Rhodobacter species are promising beneficial microbes that can improve growth performance, immunity and antioxidant capability in aquatic crustaceans. Yet the safety of Rhodobacter azotoformans for potential application in Chinese mitten crab Eriocheir sinensis is still unclear. In the present study, R. azotoformans SY5, a potential probiotic additive that can significantly improve the growth performance, immunity, antioxidant capability, and disease resistance in E. sinensis, was evaluated for safety through whole genome sequencing, antibiotic resistance, toxic metabolites, virulence, and crab tolerance assays. The results indicated that R. azotoformans SY5 only harboured the acyl carrier protein-encoding gene (acpP) that was universal in probiotic bacteria with the function of bacterial fatty acid biosynthesis, exhibited high susceptibility to aminoglycosides, penicillins, polymyxins, polyphosphates, quinolones, and tetracyclines antimicrobials, and possessed inability to produce hemolysin, hydrogen sulphide, nitrite, ammonia, and phenylpyruvate. In addition, R. azotoformans SY5 showed no pathogenicity for E. sinensis with the seven-day acute intraperitoneal LD50 value of above 6.0× 109 cfu/ml and 30-day chronic oral LD50 of above 6.0× 109 cfu/g diet. To our knowledge, this is the first report on the safety of R. azotoformans for potential application in Chinese mitten crabs.

Seagrass beds play a critical role in biodiversity maintenance, serving as nursery habitats for fisheries, and aiding in carbon and sediment sequestration in the ecosystem. These habitats receive dissolved and particulate material inputs, like nutrients and heavy metals, affecting both plant health and the ecosystem. Eelgrass (Zostera marina L.), sediments, and water were randomly collected at twenty sites along the temperate North Pacific coasts of Asia and North America to assess heavy metals concentrations (Cr, Cu, Zn, Cd, and Pb). This aimed to understand heavy metal distribution and accumulation patterns in eelgrass tissues, revealing crucial factors influencing metal accumulation. The sampling included various areas, from pristine marine reserves to human-influenced zones, covering industrial, agricultural, and aquaculture regions, enabling a thorough analysis. This study's uniqueness lies in comparing heavy metal distributions in eelgrass tissues with sediments, uncovering unique accumulation patterns. Aboveground eelgrass tissues mainly accumulated Cd, Zn, and Cu, while belowground tissues stored Cr and Pb. Aboveground eelgrass tissues proved reliable in indicating Cd and Pb concentrations in sediments. However, the correlation between Cu, Zn, and Cr in eelgrass tissues and environmental concentrations seemed less direct, requiring further investigation into factors affecting metal accumulation in seagrass. Human activities are probable major contributors to heavy metal presence in Asian marine environments, whereas oceanographic processes serve as primary metal sources in North American Pacific estuaries. Critical discoveries emphasize the necessity for ongoing research on phytotoxic thresholds and in-depth studies on the complex connections between seagrass physiology and environmental metal concentrations. Understanding these dynamics is crucial for evaluating the broader impact of heavy metal pollution on coastal ecosystems and developing effective conservation measures.

The influence of the submergence depth ratio on the Savonius hydrokinetic turbine and flow characteristics is numerically studied under different tip speed ratios. The tip speed ratio TSR (Ratio of the flow speed to blade speed) changes from 0.4 to 1.2, and the submergence depth ratio H*(Ratio of the depth to the turbine diameter) ranging from 0.22 to 1.1. The main conclusions are: (1) When the submergence depth ratio increases from 0.22 to 0.66, the flow field structure gradually becomes regular, and the power coefficient keeps increasing. (2) When the submergence depth ratio reaches up to 0.88, the curve of the power coefficient is similar to that of H* = 1.1, which means the effect of free surface can be ignored when H*>0.88. (3) According to the pressure distribution around the turbine, the free surface will increase the pressure difference on the blade due to the surface tension and blockage effect, thereby influencing the rotation of the turbine. (4) As the TSR increase, the submergence depth ratios of 0.55 and 0.88 are regarded as two demarcation points of the average power coefficient.

