacterium species under nitrogen starvation. The curdlan production in the ΔmdeA, ΔmetA, ΔmetH, and ΔmetZ mutants of methionine biosynthesis pathway of Agrobacterium sp. CGMCC 11546 were significantly impaired. Fermentation profiles of four mutants showed that the consumption of ammonia and sucrose was impaired. Transcriptome analysis of the ΔmetH and ΔmetZ mutants showed that numerous differentially expressed genes involved in the electron transfer chain (ETC) were significantly down-regulated, suggesting that methionine biosynthesis pathway affected the production of energy ATP during the curdlan biosynthesis. Furthermore, metabolomics analysis of the ΔmetH and ΔmetZ mutants showed that ADP and FAD were significantly accumulated, while acetyl-CoA was diminished, suggesting that the impaired curdlan production in the ΔmetH and ΔmetZ mutants might be caused by the insufficient supply of energy ATP. Finally, the addition of both dibasic sodium succinate as a substrate of FAD recycling and methionine significantly restored the curdlan production of four mutants. In conclusion, methionine biosynthesis pathway plays an important role in curdlan biosynthesis in Agrobacterium sp. CGMCC 11546, which affected the sufficient supply of energy ATP from the ETC during the curdlan biosynthesis.

Effects of reclamation methods and habitats on macrobenthic communities and ecological health in estuarine coastal wetlands.

This study compared the community structure of macrobenthos in bare tidal areas and vegetated regions under two reclamation patterns, fully enclosed and opened reclamation, in Yangtze wetland, China. Compared with fully enclosed reclamation areas, opened reclamation areas had higher water salinity, higher number of species and abundance, and less disturbed habitat health status. Compared with bare tidal areas, vegetated regions were more suitable for the survival of macrobenthos and its habitat health status was more stable. Salinity, pH and larger soil particle diameter were positively associated with macrobenthic diversity, while total nitrogen and total phosphorus were negatively associated. Overall, compared with fully enclosed reclamation and vegetated regions, opened reclamation and bare tidal areas had less negative effects upon macrobenthic community and habitat health. Opened reclamation is preferred for wetland reclamation, and planting indigenous plants and releasing species adapted to fresh water is beneficial to the restoration of macrobenthic communities.

Two genes related to reproductive development in the juvenile prawn, Macrobrachium nipponense: Molecular characterization and transcriptional response to nanoplastic exposure.

Plastic pollution in the form of nanoplastics poses a global threat to aquatic ecosystems and the organisms inhabiting them. However, few studies have been conducted on the effects of nanoplastic exposure on reproductive development in crustaceans. In order to address this issue, juvenile oriental river prawns (Macrobrachium nipponense) were exposed to different concentrations of 75-nm polystyrene nanoplastics (0, 5, 10, 20, 40 mg/L) for 28 days. In order to study the regulation of reproduction-related genes in the presence of nanoplastics, the Wee1 protein kinase gene (Wee1) and OTU domain ubiquitin aldehyde binding protein gene (OTUB) were selected. In this study, for the first time, the full-length cDNA of Mn-Wee1 and Mn-OTUB were cloned from M. nipponense. Homologous alignments revealed that Mn-Wee1 had a highly conserved function-critical sequence, and that Mn-OTUB was more closely related to OTUB1 than OTUB2. With increasing concentration of nanoplastics, the expression of both genes increased initially, then decreased. The inhibition of expression of Wee1 and OTUB occurred in 40 mg/L group, respectively. Analysis of the data also indicated that nanoplastic exposure might have differing effects on gene expression in M. nipponense male and female reproductive organs.

Comparison of growth performance and biochemical components between parent and hybrid offspring in the oriental river prawn, Macrobrachium nipponense.

