Ruth Ley is the Director of the Department of Microbiome Science since 2016. She is also acting as co-Speaker for the Cluster of Excellence “Controlling Microbiomes to Fight Infection” with the University of Tübingen, Germany.

Ley received a BA in Integrative Biology from the University of California at Berkeley in 1992, a PhD from the University of Colorado, Boulder in 2001. She received a NRC-NASA Fellowship for post-doctoral work with Dr. Norman Pace at CU Boulder. In 2004 she moved to Washington University School of Medicine to work with Dr. Jeffrey Gordon on the human microbiome. She was named an Instructor in 2005 and a Research Assistant Professor at Washington University School of Medicine in 2007. In July 2008, Ley joined the Department of Microbiology at Cornell University as an Assistant Professor, and in 2013 became an Associate Professor with tenure in the Department of Molecular Biology and Genetics. She is a Member of the Max Planck Society since 2016.

Ley’s awards include a Fellowship in Science and Engineering from the David and Lucile Packard Foundation, a Beckman Young Investigator Award, the NIH Director’s New Innovator Award, the ISME Young Investigator Award, and the Ernst Jung Prize for Medicine. She is a member of EMBO, of the European Academy of Microbiology, and of the American Academy of Microbiology. In 2020 she was elected to the Leopoldina German National Academy of Sciences. She is the recipient of the 2020 Otto Bayer award, and an ERC Advanced Grant (2024). In 2026 she was elected a Fellow of the Royal Society.

Ruth Ley’s early contributions to microbiome research:

Ley was one of the very first to bring next-generation sequencing and molecular microbial diversity analysis from the environmental to the biomedical sciences. Environmental microbiology was leading in the development of molecular phylogenetic approaches to characterizing uncultured microbial diversity, so that far more was known about environmental than human microbiomes. In her early work, Ley demonstrated that the microbial ecology of the gut was shaped by, and contributed to, obesity. Her landmark studies on obesity catalysed an explosion of interest in human microbiome research and brought the field of microbial ecology into mainstream biomedical sciences. In 2005-2006, three key publications for the first time showed that the gut microbiome can drive disease (at that time, microbiome diversity studies conducted in humans did not include a disease context). First, Ruth Ley, Jeffrey Gordon and colleagues observed that the gut microbiome of genetically obese mice differed in composition from that of wildtype littermates (Ley et al., PNAS 2005). Ley made this discovery with techniques she brought to the laboratory of Gordon: this includes the first publication of the UniFrac tool developed by Cathy Lozupone and Rob Knight at CU Boulder. Subsequently, Peter Turnbaugh made the discovery that the microbiome of obese mice was sufficient to confer a metabolically disordered phenotype to germfree mouse recipients (Turnbaugh et al,, Nature 2006). Concurrently, Ley made the discovery that the same disordered microbiome was associated with obesity in humans (Ley et al., Nature 2006), thus making the mouse findings relevant in humans. These three early cornerstone publications launched the study of the microbiome in the context of disease on a large scale and across biomedical disciplines.

Ley set out to place the human microbiome in the context of mammalian evolution. She led a study to characterize gut microbial diversity for over 100 mammal species, vastly expanding the known mammalian gut diversity. She then analysed this diversity for the effects of diet, gut physiology, and host phylogeny [1]. She demonstrated that the human gut microbiome is in large part unique to humans and that host phylogeny explained a portion of the variation in bacterial diversity between mammalian microbiomes. Ley has since shown that this evolutionary relationship is not restricted to Bacteria but that many gut Archaea share an evolutionary history with their mammalian hosts [2]. Evidence suggests that many gut microbes are exquisitely tuned to the molecular environment of the human body and that disruption of these relationships can form a basis for disease.

Ley formulated a new set of research aims that have guided her research programme: to elucidate how gut microbial species relate to genotypic differences between human individuals, to identify bacterial and archaeal species that share an evolutionary history with humans, and to determine the molecular basis of long-term host-microbial relationships. Ley has approached these aims with a combination of population-level observations and molecular-level investigations in the laboratory. She links inter-microbial and microbial-host interactions at the molecular scale to patterns at population and evolutionary scales.