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[This corrects the article DOI: 10.3389/fmicb.2023.1090899.].

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Introduction: The impact of parasites on gut microbiota of the host is well documented, but the role of the relationship between the parasite and the host in the formation of the microbiota is poorly understood. This study has focused on the influence that trophic behavior and resulting parasitism has on the structure of the microbiome. Methods: Using 16S amplicon sequencing and newly developed methodological approaches, we characterize the gut microbiota of the sympatric pair of whitefish Coregonus lavaretus complex and the associated microbiota of cestodes parasitizing their intestine. The essence of the proposed approaches is, firstly, to use the method of successive washes of the microbiota from the cestode's surfaces to analyze the degree of bacterial association to the tegument of the parasite. Secondly, to use a method combining the sampling of intestinal content and mucosa with the washout procedure from the mucosa to understand the real structure of the fish gut microbiota. Results and discussion: Our results demonstrate that additional microbial community in the intestine are formed by the parasitic helminths that caused the restructuring of the microbiota in infected fish compared to those uninfected. Using the desorption method in Ringer's solution, we have demonstrated that Proteocephalus sp. cestodes possess their own microbial community which is put together from "surface" bacteria, and bacteria which are weakly and strongly associated with the tegument, bacteria obtained after treatment of the tegument with detergent, and bacteria obtained after removal of the tegument from the cestodes.

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AIMS: The aim of the present study was to investigate the gastrointestinal (GI) microbiota and bacterium-specific fatty acid occurrence in the muscle and hepatic lipids of rainbow trout Oncorhynchus mykiss (Walbaum, 1792), both healthy and those naturally infected with bacterial pathogens. METHODS AND RESULTS: From June 2017 (L1) to September 2018 (L8), 74 specimens of rainbow trout Oncorhynchus mykiss (with an average weight from 139.2 ± 7.1 g (L1) to 2191.7 ± 85.1 g (L8)) were studied. Amplicon sequencing targeted to the V3-V4 region of 16S rRNA gene fragments is used for the identification of the taxonomic composition of gut bacterial communities. Firmicutes, Bacteroidetes, Proteobacteria, Tenericutes and Fusobacteria were the major phyla. Besides behavioural and physiological manifestations of the bacterial mixed disease (yersiniosis, pseudomonosis and flavobacteriosis), some disorders induced by both the infection and followed antibiotic treatment were detected in the host organism, including (1) a progressive decrease in the content of odd-chain saturated fatty acids of bacterial origin within the trout lipid molecules and (2) abnormalities in trout GI tract microbiota, such as the elimination of LAB and progressive occurrence of certain bacterial taxa, particularly Mycoplasmataceae. CONCLUSIONS: The GI bacterial flora varied principally due to Mycoplasmataceae and Lactobacillaceae, which could be considered in the search for bioindicators. The content of specific bacterium-derived fatty acids incorporated into the lipids of trout muscle and hepatic seems to be related to the prevalence of bacterial taxa, and their deficit could be regarded as an early warning sign of microbiota disturbance. SIGNIFICANCE AND IMPACT OF STUDY: Our results demonstrated that infectious disease and antibiotic treatment of reared species can cause a pertinent imbalance in their gut microbiota and reduce the abundance of specific fatty acids. This can be useful for the sustainable aquaculture industry due to the development of early indication technologies for rapid disease diagnosis.

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Microbioma Gastrointestinal , Oncorhynchus mykiss , Animales , Antibacterianos/farmacología , Bacterias/genética , Ácidos Grasos , Músculos , Oncorhynchus mykiss/microbiología , ARN Ribosómico 16S/genética

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Using the approach of sequencing the V3-V4 region of the 16S rRNA gene, we have analysed the bacterial diversity associated with the distinct compartments of the gastrointestinal tract of perch (Perca fluviatilis) and cestodes (Proteocephalus sp.) parasitizing their digestive tract. The dominant microbiota associated with cestodes (Proteocephalus sp.) was represented by bacteria from the genera Serratia, Pseudomonas and Mycoplasma. By comparing the associated microbiota of perch and cestodes, a clear difference in bacterial composition and diversity was revealed between the community from the stomach content and other parts of the gastrointestinal tract of fish. Microbiota associated with cestodes was not significantly different in comparison with microbiota of different subcompartments of perch (mucosa and content of intestine and pyloric caeca) (ADONIS, p > .05) excluding microbiota of stomach content (ADONIS, p ≤ .05). PICRUSt-based functional assessments of the microbial communities of perch and cestodes indicated that they mainly linked in terms of metabolism and environmental information processing and could play an important role in the nutrition and health of host.

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Infecciones por Cestodos/veterinaria , Enfermedades de los Peces/epidemiología , Enfermedades Gastrointestinales/veterinaria , Microbioma Gastrointestinal , Percas , Animales , Infecciones por Cestodos/epidemiología , Infecciones por Cestodos/parasitología , Femenino , Enfermedades de los Peces/parasitología , Enfermedades Gastrointestinales/epidemiología , Enfermedades Gastrointestinales/parasitología , Masculino , Percas/microbiología , Siberia/epidemiología

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Natural infection of 2 to 6-year-old perch with the cestode parasites Triaenophorus nodulosus was shown to have minor effects on the studied components of the antioxidant defense system, nucleic acids degradation, and carbohydrate metabolism enzymes in the liver of the fish. The level of infection of 1-4 parasite larvae per fish observed in wild population of perch was shown to be moderate in terms of its effect on the health of the host fish. The activity of hepatic enzymes ß-galactosidase, ß-glucosidase, cathepsin D, and glutathione S-transferase showed different responses in infected males and females, which indicates different potential resistance of fish to the stress exposure between genders.

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[This corrects the article DOI: 10.1007/s12639-019-01128-0.].