Nearly (?) sterile avian egg in a passerine bird Těšický, Martin Schmiedová, Lucie Krajzingrová, Tereza Gómez Samblás, María Mercedes Bauerová, Petra Kreisinger, Jakub Vinkler, Michal Egg microbiome Embryo Gastrointestinal tract microbiota During early ontogeny, microbiome affects development of the gastrointestinal tract, immunity, and survival in vertebrates. Bird eggs are thought to be (1) initially sterile (sterile egg hypothesis) and (2) colonized after oviposition through horizontal trans-shell migration, or (3) initially seeded with bacteria by vertical transfer from mother oviduct. To date, however, little empirical data illuminate the contribution of these mechanisms to gut microbiota formation in avian embryos. We investigated microbiome of the egg content (day 0; E0-egg), embryonic gut at day 13 (E13) and female faeces in a free-living passerine, the great tit (Parus major), using a methodologically advanced procedure combining 16S rRNA gene sequencing and microbe-specific qPCR assays. Our metabarcoding revealed that the avian egg is (nearly) sterile, but acquires a slightly richer microbiome during the embryonic development. Of the three potentially pathogenic bacteria targeted by qPCR, only Dietzia was found in E0-egg (yet also in negative controls), E13 gut and female samples, which might indicate possible vertical transfer. Unlike in poultry, we have shown that major bacterial colonization of the gut in passerines does not occur before hatching. We emphasize that protocols that carefully check for environmental contamination are critical in studies with low-bacterial biomass samples. 2024-04-22T07:25:05Z 2024-04-22T07:25:05Z 2023-12-19 journal article Martin Těšický, Lucie Schmiedová, Tereza Krajzingrová, Mercedes Gomez Samblas, Petra Bauerová, Jakub Kreisinger, Michal Vinkler, Nearly (?) sterile avian egg in a passerine bird, FEMS Microbiology Ecology, Volume 100, Issue 1, January 2024, fiad164, https://doi.org/10.1093/femsec/fiad164 https://hdl.handle.net/10481/90977 10.1093/femsec/fiad164 eng http://creativecommons.org/licenses/by-nc/4.0/ open access Atribución-NoComercial 4.0 Internacional Oxford University Press