Molecular mechanisms of adaptation in globally successful cyanobacteria

Project Rationale:

Cyanobacteria are the most abundant photosynthetic organisms on the planet. Their success is rooted in a diversity of strategies that allow them to adapt to the highly varied physical and chemical marine. This ability has allowed marine cyanobacteria to thrive in nutrient-deplete habitats, such as the oceanographic gyres.

Understanding this ecological success by studying the mechanisms of adaptation is a highly interdisciplinary scientific challenge. Our project takes a molecular approach, characterizing key molecular systems that are suited to understand adaptation strategies. It spans from genetic studies and biochemical characterization to fieldwork studying these systems in the oceans. The reward of this approach is a better understanding of adaptation strategies, which in future can be harvested, e.g. by developing technologies or efficient processes that reduce our reliance on products and energy derived from fossil fuels.

The project focusses on the study of selected key enzymes that are upregulated in the context of nutrient limitation in the globally important genus Trichodesmium [1], a diazotroph that can directly use N2 as their sole source of nitrogen. The antagonistic processes of oxygenic photosynthesis and N2 fixation can simultaneously be performed in Trichodesmium, whilst producing the biofuel hydrogen gas (H2) as a by-product.

Methodology:

The main thrust of this PhD is biochemical and structural characterization of a select number of targets, starting with the enzyme fructose 1,6-bisphosphate aldolase. Our unpublished biochemical and structural data show a physiological switch between metal-containing and metal-free enzymes, dependent on nutrient conditions. Further interests are the N2 fixation nitrogenase key functional enzymes. The aim of the PhD – to understand the ability of Trichodesmium to tailor its physiology – requires us to compare samples found in the ocean, their cultured counterparts, or heterologous cyanobacteria.

Our approach is exemplified by recent work on iron homeostasis [2]. The experimental workflow is (i) identification of specific catalysts regulated in existing transcriptomic datasets under nutrient limitation; (ii) study of specific properties through enzymatic and structural characterization and biophysical approaches; (iii) study of adaptation in environmental samples obtained on a cruise of opportunity (German GEOTRACES cruises and associated micro-nutrient limitation studies), e.g. by episodic metal supply to seawater on physiological changes (enzyme switching) by bioassay experiments; (iv) experiments towards investigating the cost (e.g. in carbon fixation rate) of an enzyme switch mechanism if the enzyme of interest is involved in photosynthesis.

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 the Institute for Life Sciences and the School of Ocean and Earth Science based at the National Oceanography Centre and at GEOMAR, Kiel, Germany to participate in a research cruise (the Achterberg group runs ca. 3 cruises per year. The PhD links research streams on marine geochemistry, including participation on a cruise of opportunity, microbiology, enzymology and structural biology. Training includes the valuable combination of fieldwork, microbial and molecular techniques and structural biology (participation in protein-crystallographic workshops / schools is offered). Strengthening an unusual and very promising combination of expertise, the PhD is truly multidisciplinary, and training results in a highly marketable skill set.