Communities of symbiotic microorganisms that colonize the gastrointestinal tract play an important role in food digestion and protection against opportunistic microbes. Diet diversity increases the number of symbionts in the intestines, a benefit that is considered to impose no cost for the host organism. However, less is known about the possible immunological investments that hosts have to make in order to control the infections caused by symbiont populations that increase because of diet diversity. Using taxonomical composition analysis of the 16S rRNA V3 region, we show that enterococci are the dominating group of bacteria in the midgut of the larvae of the greater wax moth (Galleria mellonella). We found that the number of colony-forming units of enterococci and expressions of certain immunity-related antimicrobial peptide (AMP) genes such as Gallerimycin, Gloverin, 6-tox, Cecropin-D and Galiomicin increased in response to a more diverse diet, which in turn decreased the encapsulation response of the larvae. Treatment with antibiotics significantly lowered the expression of all AMP genes. Diet and antibiotic treatment interaction did not affect the expression of Gloverin and Galiomicin AMP genes, but significantly influenced the expression of Gallerimycin, 6-tox and Cecropin-D. Taken together, our results suggest that diet diversity influences microbiome diversity and AMP gene expression, ultimately affecting an organism9s capacity to mount an immune response. Elevated basal levels of immunity-related genes (Gloverin and Galiomicin) might act as a prophylactic against opportunistic infections and as a mechanism that controls the gut symbionts. This would indicate that a diverse diet imposes higher immunity costs on organisms.

The transcription factor NF-ATc that controls gene expression in T lymphocytes and embryonic cardiac cells is expressed in three prominent isoforms. This is due to alternative splice/polyadenylation events that lead to the predominant synthesis of two long isoforms in naive T cells and a shorter NF-ATc isoform in effector T cells. Whereas the previously described isoform NF-ATc/A contains a relatively short C terminus, the longer isoforms, B and C, span extra C-terminal peptides of 128 and 246 aa, respectively. We show here that in addition to the strong N-terminal trans-activation domain, TAD-A, which is common to all three NF-ATc isoforms, NF-ATc/C contains a second trans-activation domain, TAD-B, in its C-terminal peptide. Various stimuli of T cells that induce the activity of TAD-A also enhance the activity of TAD-B, but, unlike TAD-A, TAD-B remains unphosphorylated by protein from 12-O-tetradecanoyl 12-phorbol 13-acetate-stimulated T cells. The shorter C-terminal peptide of isoform NF-ATc/B exerts a suppressive transcriptional effect. These properties of NF-ATc/B and -C might be of importance for gene regulation in naive T lymphocytes in which NF-ATc/B and -C are predominantly synthesized.