Zemao Gu

Elizabethkingia species are emerging opportunistic pathogens responsible for life-threatening nosocomial infections. Their intrinsic multidrug resistance severely limits effective antibiotic treatment, necessitating urgent development of novel therapeutic strategies. Among potential targets, outer membrane protein A (OmpA) family proteins have drawn increasing interest. However, the functional roles of OmpA family proteins in Elizabethkingia remain entirely uncharacterized, leaving their potential as targeted therapeutics unresolved. In this study, we identified a group of putative OmpA family proteins in Elizabethkingia miricola strain FL160902 and systematically investigated the contributions of five OmpA members to bacterial physiology and virulence. Targeted gene deletions revealed marked functional divergence among these paralogs. Specifically, OmpA-1 and OmpA-3 were identified as master virulence determinants; their deletion resulted in impaired serum resistance, reduced cell adhesion capacity, and diminished in vivo lethality. Their deletion also induced extensive physiological dysregulation, including enhanced biofilm formation, increased surface hydrophobicity, and heightened susceptibility to oxidative stress. In contrast, deletions of ompA-2, ompA-4, and ompA-5 resulted only in partial attenuation of virulence traits and restricted changes to specific physiological phenotypes. Collectively, these findings establish a functional hierarchy within the OmpA proteins and position OmpA-1 and OmpA-3 as high-priority molecular targets for developing precision therapeutics against this life-threatening, multidrug-resistant pathogen.

To accurately manage precise feeding and water quality regulation in the rice–duck–crayfish integrated system (RDCI), the continuous monitoring of plankton and physicochemical parameters in the water was conducted from March 2022 to January 2023 in both the RDCI and the rice–crayfish continuous culture system (RCCC). The results showed that a total of 188 phytoplankton species and 92 zooplankton species were identified in the RDCI, whereas 152 phytoplankton species and 95 zooplankton species were detected in the RCCC. The phytoplankton community composition was similar between these two systems. For zooplankton, Rotifera was the dominant group. However, Chlorophyta and Bacillariophyta were the dominant phytoplankton groups. Compared with the RCCC, the RDCI exhibited lower plankton density during the crayfish-farming stage and overwintering stage, but higher plankton biomass during the crayfish-farming stage, overwintering stage, and rice maturity stage. The diversity indices, richness indices, and evenness indices of both phytoplankton and zooplankton in the RDCI were significantly higher than those in the RCCC. Correlation analysis indicated that water temperature, dissolved oxygen, total nitrogen, and ammonia nitrogen were the key environmental factors affecting plankton community structure. In summary, compared with the RCCC, the RDCI exhibits higher plankton diversity and better evenness, suggesting a more complex and stable community structure. The species composition of plankton and related indices indicate that the RDCI mitigates the degree of eutrophication in water during both the crayfish farming and the overwintering stages, while increasing nutrients levels during the rice planting stage. This approach is beneficial for reducing non-point-source pollution in agriculture and promoting green agricultural development.

Background: Chinese soft-shelled turtle adenovirus (CSTAdV) is a new virus discovered recently that infects farmed Chinese soft-shelled turtle. In order to investigate its epizootiology and meet the requirements of timely prevention and control, it is imperative to establish an efficient diagnostic assay for CSTAdV. Results: In this study, on-site diagnostic real-time fluorescence Recombinase-aided amplification (RF-RAA) and real-time quantitative polymerase chain reaction (qPCR) detection methods were established based on the specific sequence of the viral DNA polymerase gene. The results showed that the sensitivity of the CSTAdV RF-RAA assay and qPCR assay was 1.0 × 10² copies/μL within 20 min at 42 °C, and 1.0 × 10¹ copies/μL in approximately 60 min for detecting plasmid pUC57-CSTAdV, respectively. Both the RF-RAA assay and the qPCR assay were highly specific for CSTAdV, with no cross-reaction with Soft-shelled turtle iridovirus, Trionyx sinensis hemorrhagic syndrome virus, Citrobacter freundii, Aeromonas veronii, Aeromonas hydrophila, Morganella morganii, and Vibrio cholerae. A total of 107 clinical specimens of Chinese soft-shelled turtle were tested by the RF-RAA and qPCR assays. The qPCR results were consistent with adenoviral consensus nested PCR published previously, whereas the RF-RAA assay exhibited diagnostic sensitivity (DSe) and diagnostic specificity (DSp) of 95.45% and 100%, respectively. The findings suggest that the newly developed RF-RAA and qPCR assays exhibit high accuracy in detecting CSTAdV in clinical specimens. Conclusions: Therefore, the RF-RAA and qPCR assays provide two novel alternatives for simple, sensitive and specific identification of CSTAdV for pathogen screening in the field and quantitative analysis in the laboratory.

