Dr. Anja Hemschemeier

Ass. Prof.
Room: ND 2/136
Phone: +49 234 32 - 23830
Academic Council
ORCID-iD: 0000-0001-8879-3348

Research focus

Stress responses of microalgae

Pro- and eukaryotic photosynthetically active microorganisms play an enormously important role for the ecosystem Earth. They are responsible for a large part of the photosynthetic formation of O2 and biomass and, in parallel, the assimilation of CO2, thus ensuring the survival of non-photosynthetic organisms, including humans. In their natural environment, all organisms experience stress frequently, such as the deficiency or excess of a nutrient. Because of the highly energetic processes involved in the light reactions, photosynthetic organisms must be particularly capable of responding to stress with appropriate defensive measures. Photosynthetic H2 production by microalgae represents such a stress response and serves to dissipate excess light energy to prevent oxidative damage to the cell. It is frequently induced upon nutrient deficiency, which is often accompanied by the establishment of O2-limited (hypoxic) conditions in algal cultures. Our early research has helped to understand the very elaborate fermentation metabolism of the microalga Chlamydomonas reinhardtii, which in its complexity is unusual for a eukaryote and of which H2 production is a part. In addition to providing fascinating insights into the ecology of this alga, which in turn is crucial for functional ecosystems, the study of the acclimation of microalgae to O2 deficiency is also biotechnologically relevant. On the one hand, some of the fermentation products (e.g. ethanol or lactic acid) represent industrially relevant substances, and on the other hand, algal cultures often experience hypoxic conditions in economically established cultivation tanks. In addition to charaterizing metabolism under these conditions, we are also trying to understand how the alga 'notices' that O2 is missing in the first place, and how it relays this information in the cell to activate the appropriate responses – often at the level of gene expression.

To this end, we apply transcriptomics to identify genes that respond particularly strongly to hypoxia. In the data sets, we have discovered genes and the encoded proteins, respectively, that are thought to be involved in nitric oxide (NO)-based signal transduction, such as a so-called NO-sensitive guanylate cyclase. This enzyme is very similar to the corresponding enzymes in animals and humans that are activated by NO and then form the secondary messenger cGMP. Since this messenger is ubiquitous, we also seek to identify target proteins that are directly or indirectly regulated by cGMP. Here, we suspect connections to the starch metabolism of C. reinhardtii and therefore characterize individual enzymes of starch breakdown and degradation.

Furthermore, in the course of this research we became aware of a particular class of hemoglobin-like proteins in the microalga. Contrary to common knowledge, almost all organisms – including unicellular and prokaryotic ones – possess hemoglobins and use them for many processes other than the well-known transport of O2, including catalytic formation or detoxification of NO. The microalga C. reinhardtii has twelve of these proteins, whose primary structures are very diverse. We are intrigued by the question of why a unicellular organism requires such a diversity of hemoglobins and are exploring the proteins in terms of the reactions they catalyze with a focus on possible involvement in NO metabolism. Ultimately, we want to understand the role they play in the alga. Since the discovery of the CRISPR/Cas system as a gene editing tool, we have for the first time the possibility to selectively knock out genes in C. reinhardtii or even to insert single mutations in order to decipher the cellular functions of our target proteins.


