Physiology of phototrophic and heterotrophic microalgal cultures under nutrient-­‐limi6ng condi6ons Niels T. Eriksen Sec/on of Biotechnology Aalborg University Denmark Microalgal research at Aalborg University Department of Biotechnology, Chemistry and Environmental Engineering Sec/on of Biotechnology Bioprocess Technology Microbial Bioprocesses Growth of microalgal cultures Specific growth rates depend on light intensity Self-­‐shading within cultures means that most phototrophic cultures are ligth limited Growing cultures and increasing cell concentra/ons mean more self shading, steeper light gradients, and inceased light limita/on How do we get arround the low produc/vi/es enharent to microalgal cultures beceause of light limita/on? How do we avoid/minimize light limita/on and study microalgal physiology similar ways as it is done for other microbes? How to grow microalgae for research or applied purposes Continuous flow culture
Rhodomonas, Galdieria
Control of light intensity
Lumostat photobioreactors
Synechococcus, Microcystis,
Chlamydomonas, Chlorella
How do we grow microalgae
most efficiently and study
their phyiology?
Productivity
Galdieria, Crypthcodinium
Heterotrophic microalgae
Process control
Galdieria, Crypthecodinium
Lumostat In Lumostats, the incident light intensity is automa/cally adjusted to the intensity resul/ng is rate of photosynthe/c CO2 up-­‐take in order to minimize changes in average internal light intensity CO2 is added the aera/on gas to maintain constant pH and to avoid carbon limita/on Change of light intensity are compared to changes of CO2 addi/on rate, and light intensity is frequently changed in the direc/on resul/ng in increased CO2 addi/on rate Effects from light intensity on growth are avoided/minimized, and cultures can be analysed and described using process models comparable to what is used for other microorganisms Lumostat Starch accumula/on in batch cultures of Chlamydomonas reinhard/i, NH4+ as a good N-­‐source Lumostat Starch accumula/on in batch cultures of Chlamydomonas reinhard/i, NO2-­‐ as a poor N-­‐source Heterotrophic cultures are more produc6ve than phototrophic ones Laboratory scale cultures (3 L) limited by external light If incident photosynthe/c photon flux density = 250 µmol m-­‐2 s-­‐1 Maximal produc/vity of organic carbon = 0.003 mol C L-­‐1 h-­‐1 Maximal biomass produc/vity = 0.07 g L-­‐1 h-­‐1 or 1.7 g L-­‐1 day-­‐1 Produc/vi/es are normally lower in phototrophic algae Laboratory scale cultures (3 L) limited by oxygen transfer If KLa = 400 h-­‐1, maximal oxygen transfer rate is around 0.08 mol O2 L-­‐1 h-­‐1 Maximal produc/vity of organic carbon = 0.08 mol C L-­‐1 h-­‐1 Maximal biomass produc/vity = 2 g L-­‐1 h-­‐1 or 48 g L-­‐1 day-­‐1 Such produc/vi/es have been achieved in heterotrophic algae Heterotrophic cultures offer more op6ons for process control Synthesis of DHA in heterotrophic Cryptechodinium cohnii (for feed) In heterotrophic cultures, medium composi/on determines growth limita/on E.g. phosphate or nitrogen limited/carbon and energy sufficient cultures is possible Nutrient limita/on affects biomass composi/on of C. cohnii Phosphate limited
Nitrogen limited
Other Other Starch Protein Lipid Starch Glucose limited Starch Other Protein Lipid Lipid Protein Heterotrophic cultures offer more op6ons for process control Synthesis of DHA in heterotrophic Cryptechodinium cohnii (for feed) In heterotrophic cultures, medium composi/on determines growth limita/on E.g. phosphate or nitrogen limited/carbon and energy sufficient cultures is possible Nutrient limita/on affects biomass composi/on of C. cohnii Biomass composi/on of feed-­‐algae affects biomass composi/on of mussels Phosphate limited
Nitrogen limited
Other Other Starch Protein Lipid Starch Glucose limited Starch Other Protein Lipid Lipid Protein Acknowledgements
Aalborg University, Denmark Daniel Pleissner Olav S. Graverholt
Rikke A. Schmidt
Laila Sørensen Jenni K. Sloth
Andrea Hankte University of Southern Denmark VTT, Finland
Hans Ulrik Riisgård Marilyn G. Wiebe
Ege University, Turkey Muge Isleten References Schmidt RA, Wiebe MG, Eriksen NT (2005) Biotechnol Bioeng 90: 77-­‐84 Sloth JK, Wiebe MG, Eriksen NT (2006) Enzyme Microb Technol 38: 168-­‐175 Graverholt OS, Eriksen NT (2007) Appl Microbiol Biotechnol 77: 69-­‐75 Eriksen NT, Riisgård FK, Gunther W, Iversen JJL (2007) J Appl Phycol 19: 161-­‐174 Eriksen NT (2008) Appl Microbiol Biotechnol 80:1-­‐14 Eriksen NT (2008) Biotechnol Lem 30: 1525-­‐1536 Eriksen NT, Wiebe MG (2009) G.I.T. Bioprocessing 1: 6-­‐8 Pleissner D, Wimmer R, Eriksen NT (2011) Analyt Chem 83: 175-­‐181 Pleissner D, Wimmer R, Eriksen NT (2012) Biotechnol Bioeng 109: 2005-­‐2016 Pleissner D, Eriksen NT, Lundgreen K, Riisgård HU (in press) ISRN Zoology