Seleção e identificação de bactérias probióticas para aplicação no cultivo do camarão marinho Litopenaeus vannamei

Abstract

This study focused on selecting wild shrimp Bacillus for a probiotics use in shrimp farming. Bacillus circulans and Bacillus subtilis were isolated from the Farfantepenaeus subtilis intestine and have showed antagonism against Vibrio harveyi, Vibrio alginolyticus, Vibrio vulnificus and Vibrio mimicus in in vitro tests. Afterwards, these bacteria inhibited Vibrio parahaemolyticus ATCC 17802 (VP) in a wide pH and salinity range and produced lipase, amylase and protease in vitro showing that these Bacillus had the needed requirements for in vivo experiments. Thus, juveniles of Litopenaeus vannamei were grown according to the following diet: feed + B. subtilis (BS); feed + B. circulans (BC) and feed without bacteria (Control). Every 15 days samples were collected in order to quantify the bacteria and enzyme activity. After 45 days, the shrimp’s weight fed with BS and BC was significantly higher when compared to the control group. There was a significant increase in Bacillus spp. and a Vibrio spp. reduction in the intestine and hepatopancreas, especially after the 30th and 45th day mark. The trypsin, chymotrypsin, lipase and amylase also had significant increase in shrimp fed with BC and BS, especially after the 30th day mark. After 60 days, the immune system gene expression (proPO, LGBP and HEM) increased significantly in the shrimp fed with BS and BC. In addition to these experiments, the shrimp were infected (by injection) and challenged (water) against VP. The shrimp fed with BC diet had significantly higher survival rates after the injection and there were no differences after the challenge. The proPO expression did not differ between diets after infection or challenge. There was a Vibrio spp. reduction and a significant Bacillus spp. increase in the shrimps’ intestines which were fed with BC and BS diets after the challenge. The Bacillus spp. increase in shrimp fed with BC and BS diets suggest that there was colonization in the gastrointestinal tract during all the experimental period. This may have increased the enzyme activity improving digestion and weight gain, reduced the Vibrio spp. and increased the immune system gene expression, making the shrimp more resistant to infection (BC diet). Thus, B. circulans and B. subtilis have showed the potential for its application as probiotics in shrimp farming.