摘要: DEAD-box RNA helicases play critical roles in regulating RNA metabolism and gene expression in both prokaryotes and eukaryotes. In the filamentous, heterocyst-forming cyanobacterium Anabaena PCC 7120, two DEAD-box helicases, CrhB and CrhC, are present. Here, we show that CrhC is dispensable, whereas CrhB is essential for cell viability. Using a conditional crhB mutant, we found that CrhB depletion severely impaired growth, with cells growing slowly in liquid medium containing nitrate at 30 ​°C and failing to grow on agar plates or at 20 ​°C. CrhB-depleted cells displayed cell division defects similar to those observed in the mutants of the division regulator patU3. Consistent with this, we found that HetF—the cysteine protease that specifically degrades PatU3—accumulated in CrhB-depleted cells, suggesting that CrhB regulates cell division by modulating HetF and PatU3 levels. Additionally, CrhB-depleted filaments showed delayed heterocyst differentiation upon the deprivation of combined-nitrogen, accompanied by weaker upregulation of HetR, the master regulator of differentiation. Consistent with its function in heterocyst development, crhB was upregulated in differentiating cells as early as 6 ​h after initiation of heterocyst differentiation. crhB is co-transcribed with the upstream gene rimO, which encodes a conserved methylthiotransferase that modifies a key residue in ribosomal protein S12. CrhB depletion resulted in an accumulation of RimO to toxic levels, partially accounting for the severe growth defects observed in the CrhB-depleted cells. Our findings reveal that CrhB is a key regulator of cell division, heterocyst differentiation, and ribosome modification in Anabaena, providing new insights into the functions of DEAD-box RNA helicases in bacteria.

摘要: The pathogenic bacterium Aeromonas hydrophila presents significant threats in aquaculture due to its increasing antibiotic resistance. Prior studies identified lysine acetylation (Kac) and succinylation (Ksuc) modifications at the K14 site of the ferric uptake regulator (Fur) in A. hydrophila, although the functional roles of these modifications remain unclear. In this study, we used site-directed mutagenesis of Fur at the K14 site to examine its effects across 44 antibiotics. Both lysine modifications were found to play crucial roles in modulating bacterial antibiotic resistance. To further explore these effects, we analyzed mRNA transcription levels between Δfur and wild-type strains, as well as Fur K14E and K14R strains under balofloxacin stress, using RNA-Seq. Our findings suggest that Ksuc at the Fur K14 site may suppress the transcription of 19 DNA damage repair genes and modulate several antimicrobial resistance genes. ChIP-PCR assays further demonstrated that both Kac and Ksuc at K14 directly affect Fur's binding affinity for the promoter regions of target genes. Overall, our results support the role of Kac and Ksuc in modulating Fur-driven antibiotic resistance in A. hydrophila, providing novel insights and potential strategies for combating this pathogen.

摘要: Microplastics (MPs) can adsorb antibiotics to form complex pollutants that seriously threaten the health of freshwater ecosystems. However, few studies have examined the combined ecotoxicity of MPs and multiple antibiotics in natural aquatic environments. In this study, we examined the effects of combined exposure to antibiotics and MPs on aquatic community structure in natural settings in the Beiluo River using eDNA analysis. The results revealed that antibiotic pollution in the Beiluo River mainly originates from animal husbandry and agriculture, whereas MPs mainly originate from agriculture and urban sewage. The community structure of aquatic organisms was significantly correlated with the concentrations of antibiotics and MPs (Mantel's test r ​= ​−0.58 to 0.90, p ​< ​0.05). The combined effects of antibiotics and MPs explained 24.36 ​% and 45.14 ​% of the variation in cyanobacteria and phytoplankton (VPA). Key antibiotics including tetracycline hydrochloride (r ​= ​0.89), OTC hydrochloride (r ​= ​0.87), and lincomycin hydrochloride (r ​= ​0.90) showed particularly strong associations with phytoplankton communities. The effect of MPs on antibiotic toxicity was highly dependent on the antibiotic type and MP particle size. Small-particle-size MPs (500 ​μm) predominantly impacted zoobenthos. The results of this study enhance our understanding of the complex combined effects of MPs and antibiotics on aquatic organisms, emphasizing the necessity of informed scientific management of these emerging contaminants.