Macrobrachium nipponense, as one of the large-yield farmed shrimp, is facing germplasm degradation. Genetic improvement through hybridization is one of the effective methods to solve this problem. In this study, using a three-line hybrid strategy, two-hybrid F1 populations were obtained using three local populations of M. nipponense as parents for crossbreeding. Five populations were then cultured for 3 months. Growth rate performance was measured by the hepatosomatic index, weight gain, body length growth rate and special growth rate. Biochemical components were also assessed. The results showed that the survival rate and growth performance of the hybrid progeny were better than those of the parents. The levels of triglycerides, total cholesterol, glycogen and lactic acid of the hybrid population were higher than those of the parents. This was consistent with variation in the activity of four digestive enzymes. Compared with the results of the fatty acid and amino acid analysis, it was found that the contents of polyunsaturated fatty acids such as eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acid and eight essential amino acids in the hybrid populations were significantly higher than those of their parents, and the contents of flavor amino acids were higher. The expression level of molting genes related to the growth of the parent populations was lower than that of the hybrids. These results show that crossbreeding is effective for the genetic improvement of M. nipponense germplasm. Hybrids showed advantages in growth and nutrition and multigenerational breeding will be required to form a stable germplasm.

Development of an adverse outcome pathway for nanoplastic toxicity in Daphnia pulex using proteomics.

Nanoplastics are a growing environmental and public health concern. However, the toxic mechanisms of nanoplastics are poorly understood. Here, we evaluated the effects of spherical polystyrene nanoplastics on reproduction of Daphnia pulex and analyzed the proteome of whole animals followed by molecular and biochemical analyses for the development of an adverse outcome pathway (AOP) for these contaminants of emerging concern. Animals were exposed to polystyrene nanoplastics (0, 0.1, 0.5, 1 and 2 mg/L) via water for 21 days. Nanoplastics negatively impacted cumulative offspring production. A total of 327 differentially expressed proteins (DEPs) were identified in response to nanoplastics which were further validated from gene expression and enzyme activity data. Based on these results, we propose an AOP for nanoplastics, including radical oxygen species production and oxidative stress as the molecular initiating event (MIE); followed by changes in specific signaling pathways (Jak-STAT, mTOR and FoxO) and in the metabolism of glutathione, protein, lipids, and molting proteins; with an end result of growth inhibition and decrease reproductive output. This study serves as a foundation for the development of a mechanistic understanding of nanoplastic toxicity in crustaceans and perhaps other aquatic organisms.

Characterization and rheological properties analysis of the succinoglycan produced by a high-yield mutant of Rhizobium radiobacter ATCC 19358.

Succinoglycan is an industrially important exopolysaccharide biosynthesized by bacteria. In this study, mutant strain 18052 N-11 was obtained from the wild type strain Rhizobium radiobacter ATCC 19358 by NTG mutagenesis. It has a high yield succinoglycan of 32.5 g/L cultured in a 15 L-fementer for 72 h. Succinoglycan SG-A from the wild type strain has two components, and the molecular weights were 1.55 × 107 Da and 1.26 × 106 Da, respectively. While, succinoglycan SG-N from the mutant strain was a homogeneous polysaccharide, and the molecular weight was 1.01 × 107 Da. The molecular weight of both succinoglycan was higher than those reported in literatures. DSC thermogram of SG-A showed a higher endothermic peak than that of SG-N due to the higher crystallinity of SG-A. The dynamic frequency sweep test of SG-A and SG-N showed that the elastic modulus G' and viscosity modulus G" curves intersected at 65 °C, indicating the thermally induced order-disorder conformation. The results of effect of concentrations (2.5-15%) and temperatures (25-75 °C) on apparent viscosity of SG-A and SG-N showed that the succinoglycan solutions exhibited non-Newtonian, shear-thinning behavior. Both SG-A and SG-N showed an excellent emulsification activity. The characterizations and rheological properties make SG-A and SG-N prominent candidates in food, cosmetics, pharmaceutical and petroleum industries.

Glutamine synthetase gene glnA plays a vital role in curdlan biosynthesis of Agrobacterium sp. CGMCC 11546.

