Evolution of salt tolerance in a laboratory reared population of Chlamydomonas reinhardtii

Abstract

Understanding the genetic underpinnings of adaptive traits in microalgae is important for the study of evolution and for applied uses. We used long-term selection under a regime of serial transfers with haploid populations of the green alga Chlamydomonas reinhardtii raised in liquid TAP medium containing 200 mM NaCl. After 1255 generations, evolved salt (ES) populations could grow as rapidly in high salt medium as progenitor cells (progenitor light [PL]). Transcriptome data were analysed to elucidate the basis of salt tolerance in ES cells when compared with PL cells and to cells incubated for 48 h in high salt medium (progenitor salt [PS], the short-term acclimation response). These data demonstrate that evolved and short-term acclimation responses to salt stress differ fundamentally from each other. Progenitor salt cells exhibit well-known responses to salt stress such as reduction in photosynthesis, upregulation of glycerophospholipid signaling, and upregulation of the transcription and translation machinery. In contrast, ES cells show downregulation of genes involved in the stress response and in transcription/translation. Our results suggest that gene-rich mixotrophic lineages such as C. reinhardtii may be able to adapt rapidly to abiotic stress engendered either by a rapidly changing climate or physical vicariance events that isolate populations in stressful environments.

Experimental adaptation to marine conditions by a freshwater alga

“…Changes in gene expression following long-term exposure to salt have been reported before in C. reinhardtii (Perrineau et al 2014). Short-term acclimation to about 12 gL −1 NaCl causes a reduction in photosynthesis, upregulation of glycerophospholipid signaling, and upregulation of the transcription and translation machinery.…”

A Data-Independent-Acquisition-based proteomic approach towards understanding the acclimation strategy ofMicrochloropsis gaditanaCCMP526 in hypersaline conditions

“…A simple approach for enhancing productivity coupled with high growth rate would be to manipulate the environmental parameters. Salinity is one of the primary growth influencing factors for marine microalgae, which could be controlled in an open race-way pond (Kim et al, 2016; Perrineau et al, 2014).…”

The fatter the better : selecting microalgae cells for outdoor lipid production

“…Microalgae have been shown to evolve under repeated conditions in periods of 3 to 17 months (40 to 600 generations) 11,17,133 . Similarly, bacteria and yeast have been evolved (with or without mutagenesis) in periods as short as 13 and as long as 1000 generations 13 .…”

“…Similarly, bacteria and yeast have been evolved (with or without mutagenesis) in periods as short as 13 and as long as 1000 generations 13 . Surprisingly, the speed of laboratory evolution is not determined by the microorganism growth rate or whether it has a prokaryotic or eukaryotic cellular organization 11,13,17,133 . This observation shows that the strength of the selection pressure is the most relevant factor when pushing laboratory evolution.…”

“…It was also successfully used to evolve CO 2 -tolerant strains of Chlorella sp., without assessing the stability of the improved phenotype 17 . A complete story is shown in the successful evolution of salttolerant Chlamydomonas reinhardtii strains 133 . In this example the authors demonstrated that after 17 months of repeated cultivation in increased salt concentrations there was solid evidence of genetic evolution.…”