摘要: The extensive use of cobalt nanoparticles (CoNPs) in industrial and biomedical applications has raised environmental concerns, necessitating effective mitigation strategies. This study examines the phytotoxicity and phytoremediation potential of CoNPs using Lemna minor L., a recognized Co-hyperaccumulator. CoNPs exhibited significant sublethal toxicity at concentrations ≥1000 ​μg Co²⁺/L, leading to oxidative stress and impaired growth, photosynthesis, and respiration. Despite these challenges, L. minor effectively removed over 99 ​% of CoNPs from the medium, even at high concentrations (up to 20.000 ​μg Co²⁺/L), with gravimetric cobalt concentrations reaching 1771 ​μg Co²⁺/g dry weight in plant tissues. Physiological responses to CoNPs were similar to those induced by equivalent concentrations of CoCl2, suggesting that CoNPs dissolve into Co²⁺ ions upon interaction with plants. However, ultrastructural analysis revealed distinct intracellular cobalt localization with CoNPs causing more severe chloroplast damage than ionic Co²⁺. These findings suggest two toxicity mechanisms: ionic effects from dissolved Co²⁺ and direct physical damage from intact nanoparticles. The resilience and hyperaccumulation capacity of L. minor makes it a promising candidate for the phytoremediation of cobalt-contaminated waters. The study underscores the importance of further research to elucidate CoNP environmental behavior and optimize phytoremediation approaches.

摘要: Ecological interactions in the littoral zone maintain water quality, biodiversity, and ecological services in freshwater ecosystems. Phytoplankton occupy a central position in the ecosystem due to their sensitivity to environmental changes and ecological importance for ecosystem functioning. Here, we aimed to evaluate dissimilarity in physicochemical characteristics and phytoplankton composition of the littoral zone in two reservoirs of the Belo Monte Hydroelectric Complex. We also investigated the physicochemical factors determining spatial variation in the composition, richness, and biovolume of littoral phytoplankton in the environments studied. The physical and chemical characteristics of the water displayed distinct patterns in the Xingu and Intermediate reservoirs, which drove phytoplankton biovolume and species composition. However, the richness of phytoplankton species was similar in the two reservoirs. More specifically, phytoplankton biovolume and species composition were influenced by nitrate, temperature, conductivity, and transparency. Our study increases understanding of the environmental factors determining spatial variation of littoral phytoplankton communities in reservoirs. This data improves understanding of littoral zones in reservoirs and highlights the importance of littoral phytoplankton in maintaining water quality and ecosystem services in these waterbodies.

摘要: The dissemination of antibiotic resistance genes (ARGs) has emerged as a global public health concern. However, the distribution and driving factors of ARGs, especially high-risk ARGs, in the fish gut from natural water ecosystems remain largely unclear. In the present study, high-throughput quantitative PCR (HT-qPCR) and 16S rRNA gene sequencing were deployed to determine the ARG profiles and microbial communities in the fish gut across 13 sampling sites from the Xiangjiang River, one of the major tributaries of the Yangtze River in China. In total, 120 ARG subtypes were identified, dominated by macrolide-lincosamide-streptogramin B (MLSB) resistance genes. The abundance of ARGs varied across sampling sites, with highest at Xiangxiang (XX) and lowest at Chaling (CL). Furthermore, it was observed that ARG abundance was higher in the tributaries compared to the trunk stream, with an increasing trend from upstream to downstream. At the ranks of phylum and genus, the fish gut microbiota was predominantly composed of Proteobacteria and Escherichia, respectively. Several opportunistic pathogens (Vibrio, Streptococcus, and Pseudomonas) exhibited significantly positive correlations with high-risk ARGs (floR, emrB, and ermD). Finally, the assembly of ARGs in the Xiangjiang River was dominated by deterministic processes and significantly influenced by mobile genetic elements (MGEs), environmental factors, heavy metals, and geographic location. Overall, the findings of this study illustrate the prevalence of ARGs and opportunistic pathogens in the fish gut within the Xiangjiang River, highlighting potential risks to public health. These results provide valuable insights for developing targeted strategies to manage and assess ARGs in natural water ecosystems.

摘要: Periphyton are one of the key primary producers in aquatic ecosystems, particularly in oligotrophic shallow lakes. Submerged macrophytes are capable of competing with periphyton for nutrients and light, but may also facilitate periphyton by providing surfaces for their growth, and their interaction may vary with the nutrient level in the environment. However, there is a lack of research on how macrophytes affect the growth of periphyton as lake nutrient levels increase, particularly in relatively low nutrient levels (from oligotrophic to mesotrophic). We conducted a large-scale mesocosm experiment using 13 different species of submerged macrophytes to investigate the impacts of different nutrient levels in the sediment on the interaction between periphyton and submerged macrophytes, as well as the ecological stoichiometric properties of periphyton on different substrates. We found that at very low nutrient levels, periphyton was more competitive than macrophytes; as nutrient levels increased, macrophytes become more competitive though this varied across macrophyte species; and periphyton was more competitive again when nutrient levels surpassed a certain threshold of the macrophyte. Additionally, the stoichiometry of periphyton was influenced by macrophyte species, nutrient level, substrate, and their interactions. This might be due to shading, competition for nutrients, or allelopathic substances imposed by macrophytes on periphyton. Our study demonstrated that nutrient levels in the environment can affect the growth and stoichiometry of periphyton as it interacts with submerged macrophytes. These findings enhance our understanding of primary producers’ dynamics in shallow aquatic ecosystems and have implications for restoring eutrophic lakes, e.g., through removing nutrient-rich sediment, or introducing more competitive submerged macrophytes.

