Enhancement of vibriosis resistance in Litopenaeus vannamei by supplementation of biomastered silver nanoparticles by Bacillus subtilis
Shrimp production is devastated by vibriosis in much of aquaculture production around the world. These pathogens are highly virulent and cause serious viral outbreaks in shrimp culture. The potential antibacterial effects of Bacillus subtilis silver nanoparticles (AgNPs) from the gut of Litopenaeus vannamei were studied. The AgNPs are ~ 420 nm in UV-visible spectrum, of diameter 5-25 nm with smooth spherical shape (characterised by transmission electron microscopy) and 2θ values corresponding to the presence of silver crystal (X-ray diffraction spectrum). The AgNPs showed promising activity against Vibrio parahaemolyticus (21.25 ± 2.55 mm) and V. harveyi (19.27 ± 1.36 mm) as compared with B. subtilis, silver nitrate (AgNO3) and control. Four different experiments were conducted using different feeding behaviour of L. vannamei. In comparison to the untreated control group, final weight (14.89 ± 0.03 g), weight gain (9.36 ± 0.01), specific growth rate (SGR) 14.41 ± 0.09%, feed conversion ratios (FCR) 1.47 ± 0.12, higher survival and haemocyte counts were significantly greater in shrimp fed with AgNPs. The gills of the entire experimental animal showed morphological alteration under histopathological investigation. The AgNPs were then tested for shrimp challenged with the V. parahaemolyticus. Statistical analysis revealed significant differences in shrimp survival between AgNPs, B. subtilis and control group. In the infective experimental study, cumulative survival of the control group was (10 ± 0.321%) compared to shrimp treated with AgNPs (90.66 ± 0.523%) and (71 ± 0.577%) with B. subtilis. Subsequently, real-time PCR was observed for immune-related genes to determine the mRNA levels of prophenoloxidase (proPO), anti lipopolysaccharide factor (ALF2 and 4), peroxinectin (PE), superoxide dismutase (SOD), 18S, lipopolysaccharide and β -1,3-glucan-binding protein (LGBP) and serine protein (SP). The expression of all immune-related genes (mRNA levels) studied was significantly up-regulated in the AgNPs-diet shrimp in contrast to the B. subtilis and control. This study suggests that the biomastered AgNPs give a promising potential new tool for inhibiting vibriosis in shrimp culture.
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Article made possible through the contribution of E. Sivaramasamy et al.