Understanding the variable metal concentrations in estuarine oysters Crassostrea hongkongensis: A biokinetic analysis.

Understanding the metal concentrations in oysters is important because of its relevance to human health and biomonitoring. However, metal concentrations in oysters are highly variable in nature and not well explained by metal exposure. This study examined the metal contamination in farm oysters Crassostrea hongkongensis grown in Qinzhou Bay, south China. Cadmium (Cd), zinc (Zn), nickel (Ni), and copper (Cu) concentrations in the oysters varied between 7.9 and 72.2, 282-17003, 0.37-47.7 and 37-4012 µg g-1, respectively, showing large metal variability among different individuals. Oyster metal concentrations decreased with increasing body size and significantly higher levels were observed in wet season. Low salinity and slower oyster growth due to inferior growth conditions could be responsible for the elevated metal concentrations in the wet season. Biokinetic modeling showed that the coupling of ingestion rate and growth can cause 2.8-4.2 folds differences in the oyster Cd and Zn concentrations, respectively, suggesting the significant role of oyster bioenergetics in contributing to the metal variability. Modeling data revealed that Cd and Zn concentrations in oyster tissues reach maximum levels when oysters have their lowest growth efficiency. This suggests that any factors influencing the energy budget in oysters could simultaneously alter their metal concentrations, which might be the reason why oyster metal concentrations are so variable in the natural environment.

Metal leaching from plastics in the marine environment: An ignored role of biofilm.

A large quantity of metal compounds in plastics are released into the marine environment every year. However, our understanding of the extent and mechanism by which polymer-bound metals leach into seawater is still limited. In this study, a comprehensive survey was conducted to measure the metal concentrations in commonly used plastics and evaluate the effects of environmental factors (temperature, radiation, and salinity) and the physiochemical properties (surface roughness, specific surface area, hydrophobicity, and crystallinity) of the plastics on their metal leaching into seawater. In particular, we observed the metal loss from six plastics submerged in coastal seawater for eight months and studied the role of biofilm in controlling the leaching of Sb, Sn, Pb, Ba, and Cr. Our results indicate that increased temperature enhanced the release of these metals, while exposure to ultraviolet radiation significantly increased the leaching of Sn from polylactide (PLA). High salinity facilitated the leaching of Sn from PLA and Pb from polyvinylchloride ball, however inhibited the leaching of Ba from PE wrap. The leaching rate was primarily determined by the inherent property of crystallinity. Metal loss from the plastics in the field was apparent during the first three weeks, but then was hindered by the development of biofilm. Our study provides the mechanisms underlying metal leaching from physical, chemical, and biological perspectives, which is useful for understanding the environmental risk of the plastic-containing metals.

Isotopic signatures unveil the lead sources and migration in surface mangrove sediments.

Mangrove sediments act as both sinks and secondary sources for lead (Pb), yet the sources, migration, and transformations of Pb in mangrove environments are poorly understood. In this study, Pb concentration in three mangrove sediments adjacent to different land-use types was evaluated. The Pb sources were quantitatively identified using Pb isotopes. Our data indicated minor Pb contamination in the mangrove sediments, possibly due to the relative lack of developed industry in this region. The Pb isotopic ratios suggested, on average, natural sources, coal combustion, agricultural activities, and traffic-related emissions respectively contributed approximately 61.4 %, 18.8 %, 14.0 %, and 5.8 % of the Pb accumulation in the mangrove sediments, suggesting that coal combustion and agriculture were important anthropogenic Pb sources. Significant relationships were observed between the 206Pb/207Pb ratios and total organic content (TOC) in mangrove sediments, which implied contrasting Pb cycling in two mangrove environments. We further suggested that organic matter and sulfur content significantly reduced Pb mobility and bioavailability in mangrove sediments. Our study provides isotopic method to investigate the Pb sources and migration in the mangrove environment.

Effects of nanoplastics on clam Ruditapes philippinarum at environmentally realistic concentrations: Toxicokinetics, toxicity, and gut microbiota.

Nanoplastics are ubiquitous in marine environments, understanding to what extent nanoplastics accumulate in bivalves and the adverse effects derived from their retention is imperative for evaluating the detrimental effects in the benthic ecosystem. Here, using palladium-doped polystyrene nanoplastics (139.5 nm, 43.8 mV), we quantitatively determined nanoplastic accumulation in Ruditapes philippinarum and investigated its toxic effects by combining physiological damage assessments with a toxicokinetic model and 16 S rRNA sequencing. After a 14 days exposure, significant nanoplastic accumulation was observed, up to 17.2 and 137.9 mg·kg-1 for the environmentally realistic (0.02 mg·L-1) and ecologically (2 mg·L-1) relevant groups, respectively. Ecologically relevant nanoplastic concentrations evidently attenuated the total antioxidant capacity and stimulated excessive reactive oxygen species, which elicited lipid peroxidation, apoptosis, and pathological damage. The modeled uptake (k1) and elimination (k2) rate constants (from physiologically based pharmacokinetic model) were significantly negatively correlated with short-term toxicity. Although no obvious toxic effects were found, environmentally realistic exposures notably altered the intestinal microbial community structure. This work increases our understanding of how the accumulation of nanoplastics influences their toxic effects in terms of the toxicokinetics and gut microbiota, providing further evidence of their potential environmental risks.