  • Hemschemier A, Posewitz MC, Happe T (2023) The Chlamydomonas Sourcebook (Third Edition), Volume 2 : Organellar and Metabolic Processes, Chapter 10 - Hydrogenases and hydrogen production. Pages 343-367
  • Posewitz MC, Atteia A, Hemschemier A, Happe T, Grossman AR (2023) The Chlamydomonas Sourcebook (Third Edition), Volume 2 : Organellar and Metabolic Processes, Chapter 9 - Metabolic networks during dark anoxia. Pages 317-341
  • Alavi G, Engelbrecht V, Hemschemeier A, Happe T (2023) The Alga Uronema belkae Has Two Structural Types of [FeFe]-Hydrogenases with Different Biochemical Properties. Int. J. Mol. Sci.
  • Duan J, Veliju A, Lampret O, Liu L, Yadav S, Apfel UP, Armstrong FA, Hemschemeier A, Hofmann E (2023) Insights into the Molecular Mechanism of Formaldehyde Inhibition of [FeFe]-Hydrogenases. J. Am. Chem. Soc.
  • Böhmer S, Marx C, Goss R, Gilbert M, Sasso S, Happe T, Hemschemeier A (2023) Chlamydomonas reinhardtii mutants deficient for Old Yellow Enzyme 3 exhibit increased photooxidative stress. Plant Direct
  • Duan J, Hemschemeier A, Burr DJ, Stripp ST, Hofmann E, Happe T (2022) Cyanide Binding to [FeFe]-Hydrogenase Stabilizes the Alternative Configuration of the Proton Transfer Pathway. Angew Chem Int Ed Engl.: e202216903 doi: 10.1002/anie.202216903
  • Böhmer S, Marx C, Gómez-Baraibar A, Nowaczyk MM, Tischler D, Hemschemeier A, Happe T (2020): Evolutionary diverse Chlamydomonas reinhardtii Old Yellow Enzymes reveal distinctive catalytic properties and potential for whole-cell biotransformations. Algal Research 50: 101970. doi: 10.1016/j.algal.2020.10197
  • Huwald D, Duda S, Gasper R, Olieric V, Hofmann E, Hemschemeier A (2020) Distinctive structural properties of THB11, a pentacoordinate Chlamydomonas reinhardtii truncated hemoglobin with N- and C-terminal extensions. J Biol Inorg Chem 25(2):267-283. doi: 10.1007/s00775-020-01759-2
  • Hemschemeier A, Happe T (2018): The plasticity of redox cofactors: from metalloenzymes to redox-active DNA. Nat Rev Chem 2:231–243.  doi: 10.1038/s41570-018-0029-3
  • Düner M, Lambertz J, Mügge C, Hemschemeier A (2018): The soluble guanylate cyclase CYG12 is required for the acclimation to hypoxia and trophic regimes in Chlamydomonas reinhardtii. Plant J 93(2):311-337.  doi: 10.1111/tpj.13779
  • Hemschemeier A (2017) Chlamydomonas: Anoxic Acclimation and Signaling. In Hippler M, ed, Chlamydomonas: Molecular Genetics and Physiology. Microbiology Monographs, vol 31. Springer, Cham, pp 155-199.  10.1007/978-3-319-66365-4_6
  • Scoma and Hemschemeier (2017) The hydrogen metabolism of sulfur deprived Chlamydomonas reinhardtii cells involves hydrogen uptake activities. Algal Research 26: 341-347.
  • Schuth N, Mebs S, Huwald D, Wrzolek P, Schwalbe M, Hemschemeier A, Haumann M (2017): Effective intermediate-spin iron in O2-transporting heme proteins. Proc Natl Acad Sci USA 1859:28-41.  10.1073/pnas.1706527114
  • Engelbrecht V, Rodríguez-Maciá P, Esselborn J, Sawyer A, Hemschemeier A, Rüdiger O, Lubitz W, Winkler M, Happe T (2017): The structurally unique photosynthetic Chlorella variabilis NC64A hydrogenase does not interact with plant-type ferredoxins. Biochim Biophys Acta 1858:771-778.  doi: 10.1016/j.bbabio.2017.06.004
  • Sawyer A, Bai Y, Lu Y, Hemschemeier A, Happe T (2017): Compartmentalisation of [FeFe]-hydrogenase maturation in Chlamydomonas reinhardtii. Plant J 90:1134-1143.  doi: 10.1111/tpj.13535
  • Huwald D, Schrapers P, Kositzki R, Haumann M, Hemschemeier A (2015): Characterization of unusual truncated hemoglobins of Chlamydomonas reinhardtii suggests specialized functions. Planta 242(1):167-185.  doi:10.1007/s00425-015-2294-4
  • Hemschemeier A, Happe T (2015): Eukaryotic microalgae in biotechnological applications. Biotechnology. (Frankenberg-Dinkel N, Kück U eds) De Gruyter, In press: 165-196  doi:10.1515/9783110342635-009
  • Happe T, Hemschemeier A (2014): Metalloprotein mimics - old tools in a new light. Trends Biotechnol 32(4):170-6.  doi:10.1016/j.tibtech.2014.02.004
  • Hemschemeier A (2013): Photo-bleaching of Chlamydomonas reinhardtii after dark-anoxic incubation. Plant Signal Behav 8(11):e27263.  doi:10.4161/psb.27263
  • Hemschemeier A, Casero D, Liu B, Benning C, Pellegrini M, Happe T, Merchant SS (2013): COPPER RESPONSE REGULATOR1-Dependent and -Independent Responses of the Chlamydomonas reinhardtii Transcriptome to Dark Anoxia. Plant Cell 25(9):3186-211.  doi:10.1105/tpc.113.115741
  • Esselborn J, Lambertz C, Adamska-Venkatesh A, Simmons T, Berggren G, Noth J, Siebel J, Hemschemeier A, Artero V, Reijerse E, Fontecave M, Lubitz W, Happe T (2013): Spontaneous activation of [FeFe]-hydrogenases by an inorganic [2Fe] active site mimic. Nature Chem Biol 9(10):607-9.  doi:10.1038/nchembio.1311
