Experimental work:
We compared growth curves and nutrient utilization (nitrate and phosphate) of fast-growing and bloom-forming species of 3 key plankton groups: diatoms (Phaeodactylum tricornutum, Cylindrotecha fusiformis and Thalassiosira pseudonana), dinoflagellates (Alexandrium minutum and Prorocentrum micans) and coccolitophore (Emiliania huxleyi). We focused our studies on nutrient (C, N, P, S) allocation in diatoms as they have the highest potential for obtaining products of interest, especially P. tricornutum, which have low silicon requirement.
We cultivated monocultures of P. tricornutum in triplicate and sampled for elemental and biochemical analysis, focusing on the first 12 h, to follow the draw-down of phosphate in the media and its conversion to different phosphate molecules within the cell. We optimized sample preparation for XRMA to avoid the interference of the nutrient-rich media. We also combined the method for biochemical analysis used in Dr. Vaidyanathan's lab for proteins, carbohydrates and pigments determination, with a method to analyse phospholipids, and set up a method for the analysis of intracellular dissolved nutrients and dissolved silicate analysis. Finally, we established collaborations with other researchers for the analysis of polyphosphate (Dr. S. Duhamel, LDEO-Columbia University, USA) and DNA/RNA (Dr. Elisa Berdalet, Institute of Marine Sciences, ICM-CSIC, Spain). Part of this samples are going to be used to describe a new model to convert from elemental to biochemical composition, since the models tried so far are not valid for diatoms.
We cultivated all the species described above, plus a phosphate-limited P. tricornutum, and collected samples during the exponential and stationary phases of the growth curve. We used this data to compare the elemental compositions obtained with both the novel single-cell method and the bulk analysis method. To do so, we set up new methods for the analysis of particulate organic phosphorus and carbon, nitrogen and sulphur elemental analysis using filters, a procedure not used routinely in Dr. Vaydianathan's lab. Dinoflagellate samples were also cultivated for training in ToF-SIMS analysis.
Field work:
With the help of Dr. Claire Widdicombe, Plymouth Marine Laboratory, we obtained samples from the Western Channel Observatory to determine the elemental composition of single diatom cells by XRMA from four different months with contrasting environmental regimes. We are analysing this data to build new regressions element vs. volume that will be used to develop more accurate biogeochemical models of the C-cycle. We will use our model obtained with cultures to convert from elemental to biochemical composition.
Dissemination:
Part of the results have already been disseminated through conferences: 2016 Challenger Society - Oceans and Climate, 5-9 September 2016, Liverpool, UK, and 6th UK Algae Conference, Sheffield, UK.
Professional development training:
The University of Sheffield is an ideal place for the professional development of early-career researchers. During her time at the University of Sheffield, the fellow successfully completed the Sheffield Teaching Assistant program, leading to a certification as an Associate Fellow of the UK Higher Education Academy (AFHEA). The fellow also had the opportunity to join leadership and writing in the sciences workshops, as well as to participate in several outreach events organized by The University of Sheffield.