Interspecies calibration for biomonitoring metal contamination in coastal waters using oysters and mussels.

Differences in metal bioaccumulation among species make it difficult to compare biomonitoring results obtained using different marine bivalve species. To address this challenge and improve the interpretation of biomonitoring data, we studied the toxicokinetic mechanisms underlying these differences and developed a method to estimate seawater metal concentrations based on metal concentrations in the organisms. We transplanted six common species of oysters and mussels found in Chinese coastal waters into the Jiulong River estuary and monitored metal concentrations in the organisms, water, and suspended particles every three days over a six-week period. A one-compartment first-order toxicokinetic model was used to describe the relationship between metal bioaccumulation and metal concentrations in the environment. The model parameters, including aqueous uptake (ku) and dietary assimilation (kp) rate constants, and elimination rate constant (ke), were estimated using a Markov Chain Monte Carlo fitting method with a priori information from a systematic review we conducted. The toxicokinetic model successfully fitted the temporal changes in metal bioaccumulation in all six bivalve species and explained the interspecies differences. Using the calibrated models, we were able to calculate metal concentrations in the seawater at the bivalve collection sites and enable comparisons of biomonitoring data across multiple species. In conclusion, we have established a toxicokinetic framework to explain interspecies differences in metal bioaccumulation in six commonly found bivalves and provided a useful tool for interpreting biomonitoring data in coastal environments.

Cloning and expression of two anti-lipopolysaccharide factors in Eriocheir hepuensis under Vibrio alginolyticus-induced stress.

Anti-lipopolysaccharide factors (ALFs) are small basic proteins that exhibit broad-spectrum antiviral properties and antibacterial activity. In this research, we cloned and studied two Eriocheir hepuensis ALFs, EhALF2 and EhALF3. The results showed that the open reading frame lengths of EhALF2 and EhALF3 were 363 and 372 bp, encoding 120 and 123 amino acids, respectively. Their sequences both contained an Lipopolysaccharide-binding (LPS) domain and were highly similarity to other crab ALFs. qRT-PCR showed that EhALF2 and EhALF3 were detected in nine examined tissues and were expressed the highest in the haemocytes. After challenge with Vibrio alginolyticus, in the hepatopancreas, the expression levels of EhALF2 and EhALF3 reached the highest levels at 48 and 3 h, respectively. In the heart, the expression levels of the two genes were highest at 12 h. These results indicate that EhALF2 and EhALF3 could participate in the resistance of E. hepuensis to V. alginolyticus stress within a short time. They have potential applications in the study of environmental stress markers and disease-resistance factors in E. hepuensis.

The characterization, expression and activity analysis of three superoxide dismutases in Eriocheir hepuensis under azadirachtin stress.

Superoxide dismutase (SOD) can effectively eliminate of excess ROS, which causes oxidative damage to lipids, proteins, and DNA. In this study, we cloned the CuZn-SOD, cMn-SOD1, and cMn-SOD2 genes in Eriocheir hepuensis, and found that the coding sequence (CDS) lengths were 627 bp, 861 bp and 1062 bp, which encoded 208, 286, and 353 amino acids, respectively. Phylogenetic analysis indicated that all SOD genes were evolutionarily conserved, while cMn-SOD2 had an extra gap (67 amino acids) in the conserved domain compared with cMn-SOD1 without huge changes in the tertiary structure of the conserved domain, suggesting that cMn-SOD2 may be a duplicate of cMn-SOD1. qRT-PCR showed that the three SOD genes were widely expressed in all the tested tissues, CuZn-SOD and cMn-SOD1 were mostly expressed in the hepatopancreas, while cMn-SOD2 was mostly expressed in thoracic ganglia. Under azadirachtin stress, the oxidation index of surviving individuals, including the T-AOC, SOD activity, and MDA contents increased in the early stage and then remained steady except for a decrease in MDA contents in the later stage. qRT-PCR showed that the three SOD genes displayed the same trends as SOD activity in surviving individuals, and the highest expressions of CuZn-SOD in the hepatopancreas, heart, and gill were 14.16, 1.41, and 30.87 times that of the corresponding control group, respectively. The changes were 1.35, 5.77 and 3.33 fold for cMn-SOD1 and 1.62, 1.71 and 1.79 fold for cMn-SOD2, respectively. However, the activity and expression of SOD genes in dead individuals were lower than that observed in surviving individuals. These results reveal that SOD plays a significant role in the defence against azadirachtin-induced oxidative stress.

