Effect of orally administered probiotic E. coli strain Nissle 1917 on intestinal mucosal immune cells of healthy young pigs

Several beneficial effects of probiotics have been described in studies using rodent disease models and in human patients; however, the underlying mechanisms remained mostly unclear. Only a few studies focused on the effects of probiotics on the intestinal mucosal immune system. Here, we studied the effect of the probiotic strain E. coli Nissle 1917 (EcN) administered orally to young pigs at two concentrations (10(9) and 10(11)CFU/d for 21 days) on the gut-associated lymphatic tissue. This probiotic strain was shown recently to reduce recurrence of inflammation in ulcerative colitis patients. We quantified the number and distribution of intestinal immune cells (granulocytes, mast cells, CD4+, CD8+, CD25+, IgA+ lymphocytes) and the mucosal mRNA expression of cytokines (IFN-gamma, TNF-alpha, TGF-beta, IL-10) and antimicrobial peptides (PR-39, NK-lysin, prepro-defensin-beta 1, protegrins). The number and distribution of cells were highly different between small intestinal and colon segments in all groups, but were not influenced by EcN, except high dose EcN fed pigs (10(11) CFU/d) showing an increase in mucosal CD8+ cells in the ascending colon. The mRNA analysis revealed no changes associated with EcN feeding. In conclusion, according to our analyses EcN has only minor effects on the distribution of mucosal immune cells in the gut of healthy individuals. The well-established preventive effects of EcN might therefore be relate to other mechanisms than simple modulation of immune cell distribution.     

Fungal toxins affect the fitness and stable isotope fractionation of Collembola

We investigated the effect of the fungal toxin sterigmatocystin on the fitness and stable isotope fractionation of two Collembola species (Folsomia candida and Heteromurus nitidus) feeding on mixed vs. single diets. Four knock out mutants of Aspergillus nidulans with the sterigmatocystin production blocked at different steps along the biosynthetic pathway were combined in mixed diets with either the high quality fungus Cladosporium cladosporioides or the low quality fungus A. nidulans (wildtype). Using fungi labeled with stable isotopes (¹³C and ¹⁵N) we evaluated the incorporation of carbon and nitrogen from individual fungi. We hypothesised that (i) Collembola fitness decreases with the putative toxicity of the fungi (ii) Collembola benefit from ingestion of mixed diets due to toxin dilution and (iii) fractionation of ¹³C and ¹⁵N is more pronounced in more toxic diets. Mixed diets did not uniformly improve fitness. Toxin dilution, however, played an important role in Collembola fitness. The fractionation of ¹³C and ¹⁵N varied with sterigmatocystin mutant strains, and Collembola species often differed from the expected enrichment per trophic level. The results show that fungal toxin production may affect stable isotope fractionation, presumably by altering consumer excretion rates necessary for detoxification.     

Olfactory cues associated with fungal grazing intensity and secondary metabolite pathway modulate Collembola foraging behaviour

Fungal secondary compounds play an important role for springtail food choice and fitness. Little is known, however, on the role of olfactory cues for Collembola foraging behaviour and whether Collembola can olfactorily perceive volatiles associated with fungal secondary metabolite pathways. We investigated the ability of three species of Collembola (Folsomia candida, Heteromurus nitidus and Supraphorura furcifera) to use olfactory cues for discriminating between fungi of different phylogenetic affiliation (Aspergillus nidulans, Cladosporium cladosporioides, Ascomycota; Laccaria bicolor, Basidiomycota) and toxicity using fungal strains of A. nidulans with reduced secondary metabolite production. Furthermore, we studied if olfactory cues from hyphae injured by grazing affect the foraging behaviour of Collembola. We hypothesized that (i) Collembola are able to olfactorily perceive and respond to fungal species/strains with different secondary metabolite pathways and that (ii) Collembola are able to sense fungal mycelia injured by grazing. Each of the Collembola species studied preferentially oriented their foraging towards fungal strains of A. nidulans with suppressed secondary metabolites, and in particular towards the mutant where the global regulator for secondary metabolites (ΔlaeA) has been silenced. Two of the three Collembola species (H. nitidus and S. furcifera) sensed olfactory cues of previously grazed fungi and moved towards ungrazed fungi, however, the response of S. furcifera was restricted to fungi extensively exposed to grazing (5 days) suggesting that the response varies between Collembola species.Overall, the results support the first and second hypothesis indicating that Collembola (1) are able to olfactorily differentiate fungi of different toxicity and move towards more palatable fungi, and (2) showed a lesser preference for fungi previously exposed to grazing.