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Title: Salt stress in two Chlamydomonas species : novel insights into biofuel production from microalgae
Author: Hounslow, Emily P. H.
ISNI:       0000 0004 5992 1496
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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This thesis aims to find ways of increasing lipid content in algal biomass for biofuel production, by using complimentary metabolomic and proteomic data to increase understanding of the mechanisms that control lipid accumulation. Salt stress was investigated as a potential lipid trigger in two microalgae: a starchless mutant (CC-4325) of the model species Chlamydomonas reinhardtii and the snow alga Chlamydomonas nivalis. Gas chromatographic fatty acid (FA) analysis of both algae grown in a range of salt concentrations revealed a complex relationship between salinity and lipid accumulation in the two species. iTRAQ proteomic analysis was used to study the molecular mechanisms of each species under salt stress. Chlamydomonas reinhardtii showed little accumulation of lipids under salt stress, but some changes in lipid profile. Part of these analyses have been published in a study by Hounslow et al. (2016a). Chlamydomonas nivalis cells showed a large increase over time of the monounsaturated FA C18:1cis when grown in 0.2 M NaCl. As monounsaturated FAs are one of the best FA types for biofuel properties, an increase in this FA is ideal for biofuel production. Use of C. nivalis as a homologous species to C. reinhardtii revealed novel proteomic analysis of lipid accumulation in this species, and a comparison of the proteomic responses of both species under salt stress was used to elucidate why salt triggers lipid accumulation in one species but not the other. Most notably, the rate-limiting enzyme in the fatty acid biosynthesis pathway, acetyl CoA-carboxylase, was found to be down-regulated in C. reinhardtii cultures in 0.2 M NaCl, but was not affected in C. nivalis cultures in 0.2 M NaCl. A number of enzymes involved in the availability of acetyl CoA for fatty acid synthesis were differently affected by salt stress in the two species. Halotolerance appears to play an important role in the ability of cultures to accumulate lipids under salt conditions. The work in this thesis has contributed to two recent publications. The problem of reliable lipid quantification techniques for microalgae was discussed using experimental data and is addressed in a comprehensive published review by Hounslow et al. (2016b). This review includes analysis of method requirements and construction of decision trees to guide future researchers.
Supervisor: Wright, Phillip C. ; Gilmour, D. James Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available