Metabolic scaling: individual versus intraspecific scaling of Nile tilapia (Oreochromis niloticus).

We examined intraspecific scaling of the resting metabolic rate (RMR) of Nile tilapia (Oreochromis niloticus) under different culture conditions and further explored the allometric relationships between organ mass (heart, liver, brain, gills, viscera, and red muscles) and blood parameters (erythrocyte size and red blood cell counts) and body mass. Oreochromis niloticus were bred in individual and group cultures. The scaling exponent of the RMR in the individual cultures was b = 0.620-0.821 (n = 30) and that in the group culture was b = 0.770 [natural logarithm (ln) RMR = 0.770 ln M - 1.107 (n = 76)]. The results of the two experimental methods were similar and were not significantly different from 0.75 (3/4), as predicted by the metabolic theory of ecology. The active and inactive organs were scaled with body mass by an exponent of 0.940 and 1.012, respectively. There was no significant relationship between the blood parameters and body mass. These results suggest that the differences in the culture methods may not have affected the allometric scaling of O. niloticus metabolism. The proportion of active and inactive organs contributed to allometric changes in the metabolic rate with body mass. Red blood cells in fish are not generally representative, and cell size can only partially explain the allometric scaling of metabolism.

Extracellular Amylase Is Required for Full Virulence and Regulated by the Global Posttranscriptional Regulator RsmA in Xanthomonas campestris Pathovar campestris.

As with many phytopathogenic bacteria, the virulence of Xanthomonas campestris pv. campestris, the causal agent of black rot disease in cruciferous plants, relies on secretion of a suite of extracellular enzymes that includes cellulase (endoglucanase), pectinase, protease, and amylase. Although the role in virulence of a number of these enzymes has been assessed, the contribution of amylase to X. campestris pv. campestris virulence has yet to be established. In this work, we investigated both the role of extracellular amylase in X. campestris pv. campestris virulence and the control of its expression. Deletion of XC3487 (here renamed amyAXcc), a putative amylase-encoding gene from the genome of X. campestris pv. campestris strain 8004, resulted in a complete loss of extracellular amylase activity and significant reduction in virulence. The extracellular amylase activity and virulence of the amyAXcc mutant could be restored to the wild-type level by expressing amyAXcc in trans. These results demonstrated that amyAXcc is responsible for the extracellular amylase activity of X. campestris pv. campestris and indicated that extracellular amylase plays an important role in X. campestris pv. campestris virulence. We also found that the expression of amyAXcc is strongly induced by starch and requires activation by the global posttranscriptional regulator RsmA. RsmA binds specifically to the 5'-untranslated region of amyAXcc transcripts, suggesting that RsmA regulates amyAXcc directly at the posttranscriptional level. Unexpectedly, in addition to posttranscriptional regulation, the use of a transcriptional reporter demonstrated that RsmA also regulates amyAXcc expression at the transcriptional level, possibly by an indirect mechanism.

Intestinal Tract Microbe Communities Associated with Horseshoe Crabs from Beibu Gulf, China.

Until now, there has been little research on the intestinal microbial community of horseshoe crabs. To fill this gap, we investigated the microbiome composition of the Chinese horseshoe crab, Tachypleus tridentatus, and the mangrove horseshoe crab, Carcinoscorpius rotundicauda. We sequenced the 16S rRNA gene of intestinal bacterial species and compared the microbial community structure and diversity. Next, we show that the total effective bacterial sequence was 36,865 reads, and the average annotated operational taxonomic unit (OTU) number was 240. Through hierarchical clustering analysis and principal coordinate analysis samples from two horseshoe crab species, we found that the intestinal flora of the same horseshoe crab species was relatively concentrated, while the microbiome of a different horseshoe crab species were significantly separated. Cluster analysis showed that two samples, one from Chinese horseshoe crabs and one from mangrove horseshoe crabs, had similar microbial community structure, while other samples were relatively discrete. The gut microbiota of the mangrove horseshoe crab were dominated by the phyla Tenericutes (42.71%), Firmicutes (24.27%), and Proteobacteria (20.39%), while the top three phyla in the Chinese horseshoe crab intestinal tract were Tenericutes (57.19%), Proteobacteria (22.14%), and Bacteroidetes (7.38%). To intuitively understand the similarity and overlap of the OTU composition of each group, we performed Venn diagram analysis. The two species shared 284 OTUs, accounting for 81.8% of the total. This indicates that although there is high similarity between mangrove and Chinese horseshoe crab in gastrointestinal microbial community structure, there are also some differences, which deserve further discussion.

Streptomyces qinzhouensis sp. nov., a mangrove soil actinobacterium.

