Bio:
Dr. Ondřej Prášil holds a Master's degree in Biophysics - Charles University (1987) and a PhD in Microbiology and Plant Physiology - University of South Bohemia (1995). He is currently the Senior Scientist of the Center Algatech at the Institute of Microbiology of the Czech Academy of Sciences (CAS). He has a background in Biophysics (Raman spectroscopy), with a focus on phytoplankton photosynthesis, working mainly on the following topics: Regulation and stress physiology of phytoplankton photosynthesis; Biological oceanography; Effects of global change on photosynthetic microorganisms; Ocean acidification and ecophysiology of algal and cyanobacterial photosynthesis; Development of biophysical, mostly optical instrumentation.
Dr. Ondřej Prášil is a lecturer (currently full Professor) of University of South Bohemia and the founder and head of the Center Algatech, Institute of Microbiology of CAS. He is an invited guest lecturer at courses overseas. He is also a member of the boards of the study programs Biophysics and Physiology (for Ph.D. students) at the Faculty of Science, University of South Bohemia in České Budějovice, Biophysics at the Palacký University in Olomouc and Biophysics at the Faculty of Mathematics and Physics, Charles University in Prague.
His research focuses on the ecophysiology of phytoplankton. He has published more than 120 papers (with 4500 citations and h-index 36 in Google Scholar). After working for several years on the ecophysiology of Crocosphaera watsonii (UCYN-B)–A widespread N2-fixing unicellular marine cyanobacterium, he worked on the ecophysiology of globally important diazotrophic cyanobacterium UCYN-A (nitroplast). Recent work focuses on the photophysiology of symbiosis between the haptophyte host and UCYN-A.
Absract：
The diazotrophic cyanobacterium UCYN-A shows unusual degree of metabolic streamlining1 suggesting obligate symbiosis with its haptophyte host Braarudosphaera bigelowii2. Recently, it has been shown that UCYN-A shows several signs of organellar integration with its host and has been named “nitroplast”3. I will report results of the laboratory experiment studying the metabolic coupling between the host and UCYN-A and how these results can be used in modelling its global distribution.
N2 fixation in UCYN-A occurs only during the light period and is strictly light dependent and stops immediately when cells are transferred into dark. The light-dependent rate of N2 fixation in UCYN-A saturates at significantly lower light intensities than the saturation of the photosynthesis of the host. N2 fixation of the symbiont seems to be under circadian rhythm, cells do not fix N2 when exposed to light during the subjective night period. The light-dependent N2 fixation of the symbiont continues for several hours even if the photosynthesis of the host is fully inhibited by DCMU. This indicates that there exists a pool of reduced carbon produced by the host that fuels N2 fixation even when its photosynthesis is inhibited. On the other hand, N2 fixation can be inhibited by compounds that block thylakoid membrane electron flow in the symbiont or that collapse the transmembrane gradient. Our results confirm the active and indispensable role of Photosystem 1 in supplying reductant and/or ATP to N2 fixation in UCYN-A.
