How marine algae cope with changing ocean conditions
Human activities are changing the ocean on a global scale, with seawater in some regions becoming warmer, more acidic, and less well mixed. One possible result of reduced ocean mixing is that nutrients, which act like fertilizer for marine algae, could become less available near the sea surface. It remains largely unknown how these changes affect the marine algae that provide oxygen for Earth’s atmosphere and form the basis for ocean food webs. Recently an article was published in Nature Microbiology, co-authored by UvA aquatic microbiologist Susanne Wilken, demonstrating that the microalga Micromonas commoda shows a specialized adaption strategy in response to phosphorus limitation.
Marine algae contribute 50% to global carbon fixation, provide oxygen for the Earth’s atmosphere and form the basis for ocean food webs. Understanding their responses to changing ocean conditions is therefore crucial for predictions of future carbon cycling. One thing scientists know for sure is that the diverse groups of algae react differently to variations in ocean conditions, both seasonally and over longer time periods. Learning how these different groups respond is key to understanding how ocean ecosystems change over periods from months to decades.
Many researchers are studying how these changes could affect the microscopic marine algae that provide oxygen for Earth’s atmosphere and form the basis for ocean food webs. Unfortunately, studying the responses of specific types of algae in the open ocean is very difficult, because ocean conditions are always fluctuating, as are the types of algae present. For this reason, scientists have turned to laboratory studies. At the Monterey Bay Aquarium Research Institute (MBARI) in California researchers have been working on a new way of culturing algae in steady-state cultures using high-tech incubation chambers called photo-bioreactors. These devices allow the researchers to grow algae under precisely controlled levels of light, temperature, and nutrients.
Dr. Susanne Wilken, aquatic microbiologist at the UvA Institute for Biodiversity and Ecosystem Dynamics, contributed to such a photo-bioreactor experiment during her postdoctoral research at MBARI: ‘We performed experiments in photo-bioreactors that allow simulation of growth conditions representative of those encountered in large parts of the ocean with constant but limiting supply of phosphate for algal growth. We analyzed the molecular mechanisms underlying the acclimation to phosphate limitation by combining biophysical with molecular techniques.’ The results of this experiment are now published in Nature Microbiology.
Algal responses to nutrient limitation
For this study the scientists grew a tiny, swimming alga called Micromonas commoda under conditions in which phosphate, a key algal nutrient, was kept at relatively low levels. Throughout their experiment, the researchers drew off small samples of algae and used sophisticated proteomic techniques to figure out which types of proteins are produced by the algae under low- and high-phosphate conditions. This revealed sets of phosphate-responsive proteins that are widely used by different algae, but also proteins that are unique to Micromonas.
‘We further identify an evolutionarily ancient photoprotection mechanism that is activated under phosphate limitation, which might allow this alga to very rapidly resume growth after encountering higher concentrations of phosphate,’ explains Wilken. ‘This mechanism also suggests that there could be interactive effects of changing phosphate and light conditions as expected to occur in our future oceans.’
Original journal article:
Jian Guo, Susanne Wilken, Valeria Jimenez, Chang Jae Choi, Charles Ansong, Richard Dannebaum, Lisa Sudek, David S. Milner, Charles Bachy, Emily Nahas Reistetter, Virginia A. Elrod, Denis Klimov, Samuel O. Purvine, Chia-Lin Wei, Govindarajan Kunde-Ramamoorthy, Thomas A. Richards, Ursula Goodenough, Richard D. Smith, Stephen J. Callister & Alexandra Z. Worden. ‘Specialized proteomic responses and an ancient photoprotection mechanism sustain marine green algal growth during phosphate limitation’, Nature Microbiology - 25 June 2018. DOI: https://doi.org/10.1038/s41564-018-0178-7