Motility and the expression of the flagellin protein FliC are negatively regulated by quorum sensing in Edwardsiella tarda

AI-2 quorum sensing signal disrupts coral symbiotic homeostasis and induces host bleaching

Symbiotic microorganisms play critical ecophysiological roles that facilitate the maintenance of coral health. Currently, information on the gene and protein pathways contributing to bleaching responses is lacking, including the role of autoinducers. Although the autoinducer AI-1 is well understood, information on AI-2 is insufficient. Here, we observed a 3.7-4.0 times higher abundance of the AI-2 synthesis gene luxS in bleached individuals relative to their healthy counterparts among reef-building coral samples from the natural environment. Laboratory tests further revealed that AI-2 contributed significantly to an increase in coral bleaching, altered the ratio of potential probiotic and pathogenic bacteria, and suppressed the antiviral activity of specific pathogenic bacteria while enhancing their functional potential, such as energy metabolism, chemotaxis, biofilm formation and virulence release. Structural equation modeling indicated that AI-2 influences the microbial composition, network structure, and pathogenic features, which collectively contribute to the coral bleaching status. Collectively, our results offer novel potential strategies for coral conservation based on a signal manipulation approach.

Autoinducers modulation as a potential anti-virulence target of bacteria by phenolic compounds

OBJECTIVE

The goal of this study was to determine the effects of phenolic extracts from grape (GrPE), pomegranate (PoPE), and persimmon (PePE) by-products on bacterial virulence activities such as biofilms, motility, energy-dependent efflux pumps, and β-lactamase activity, which are modulated primarily by quorum sensing (QS), defining their potential applications.

METHOD

The microdilution method was used to determine the minimum inhibitory concentration (MIC) and sub-inhibitory concentrations (SICs) of the extracts against reference pathogenic bacteria. The antibacterial mode of action was determined by labelling bacterial cells in in vivo cell-tracking experiments.

RESULTS

Antibiograms showed that PoPE inhibited bacteria at lower concentrations, and PePE had a stronger effect against Klebsiella pneumoniae. Both extracts caused significant cell membrane damage (CMD), whereas GrPE did not. At SICs, all extracts showed anti-QS activity, especially PePE, which inhibited violacein and pyocyanin production at 1/128 × MIC. Additionally, QS autoinducers found in Chromobacterium violaceum and Pseudomonas aeruginosa were modulated by the extracts; PePE showed the highest modulation. Antibiofilm assays revealed that GrPE, at MIC and 2 × MIC, acted as a potent antibiofilm agent against biofilms of Pseudomonas putida, Bacillus cereus, and Staphylococcus aureus, which was related to disruption of swarming motility by GrPE. All extracts, especially PoPE, exerted a potent effect against the activation of efflux pumps of P. aeruginosa as well as β-lactamase activity in K. pneumoniae.

CONCLUSION

Results suggest that the anti-virulence potential of the extracts may be related to their effect as extracellular autoinducer modulators. This study allowed to define potential applications of these extracts.

Current status and development prospects of aquatic vaccines

Diseases are a significant impediment to aquaculture's sustainable and healthy growth. The aquaculture industry is suffering significant financial losses as a result of the worsening water quality and increasing frequency of aquatic disease outbreaks caused by the expansion of aquaculture. Drug control, immunoprophylaxis, ecologically integrated control, etc. are the principal control strategies for fish infections. For a long time, the prevention and control of aquatic diseases have mainly relied on the use of various antibiotics and chemical drugs. However, long-term use of chemical inputs not only increases pathogenic bacteria resistance but also damages the fish and aquaculture environments, resulting in drug residues in aquatic products, severely impeding the development of the aquaculture industry. The development and use of aquatic vaccines are the safest and most effective ways to prevent aquatic animal diseases and preserve the health and sustainability of aquaculture. To give references for the development and implementation of aquatic vaccines, this study reviews the development history, types, inoculation techniques, mechanisms of action, development prospects, and challenges encountered with aquatic vaccines.

