Response of the Litopenaeus vananmei intestinal bacteria and antioxidant system to rearing density and exposure to Vibrio paraheamolyticus E1

Abstract Intestinal bacteria and bacterial metabolic products are indispensable components of both invertebrate and vertebrate physiology, directly influencing many functions including host energy absorption and metabolism, intestinal barrier integrity and immune function. To investigate the influence of rearing density on shrimp intestinal health, antioxidant responses and disease susceptibility, we simultaneously monitored the dynamic changes of intestinal bacteria and antioxidant enzymes activities in Litopenaeus vananmei under two different rearing densities (400 and 800 shrimp/m3) and further investigated the difference in response to Vibrio paraheamolyticus E1 (VPE1) challenge. We showed that the phyla Proteobacteria, Bacteroidetes, Planctomycetes and Firmicutes were the predominant microflora in all treatment groups. Rearing L. vannamei at high density for 15 days resulted in the reduction of Bacteroidetes and Firmicutes and increase of Planctomycetes. At the genus level, high rearing density induced reduction of Pseudoalteromonas and Blastopirellula, and an increase of Photobacterium and Vibrio. Notably, the relative abundance of Ascidiaceihabitans and Flavobacteria NS10_marine_group increased in the low rearing density groups after VPE1 challenge, suggesting that these two types of bacteria might have an important role in resisting to VPE1 infection. High density stress caused suppression of total superoxide dismutase (T-SOD), catalase (CAT), and glutathione peroxidase (GPX) activities in shrimp. Hence, high density stress altered the functional composition of shrimp intestinal bacteria and damaged the antioxidant system, which increased pathogen susceptibility.