Mangrove swamp is one of the world’s richest and most productive marine ecosystems. This ecosystem also has a great ecological importance, but is highly susceptible to anthropogenic disturbances. The balance of mangrove ecosystem depends largely on the microbial communities in mangrove sediments. Thus, understanding how the mangrove microbial communities respond to spatial differences is essential for more accurate assessment of mangrove ecosystem health. To this end, we performed the first medium-distance (150 km) research on the biogeographic distribution of mangrove microbial communities. The hypervariable regions of 16S rRNA gene was sequenced by Illumina to compare the microbial communities in mangrove sediments collected from six locations (i.e. Zhenzhu harbor, Yuzhouping, Maowei Sea, Qinzhou harbor, Beihai city and Shankou) along the coastline of Beibu Gulf in Guangxi province, China. Collectively, Proteobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, Parvarchaeota, Acidobacteria and Cyanobacteria were the predominant phyla in the mangrove sediments of this area. At genus level, the heat map of microbial communities reflected similarities between study sites and was in agreement with their biogeographic characteristics. Interestingly, the genera Desulfococcus, Arcobacter, Nitrosopumilus and Sulfurimonas showed differences in abundance between study sites. Furthermore, the principal component analysis (PCA) and unweighted UniFrac cluster tree of beta diversity were used to study the biogeographic diversity of the microbial communities. Relatively broader variation of microbial communities was found in Beihai city and Qinzhou harbour, suggesting that environmental condition and historical events may play an important role in shaping the bacterial communities as well. This is the first report on medium-distance range distribution of bacteria in the mangrove swamp ecosystem. Our data is valuable for monitoring and evaluation of the impact of human activity on mangrove habitats from the perspective of microbiome.

(1) Background: Singapore grouper iridovirus (SGIV) can cause extensive fish deaths. Therefore, developing treatments to combat virulent SGIV is of great economic importance to address this challenge to the grouper aquaculture industry. Green tea is an important medicinal and edible plant throughout the world. In this study, we evaluated the use of green tea components against SGIV infection. (2) Methods: The safe working concentrations of green tea components were identified by cell viability detection and light microscopy. Additionally, the antiviral activity of each green tea component against SGIV infection was determined with light microscopy, an aptamer (Q5c)-based fluorescent molecular probe, and reverse transcription quantitative PCR. (3) Results: The safe working concentrations of green tea components were green tea aqueous extract (GTAE) ≤ 100 μg/mL, green tea polyphenols (TP) ≤ 10 μg/mL, epigallocatechin-3-gallate (EGCG) ≤ 12 μg/mL, (-)-epigallocatechin (EGC) ≤ 10 μg/mL, (-)-epicatechin gallate (EGC) ≤ 5 μg/mL, and (-)-epicatechin (EC) ≤ 50 μg/mL. The relative antiviral activities of the green tea components determined in terms of MCP gene expression were TP > EGCG > GTAE > ECG > EGC > EC, with inhibition rates of 99.34%, 98.31%, 98.23%, 88.62%, 73.80%, and 44.31%, respectively. The antiviral effect of aptamer-Q5c was consistent with the results of qPCR. Also, TP had an excellent antiviral effect in vitro, wherein the mortality of fish in only the SGIV-injection group and TP + SGIV-injection group were 100% and 11.67%, respectively. (4) Conclusions: In conclusion, our results suggest that green tea components have effective antiviral properties against SGIV and may be candidate agents for the effective treatment and control of SGIV infections in grouper aquaculture.

High-throughput sequencing has significantly advanced the exploration of fish immune mechanisms, enabling a more detailed understanding of immune responses and their underlying molecular pathways. In this study, we applied comparative transcriptomics and single-cell RNA sequencing to investigate the immune mechanisms of tilapia in response to different pathogenic bacteria. Our results demonstrated that nonspecific cytotoxic cells (NCCs) and monocytes/macrophages (Mos/Mφs) mounted the most pronounced responses to both Streptococcus agalactiae and Aeromonas hydrophila infections. Moreover, Mos/Mφs exhibited distinct differentiation patterns depending on the bacterial challenge. Collectively, these findings offer new insights into the antibacterial immune strategies of lower vertebrates.

The escalating problem of copper (Cu) and cadmium (Cd) pollution in aquatic environments poses a significant threat to the ovarian tissue and reproductive capacity of fish, hindering the development of the aquaculture industry. However, the combined effects of Cu and Cd on fish gonadal development remain unclear. In this study, the fish species Nile tilapia was stressed with rearing water containing 300 μg/L Cu²⁺ and 100 μg/L Cd²⁺ for 30 days, followed by an intraperitoneal injection of luteinizing hormone-releasing hormone (LHRH-α) and human chorionic gonadotropin (HCG) at various concentrations. We investigated the ovarian transcriptome profiles before and after injection. Prior to injection, combined treatment with Cu and Cd resulted in reproductive dysfunction and metal ion imbalance in tilapia. Transcriptomic profiling revealed differential gene annotation concentrated in the MAPK signaling pathway and regulation of GTPase activity. Post-injection, all concentrations of LHRH-α and HCG groups showed an upregulated gonadosomatic index (G.S.I) and higher levels of vitellogenin (VTG), gonadotropin-releasing hormone (GnRH), gonadotropin (GTH), and estrogen (E2) in serum compared to the negative control group. Transcriptomic analysis revealed alterations in various ovarian signaling pathways, preliminarily revealing the in vivo molecular mechanisms and differences in LHRH-α and HCG. The findings from this study could help us better understand how to counteract the effects of combined Cu and Cd exposure on tilapia ovarian development, which has significant implications for the Nile tilapia aquaculture industry.