  • Hemschemeier A, Düner M, Casero D, Merchant SS, Winkler M, Happe T (2013): Hypoxic survival requires a 2-on-2 hemoglobin in a process involving nitric oxide. Proc Natl Acad Sci U S A 110(26):10854-9.  doi:10.1073/pnas.1302592110
  • Li-Beisson Y, Peltier G, Knörzer P, Happe T, Hemschemeier A (2013): Hydrogen and biofuel production in the chloroplast. Plastid biology in the series Advances in Plant Biology. (Theg S, Wollman FA (eds)) Springer, In press: 559-585.  doi:10.1007/978-1-4939-1136-3_19
  • Noth J, Krawietz D, Hemschemeier A, Happe T (2013): Pyruvate:ferredoxin oxidoreductase is coupled to light-independent hydrogen production in Chlamydomonas reinhardtii. J Biol Chem 288(6):4368-77.  doi:10.1074/jbc.M112.429985
  • Pape M, Lambertz C, Happe T, Hemschemeier A (2012): Differential Expression of the Chlamydomonas [FeFe]-Hydrogenase-Encoding HYDA1 Gene Is Regulated by the COPPER RESPONSE REGULATOR1. Plant Physiol 159(4):1700-12.  doi:10.1104/pp.112.200162
  • Philipps G, Happe T, Hemschemeier A (2012): Nitrogen deprivation results in photosynthetic hydrogen production in Chlamydomonas reinhardtii. Planta 235(4):729-45.  doi:10.1007/s00425-011-1537-2
  • Hemschemeier A, Happe T (2011): Alternative photosynthetic electron transport pathways during anaerobiosis in the green alga Chlamydomonas reinhardtii. Biochim Biophys Acta 1807(8):919-926.  doi:10.1016/j.bbabio.2011.02.010
  • Philipps G, Krawietz D, Hemschemeier A, Happe T (2011): A pyruvate formate lyase-deficient Chlamydomonas reinhardtii strain provides evidence for a link between fermentation and hydrogen production in green algae. Plant J 66(2):330-340.  doi:10.1111/j.1365-313X.2011.04494.x
  • Hemschemeier A, Müllner K, Rühle T, Happe T (2010): Hydrogen generation by microbial cultures. Biomass to biofuels. (Vertes A, Qureshi N, Blaschek H, Yukawa H (eds)), Wiley and Sons, Ltd, West Sussex, UK, 359-385.  doi:10.1002/9780470750025.ch18
  • Lambertz C, Hemschemeier A, Happe T (2010): Anaerobic expression of the ferredoxin-encoding FDX5 gene of Chlamydomonas reinhardtii is regulated by the Crr1 transcription factor. Eukaryot Cell 11:1747-1754.  doi:10.1128/EC.00127-10
  • Winkler M, Hemschemeier A, Jacobs J, Stripp S, Happe T (2010): Multiple ferredoxin isoforms in Chlamydomonas reinhardtii - Their role under stress conditions and biotechnological implications. Eur J Cell Biol 12:998-1004.  doi:10.1016/j.ejcb.2010.06.018
  • Hemschemeier A, Melis A, Happe T(2009): Analytical approaches to photobiological hydrogen production in unicellular green algae. Photosynth Res 2009 Mar 17.  doi:10.1007/s11120-009-9415-5
  • Jacobs J, Pudollek S, Hemschemeier A, Happe T (2009): A novel, anaerobically induced ferredoxin in Chlamydomonas reinhardtii. FEBS Lett 583:325-329.  doi:10.1016/j.febslet.2008.12.018
  • Rühle T, Hemschemeier A, Melis A, Happe T (2008): A novel screening protocol for the isolation of hydrogen producing Chlamydomonas reinhardtii strains. BMC Plant Biology 8:107-112.  doi:10.1186/1471-2229-8-107
  • Hemschemeier A, Fouchard S, Cournac L, Peltier G, Happe T (2008): Hydrogen production by Chlamydomonas reinhardtii: an elaborate interplay of electron sources and sinks. Planta 227:397-407.  doi:10.1007/s00425-007-0626-8
  • Hemschemeier A, Jacobs J, Happe T (2008): Biochemical and physiological characterization of the pyruvate formate-lyase Pfl1 of Chlamydomonas reinhardtii, a typically bacterial enzyme in a eukaryotic alga. Eukaryot Cell 7:518-526. doi:10.1128/EC.00368-07
  • Fouchard S, Hemschemeier A, Caruana A, Pruvost J, Legrand J, Happe T, Peltier G, Cournac L (2005): Autotrophic and mixotrophic hydrogen photoproduction in sulphur-deprived Chlamydomonas cells. Appl Env Microbiol 71:6199-6205.  10.1128/AEM.71.10.6199-6205.2005
  • Hemschemeier A, Happe T (2005): The exceptional photofermentative hydrogen metabolism of the green alga Chlamydomonas reinhardtii. Biochem Soc Trans 33:39-41.  doi:10.1042/BST0330039
  • Winkler M, Maeurer C, Hemschemeier A, Happe T (2004): The isolation of green algal strains with outstanding H2-productivity. Biohydrogen III, (Miyake J, Igarashi Y, Rögner M, eds), Elsevier Science, Oxford, 103-115.  doi:10.1016/B978-008044356-0/50009-9
  • Winkler M, Hemschemeier A, Gotor C, Melis A, Happe T (2002): [Fe]-hydrogenases in green algae: photo-fermentation and hydrogen evolution under sulfur deprivation. Int J Hydrogen Energy 27:1431-1439.  doi:10.1016/S0360-3199(02)00095-2
  • Happe T, Hemschemeier A, Winkler M, Kaminski A (2002): Hydrogenases in green algae: do they save the algae´s life and solve our energy problems? Trends Plant Sci 7:246-250.  doi:10.1016/S1360-1385(02)02274-4