Dr. Michelle M. Gehringer
DFG-Schwerpunktprogram SPP 1833 - Building a Habitable Earth
Expanding the “bio” in Biogeochemistry: Cyanobacteria and the Great Oxygenation Event.
Cyanobacteria are largely responsible for generating the oxygen in our present day atmosphere during the Great Oxygenation Event (GOE). Our project will investigate this process using a two pronged approach of growing cyanobacteria in the laboratory and comparing them to fossilised cyanobacteria in the geological record.
Dr Patricia Sanchez-Baracaldo assesses which strains of modern day cyanobacteria are most closely related to the earliest cyanobacterial species thought to have occurred during the transition to a more oxygen rich atmosphere. Dr. Claudia Colesie and I will measure CO2 uptake rates in cultures of selected cyanobacterial strains using reduced O2 levels existing prior to the GOE.
Cyanobacteria are experts at surviving changing environmental conditions. I will measure how they cope with the oxidative stress generated during photosynthesis using microsensors and molecular methods.
Prof. Martin Van Kranendonk of the University of New South Wales, Australia, has extensive expertise in studying the biogeochemical record covering the transition from the Archean into the Proterozoic. He and his research group, based within the Australian Astrobiology Centre, are providing support in obtaining samples for microscopic comparison against the morphologies of our cyanobacterial cultures grown under reduced oxygen availability. He is helping us to interpret our laboratory generated biogeochemical data against the established geological record.
This project is an excellent example of how scientists from different disciplines can contribute to a common goal, namely investigating the oxygenation of the Earth’s atmosphere during the late Archean, over 2.4 Ga.
Cyanobacteria and Symbiosis
The ability of cyanobacteria to form symbiotic associations with eukaryotes is well known. I undertook a study of the diversity of these symbiotic cyanobacteria within the roots of the Australian cycad species, Macrozamia, and identified that there is no specific association between host plant species and a specific cyanobacterial symbiont speices in plants growing in the wild. We identified the production of nodularin and a nodularin variant by 2 endosymbiont Nostoc species and further detected the production of these toxins in planta.
Cyanobacterial toxin production
I am currently investigating the regulation of hepatotoxin production in nitrogen fixing cyanobacterial species of Nodularia and Nostoc. The synthesis of microcystin and nodularin appear to be closely linked to environmental stress conditions, most notably light and nutrient availability. We are investigating the synthesis of toxin against the background of photosynthesis measured by CO2 uptake rates.
My initial work focused on the toxic effects of microcystin on the liver. I identified a role for glutathione peroxidase involvement in the detoxification of microcystin in mouse liver. Currently my PhD student and I are looking at the effects of BMAA on primary neurons and glial cells. We are the first group to identify BMAA induction of Reactive Oxygen Species in glial cells, which may contribute to the development of Alzheimer’s Disease (AD) and Amyotrophic Lateral Sclerosis (ALS).
The availability of nitrogen is crucial to life on earth. Elucidation of the diversity of nitrogen fixation genes in extreme environments may offer greater insights into the origins of this important biological pathway. My PhD student Reut Abramovich, is currently investigating the diversity of nifH genes in the stromatolites of Shark Bay and Paralana Hot Springs, Australia.
Dr Will Cuddy investigated the potential benefits of cyanobacteria on the growth of wheat plants during the course of his PhD.