Phototrophy in the deep blue sea: understanding the conditions under which different solar energy capture strategies are optimal

Programme website: http://inspire-dtp.ac.uk

Project Rationale:
Solar energy ultimately drives all biogeochemical cycles and sustains planetary habitability. In the oceans, diverse microbes absorb this solar energy and many use it in photoautotrophic processes that ‘fix’ new carbon, thereby sustaining the carbon cycle. Often, however, carbon-fixation is limited by available nutrients (for example iron) but light is still absorbed to drive photoheterotrophic processes [1]. There is an increasing appreciation of the importance and role of this photoheterotrophic metabolism in ocean systems, but the costs and benefits of these different forms of metabolism are still not well understood. Diatoms, for example, have been shown to complement chlorophyll (photoautotrophic) with proteorhodopsin (photoheterotrophic) strategies that may lower the iron requirement of the cell [2,3]. This project aims to couple experimental and modelling approaches to understand the conditions under which different solar energy capture strategies are optimal. This will provide important new insights into the use of solar energy to sustain the planetary system, and how the system evolved and will adapt in a future ocean.

Methodology:
Two laboratory test systems will be used to generate datasets to experimentally understand the energy benefits and costs of different solar energy capture strategies under different light and nutrient supply ratios.
(1) In a eukaryotic system, diatoms that have proteorhodopsin (PR) will be cultured under various light and nutrient availabilities to represent key oceanic regimes. The resource allocation to different solar energy capture strategies (including chlorophyll-based linear and cyclic electron flow as well as PR-based) will be determined using a suite of molecular and biophysical measurements available in the laboratories of Bibby and Moore. These experiments will be complemented by attempts to generate a regulatory knockout mutant of the PR using CRISPR-Cas in the diatom in the laboratory of Wheeler (MBA).
(2) Using a prokaryotic synthetic system PR will be engineered into the cyanobacteria Synechococcus [4, 5]. This will generate a unique experimental system in which the energy benefit of PR versus chlorophyll-based light capture can be assessed.
The above approach will be used to generate data from which the energetic costs and benefits of different solar capture processes can be constrained. This information will be used to model the metabolic cost and benefit of such processes, which can in turn be used to understand how captured light energy is used in oceanic systems. [3].

Training:
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at Ocean and Earth Science/MBA. Specific training will include:
Physiological analysis of photosynthesis using spectroscopic techniques including Fast Repetition Rate Fluorometry (FRRF). Design and construction of genetically engineered phytoplankton cells using molecular biology techniques (on cyanobacteria in UoS and on diatoms in MBA). Support will be given to analyze and model the outputs of experimental datasets [6]. The student will join a vibrant research community in Southampton and will be able to visit the collaborators, including at MBA. There will be further opportunities to participate in research cruises and to present research at UK and international conferences.