EsR240, a non-coding sRNA, is required for the resistance of Edwardsiella tarda to stresses in macrophages and for virulence

The mechanism of Se(IV) multisystem resistance in Stenotrophomonas sp. EGS12 and its prospect in selenium-contaminated environment remediation

Human activities have led to elevated levels of selenium (Se) in the environment, which poses a threat to ecosystems and human health. Stenotrophomonas sp. EGS12 (EGS12) has been identified as a potential candidate for the bioremediation of repair selenium-contaminated environment because of its ability to efficiently reduce Se(IV) to form selenium nanospheres (SeNPs). To better understand the molecular mechanism of EGS12 in response to Se(IV) stress, a combination of transmission electron microscopy (TEM), genome sequencing techniques, metabolomics and transcriptomics were employed. The results indicated that under 2 mM Se(IV) stress, 132 differential metabolites (DEMs) were identified, and they were significantly enriched in metabolic pathways such as glutathione metabolism and amino acid metabolism. Under the Se(IV) stress of 2 mM, 662 differential genes (DEGs) involved in heavy metal transport, stress response, and toxin synthesis were identified in EGS12. These findings suggest that EGS12 may respond to Se(IV) stress by engaging various mechanisms such as forming biofilms, repairing damaged cell walls/cell membranes, reducing Se(IV) translocation into cells, increasing Se(IV) efflux, multiplying Se(IV) reduction pathways and expelling SeNPs through cell lysis and vesicular transport. The study also discusses the potential of EGS12 to repair Se contamination alone and co-repair with Se-tolerant plants (e.g. Cardamine enshiensis). Our work provides new insights into microbial tolerance to heavy metals and offers valuable information for bio-remediation techniques on Se(IV) contamination.

AroC, a Chorismate Synthase, is Required for the Formation of Edwardsiella tarda biofilms

Biofilms contribute to the resistance of Edwardsiella tarda to antibiotics and host immunity. AroC in the shikimate pathway produces chorismate to synthesize crucial intermediates such as indole. In this study, the differences between biofilms produced by aroC mutants (△aroC), wild-type (WT) strains, and △aroC complementary strains (C△aroC) were detected both in vitro with 96-well plates, tubes, or coverslips and in vivo using a mouse model of subcutaneous implants. When examining potential mechanisms, we found that the diameters of the movement rings in soft agar plates and the flagellar sizes and numbers determined by silver staining were all lower for △aroC than for WT and C△aroC. Moreover, qRT-PCR showed that the transcription levels of flagellar synthesis genes, fliA and fliC, were reduced in △aroC. AroC, FliC, or FliA may accompany the motility of △aroC strains. In addition, compared with the WT and C△aroC, the amounts of indole in △aroC were significantly decreased. Notably, the formation of biofilms by these strains could be promoted by exogenous indole. Therefore, the aroC gene could affect the biofilm formation of E. tarda concerning its impact on flagella and indole.

RNA-Sequencing Analyses of Small Bacterial RNAs and their Emergence as Virulence Factors in Host-Pathogen Interactions

Proteins have long been considered to be the most prominent factors regulating so-called invasive genes involved in host-pathogen interactions. The possible role of small non-coding RNAs (sRNAs), either intracellular, secreted or packaged in outer membrane vesicles (OMVs), remained unclear until recently. The advent of high-throughput RNA-sequencing (RNA-seq) techniques has accelerated sRNA discovery. RNA-seq radically changed the paradigm on bacterial virulence and pathogenicity to the point that sRNAs are emerging as an important, distinct class of virulence factors in both gram-positive and gram-negative bacteria. The potential of OMVs, as protectors and carriers of these functional, gene regulatory sRNAs between cells, has also provided an additional layer of complexity to the dynamic host-pathogen relationship. Using a non-exhaustive approach and through examples, this review aims to discuss the involvement of sRNAs, either free or loaded in OMVs, in the mechanisms of virulence and pathogenicity during bacterial infection. We provide a brief overview of sRNA origin and importance, and describe the classical and more recent methods of identification that have enabled their discovery, with an emphasis on the theoretical lower limit of RNA sizes considered for RNA sequencing and bioinformatics analyses.

Roles of EvpP in Edwardsiella piscicida-Macrophage Interactions

Edwardsiella piscicida is found to be an important facultative intracellular pathogen with a broad host range. These organisms can replicate and survive within host macrophages to escape from the subversion of the immune defense. E. piscicida-macrophage interaction is very important in determining the outcome of edwardsiellasis. As an effector protein of E. piscicida T6SS, EvpP has been determined to be a very important virulence factor for E. piscicida, although its precise role in E. piscicida-macrophage interactions is not yet clear. In this study, the roles of EvpP in E. piscicida-macrophage interactions were characterized. Here, we constructed the deletion mutants of evpP (ΔevpP) and complementation (ΔevpP-C) by the allelic exchange method. Compared to wild type strain (WT), ΔevpP was found to be attenuated for growth within macrophages. In line with this observation, we found its survival capacity was lower than WT under oxidative and acid stress in vitro, which simulate conditions encountered in host macrophages. Attenuation of ΔevpP also correlated with enhanced activation of macrophages, as reflected by augmented NO production in ΔevpP-treated macrophages. Moreover, compared to WT, ΔevpP induced markedly increased apoptosis of macrophages, characterized by increased Annexin V binding and the activation of cleaved caspase-3. These findings provided strong evidence that EvpP is involved in the process of E. piscicida-macrophage interactions and is required for its survival and replication in macrophages. Thus, we propose that EvpP might be an important factor that controlling the fate of E. piscicida inside macrophages. To further exploring the underlying mechanism of EvpP action, the cDNA library was constructed from E. piscicida-infected macrophages and a yeast two-hybrid screen was performed to search for cellular proteins interacting with EvpP. Ribosomal protein S5 (RPS5) was identified as a target of EvpP. Furthermore, the interaction was validated with co-immunoprecipitation assay. This result implies that the observed effect of EvpP on macrophages might be related to RPS5-mediated regulation, contributing to a better understanding of the mechanisms of EvpP involved in E. piscicida-macrophage interactions.