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Background: Algal cells produce neutral lipid when stressed and this can be used to generate biodiesel.Objective: Salt stressed cells of the model microalgal species Chlamydomonas reinhardtii were tested for their suitability to produce lipid for biodiesel.Methods: The starchless mutant of C. reinhardtii (CC-4325) was subjected to salt stress (0.1, 0.2 and 0.3 M NaCl) and transesterification and GC analysis were used to determine fatty acid methyl ester (FAME) content and profile.Results: Fatty acid profile was found to vary under salt stress conditions, with a clear distinction between 0.1 M NaCl, which the algae could tolerate, and the higher levels of NaCl (0.2 and 0.3 M), which caused cell death. Lipid content was increased under salt conditions, either through long-term exposure to 0.1 M NaCl, or short-term exposure to 0.2 and 0.3 M NaCl. Palmitic acid (C16:0) and linolenic acid (C18:3n3) were found to increase significantly at the higher salinities.Conclusion: Salt increase can act as a lipid trigger for C. reinhardtii.

Background Chlamydomonas reinhardtii is a model green alga strain for molecular studies; its fully sequenced genome has enabled omic-based analyses that have been applied to better understand its metabolic responses to stress. Here, we characterised physiological and proteomic changes between a low-starch C. reinhardtii strain and the snow alga Chlamydomonas nivalis, to reveal insights into their contrasting responses to salinity stress. Results Each strain was grown in conditions tailored to their growth requirements to encourage maximal fatty acid (as a proxy measure of lipid) production, with internal controls to allow comparison points. In 0.2 M NaCl, C. nivalis accumulates carbohydrates up to 10.4% DCW at 80 h, and fatty acids up to 52.0% dry cell weight (DCW) over 12 days, however, C. reinhardtii does not show fatty acid accumulation over time, and shows limited carbohydrate accumulation up to 5.5% DCW. Analysis of the C. nivalis fatty acid profiles showed that salt stress improved the biofuel qualities over time. Photosynthesis and respiration rates are reduced in C. reinhardtii relative to C. nivalis in response to 0.2 M NaCl. De novo sequencing and homology matching was used in conjunction with iTRAQ-based quantitative analysis to identify and relatively quantify proteomic alterations in cells exposed to salt stress. There were abundance differences in proteins associated with stress, photosynthesis, carbohydrate and lipid metabolism proteins. In terms of lipid synthesis, salt stress induced an increase in dihydrolipoyl dehydrogenase in C. nivalis (1.1-fold change), whilst levels in C. reinhardtii remained unaffected; this enzyme is involved in acetyl CoA production and has been linked to TAG accumulation in microalgae. In salt-stressed C. nivalis there were decreases in the abundance of UDP-sulfoquinovose (− 1.77-fold change), which is involved in sulfoquinovosyl diacylglycerol metabolism, and in citrate synthase (− 2.7-fold change), also involved in the TCA cycle. Decreases in these enzymes have been shown to lead to increased TAG production as fatty acid biosynthesis is favoured. Data are available via ProteomeXchange with identifier PXD018148. Conclusions These differences in protein abundance have given greater understanding of the mechanism by which salt stress promotes fatty acid accumulation in the un-sequenced microalga C. nivalis as it switches to a non-growth state, whereas C. reinhardtii does not have this response.

In article number https://doi.org/10.1002/smll.201701777, David Coles, David G. Lidzey, and co‐workers place living photosynthetic bacteria into a photonic microcavity. The system is shown to enter a strong‐coupling regime, whereby the cavity modifies the energy of the bacterial light harvesting system. The energy of light harvesting antennae can be tuned by changing the length of the optical cavity, while the bacteria remain alive.

This review examines the available literature on quantifying lipids in microalgae suitable for biofuels research. It discusses their advantages and disadvantages, their prevalence in the literature, and draws conclusions about the best way to approach choosing a suitable lipid measurement technique for microalgal biofuels research. We conclude that the method must be chosen based on the following key criteria: (1) the level of detail required in the results, and (2) the amount of biomass that can be spared for the assay. This review establishes that no method can be used as a "golden standard" for all microalgae. However, we present a systematic decision chart to choose the best measurement method or combination of methods to provide a guide to those wishing to understand the differences between the myriad of lipid measurement techniques.Practical applications: This review will allow researchers new to the field to choose the most appropriate techniques for quantifying lipids in the microalgal species under study. The review is also intended to act as a gateway to the wider literature and will enable researchers to look in depth at a particular technique before carrying out experimental work.