摘要: Estimating the population abundance of marine wildlife is fundamental for developing evidence-based management strategies. However, standard field-based methods for estimating marine animal abundance can be time-consuming and costly, and may not effectively monitor populations over long time frames or large spatial scales. In this study, we attempted to utilize local ecological knowledge (LEK) to estimate population abundance of a marine mammal by collecting interview-based sighting data from a large-scale fisher questionnaire survey in the mainland of China for the Indo-Pacific humpback dolphin (Sousa chinensis). To validate our findings, we compared this information with data obtained from standard field surveys published in the literature. Despite the inability to accurately predict absolute abundance, all four indices (encounter rate, encounter rate in the past decade, sighting frequency, and mean annual sightings in the past five years) derived from interview sighting history had a highly significant correlation with abundance rank from field survey. In addition, the severe population declines and identified causes (water pollution, habitat destruction, overfishing, and bycatch) reported by respondents also aligned closely with independent field survey data. This is the first time that interview data have been shown to provide accurate quantitative information on a marine species’ relative abundance. We therefore propose that interview-based surveys can serve as a valuable monitoring technique to assess the population status of cetaceans and other distinctive marine megafauna, particularly in systems where field survey programs are limited in scale and scope.

摘要: Somatostatin (SST), named for its ability to inhibit pituitary growth hormone (GH) secretion, is involved in multiple physiological processes though somatostatin receptors (SSTRs). Both in vitro and in vivo studies have demonstrated that SSTR2 mediates GH inhibition by SST. However, whether a deficiency of SSTR2 promotes the somatic growth of fish is unclear. In this study, both sstr2a and sstr2b were predominantly expressed in the pars distalis of the pituitary gland, with sstr2a showing higher expression levels than sstr2b. Mutation of sstr2a was performed in tilapia using the CRISPR/Cas9 system. The sstr2a^−/− mutants exhibited a significant increase in body weight at 60, 120, and 180 days post fertilization (dpf) when reared in mixed populations with wild type (WT) fish, being 43 ​% heavier than WT fish at 180 dpf. The sstr2a^−/− mutants also demonstrated better growth than WT fish under the separate-tank culture condition, with higher body weight, length, height, and width, weight gain rate, and specific growth rate, as well as lower food intake and feed coefficient, but no difference in condition factor. Furthermore, among female and male sstr2a^−/− mutants and WT controls, the growth of male sstr2a^−/− mutants was the highest, followed by female sstr2a^−/− mutants, then WT males and WT females. No differences were observed between sstr2a^−/− mutants and WT fish in the mean area and number of muscle fibers per visual field under the microscope. However, there were fewer lipid droplets in the liver in sstr2a^−/− mutants than in WT fish. The deficiency of SSTR2a also led to elevated circulating GH and IGF-1 levels and up-regulated expression of GH/IGF axis genes. Overall, the first established sstr2a^−/− mutant line in fish not only holds significant potential to develop into a fast-growth strain of tilapia, but also provides an excellent model for understanding the regulation of growth and metabolism in teleosts.

摘要: Sphaerothecum destruens, an emerging aquatic pathogen, presents significant threats to biodiversity conservation and aquaculture sustainability due to its broad host range and close association with the invasive Pseudorasbora parva. This study reports the first detection of S. destruens in freshwater fish from the Po River basin (Italy), encompassing both native and non-native species. Molecular analysis revealed S. destruens infection in four positive Barbus barbus specimens and identified four additional potential positive samples, including Barbus barbus, Pseudorasbora parva, and Padogobius bonelli. Prevalence rates varied across sampling sites, with infection rates of 3.45 ​% in Moncalieri, 19.23 ​% in Murazzi, and 5.26 ​% in San Mauro. Notably, species-specific prevalence was highest in Pseudorasbora parva (50 ​%) and Padogobius bonelli (33.33 ​%) at Murazzi. Prevalence in Barbus barbus was site-dependent, with rates of 4.17 ​%, 42.86 ​%, and 8.00 ​% recorded at Moncalieri, Murazzi, and San Mauro, respectively. The findings reveal site-specific variability in S. destruens prevalences, influenced by environmental conditions and the presence of invasive species like P. parva, which act as reservoirs and vectors for pathogen dissemination. The results underscore the importance of molecular diagnostic tools for detecting asymptomatic infections, which are often overlooked using conventional approaches. To mitigate the ecological and economic impacts of S. destruens, targeted management strategies are essential, focusing on limiting the spread of S. destruens and implementing proactive surveillance. These measures are critical for protecting aquatic biodiversity in the Po River basin and other vulnerable ecosystems.