Curdlan is a neutral linear exopolysaccharide produced by Agrobacterium spp. under nitrogen-limiting conditions. In this study, we explored the role of glnA in curdlan biosynthesis in Agrobacterium sp. CGMCC 11546. The curdlan production of the ΔglnA strain was impaired, decreasing by 93% compared with that of the wild-type strain after 96 h fermentation. Analysis of fermentation profiles revealed that cell growth and utilization of carbon and nitrogen sources were impaired in the ΔglnA strain. Transcriptome analysis indicated that various of genes involved in curdlan biosynthesis were downregulated after 24 h fermentation in the ΔglnA strain, particularly genes involved in heme synthesis and the electron transport chain, which are essential for energy generation. Metabolomics analysis revealed flavin adenine dinucleotide (FAD) and adenosine diphosphate (ADP) accumulation in the ΔglnA strain, suggesting insufficient energy supply. Furthermore, glnA overexpression led to an 18% increase in the curdlan yield of the ΔglnA mutant compared with that of the wild-type strain after 96 h fermentation. Taken together, the findings demonstrate that glnA plays a vital role in curdlan biosynthesis by supplying ATP via regulating the expression of genes involved in heme synthesis and the electron transport chain.

Characterization and improvement of curdlan produced by a high-yield mutant of Agrobacterium sp. ATCC 31749 based on whole-genome analysis.

Curdlan is a bacterial, water-insoluble, linear homopolysaccharide that has been widely used in the food industry. In this study, genome information of strain CGMCC 11546, a UV-induced high-yield mutant of the model curdlan-producing strain Agrobacterium sp. ATCC 31749, was used to investigate the molecular mechanism of curdlan biosynthesis. The maximum curdlan yield of 47.97 ± 0.57 g/L was obtained from strain CGMCC 11546 by using optimal media containing 60 g/L sucrose, 6 g/L yeast, 2 g/L KH2PO4, 0.4 g/L MgSO4·7H2O, 2 g/L CaCO3, 0.1 g/L FeSO4·7H2O, 0.04 g/L MnSO4, and 0.02 g/L ZnCl2 at 30 °C and 280 rpm after 96 h of fermentation. The gel strength of curdlan was improved by 41 % by knocking out the ß-1,3-glucanase genes exoK and exsH of strain CGMCC 11546. Furthermore, the application of curdlan from the ΔexoK-exsH strain in noodles significantly improved the eating quality of both raw and cooked noodles.

Two sigma and two mu class genes of glutathione S-transferase in the waterflea Daphnia pulex: Molecular characterization and transcriptional response to nanoplastic exposure.

Two isoforms of Glutathione S-Transferase (GST) genes, belonging to mu (Dp-GSTm1 and Dp-GSTm2) and sigma (Dp-GSTs1 and Dp-GSTs2) classes, were cloned and characterised in the freshwater Daphnia pulex. No signal peptide was found in any of the four GST proteins, indicating that they were cytosolic GST. A highly conserved glutathione (GSH) binding site (G-site) occurred in the N-terminal sequence, and a substrate binding site (H-site), interacting non-specifically with the second hydrophobic substrate, was present in the C-terminal. A Tyr residue, for the stabilization of GSH, was found to be conserved in the analysed sequences. The secondary and tertiary structures indicated that these genes possess the typical cytosolic GST structure, including a conserved N-terminal domain with a ßαßαßßα motif. The µ loop (NVGPAPDYDR and NFIGAEWDR in Dp-GSTm1 and Dp-GSTm2, respectively) was identified between the ßαß (ß1α1ß2) and αßßα motifs (α2ß3ß4α3) in the N-terminal domain. The expressions of Dp-GSTs1, Dp-GSTs2, and Dp-GSTm1 were higher in other age groups compared to the newly-born neonates (1 d); however, the expression of Dp-GSTm2 first increased and then decreased with age. Gene expression was significantly reduced by high concentration (1 and 2 mg/L) of 75 nm polystyrene nanoplastic. However, nanoplastic exposure at the predicted environmental concentration (1 µg/L) had a low effect. Exposure of mothers to nanoplastic (1 µg/L) elevated the Dp-GSTs2 level in their neonates. These results improve our understanding on the response of different types of Daphnid GST to environmental contaminants, especially nanoplastic.