Ptitsegradskaya, Sergiev Posad, Moscow Province, 141311 Russia, e-mail olga@vnitip.ru; 2JSC «Biotrof», Kolpino, St. Petersburg, 192288 Russia, e-mail nikonov@biotrof.ru Acknowledgements: Supported by grant from Russian Science Foundation (project ¹ 14-16-00140 «Modern views on the intestinal microflora of poultry in different diets: molecular genetic approaches») Received September 13, 2016 A b s t r a c t Microorganisms which inhabit gut play great role in providing with nutrients, antibiotics, hormones and vitamins necessary for poultry health and performance. <...> The structure of gut microflora in poultry embryos is of particular interest and debated because of very few publications on the problem. <...> Despite embryo intestine is commonly considered sterile there are several reports on gut colonization by microorganisms in embryos during ontogenesis. <...> Using T-RFLP (Terminal Restriction Fragment Length Polymorphism) analysis to generate a fingerprint of a microbial community we compared gut flora in chick embryos on days 6 and 17 to those in 26-day, 150-day and 300-day old Hisex White layers. <...> Clostridia, Bacteroides, Negativicutes, Actinomycetales, Bifidocteriales were also found in contrast to earlier reports of their presence only in chicks at hatching and in adult poultry gut. <...> Moreover, in the embryo gut we found the causal agents of dangerous animal disease, Burkholderia sp., Pseudomonas sp., Salmonella sp., Klebsiella sp. and Rickettsiales bacteria. <...> Interestingly, the embryo gut biodiversity on day 6 was higher as compared to day 17 (75±2.75 phylotypes vs 30±1.20 phylotypes). <...> In the layers aged 26, 150 and 300 days the diversity was much higher (over 175±8.12 phylotypes) as compared to embryos due to new members involved into gut bacterial community. <...> Moreover, the poultry aged 300 days was lower both in the total diversity and in the percentage of unidentified microorganisms when compared to 26-day and 150-day old hens. <...> In the adults, the predominating microbial taxa changed, in particular, Clostridia and Negativicutes became more abundant whereas Bacillales and Bifidobacteriales were depressed. <...> Our findings indicate gut colonization by Lactobacilales and pathogenic Listeria sp., Pantoea sp., Enterobacter sp., Mycoplasma sp., Acinetobacter sp., Pasteurellaceae, Campylobacteraceae <...>