Abstract
With the widespread occurrence of aquaculture diseases and the broad application of antibiotics, drug-resistant pathogens have increasingly affected aquatic animals’ health. Marine probiotics, which live under high pressure in a saltwater environment, show high potential as a substitute for antibiotics in the field of aquatic disease control. In this study, twenty strains of non-hemolytic bacteria were isolated from the intestine of wild oysters and perch, and a model of Caenorhabditis elegans infected by Vibrio anguillarum was established. Based on the model, ML1206, which showed a 99% similarity of 16S rRNA sequence to Planococcus maritimus, was selected as a potential marine probiotic, with strong antibacterial capabilities and great acid and bile salt tolerance, to protect Caenorhabditis elegans from being damaged by Vibrio anguillarum. Combined with plate counting and transmission electron microscopy, it was found that strain ML1206 could significantly inhibit Vibrio anguillarum colonization in the intestinal tract of Caenorhabditis elegans. Acute oral toxicity tests in mice showed that ML1206 was safe and non-toxic. The real-time qPCR results showed a higher expression level of genes related to the antibacterial peptide (ilys-3) and detoxification (ugt-22, cyp-35A3, and cyp-14A3) in the group of Caenorhabditis elegans protected by ML1206 compared to the control group. It is speculated that ML1206, as a potential probiotic, may inhibit the infection caused by Vibrio anguillarum through stimulating Caenorhabditis elegans to secrete antibacterial effectors and detoxification proteins. This paper provides a new direction for screening marine probiotics and an experimental basis to support the potential application of ML1206 as a marine probiotic in aquaculture.
Highlights
In recent years, with the development of the aquaculture industry and continuous expansion of intensive aquaculture, aquacultural diseases have increasingly been seen, which has caused substantial economic losses to the whole maricultural industry
To ensure there would be no hemolytic activity for probiotics upon acting on the host, which could lead to rupture of the host’s red blood cells, a hemolytic test was performed as a prerequisite, to screen and eliminate bacterial strains with active hemolytic activity
Probiotics as microecological agents have been more widely used to enhance the immune function of aquatic animals, reduce the occurrence of diseases, purify water, and promote green and sustainable development in aquaculture [37]
Summary
With the development of the aquaculture industry and continuous expansion of intensive aquaculture, aquacultural diseases (such as bacterial diseases, fungal diseases, and viral diseases [1,2,3,4]) have increasingly been seen, which has caused substantial economic losses to the whole maricultural industry. To reduce the occurrence of aquacultural diseases, antibiotics have been widely used in the aquacultural industry for both preventive and therapeutic purposes. Long-term usage of antibiotics will lead to the drug resistance of pathogens and environmental pollution [5]. Probiotics are widely considered as microorganisms with health benefits to the host, and are often used for disease control in aquaculture, especially for bacterial diseases. A diverse variety of Gram-positive and Gram-negative bacteria can be probiotics, including. Bacillus subtilis [6], Lactobacillus spp. The various disease control mechanisms by probiotics include enhancement of immune response [9,10], competitive adhesion [11,12], pathogen antagonism [13,14], and disturbance of quorum sensing system [15]
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