Impacts of nitrite exposure and recovery on the intestinal organization, physiological indices, and microbial diversity of Litopenaeus vannamei

Nitrite constitutes a critical factor that constrains the growth and survival of shrimp. In the present investigation, we examined the dynamic alterations in intestinal tissue structure, physiological responses, and bacterial community composition due to nitrite exposure and subsequent recovery. Our findings indicated that short-term exposure to nitrite resulted in a significant reduction (P < 0.05) in the activity of the antioxidant enzyme catalase, accompanied by a notable increase (P < 0.05) in the activity of glutathione peroxidase. Furthermore the activities of the immune-related enzymes acid phosphatase and alkaline phosphatase exhibited significant declines (P < 0.05). Conversely, the activities of lactate dehydrogenase and pyruvate kinase were significantly elevated (P < 0.05) in order to provide energy for the shrimp's response to nitrite exposure. After recovery treatment, all enzyme activities progressively reverted to baseline control level. The exposure to nitrite inflicted a certain degree of damage to the intestinal tissue, resulting in the apparent shedding of the intestinal villi. After a recovery period of 48 h, the intestinal villi instigated a gradual restoration to their normal condition. Sequencing of 16S rRNA revealed that nitrite exposure resulted in significant alterations in the diversity of the intestinal microbiota, evidenced by a marked reduction in the Ace index and the Shannon index (P < 0.05). However, at the genus level, an increase in the abundance of potentially pathogenic bacteria, such as Vibrio, was observed after exposure, disrupting the functional integrity and stability of the shrimp intestinal microbiota to some extent. After 48 h of recovery, the dominant genus essentially recuperated to a level comparable to those of the control group. In addition, it was found that Nannocystis and Chromobacterium may assume crucial roles in the restoration of intestinal homeostasis. These findings provide a significant theoretical foundation for understanding the impacts of nitrite exposure and subsequent recovery on intestinal tissue.