Brief description of Prof. Dr. Nicole Dubilier's achievements

Prof. Dr. Nicole Dubilier's research has fueled a major change in our understanding of the importance, diversity and function of symbiosis in marine environments. When she began working on symbioses between marine invertebrates and chemosynthetic bacteria in 1992, it was assumed that most invertebrates harbor one or at most two symbionts, and that only a few bacterial lineages were able to establish such symbioses in rare evolutionary events in a few animal groups. Her work has consistently revealed that the phylogenetic and functional diversity of chemosynthetic symbionts is much higher than previously recognized, that chemosynthetic bacteria have been highly successful in independently establishing symbioses with many animal hosts in convergent evolution, and that numerous animal groups benefit from such associations. Her research has highlighted the remarkable diversity of chemosynthetic symbioses in shallow-water environments such as coral reef sediments and sea-grass beds, habitats previously assumed to be driven only by photosynthesis. Thus, her research has challenged the paradigm that the establishment of chemosynthetic symbioses was a rare evolutionary event with only a few lineages of free-living bacteria able to establish associations with marine invertebrates. Her research has shown that multiple lineages of free-living bacteria from several phyla were able to successfully colonize hosts from numerous protists and animal groups, many of which occur in shallow-water environments. Finally, Prof. Dr. Dubilier's research has provided a critical contribution to marine biology by showing how wide-spread symbioses between marine invertebrates and bacteria are in terms of geography, animal and bacterial diversity, and habitats ranging from coastal sediments to the deep-sea.

Through interdisciplinary and collaborative efforts using a wide range of methods that includes high-resolution and correlative imaging analyses, metagenomics, metaproteomics, metabolomics, physiology, and deep-sea in situ analyses and experimentation, Prof. Dr. Nicole Dubilier has discovered novel symbionts and metabolic interactions in marine invertebrates from a wide range of shallow-water and deep-sea habitats. She provided the first evidence for a heterotrophic, sulfate-reducing endosymbiont in a marine worm from Mediterranean seagrass beds, and showed how this symbiont is engaged in syntrophic sulfur cycling with a co-occurring sulfur-oxidizing symbiont (Dubilier et al. Nature 2001). She described the first metagenomic analysis of a complex symbiotic microbial consortium as well the first genomic analysis of a chemosynthetic symbiont (Woyke et al. Nature 2006). She recently expanded our understanding of the energy sources that drive primary production in the teeming biological communities at hydrothermal vents by showing that hydrogen is used as an energy source by chemosynthetic symbionts (Petersen et al. Nature 2011, cover story). The significance of this finding is that the vast array of chemosynthetic symbioses were previously thought to be fuelled by only two energy sources, reduced sulfur compounds and methane. In 2012, she discovered novel pathways for coping with energy and nutrient limitation in chemosynthetic symbiotic bacteria. These include (i) a previously undescribed variant of the 3-hydroxypropionate bi-cycle pathway for CO2 fixation, (ii) the use of carbon monoxide as an energy source, a substrate previously not known to play a role in marine invertebrate symbioses, and (iii) novel energy efficient steps in CO2 fixation and sulfate reduction (Kleiner et al. PNAS 2012). More recently, she discovered novel bacterial symbionts in deep-sea mussels from asphalt volcanoes in the Gulf of Mexico that can use components of the oil and gas that are spewed from these tar seeps (Rubin et al. Nature Microbiology. 2017). Furthermore, this study revealed that free-living oil-degrading bacteria from the Deepwater Horizon oil well blow-out use the same pathways as the mussel symbionts to degrade oil components. These studies have challenged another paradigm, that only two energy sources fuel chemosynthetic symbiotic primary production, sulfide and methane. This paradigm existed since the first descriptions of chemosynthetic symbioses in the early 1980s. Prof. Dr. Dubilier's research has shown that hydrogen, carbon monoxide, and oil components can be used as an energy source by symbionts of mussels and worms and that the symbionts of other hydrothermal vent animals have the genetic potential to use some of these energy sources.

Given that many of the novel pathways that Prof. Dr. Dubilier has discovered appear to be widespread in free-living marine bacteria based on comparative genomic analyses, the relevance of her research is not limited to marine symbioses but expand our understanding of the function and metabolism of free-living microorganisms that drive primary production in marine environments.

In her most recent research, Prof. Dr. Dubilier challenged the paradigm that symbiont strain diversity destabilizes intimate mutualisms. Using high-throughput metagenomic and metatranscriptomic sequencing, her lab revealed that individual deep-sea mussels from hydrothermal vents host up to sixteen strains of intracellular symbionts (Ansorge et al. Nature Microbiology. 2019). These symbiont strains differed extensively in key functions, such as the use of energy and nutrient sources, aerobic and anaerobic respiration, toxin-related genes and defense mechanisms against viruses. Moreover, most of these strain-specific genes were expressed, underscoring their functional significance. By developing a theoretical framework that could help explain the stability of diverse symbiont populations in symbioses ranging from corals to the human gut, Prof. Dr. Dubilier's study provided a conceptual advance in our understanding of beneficial associations.

Prof. Dr. Dubilier's outstanding achievements are visible in her numerous invitations to give plenary and keynote lectures, and the prizes and recognitions she has received for her research. She was awarded Germany highest and most prestigious research prize, the Gottfried Wilhelm Leibniz Prize in 2014 (2.5 M€), and was the only scientist from an institute outside of the USA to receive the Gordon and Betty Moore Marine Microbiology Investigator Award (2.0 M€). Furthermore, she also received a highly competitive European Research Council Advanced Grant in 2014 (2.5 M€). She was elected to the European Molecular Biological Organization in 2018, the German National Academy of Sciences (Leopoldina) in 2015, and to the American Academy of Microbiology in 2013. She was the Chair (2016 and 2017) of the largest microbiology meeting in the world, ASM Microbe, has chaired two Gordon Research Conferences (2017), and is the current President of the largest society for microbial ecology, ISME. She has mentored numerous students that have gone on to build successful careers in academia and industry, and has been a strong contributor to community building through her service on numerous editorial boards, as well as advisory, panel and steering committees. Finally, she regularly engages in scientific outreach through TV and radio interviews, and talks for the general public.

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