The development of microbial communities is important for the growth of the fat greenling Hexagrammos otakii; however, the relationship between microbial communities and fish diet is poorly understood. Here, we used metagenomics sequencing to investigate the gut microbiota of H. otakii at three key time points during development. The gut microbial diversity and community composition of H. otakii presented stage-specific signatures and appeared to shift with different diets and environmental conditions such as NH4 + -NO2- etc. Metagenomics analysis indicated that the dominant phyla were Proteobacteria and Firmicutes. With dietary changes from rotifers and Artemia to formulated feed, the dominant genera shifted from Vibrio and Photobacterium to Lactococcus, and variations in the gut microbiota increased with age. Based on metagenomics functional annotation using the Kyoto Encyclopedia of Genes and Genomes database, growth and diet at different stages affected the metabolic function of the gut microbiome by activating carbohydrate and amino acid metabolism while weakening lipid and nucleotide metabolism. In addition, as predicted by the Carbohydrate-Active enZymes database, glycoside hydrolase and glycosyl transferases may be involved in food degradation. Our results suggest that the H. otakii gut microbiota assembly was coupled to animal development and host age-associated biotic features and changes. Diet had a considerable effect on these distinct communities at different times, indicating that the fish gut microbiota rapidly adapted to dietary shifts. The microbiota therefore likely plays an indispensable role in nutrient turnover and fermentation. These findings can provide guidance for the development of probiotics and the application of feed additives.

BackgroundZostera marina L., or eelgrass, is the most widespread seagrass species throughout the temperate northern hemisphere. Unlike the dry seeds of terrestrial plants, eelgrass seeds must survive in water, and salinity is the key factor influencing eelgrass seed germination. In the present study, transcriptome and proteome analysis were combined to investigate the mechanisms via which eelgrass seed germination was stimulated by low salinity, in addition to the dynamics of key metabolic pathways under germination.ResultsAccording to the results, low salinity stimulated the activation of Ca2+ signaling and phosphatidylinositol signaling, and further initiated various germination-related physiological processes through the MAPK transduction cascade. Starch, lipids, and storage proteins were mobilized actively to provide the energy and material basis for germination; abscisic acid synthesis and signal transduction were inhibited whereas gibberellin synthesis and signal transduction were activated, weakening seed dormancy and preparing for germination; cell wall weakening and remodeling processes were activated to provide protection for cotyledon protrusion; in addition, multiple antioxidant systems were activated to alleviate oxidative stress generated during the germination process; ERF transcription factor has the highest number in both stages suggested an active role in eelgrass seed germination.ConclusionIn summary, for the first time, the present study investigated the mechanisms by which eelgrass seed germination was stimulated by low salinity and analyzed the transcriptomic and proteomic features during eelgrass seed germination comprehensively. The results of the present study enhanced our understanding of seagrass seed germination, especially the molecular ecology of seagrass seeds.

Turbulent mixing plays an important role in shaping the circulation and distribution of heat and carbon within the climate system. Underwater gliders are ideal turbulence observation platforms, but appropriate control parameters are required for them to achieve high-precision and large-scale continuous turbulence measurement, for which speed and endurance are two important indicators. Taking these indicators as the optimization objectives, this study establishes an optimization model for the control parameters of underwater gliders, which integrates two gliding strategy models, a dynamic model, and an energy consumption model. The multi-objective optimization of both conventional gliding strategy and our pitch adjustment strategy is performed with non-dominated sorting genetic algorithm-II to obtain the optimal control parameters. After the optimization, both gliding strategies can achieve an ideal gliding speed for turbulence observation, with the gliding range increased by more than 6% in the diving phase and more than 10% in the climbing phase. The proposed optimization model is verified to be effective with a sea trial performed by Petrel-L underwater glider. After proper modifications, the proposed method is expected to be further applied to other types of gliders.

