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Research
Our current themes are:
Ancient ocean analogue ecosystems
The overarching aim of our research is to unravel the explicit links between microenvironmental processes and global scale transitions in Earth’s redox landscape during the Precambrian. We therewith work towards a biologically nuanced perspective on Earth’s oxygenation history. What can we learn from modern ecosystems that represent analogues to the ancient Earth? How would microbial metabolic transitions and interactions have impacted oxygen accumulation in the context of changes in the redox state of Earth, evolutionary onset of metabolisms and changes in the Earth-Moon system through deep time? We approach these questions by constraining the potential role of different types of photosynthesis during major Earth oxygenation events by studying natural and artificial analogs of Precambrian ecosystems that have been understudied so far – namely microbial mats and algal blooms in anoxic lakes.


Critical in understanding the pattern of Earth’s oxygenation is the regulation of O2 production by cyanobacteria. Reduced sulfur, iron and arsenic are key controls on cyanobacterial photosynthesis, and were pervasive in productive coastal oceans and within microbial mats of the Precambrian. Arsenite or sulfide might have driven the first forms of photosynthesis. We therefore study (1) the kinetics of sulfide and arsenite oxidation dependent on e.g. light, (2) the molecular mechanisms underpinning the transition between oxygenic and anoxygenic photosynthesis and (3) the environmental and microbial controls on the balance between phototrophic modes in cyanobacterial mats and the impact on O2 export.



Environmental arsenic cycling
Arsenic contamination is of concern around the world due to its ubiquity and short- and long-term effects on human health. We are therefore in urgent need to limit human exposure to arsenic. Understanding its mobility in the environment is, however, hindered by the complex abiotic and biotic interactions of arsenic with e.g. iron, sulfur and organic matter. We therefore aim to develop novel methods that aid to resolve micro-scale processes in soil and sediment – processes that ultimately dictate arsenic redox cycling and mobility. We are particularly interested in using these tools to characterize light-driven arsenic cycling in benthic systems.


Another important focus is to develop an understanding of arsenic transfer in the larger food web. In high concentrations, arsenic is considered toxic and given its similarity to phosphate, it can easily be incorporated by organisms and may block and interfere with several vital processes. Particularly primary producers, such as cyanobacteria and chlorophytes, incorporate arsenic into carbohydrates and lipids. We aim to (1) characterize the type and origin of organic arsenicals in microbial mats in Andean lagoons and lakes and (2) track their transfer across the food web. Our model organism is Artemia salina, a salt shrimp, feeding on arsenic rich algae, in which we track the fate of organic arsenicals using a combination of classical and image-based mass spectrometry approaches, keeping an eye on its microbiome.


Miraculous diatoms
Diatoms are eukaryotic oxygenic phototrophs and among the most important primary producers globally. Due to their convoluted evolutionary history, diatoms are characterized by a highly unorthodox combination of genes derived from two secondary endosymbionts and from excessive horizontal gene transfer. Even the organization of organelles is exceptional, with, for instance, mitochondria and plastids in very close proximity within the cell. Thus, diatoms may drive processes that are unknown in other Eukaryotes, especially in the absence of light and photosynthesis. We therefore aim to illuminate the metabolic “dark side” of these phototrophs.


Benthic cycling of reactive oxygen species
Reactive oxygen species (ROS), such as hydrogen peroxide or superoxide, are ubiquitously produced in every aerobic environment and organism. While high concentrations can be cell damaging, ROS were also discovered to be key messenger molecules in cellular pathways and are thus now regarded as “Jekyll and Hyde” molecules. We are particularly interested in the biotic mechanisms of production and scavenging in illuminated sediments and mats. Our favourite study organisms are large benthic foraminifera that thrive in coral reef sediments and substantially shape the sedimentary ROS budget.
