LAUSR

Abstract Identifying the intestinal microorganisms involved in host immune functions could supply information for understanding the interaction between microbes and the host. The composition and comparison of the intestinal bacterial community in larval and adult Lethenteron reissneri are discussed. Significant differences could be observed in the bacterial community composition and the abundance of specific members. At the genus level, Aeromonas was detected as one of the dominant members in larvae, while Simplicispira was dominant in adult L. reissneri. Using isolated gut-derived Aeromonas as the antigen, the stimulation of adult L. reissneri could lead to the up-regulation of variable lymphocyte receptors (VLRs), such as VLRA, VLRB, and VLRC, in the mRNA level. Furthermore, the abundance of Aeromonas increased by 3.6 times after the lipopolysaccharide (LPS) stimulation in adult L. reissneri. Therefore, gut-derived Aeromonas were considered involved in the adaptive immune response of adult L. reissneri. The analysis of the bacterial community composition in the gut content of L. reissneri will broaden the understanding of this unique organism. The comparison of the intestinal bacterial composition between larval and adult L. reissneri will supply information for specific members that are involved in the adaptive immune system development in lampreys.