Comparisons of mammalian gut microbiota across different environmental conditions shed light on the diversity and composition of gut bacteriome and suggest consequences for human and animal health. Gut bacteriome comparisons across different environments diverge in their results, showing no generalizable patterns linking habitat and dietary degradation with bacterial diversity. The challenge in drawing general conclusions from such studies lies in the broad terms describing diverse habitats ("wild", "captive", "pristine"). We conducted 16S ribosomal RNA gene sequencing to characterize intestinal microbiota of free-ranging sympatric chimpanzees and gorillas in southeastern Cameroon and sympatric chimpanzees and gorillas in a European zoo. We conducted participant-observation and semi-structured interviews among people living near these great apes to understand better their feeding habits and habitats. Unexpectedly, bacterial diversity (ASV, Faith PD and Shannon) was higher among zoo gorillas than among those in the Cameroonian forest, but zoo and Cameroonian chimpanzees showed no difference. Phylogeny was a strong driver of species-specific microbial composition. Surprisingly, zoo gorilla microbiota more closely resembled that of zoo chimpanzees than of Cameroonian gorillas. Zoo living conditions and dietary similarities may explain these results. We encourage multidisciplinary approach integrating environmental sampling and anthropological evaluation to characterize better diverse environmental conditions of such investigations. Over the last decade, numerous studies have demonstrated the importance of environmental changes on the mammalian gut microbiome, which is strongly associated with host metabolic, immune, and neurological functions 1. Broad-ranging influences, including host genetics, living conditions, diet, stress, and antibiotic use can affect gut microbial diversity 2-5. Among these influences, diet and living conditions have been evaluated for human and animal populations, entailing significant effects on gut microbiota and consequences for human and animal health. Adverse microbial profile shifts, for instance, have been associated with dysbiosis and wide-ranging diseases among human beings, from obesity to pediatric environmental enteropathy, and from autism to asthma 2,6,7. Outside of laboratory conditions, disentangling the effects of living and dietary conditions on gut microbial composition from other influences remains a complex question. In humans, such questions have catalyzed multiple studies comparing environmental and gut microbiota between "westernized" and "rural" peoples 8-10. Among other mammalian populations, degradation in habitat quality affects the diversity of available flora and fauna for consumption, and in some cases, is associated with declines in microbial gut composition 11-14. Microbiome OPEN