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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - EcoLipid (Ecophysiology of membrane lipid remodelling in marine bacteria)

Teaser

Summary

\"Membrane lipids form the structural basis of all cells. In bacteria Escherichia coli uses predominantly phosphorus-containing lipids (phospholipids) in its cell envelope, including phosphatidylethanolamine and phosphatidylglycerol. However, beyond E. coli a range of lipids are found in bacterial membranes, including phospholipids as well as phosphorus (P)-free lipids such as betaine lipids, ornithine lipids, sulfolipids and glycolipids. In the marine environment, it is well established that P availability significantly affects lipid composition in the phytoplankton, whereby non-P sulfur-containing lipids are used to substitute phospholipids in response to P stress. This remodeling offers a significant competitive advantage for these organisms, allowing them to adapt to oligotrophic environments low in P. Until very recently, abundant marine heterotrophic bacteria were thought to lack the capacity for lipid remodelling in response to P deficiency. However, recent work by myself and others has now demonstrated that lipid remodelling occurs in many ecologically important marine heterotrophs, such as the SAR11 and Roseobacter clades, which are not only numerically abundant in marine waters but also crucial players in the biogeochemical cycling of key elements. However, the ecological and physiological consequences of lipid remodeling, in response to nutrient limitation, remain unknown. This project aims to provide a mechanistic understanding of the physiological response of lipid remodelling to nutrient limitation using model marine bacteria. It seems to bridge the gap in our understanding of lipid remodeling and its potential biological and ecological consequences. The project aims to use a synthesis of molecular biology, microbial physiology, and \"\"omics\"\" approaches to reveal the fitness trade-offs of lipid remodelling in cosmopolitan marine heterotrophic bacteria, providing novel insights into the ecophysiology of lipid remodelling and its consequences for marine nutrient cycling.\"

Work performed

The project is further divided into three main work packages. Progress in the first reporting period includes
1) comparative lipidomics experiments using Ruegerial pomeroyi as the model and the identification of the novel glutamine-containing lipids in this bacterium and its role in the adaptation to phosphorus stress. This work has recently been accepted in publication in the ISME Journal (Smith et al., 2018).
2) Mechanistic insight into lipid remodelling. We have successfully generated several mutants, including plcP, olsAB, glsB which will be used in this work package. We have also successfully tested the methodology of isotope labelling using radio-active compounds. We have also purified and biochemically characterized the key enzyme PlcP which is essential in lipid remodelling. this work has recently been published in Applied and Environmental Microbiology (Wei et al., 2018).
3) We have successfully isolated several bacterial phages which infect our model bacteria. This will be used to understand the role of remodeling in phage interaction. We have successfully obtained several eukaryotes and managed to maintain and grow them successfully in the laboratory.

Final results

The project aims to bridge a knowledge gap in our understanding of lipid remodelling and its potential biological and ecological consequences. We have made significant progress in all work packages and established methods and protocols during the first reporting period in order to test our hypotheses. The project is therefore on track to transform our understanding of the ecophysiology of adaptation to nutrient limitation in model marine bacteria and open up a whole new horizon for future investigation of the role in nature systems.