Changes in the intestine barrier function of Litopenaeus vannamei in response to pH stress.

pH of water environment affects the survival of aquatic animals. Intestine barrier function influences the health of animals, which is related to its mucosa structure, immune components, and microbial communities. In this study, we investigated the histological structure, digestive and metabolic capacity, immune responses, and microbial composition in the intestine of Litopenaeus vanmei under three different conditions: control (pH 8.3), low pH stress (pH 6.9), and high pH stress (pH 9.7) for 72 h. The results showed both low and high pH stress disrupted the intestine morphological structure, and induced variations in the activities of digestive (AMS, LPS, Tryp, and Pep) and metabolic (HK, PK, CCO, and LDH) enzymes. Low and high pH stress also increased oxidative stress (MDA, LPO, PC, and ·O2- generation), and decreased the antioxidant enzyme activities (T-AOC, SOD, and GST); shrimp enhanced CAT activity and HSP70, Trx, MT and Fer gene transcripts as defense mechanism. Additionally, Immune confusion was also found in the shrimp intestine in response to low and high pH stress, including the antibacterial ability (T-NOS, PO, proPO, ALF, and Lys), pathogen recognition (TLR and Lec), apoptosis (Casp, IAP and p53), and mucus homeostasis (Muc-1, Muc-2, Muc-5AC, Muc-5B, and Muc-19). pH exposure also decreased the diversity of the intestine bacterial, disturbed the composition of microbiota, and decreased the microbial metabolite SCFA contents. Our results indicated that acute pH stress can impair the intestine barrier function of white shrimp, probably via destroying mucosa structure, confusing digestion and metabolism, inducing oxidative stress, disordering immunity, and disrupting the microbial composition.