Kremer Natacha

Research interests

The goal of my research is to bring an evolutionary perspective to the study of symbiosis, through the understanding of molecular interactions between partners.

Animals live in symbiosis with controlled bacterial communities in contrasting and changing environments. Symbionts can impact the phenotype of their host positively (e.g., by providing nutrients or protecting their host from pathogens) or negatively (by imposing a fitness cost). These partner interactions evolve in response to different selection pressures, making the associations dynamic along the continuum between parasitism and mutualism, and may also vary the degree of dependence between partners. I am particularly interested in the evolution of these symbiotic associations in response to different selection pressures, and in characterizing the molecular mechanisms underlying these changes.

Current projects

Understanding the interactions between the bedbug and its microbiota, to control its populations by breaking the symbiotic association

Funding Pack Ambition Recherche (région Auvergne Rhône-Alpes) 2019-2024 / SymBed Project/ Collaboration with BF2i and IZInovation / PhD Marius Poulain.

Funding ANR PRC 2021-2025 / FBI Project / Collaboration with BF2i and LECA. 

Rapid Evolution of symbiotic interaction in response to stress

Funding JCJC ANR 2017-2021 / RESIST Project / PhD Alexis Bénard

Impact of commensal and endosymbiotic bacteria on viral infection in insects

Funding Labex Ecofect 2017-2019 / ComEndoVir Projet/ Co-PI with F. Leulier (IGFL) / Post-doc Vincent Raquin

Previous research

Post-doc - Establishment and maintenance of the  squid/vibrio symbiosis

2010-2014. University of  Madison-Wisconsin, USA. Supervision : Margaret McFall-Ngai

During my post-doc, I worked on the mutualistic association between the sepiola Euprymna scolopes and the bioluminescent bacterium Vibrio fischeri, acquired anew each generation from the surrounding water. V. fischeri represents less than 0.1% of the bacterioplankton, but surprisingly, it is the only bacterium able to efficiently colonize the light organ of the squid. As the initiation of symbiosis can be easily reproduced in the laboratory, this association constitutes a particularly interesting model to study, in real time, the initial communication between the two partners of the symbiotic association. Using comparative transcriptomics and functional approaches, I characterized the first molecular dialogue between the two partners, just after their first contact.
Another interesting question is to understand how this symbiotic association is maintained, since we observe a daily phenomenon of expulsion then recolonization of bacteria in the light organ. This daily rhythm is associated with a coordinated change in gene expression in both the host and the bacteria, and it has been shown that the symbiotic population is maintained under hypoxic conditions. My second project was therefore to understand how the oxidative environment controls, and is controlled, by the symbiosis.

PhD - Evolution of dependancy in Wolbachia symbioses

2005-2009. University Lyon 1, Lyon, France. Supervision : Fabrice Vavre

During my thesis, I worked on the intracellular bacterium Wolbachia, which induces a wide range of phenotypic effects on its hosts, from facultative reproductive parasitism in arthropods to obligate mutualism in nematodes.
The hymenopteran Asobara tabida is one of the few species where Wolbachia is required for the ovogenesis of its arthropod host. It thus constitutes a particularly relevant study model to investigate the mechanisms underlying this recent evolutionary transition.
I first investigated the variability of Wolbachia dependence within the genus Asobara. Using various transcriptomic approaches, I then characterized the molecular mechanisms involved in the dependence between A. tabida and Wolbachia, and highlighted processes associated with oxidative stress, programmed cell death, and development. Finally, I examined the extent to which Wolbachia impacts the physiology of its host by studying iron metabolism in various symbiotic associations.
These studies revealed that dependence is not always associated with the contribution of new functions. Rather, it may reflect compensatory mechanisms in the host, in response to physiological perturbations induced by the presence of the symbiont. More generally, these results invite us to consider the effects and consequences of the presence of symbionts beyond the mechanisms that allow their persistence within populations.