## 3 Results  
### Bacterial Composition of Faecal Microbiota Transplant from the Healthy Donor  
NGS analysis of the FMT sample (Figure 1A) showed that 97% of the faecal microbiota consisted of the following three phyla: Firmicutes (45%), Actinobacteria (synonymum Actinobacteria93%), and Bacteroidetes (synonymum Bacteroidota19%). From among the other present phyla, we detected Proteobacteria (2%), and regarding phyla where their proportion in FMT did not exceed 1%, we detected Desulfobacteria and Verrucomicrobia (synonymum Verrucomicrobiota0.002%). The clustered heat map (Figure 1B) illustrates the hierarchical clustering of samples (FMT 1, 2) based on their relative proportions. The colour intensity ranges from dark blue (\(-6\)), representing the minimum relative abundance, to dark red (\(6\)), indicating the maximum relative abundance. The predominant families in the faecal microbiota of the donor included Bifidobacteriaceae, Ruminococcaceae, Coriobacteriaceae, Rikenellaceae, Sutterellaceae, Oscillospiraceae, and Lachnospiraceae (Figure 1B (1)). Within the strain Firmicutes, Oscillospirales (13%) was one of the most abundant orders, represented mainly by the family Ruminococcaceae (Figure 1B (1), 10%) with the genera _Faecalibacterium_, _Subdoligranulum_, and _CAG_-352 (Figure 1B (2)). Particularly noteworthy is the substantial proportion of significant butyrate producers, including representatives of species such as _Faecalibacterium prausnitzii_, _Coprooccus catus_, and _Eubacterium rectale_ (Figure 1B (3)). These species play a crucial role in maintaining intestinal health in humans. Additionally, the presence of _Streptococcus salivarius_ (Figure 1B (3),C (1)), known for its probiotic effects in preventing oral infections, is also worth mentioning. Other genera of the strain Firmicutes present in FMT were _Fusicatenbacter_, _Alistiques_, _Blautia_, _Roseburia_, _Oscillibacter_, _Enterococcus_, and genus _Romboutsia_ (Figure 1B (2)). Figure 1: Bacterial composition of faecal microbiota transplant from a healthy FMT donor (**A**). The Krona diagram depicts the result of taxonomic analysis of the FMT donor at the strain level. A heatmap of species abundance clustering (**B**). The heatmap shows the hierarchical clustering of samples based on the relative abundance. The relative values illustrated in the heatmap by colours: minimum relative abundance—dark blue (\(-6\)), maximum relative abundance—dark red (\(6\)), provide picture of abundance of clusters among two replicates same sample of FMT (FMT, \(n=2\)) at the level of (\(1\)) family, (\(2\)) genus, and (\(3\)) species. Taxonomy tree of FMT donors, expressed as a percentage of the relative abundance of species in the selected taxon (**C**). The first number below the taxonomic name represents the percentage in the entire taxon, while the second number represents the percentage in the selected taxon. In contrast to the phylum Firmicutes, which exhibited a more diverse composition of genera, Actinobacteria were predominantly represented by the family Bifidobacteriaceae (Figure 1B (1); 29.3%), with a high proportion of only one genus, _Bifidobacterium_ (Figure 1B (2)). The highest relative abundance was observed mainly in species known to significantly contribute to the maintenance of human gut health, including _Bifidobacterium adolescents_ (22.4%), _B. longum_ (4.7%), _B. catenulatum_ (1.25%), and _B. animalis_ (0.16%) (Figure 1C (2)). Analysis of data obtained by sequencing also revealed the presence of the most abundant families within the Bacteroidetes phylum, namely Rikenellaceae and Tannerellaceae (Figure 1B (1)), along with their beneficial species _Parobacteroides merdae_ and _Parobacteroides goldsteini_ (Figure 1B (3)). Additionally, the family Bacteroidetes with the genus _Bacteroides_, as well as the families Barnesiellaceae and Marinifilaceae, were also identified. NGS analysis of data confirmed that no pathogenic species were detected in the faecal microbiota transplant from the healthy donor.