A novel Streptomyces strain (SSL-25T) was isolated from mangrove soil sampled at QinzhouBay, PR China. The isolate was observed to be Gram-stain-positive and to form greyish-white aerial mycelia that differentiated into straight spore chains with smooth-surfaced spores on International Streptomyces Project 2 medium. The cell-wall peptidoglycan was determined to contain ll-diaminopimelicacid. The cell-wall sugars were glucose and mannose. The predominant menaquinones were MK-9 (H6), MK-9 (H8) and MK-9 (H4). The major polar lipids contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and several unidentified phospholipids. The predominant cellular fatty acids were C16:0, iso-C16:0 and summed feature 3 (C16:1ω7c/C16:1ω6c). The genome size of strain SSL-25T was 8.1 Mbp with a G+C content of 71.5 mol%. Phylogenetic analysis indicated that strain SSL-25T is closely related to Streptomyces tsukubensis NRRL 18488T (99.4 % sequence similarity). However, the digital DNA-DNA hybridization (39.8 %) and average nucleotide identity (91.3 %) values between them showed that it represents a distinct species. Furthermore, the results of morphological, physiological and biochemical tests allowed further phenotypic differentiation of strain SSL-25T from S. tsukubensis NRRL 18488T. Therefore, based on these results, it is concluded that strain SSL-25T represents a novel Streptomyces species, for which the name Streptomyces qinzhouensis sp. nov. is proposed. The type strain is SSL-25T (=CICC 11054T=JCM33585T).

The complete mitochondrial genome of Cerithidea sinensis (Philippi, 1848).

Cerithidea sinensis is a common and important component of mangrove ecosystem. In this study, the mitochondrial genome of C. sinensis was determined for the first time using next-generation sequencing; the overall base components of mitogenome consisting of 15633 bp was 31.14% for A, 35.70% for T, 16.65% for G, 16.51% for C, and its GC content was 33.16%. The mitochondrial circular genome was composed of 13 protein-coding genes, 22 tranfer RNAs, and 2 ribosomal RNAs. Polygenetic analysis showed that the C. sinensis was more closed to Semisulcospira libertina than Turritella bacillum and Tylomelania sarasinorum. We may speculate that the C. sinensis is evolved from freshwater species.

The complete mitochondrial genome of Trachypenaeus curvirostris (Stimpson, 1860).

Trachypenaeus curvirostris is a common and important shrimp species in the shallow waters of Indo-West Pacific. In this study, the mitochondrial genome of T. curvirostris was determined for the first time using next-generation sequencing; the overall base components of mitogenome consisting of 15968 bp was 35.16% (5614 bp) for A, 33.51% (5351 bp) for T, 11.54% (1842 bp) for G, 19.80% (3161 bp) for C, and its GC content was 31.34%. The mitochondrial circular genome was composed of 13 protein-coding genes, 22 transfer RNAs, 1 D-loop and 2 ribosomal RNAs. Polygenetic analysis showed that the T. curvirostris was more closed to Parapenaeopsis hardwickii.

The complete mitochondrial genome of Neritina violacea.

Neritina violacea is a common and important component of mangrove ecosystem. In this study, the mitogenome of N. violacea was determined for the first time using next-generation sequencing; the overall base components of mitogenome consisting of 15,710 bp was 31.37% for A, 34.91% for T, 19.47% for G, 14.25% for C, and its GC content was 33.72%. The mitogenome was composed of 13 protein-coding genes, 22 tranfer RNAs, and 2 ribosomal RNAs. Polygenetic analysis showed that the N. violacea was more close to N. Usnea and Theodoxus fluviatilis. We speculated that the N. violacea was evolved from freshwater species.

[External morphological characteristics during the embryonic development of Portunus pelagicus].

The embryonic development of Portunus pelagicus was studied under laboratory conditions at a water temperature of 25-26 Degrees Celsius, salinity of 30, and pH of 7.8-8.4. The embryogenesis of Portunus pelagicus was divided into six stages: cleavage, blastula, gastrula, nauplius, metanauplius, and protozoea. Embryogenesis lasted about 300 h post spawning. Eggs began superficial cleavage about 28 h after spawning when the nucleus appeared at the surface of the egg till the egg divided into 16 cells. The blastula stage was observed about 40 h post spawning and gastrula stage appeared when the presumptive endoderm and other cells near them invaginated. The fourth-stage of embryogenesis, nauplius, was characterized by three pairs of appendages appearing about 90 h post spawning, while metanauplius, the fifth-stage of embryogenesis, was characterized by five pairs of appendages, which appeared about 110 h post spawning. The sixth stage of embryogenesis was protozoea, which was characterized by seven pairs of appendages appearing about 140 h post spawning. The compound eye, heart and pigment cells were also found in the protozoea stage. After the natatory seta formed on the top of maxilliped, the protozoea developed into the zoea at the time of hatching (about 300 h post spawning).