The Microbial Mechanisms of a Novel Photosensitive Material (Treated Rape Pollen) in Anti-Biofilm Process under Marine Environment

Marine biofouling is a worldwide problem in coastal areas and affects the maritime industry primarily by attachment of fouling organisms to solid immersed surfaces. Biofilm formation by microbes is the main cause of biofouling. Currently, application of antibacterial materials is an important strategy for preventing bacterial colonization and biofilm formation. A natural three-dimensional carbon skeleton material, TRP (treated rape pollen), attracted our attention owing to its visible-light-driven photocatalytic disinfection property. Based on this, we hypothesized that TRP, which is eco-friendly, would show antifouling performance and could be used for marine antifouling. We then assessed its physiochemical characteristics, oxidant potential, and antifouling ability. The results showed that TRP had excellent photosensitivity and oxidant ability, as well as strong anti-bacterial colonization capability under light-driven conditions. Confocal laser scanning microscopy showed that TRP could disperse pre-established biofilms on stainless steel surfaces in natural seawater. The biodiversity and taxonomic composition of biofilms were significantly altered by TRP (p < 0.05). Moreover, metagenomics analysis showed that functional classes involved in the antioxidant system, environmental stress, glucose−lipid metabolism, and membrane-associated functions were changed after TRP exposure. Co-occurrence model analysis further revealed that TRP markedly increased the complexity of the biofilm microbial network under light irradiation. Taken together, these results demonstrate that TRP with light irradiation can inhibit bacterial colonization and prevent initial biofilm formation. Thus, TRP is a potential nature-based green material for marine antifouling.

Functional Gene Expression in Shark Bay Hypersaline Microbial Mats: Adaptive Responses

Microbial mat communities possess extensive taxonomic and functional diversity, which drive high metabolic rates and rapid cycling of major elements. Modern microbial mats occurring in hypersaline environments are considered as analogs to extinct geobiological formations dating back to ∼ 3.5 Gyr ago. Despite efforts to understand the diversity and metabolic potential of hypersaline microbial mats in Shark Bay, Western Australia, there has yet to be molecular analyses at the transcriptional level in these microbial communities. In this study, we generated metatranscriptomes for the first time from actively growing mats comparing the type of mat, as well as the influence of diel and seasonal cycles. We observed that the overall gene transcription is strongly influenced by microbial community structure and seasonality. The most transcribed genes were associated with tackling the low nutrient conditions by the uptake of fatty acids, phosphorus, iron, and nickel from the environment as well as with protective mechanisms against elevated salinity conditions and to prevent build-up of ammonium produced by nitrate reducing microorganisms. A range of pathways involved in carbon, nitrogen, and sulfur cycles were identified in mat metatranscriptomes, with anoxygenic photosynthesis and chemoautotrophy using the Arnon–Buchanan cycle inferred as major pathways involved in the carbon cycle. Furthermore, enrichment of active anaerobic pathways (e.g., sulfate reduction, methanogenesis, Wood–Ljungdahl) in smooth mats corroborates previous metagenomic studies and further advocates the potential of these communities as modern analogs of ancient microbialites.

Mechanisms of quorum sensing and strategies for quorum sensing disruption in aquaculture pathogens

In many countries, infectious diseases are a considerable threat to aquaculture. The pathogenicity of micro-organisms that infect aquaculture systems is closely related to the release of virulence factors and the formation of biofilms, both of which are regulated by quorum sensing (QS). Thus, QS disruption is a potential strategy for preventing disease in aquaculture systems. QS inhibitors (QSIs) not only inhibit the expression of virulence-associated genes but also attenuate the virulence of aquaculture pathogens. In this review, we discuss QS systems in important aquaculture pathogens and focus on the relationship between QS mechanisms and bacterial virulence in aquaculture. We further elucidate QS disruption strategies for targeting aquaculture pathogens. Four main types of QSIs that target aquaculture pathogens are discussed based on their mechanisms of action.