Evaluation and enhancement of microalgal strain chlamydomonas reinhardtii for biodiesel production

Abstract

Microalgae-derived biodiesel is perceived as the most promising candidate for next generation biofuel due to its sustainability and biodegradability. In this study, microalgal strain Chlamydmonas reinhardtii has been extensively evaluated and enhanced to be more suitable for biodiesel production. In order to upgrade C. reinhardtii, it was randomly mutagenized using a chemical mutagen, Ethyl Methane Sulfonate. As a result, a lipid-overproducing and fast-growing mutant #128 was screened. Its neutral lipid content was twice that of wild type throughout the growth period from exponential to N-depleted phase, when measured in terms of photoluminescence. Measured with flow cytometer, #128’s mean fluorescence was 866.51 compared to wild type’s 691.21. Confocal microscope images of BODIPY 505/515-stained cells clearly revealed that #128 contains larger and more abundant lipid bodies. Fatty acid content analyzed by gas chromatography also showed higher fatty acid content for #128 in exponential and stationary phase as well as after N-starvation. Mutant #128 contained higher quantities of C16:0, C16:1, C18:1n9c, C19:2n6t, and C18:3n6c fatty acids than the wild type. By N-starvation, fatty acid methyl ester (FAME) content of mutant #128 increased 2.3-fold while that of wild type increased 1.9-fold. As growth rate is another important factor for biodiesel commercialization, growth rate and lipid productivity were also analyzed. Not only did #128 accumulate more lipids, it also grew faster and accumulated more biomass. With the initial seeding dry cell weight of 0.10 g/L, #128 accumulated 0.93g/L of biomass compared to wild type’s 0.86 g/L. Lipid productivity of #128 reached 1.282 g L-1 d-1, whereas wild type reached 1.019 g L-1 d-1. From 2D gel electrophoresis and MALDI-TOF analysis of N-starved samples, it was found that beta-subunit of mitochondrial ATP Synthase and two-component response regulator PiIR may relate to #128’s superior characteristics. While extensive st...