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Title: Detecting carbon uptake by individual algae in multi-species assemblages

item MURDOCK, JUSTIN - Tennessee Technological University

Submitted to: Limnology and Oceanography Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2015
Publication Date: 11/3/2015
Publication URL:
Citation: Murdock, J.N. 2015. Detecting carbon uptake by individual algae in multi-species assemblages. American Society of Limnology and Oceanography. 14(2):124-137 DOI:10.1002/lom3.10078.

Interpretive Summary: Algae are an important part of aquatic ecosystems because they regulate food availability, nutrient cycling rates, and water column oxygen availability. Algae are also gaining importance as biofuel feedstock and components of carbon dioxide removal technologies. Changing water quality in lakes and streams alters algal species composition, and different species likely have varying metabolic responses to these changes. However, there is little information about how changes in algal species composition will impact algae’s role in nutrient cycling and carbon sequestration because there are currently many technical limitations in separating species and/or measuring the biochemistry of small quantities of algal cells. This study provides a new method to detect how individual algal cells acquire and use carbon. Infrared spectroscopy was used to track which algal cells took up carbon dioxide that was labeled with a heavy isotope of carbon. The method also determines into which part of the cell (for example protein, lipid, or carbohydrate) the new carbon was allocated. This technique can be used to better manage agriculturally influenced aquatic systems because it can be used to get a better understanding of which algal species will thrive under varying environmental conditions. This method can also potentially help to refine species selection for maximum carbon removal or biomass production in bioengineering and pollutant reduction applications.

Technical Abstract: Knowing how different algal species utilize carbon (C) can help predict how assemblage changes will alter energy input and flow in ecosystems, and can help refine algal species selection for bioengineering applications. Fourier-transform infrared (FTIR) microspectroscopy was used to measure inorganic 13C isotope incorporation into individual algal cells in a single species, a two species assemblage, and a natural phytoplankton assemblage. Shifts in spectral peaks were observed in all species. Comparison of the shifts in spectral peaks associated with carbohydrates, proteins, and lipids following 13C incorporation allowed for the detection of both which individuals took in C, and which major macromolecules the new C was used to make. In the natural phytoplankton assemblage, a diatom and green algae species had noticeable peak shifts in protein/carbohydrate, and protein/lipid peaks, respectively. Concurrently, two euglenoid species showed little shifts in 13C spectra, which matches their ability to use organic C. FTIR microspectroscopy is a label-free method, but adding a label such as 13C isotope can greatly expand the instrument’s capabilities in biological analysis by tracking nutrients between inorganic and organic states and into macromolecules of individual algae.