BACKGROUND: We set out to explore associations between the stool bacteriome profiles and early-onset islet autoimmunity, taking into account the interactions with the virus component of the microbiome. METHODS: Serial stool samples were longitudinally collected from 18 infants and toddlers with early-onset islet autoimmunity (median age 17.4 months) followed by type 1 diabetes, and 18 tightly matched controls from the Finnish Diabetes Prediction and Prevention (DIPP) cohort. Three stool samples were analyzed, taken 3, 6, and 9 months before the first detection of serum autoantibodies in the case child. The risk of islet autoimmunity was evaluated in relation to the composition of the bacteriome 16S rDNA profiles assessed by mass sequencing, and to the composition of DNA and RNA viromes. RESULTS: Four operational taxonomic units were significantly less abundant in children who later on developed islet autoimmunity as compared to controls-most markedly the species of Bacteroides vulgatus and Bifidobacterium bifidum. The alpha or beta diversity, or the taxonomic levels of bacterial phyla, classes or genera, showed no differences between cases and controls. A correlation analysis suggested a possible relation between CrAssphage signals and quantities of Bacteroides dorei. No apparent associations were seen between development of islet autoimmunity and sequences of yet unknown origin. CONCLUSIONS: The results confirm previous findings that an imbalance within the prevalent Bacteroides genus is associated with islet autoimmunity. The detected quantitative relation of the novel "orphan" bacteriophage CrAssphage with a prevalent species of the Bacteroides genus may exemplify possible modifiers of the bacteriome.

BioMediTech Computational Biology University of Tampere Tampere Finland

Department of Pediatrics 2nd Faculty of Medicine Charles University Prague and University Hospital Motol Prague Czech Republic

Department of Pediatrics and Adolescent Medicine Turku University Hospital Turku Finland

Department of Pediatrics and Research Centre of Applied and Preventive Cardiovascular Medicine University of Turku Turku Finland

Department of Pediatrics University of Oulu and Oulu University Hospital Oulu Finland

Fimlab Laboratories Pirkanmaa Hospital District Tampere Finland

Immunogenetics Laboratory University of Turku and Turku University Hospital Turku Finland

School of Health Sciences University of Tampere Tampere Finland

School of Medicine Department of Virology University of Tampere Tampere Finland

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