New perspectives on ocean photosynthesis

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 in powering vital cellular processes such as CO₂ concentration and nutrient uptake [2]. However, the mechanistic basis of different photoheterotrophic processes and how/when they are used are not well understood [3]. This project aims to couple in situ and experimental approaches to understand the conditions under which different solar energy capture strategies are used and the cellular processes they maintain. 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

(1)       A laboratory system will be used to understand the benefits and costs of different solar energy capture strategies under different light and nutrient supply ratios. Natural phytoplankton cultures (cyanobacteria and diatoms) will be grown under a range of conditions to induce changes in photosynthetic strategy. A suite of physiological (FRRf) and molecular (transcriptomic) approaches will be used to identify the mechanistic basis and cost/benefit profile of different photosynthetic strategies.

(2)       Further extant and heterologous genes will be engineered into the cyanobacteria Synechococcus [3]. This will generate a unique experimental system in which the benefit of different photosynthetic strategies can be assessed.

(3)       A NERC-funded oceanic cruise (to the South Atlantic/Southern Ocean) will be used as a platform to collect samples of natural phytoplankton. A suite of physiological and transcriptomic approaches will determine the photosynthetic strategy used across natural oceanic gradients and thus provide a broader context to the laboratory work.

The above approach will generate data from which the energetic ‘costs and benefits’ of different solar capture processes can be constrained. This information will be used to model such processes, which can in turn be used to understand how captured light energy is used in oceans [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. Specific training will include the student being introduced to the use of active chlorophyll fluorometry for the assessment of phytoplankton physiology and electron transport; training in at-sea experimentation will also be provided. Additionally, the student will be trained in molecular techniques needed to manipulate cyanobacteria and in the data analysis techniques to facilitate understanding of gene expression at the cellular. As indicated above, there will be the opportunity to undertake fieldwork to sample natural communities at sea, likely in the South Atlantic/Southern Ocean.