Bacillus velezensis WLYS23 strain possesses antagonistic activity against hybrid snakehead bacterial pathogens

Abstract

Aim:The aims of this study were to screen an antagonistic probiotic for the prevention and control of bacterial diseases in snakehead fish and to evaluate the antimicrobial activities, biosafety and biocontrol effect of the antagonistic strain. Methods and Results: In this study, the WLYS23 strain exhibiting the most effective antagonistic properties against several fish pathogens was selected from the intestine of healthy snakehead fish. The strain was identified as Bacillus velezensis based on morphological, physiological and biochemical characteristics, and phylogenetic analysis. This strain showed amylase, cellulase, protease and lipase activities according to extracellular enzyme activity assays. Moreover, the cell-free extract of the WLYS23 strain exhibited strong antibacterial activity, with MICs of ≤64 lg ml À1 for most fish pathogens. Additionally, the cell-free extract was heat and pH stable, and resistant to protease, whereas their antimicrobial activities were significantly influenced by metal ions at high concentration. The WLYS23 strain and its cell-free extract were safe for snakehead and zebrafish. The disease resistance of snakehead fish was significantly increased following administration of the WLYS23 strain and its cell-free extract respectively. The complete genome of the WLYS23 strain was sequenced and found to harbour seven gene clusters encoding secondary metabolites with antimicrobial activity. Conclusion:The WLYS23 strain possesses great potential as a biocontrol agent, which can be commercially developed to improve disease control in freshwater aquaculture. Significance and Impact of the Study: Snakehead fish are important commercially farmed fish worldwide. However, the bacterial diseases caused by Aeromonas sp. and Nocardia seriolae in farmed snakehead fish lead to huge economic losses. Safe, economical and efficient probiotics are limited to prevent and control these diseases. Here, we provide a promising biocontrol agent with antagonistic activity against bacterial diseases of snakehead.

Development of a Multicomponent Microbiological Soil Inoculant and Its Performance in Sweet Potato Cultivation

“…Strain B. velezensis SZMC 24986 showed promising in vitro antagonism against all of the tested strains of fungal species known as plant pathogens. The antibacterial and antifungal effects of this species were described earlier [54][55][56], which supports this strain as a potential candidate for biocontrol purposes. Nitrogen-fixing bacteria play an important role in the soil, therefore they are becoming important parts of multicomponent soil inoculants [57].…”

Screening and characterization of Bacillus velezensis LB-Y-1 toward selection as a potential probiotic for poultry with multi-enzyme production property

“…The characterizations of LB-Y-1 were done using the method explained by Zhang D. F. et al (2021) with minor modifications. The characteristic colonies were gram stained, and bacteria were examined for morphology under a light microscope (Olympus CX40, Olympus Optical Co. Ltd., Hamburg, Germany) and a scanning electron microscopic (SEM, Inspect F50, FEI Company, Hillsboro, OR, United States; Bajpai et al, 2016 ).…”

“…In order to further examine the potential of LB-Y-1 to produce multi-enzymes, the activity of amylase and lipase in the LB-Y-1 were determined using the solid agar plate method ( Zhang D. F. et al, 2021 ). Briefly, after cultured in LB broth at 37°C overnight, the strain was stab-inoculated on the surface of LB agar plate containing 1.5% soluble starch or 1% triglyceride tributyrate (four replicates were made of each assay).…”

Screening of new Paenibacillus polymyxa S3 and its disease resistance of grass carp (Ctenopharyngodon idellus)

“…At the same time, the risk of fish disease has increased. Studies have shown that viruses, bacteria, fungi and parasites are the main causes of fish diseases, with bacterial diseases accounting for the highest proportion and causing the greatest losses (Garrido‐Olvera et al, 2022; Kibenge, 2019; Scholz et al, 2021; Zhang, Han, et al, 2021; Zhang, Xiong, et al, 2021). Aeromonas hydrophila is one of the pathogenic bacteria in fish, which can not only cause septicaemia in fish, but also pose a threat to human health.…”

“…In recent years, the development of fish probiotics has attracted the interest of many researchers, because these probiotics can not only inhibit the growth of fish pathogenic bacteria, but also without pollution to the environment. Zhang, Han, et al (2021); Zhang, Xiong, et al (2021) showed that Bacillus velezensis WLYS23 screened in the gut of hybrid snakehead has antagonism to 20 species of fish pathogens such as Aeromonas hydrophila , Aeromonas veronii , Aeromonas aquariorum , Aeromonas shigelloides and Nocardia seriolae . Streptomyces amritsarensis N1‐32 screened from soil by Li and Chen (2019) has an antagonistic effect on 10 fish pathogens such as Aeromonas hydrophila , Aeromonas veronii , Aeromonas caviae .…”