The integration of sterilization capabilities into sensing platforms is a crucial step in mitigating the significant health risks associated with the persistence of pathogenic bacteria. In this study, we developed a photoelectrochemical (PEC) pathogenic bacteria sensing platform integrated with sterilization function. The platform was based on the g-C3N4 nanosheets decorated with AuNPs and Poly(3-thiophene boronic acid) (PTBA). The incorporation of AuNPs and PTBA proved highly beneficial for enhancing the PEC and photocatalytic performance of bulk g-C3N4. Leveraging the boronic acid group of PTBA, we achieved the selective capture of pathogenic bacteria on the surface of the electrode. The platform showed a high detection sensitivity towards Escherichia coli (E. coli) with a low limit detection (30.5 cfu/mL). Furthermore, the sensing platform demonstrated an exceptional antibacterial rate (99.9 %) resulting from the photoelectrocatalytic effect of PTBA/AuNPs/g-C3N4. This research presents a potential application of the platform as a self-cleaning biosensor for pathogenic diagnosis.

CXCL8 is a high-profile chemokine in vertebrates. In our previous study, CXCL8_L1b was first identified in Japanese flounder and triggered varying immune responses in infected fish compared with Japanese flounder CXCL8_L1a (JfCXCL8_L1a). To further understand the immune functions of Japanese flounder CXCL8_L1b (JfCXCL8_L1b), in vitro and in vivo experiments were performed using the recombinant protein rCXCL8_L1b. Our results showed that rCXCL8_L1b significantly induced all the detected immune genes except IgM and IgD in peripheral blood leukocytes (PBLs) of Japanese flounder. Intramuscular injection of Keyhole Limpet Hemocyanin (KLH) did not cause inflammation responses in fish muscle. In the spleen of injected fish, IgM was the only detected gene expression. In contrast, all detected genes in the KLH group were significantly up-regulated in the head kidney, indicating the primary immune organ response to KLH was the head kidney instead of the spleen. At the injection site, we observed significantly induced receptor gene CXCR1 in KLH + rCXCL8_L1a, KLH + rCXCL8_L1b, and KLH + rCXCL8_L1a + rCXCL8_L1b groups on day 1, while significantly induced receptor gene CXCR2 was only observed in the KLH + rCXCL8_L1b group on day 3. Conversely, gene expression of JfCXCL8_L1a and CXCR2 were down-regulated in the head kidney of the KLH + rCXCL8_L1b group compared with the KLH + rCXCL8_L1a group. Intramuscular injection of KLH significantly induced an antibody titer response to KLH at weeks 2 and 4. Compared with rCXCL8_L1a, rCXCL8_L1b, as the immunologic adjuvant of KLH, significantly enhanced the antibody titer response to KLH at weeks 2 and 4. Collectively, this study reveals that JfCXCL8_L1a and JfCXCL8_L1b have different immune pathways, and JfCXCL8_L1b plays a significant role in enhancing the adaptive immunity of T cell-dependent antigen.

Marine sulfide is mainly produced by the reduction of sulfate. Eutrophication and anoxic conditions caused by tidal fluctuations have accelerated the production of sulfide and widened its distribution. Sulfide has toxic effects on aquatic animals, and it has important effects on physiological activities such as feeding and respiration in buried bivalves. The aim of this study was to estimate the impact of sulfide on the energy budget of the intertidal bivalve Mercenaria mercenaria. Acute toxicity experiments were first conducted on small (SS), medium (MS), and large (LS) size clams, and then clearance rate (CR), absorption efficiency (AE), respiration rate (RR), and ammonia excretion rate (ER) were measured at 24, 48, 72, and 96 h using 0 (control group), safe concentration (low sulfide group), and 96 h half-lethal concentration (high sulfide group) as sulfide concentration gradients, and scope for growth (SFG) was calculated. The results indicated that sulfide reduced the CR, AE, RR, and ER of M. mercenaria, and these indicators were lower in the high sulfide group than in the low sulfide group. The sulfide concentration and exposure time had significant effects on CR, AE, RR, and SFG. The CR of the SS low sulfide group reached its maximum value at 48 h, and the CR of the LS low sulfide and high sulfide groups reached their maximum values at 96 h and 48 h, respectively. SFG experienced a significant decrease with the extension of time, and for both MS and LS, the SFG of sulfide-treated groups was negative at all times, with the exception of 24 h. These results suggest that M. mercenaria exhibits metabolic inhibition and metabolic compensation in response to sulfide exposure. This study provides important insights for comprehending the physiological response of buried bivalves in sulfide environments and provides a scientific fundation for implementing corresponding culture measures.