The lip gene contributes to the virulence of Aeromonas veronii strain TH0426.

Aeromonas veronii (A. veronii) is a pathogen that can infect aquatic organisms and mammals and has caused irrecoverable economic losses to the aquaculture industry. The results of an epidemiological investigation showed that the number of cases of A. veronii have increased gradually in recent years, and its drug resistance and virulence has shown an upward trend. In this study, we constructed an A. veronii mutant strain Δlip, by homologous recombination and studied its function. The results showed that there was no significant difference in the biofilm formation ability between the Δlip and the wild-type strain, but the toxicity of the Δlip to EPC cells and its ability to adhere to EPC cells were significantly reduced. The LD50 value of the Δlip to zebrafish was 7.40-fold higher than that of the wild-type strain. In addition, after 24 h and 72 h, the bacterial loads of the Δlip in the organs of crucian carp were significantly lower than those in the wild-type strain. In conclusion, the mutant strain Δlip led to a decrease in the adhesion and virulence of the wild-type strain, which lays a foundation to further understand lip gene function and the pathogenic mechanism of A. veronii.

Construction and immune efficacy of recombinant Lactobacillus casei expressing OmpAI of Aeromonas veronii C5-I as molecular adjuvant.

Despite advancements in diagnosis and control, Aeromonas infections are considered the leading cause of economic aquaculture loss. In this study, to enhance DNA vaccine efficacy against Aeromonas infections, a fused DNA fragment (1504 bp) of the OmpAI gene from Aeromonas veronii (A. veronii) combined with the C5-I gene from the common carp was generated with splicing by overlapping PCR (SOE-PCR) and expressed in Lactobacillus casei strain CC16. Protein C5-I served as a molecular adjuvant for the antigen OmpAI. Two types of fusion antigens were developed (anchored and secretory). Generally, anchored-type antigens are more effective in inducing immune responses in fish than secretory antigens. Western blot analysis showed that the bands of both antigens were present at 58 kDa. After oral immunization, both DNA vaccines enhanced the serum levels of AKP, ACP, SOD and LZM in immunized carp; the genes IL-10, IL-1ß, TNF-α, and IFN-γ in the heart, liver, spleen, head kidney, and intestinal tract were upregulated; and a stronger phagocytic response was triggered in immunized fish. In addition, common carp administered the fused antigens were more protected from Aeromonas challenge (60-73.3% protection). Recombinant Lactobacillus bacteria expressing the fused protein showed a greater propensity for colonization in the intestinal tract in immunized fish than in controls. Here, we provide a promising approach to improve DNA vaccine immunogenicity for protecting common carp from A. veronii infections.

[Water environmental simulation of main contaminations in the Qiantang River at low water period].

Technical framework for water environment simulation of contaminations is established based on visualization and a spatial environmental model is built. The main two contaminations, namely NH: -N and TP, are simulated on the platform of MapInfo and Delft3D in the Qiantang River at the low water period, to analyze its space-time diversity. For NH4+ -N, the measured values are 0.19 mg/L and 0.66 mg/L larger than simulated values at the Lanjiang River mouth and the Yanlingwu, 0.16 mg/L, 0.54 mg/L and 0.49 mg/L smaller at the Zhaixi, the Yushan and the Yuanpu. For TP, the measured values are 0.13 mg/L and 0.14 mg/L higher than simulated values at the Meicheng Water facility and Yanlingwu. However, the measure values are slightly lower than simulated ones at Zhaixi, Yushan, Puyang River mouth and Yuanpu, the trend of which accords with actual situation. The results indicate that the contaminations of the Qiantang Reach mostly come from the Lanjiang River, the Fuchun River and the Puyang River on the upstream, among which the Lanjiang River and the Puyang River have a very high concentration of polluted materials, which means bad water quality, and influence the water downstream. The Lanjiang River becomes the chief contaminative source in the Fuchun River. When the discharge from the Xin'an River Dam is small, the recirculation region may be formed and makes part of the Xin'an Reach contaminated. Otherwise, when the discharge is large, the water quality in the Fuchun River is apparently improved. And the Puyang River, which brings the contaminations from the upstream, along with the polluted water let into it from the industries along the reach, has significant impacts on the water quality in Qiantang Reach.