Biofilm formation of Hafnia paralvei induced by c-di-GMP through facilitating bcsB gene expression promotes spoilage of Yellow River carp (Cyprinus carpio).

Hafnia paralvei, a Gram-negative foodborne pathogen, is found ubiquitously in various aquatic animals and seafoods, which can form biofilm as a dominant virulence factor that contributes to its pathogenesis. However, the biofilm formation mechanism of H. paralvei and its effect on food spoilage has not been fully characterized. Here we show that biofilm formation, is regulated by c-di-GMP which mediated by bcsB, can increase the spoilage ability of H. paralvei. We found that GTP was added exogenously to enhance the synthesis of c-di-GMP, which further promoted biofilm formation. The gene dgcC, one of 11 genes encoding GGDEF domain-containing proteins in H. paralvei, was significantly upregulated with GTP as substrate. The upregulation of dgcC contributes to a significant increase of c-di-GMP and the formation of biofilm. In addition, the overexpression of dgcC induced upregulation of bcsB, a reported effector protein encoding gene, which was further demonstrated that overexpression of bcsB can encourage the synthesis of bacterial cellulose and biofilm formation. The effect of biofilm formation induced by c-di-GMP on spoilage of Yellow River carp (Cyprinus carpio) was evaluated by sensory evaluation, the total viable count, and the total volatile basic nitrogen, which showed that biofilm formation can significantly increase the spoilage ability of H. paralvei on C. carpio. Our findings provide the regulation of c-di-GMP on expression of bcsB, that can contribute to biofilm formation and spoilage ability of H. paralvei, which is favor to understanding the pathogenesis of Hafnia paralvei and its role in food spoilage.

Polystyrene microplastics promote intestinal colonization of Aeromonas veronii through inducing intestinal microbiota dysbiosis.

The premise that pathogen colonized microplastics (MPs) can promote the spread of pathogens has been widely recognized, however, their role in the colonization of pathogens in a host intestine has not been fully elucidated. Here, we investigated the effect of polystyrene MPs (PS-MPs) on the colonization levels of Aeromonas veronii, a typical aquatic pathogen, in the loach (Misgurnus anguillicaudatus) intestine. Multiple types of MPs were observed to promote the intestinal colonization of A. veronii, among which PS-MPs exhibited the most significant stimulating effect (67.18% increase in A. veronii colonization). PS-MPs inflicted serious damage to the intestinal tracts of loaches and induced intestinal microbiota dysbiosis. The abundance of certain intestinal bacteria with resistance against A. veronii colonization decreased, with Lactococcus sp. showing the strongest colonization resistance (73.64% decline in A. veronii colonization). Fecal microbiota transplantation was performed, which revealed that PS-MPs induced intestinal microbiota dysbiosis was responsible for the increased colonization of A. veronii in the intestine. It was determined that PS-MPs reshaped the intestinal microbiota community to attenuate the colonization resistance against A. veronii colonization, resulting in an elevated intestinal colonization levels of A. veronii.

Quorum sensing signal autoinducer-2 promotes hydrogen peroxide degradation in water by Gram-positive bacteria.

Hydrogen peroxide is widely used to remedy bacterial and parasitic infections, but its excessive use will cause severe damage to aquatic animals. Moreover, there is no safe, efficient and low-cost method to degrade residual hydrogen peroxide in water. Here we developed a hydrogen peroxide removal mechanism by which autoinducer-2 (AI-2), a quorum sensing signal molecule that can promote the hydrogen peroxide degradation by Gram-positive bacteria. Here, we investigated the promotion effect of AI-2 on hydrogen peroxide degradation by Deinococcus sp. Y35 and the response of the antioxidant system. We further sought to understand the key mechanism underlying the promotion effect of AI-2 on hydrogen peroxide degradation is that, AI-2 contributed to the resistance of strain Y35 to oxidative stress induced by hydrogen peroxide, and altered membrane permeability of strain Y35 that allowed more hydrogen peroxide to enter bacterial cells and be degraded. Additionally, AI-2 can also encourage multiple Gram-positive bacteria to degrade hydrogen peroxide. Accordingly, our study serves as a reference for the regulation mechanism of the signal molecule AI-2 and provides the development of new strategies for hydrogen peroxide degradation.

Elimination of Microcystis aeruginosa through Leuconostoc mesenteroides DH and its underlying mechanism.

Microcystis aeruginosa is ubiquitously found in various water bodies and can produce microcystins (MCs), which threaten the health of aquatic animals and human beings. The elimination of excessive M. aeruginosa is beneficial for the protection of the ecosystems and public health. In this regard, algae-lysing bacteria have been extensively studied as an effective measure for their eradication. However, the active substances generated by algae-lysing bacteria are limited. For this study, we reveal that the phenyllactic acid (PLA) produced by Leuconostoc mesenteroides DH exhibits high efficacy for the removal of M. aeruginosa, and explore the elimination mechanism of strain DH on M. aeruginosa. It was found that a cell-free supernatant of strain DH possessed high removal activities against M. aeruginosa. Abundant reactive oxygen species were induced in algal cells following exposure to strain DH supernatant, as well as superoxide dismutase and catalase responses. Furthermore, the integrity of algal cell membranes and photosynthesis was seriously damaged. Interestingly, added exogenous eugenol significantly inhibited the synthesis of active substance produced by strain DH, which further identified that PLA is one of the active substances that contribute to the eradication of M. aeruginosa on the basis of metabolomics analysis. Our finding demonstrated, for the first time, that PLA (as an anti-cyanobacterial compound) can be used for the removal of M. aeruginosa, which provides a theoretical basis for the control of M. aeruginosa.

Voluntary Vaccination through Self-organizing Behaviors on Locally-mixed Social Networks.

Voluntary vaccination reflects how individuals weigh the risk of infection and the cost of vaccination against the spread of vaccine-preventable diseases, such as smallpox and measles. In a homogeneously mixing population, the infection risk of an individual depends largely on the proportion of vaccinated individuals due to the effects of herd immunity. While in a structured population, the infection risk can also be affected by the structure of individuals' social network. In this paper, we focus on studying individuals' self-organizing behaviors under the circumstance of voluntary vaccination in different types of social networks. Specifically, we assume that each individual together with his/her neighbors forms a local well-mixed environment, where individuals meet equally often as long as they have a common neighbor. We carry out simulations on four types of locally-mixed social networks to investigate the network effects on voluntary vaccination. Furthermore, we also evaluate individuals' vaccinating decisions through interacting with their "neighbors of neighbors". The results and findings of this paper provide a new perspective for vaccination policy-making by taking into consideration human responses in complex social networks.