Brain-gut microbiota interactions are intensively studied in connection with various neurological and psychiatric diseases. While anorexia nervosa (AN) pathophysiology is not entirely clear, it is presumably linked to microbiome dysbiosis. We aimed to elucidate the gut microbiota contribution in AN disease pathophysiology. We analyzed the composition and diversity of the gut microbiome of patients with AN (bacteriome and mycobiome) from stool samples before and after renourishment, and compared them to healthy controls. Further, levels of assorted neurotransmitters and short-chain fatty acids (SCFA) were analyzed in stool samples by MS and NMR, respectively. Biochemical, anthropometric, and psychometric profiles were assessed. The bacterial alpha-diversity parameter analyses revealed only increased Chao 1 index in patients with AN before the realimentation, reflecting their interindividual variation. Subsequently, core microbiota depletion signs were observed in patients with AN. Overrepresented OTUs (operation taxonomic units) in patients with AN taxonomically belonged to Alistipes, Clostridiales, Christensenellaceae, and Ruminococcaceae. Underrepresented OTUs in patients with AN were Faecalibacterium, Agathobacter, Bacteroides, Blautia, and Lachnospira. Patients exhibited greater interindividual variation in the gut bacteriome, as well as in metagenome content compared to controls, suggesting altered bacteriome functions. Patients had decreased levels of serotonin, GABA, dopamine, butyrate, and acetate in their stool samples compared to controls. Mycobiome analysis did not reveal significant differences in alpha diversity and fungal profile composition between patients with AN and healthy controls, nor any correlation of the fungal composition with the bacterial profile. Our results show the changed profile of the gut microbiome and its metabolites in patients with severe AN. Although therapeutic partial renourishment led to increased body mass index and improved psychometric parameters, SCFA, and neurotransmitter profiles, as well as microbial community compositions, did not change substantially during the hospitalization period, which can be potentially caused by only partial weight recovery.

The change in the gut microbiome and microbial metabolites in a patient suffering from severe and enduring anorexia nervosa (AN) and diagnosed with small intestinal bacterial overgrowth syndrome (SIBO) was investigated. Microbial gut dysbiosis is associated with both AN and SIBO, and therefore gut microbiome changes by serial fecal microbiota transplantation (FMT) is a possible therapeutic modality. This study assessed the effects of FMT on gut barrier function, microbiota composition, and the levels of bacterial metabolic products. The patient treatment with FMT led to the improvement of gut barrier function, which was altered prior to FMT. Very low bacterial alpha diversity, a lack of beneficial bacteria, together with a great abundance of fungal species were observed in the patient stool sample before FMT. After FMT, both bacterial species richness and gut microbiome evenness increased in the patient, while the fungal alpha diversity decreased. The total short-chain fatty acids (SCFAs) levels (molecules presenting an important source of energy for epithelial gut cells) gradually increased after FMT. Contrarily, one of the most abundant intestinal neurotransmitters, serotonin, tended to decrease throughout the observation period. Overall, gut microbial dysbiosis improvement after FMT was considered. However, there were no signs of patient clinical improvement. The need for an in-depth analysis of the donor´s stool and correct selection pre-FMT is evident.

Recurrent aphthous stomatitis (RAS) is the most common disease of the oral mucosa, and it has been recently associated with bacterial and fungal dysbiosis. To study this link further, we investigated microbial shifts during RAS manifestation at an ulcer site, in its surroundings, and at an unaffected site, compared with healed mucosa in RAS patients and healthy controls. We sampled microbes from five distinct sites in the oral cavity. The one site with the most pronounced differences in microbial alpha and beta diversity between RAS patients and healthy controls was the lower labial mucosa. Detailed analysis of this particular oral site revealed strict association of the genus Selenomonas with healed mucosa of RAS patients, whereas the class Clostridia and genera Lachnoanaerobaculum, Cardiobacterium, Leptotrichia, and Fusobacterium were associated with the presence of an active ulcer. Furthermore, active ulcers were dominated by Malassezia, which were negatively correlated with Streptococcus and Haemophilus and positively correlated with Porphyromonas species. In addition, RAS patients showed increased serum levels of IgG against Mogibacterium timidum compared with healthy controls. Our study demonstrates that the composition of bacteria and fungi colonizing healthy oral mucosa is changed in active RAS ulcers, and that this alteration persists to some extent even after the ulcer is healed.

Annelids and mollusks, both in the superphylum of Lophotrochozoa (Bilateria), are important ecological groups, widespread in soil, freshwater, estuarine, and marine ecosystems. Like all invertebrates, they lack adaptive immunity; however, they are endowed with an effective and complex innate immune system (humoral and cellular defenses) similar to vertebrates. The lack of acquired immunity and the capacity to form antibodies does not mean a lack of specificity: invertebrates have evolved genetic mechanisms capable of producing thousands of different proteins from a small number of genes, providing high variability and diversity of immune effector molecules just like their vertebrate counterparts. This diversity allows annelids and mollusks to recognize and eliminate a wide range of pathogens and respond to environmental stressors. Effector molecules can kill invading microbes, reduce their pathogenicity, or regulate the immune response at cellular and systemic levels. Annelids and mollusks are “typical” lophotrochozoan protostome since both groups include aquatic species with trochophore larvae, which unite both taxa in a common ancestry. Moreover, despite their extensive utilization in immunological research, no model systems are available as there are with other invertebrate groups, such as Caenorhabditis elegans or Drosophila melanogaster, and thus, their immune potential is largely unexplored. In this work, we focus on two classes of key soluble mediators of immunity, i.e., antimicrobial peptides (AMPs) and cytokines, in annelids and bivalves, which are the most studied mollusks. The mediators have been of interest from their first identification to recent advances in molecular studies that clarified their role in the immune response.