Herbivorous protistan grazers are ubiquitous and abundant in marine and temperate freshwater environments. However, little is known about the algivorous ciliates and their feeding habits in outdoor mass algal cultures. In this study, we report on one hypotrich ciliate, identified as Sterkiella histriomuscorum, from the outdoor mass culture of Scenedesmus in Arizona, USA. A long-term field survey revealed that this species often occurs in Scenedesmus culture in spring and summer, and can graze very heavily on Scenedesmus cells. By isolating Sterkiella cells and then observing them via light microscopy and electron microscopy, detailed information about the morphology, ultrastructure, excystment process, and feeding characteristics of the ciliate was obtained. Specifically, it seems that S. histriomuscorum has a range of different strategies for excystment, and the sharp change in the ion concentration in the environment around the cyst results in osmotic shock, which likely facilitates the excystment. Feeding experiments revealed that S. histriomuscorum preferred to graze on chlorophytes as well as the diatom Phaeodactylum tricornutum and had no interaction with chrysophytes or cyanobacteria. Molecular phylogenetic analysis based on the SSU rRNA gene sequence indicated that both the genus Sterkiella and the species S. histriomuscorum are non-monophyletic. The information obtained from this study will help advance our understanding of the biodiversity and ecological function of S. histriomuscorum, and will also be very useful in the development of early warning systems and control measures for preventing or treating this contaminant in microalgal mass cultures.

Hybrid yellow catfish (Tachysurus fulvidraco♀ × Tachysurus vachelli♂) is a significant aquaculture variety in China. It is easy to be infected by trichodinids, causing serious economic losses. However, the species investigation of trichodinids on hybrid yellow catfish is relatively deficient, which seriously hinders the prevention and control of trichodiniasis. Hence, trichodinids were collected in a hybrid yellow catfish farm in Hubei Province from June 2022 to October 2023 and identified by morphological and molecular biology methods. A new species Tripartiella luhuensis sp. nov. and nine Trichodina species were described. Phylogenetic analyses demonstrated that T. luhuensis nested in the Trichodinella‐Tripartiella‐Paratrichodina clade, indicating that the genus Tripartiella is not a monophyletic group. Besides, Trichodinid species from Siluriformes hosts have relatively similar evolutionary positions. Histopathological analysis revealed that the parasitism of trichodinids caused mechanical damage and mucus hypersecretion to gill of the host. The present study reports trichodinid species on hybrid yellow catfish for the first time and adds one new species to the genus Tripartiella. We also indicate the importance of preventing and controlling trichodiniasis in hybrid yellow catfish farming.

Elizabethkingia miricola is a multidrug-resistant pathogen that can cause life-threatening infections in immunocompromised humans and outbreaks in amphibians. However, the specific virulence factors of this microorganism have not been described. In this study, we identified the polysaccharide biosynthesis protein-encoding gene capD, which is located in the conserved region of the Wzy-dependent capsule synthesis gene cluster in the E. miricola strain FL160902, and investigated its role in the pathogenesis of E. miricola. Our results revealed that the capD deletion strain (ΔcapD) lost its typical encapsulated structure, with a 45% reduction in cell wall thickness. CapD affects wza expression in the capsule polysaccharide synthesis pathway. Furthermore, the survival rates were significantly reduced in ΔcapD in response to complement-mediated killing, desiccation stress, and macrophage phagocytosis, whereas biofilm formation, surface hydrophobicity, and adherence to both endothelial and epithelial cells were increased. Additionally, the deletion of capD sharply attenuated the virulence of E. miricola in a frog infection model. Complementation of the capD gene restored the biological properties and virulence to wild-type levels. Overall, these findings suggest that CapD contributes to polysaccharide synthesis and plays a crucial role in the pathogenesis of E. miricola.