Effects of Tetraselmis subcordiformis (Wille) Butcher with antimicrobial peptides as feed additives on gut microbial community and immunity of turbot (Scophthalmus maximus L.)

Abstract

As harmless alternative of antibiotics, two antimicrobial peptides (AMPs), including anti-lipopolysaccharide factor isoform 3 (ALFPm3) and cathelicidin (CATHPb1), were co-expressed in the common fish food Tetraselmis subcordiformis. Lysates from T. subcordiformis transformant were able to inhibit the bacterial growth of Staphylococcus aureus, Vibrio parahaemolyticus, and Vibrio splendidus. To test the effects of AMPs in vivo, turbot (Scophthalmus maximus) underwent three dietary treatments, including commercial feeds (CON group), commercial feeds mixed with wild-type T. subcordiformis (WT group), and commercial feeds mixed with a mutant strain of T. subcordiformis (CSD group). Compared to CON group, both CSD and WT groups showed an increase in both the relative abundance and diversity of beneficial bacteria. The content of malondialdehyde was reduced and the enzymatic activities of lysozyme were increased in plasma. Comparisons of the biochemical factors in CSD group with those in CON group revealed that the relative abundance of Vibrio was decreased from 92.7% to 75.1%, and the number of bacteria containing the potentially pathogenic phenotypes was reduced. In the CSD group, the enzymatic activities of catalase and the expression levels of IgM, NKEF, IFNγ, MHC I, and IL-8R were higher compared to the WT group, whereas the levels of both TNFα and IL-1β were reduced. These results indicated that as an oral delivery vehicle for the AMPs, T. subcordiformis transformant improved the immunity, inflammatory response, and gut microbiome community of turbot.