Isolation and characterization of a starchless mutant of Chlorella pyrenoidosa STL‐PI with a high growth rate, and high protein and polyunsaturated fatty acid content

Abstract

The growth characteristics, biochemical composition and ultrastructure of a novel starchless mutant of Chlorella pyrenoidosa, designated as STL-PI, are compared to the same characteristics of its parental strain, C. pyrenoidosa 82T. The STL-PI mutant had a 22 ± 5% higher growth rate, and 24.5 ± 4.2% more protein than the parental strain, 82T. Furthermore, the STL-PI mutant accumulated 20.4% more polyunsaturated fatty acids and 18% less saturated fatty acids than the parental 82T. When the parental 82T was cultured in a nitrogen-free media, their starch content increased from 6.8 ± 2.8% to 22.5 ± 3.1%. In contrast, the STL-PI mutant produced no starch, regardless of the growth conditions. Instead, the mutant cells responded to nitrogen limitation by further increasing their lipid content from 25.2 ± 1.2% to 38.0 ± 2.3% per dry weight. Transmission electron micrography revealed that nitrogen limitation typically stimulates the formation of starch granules in the chloroplast of 82T cells. Yet no starch granules were observed in the STL-PI cells. Instead, only the formation of large lipid globules was observed in the mutant cells. These results demonstrate that the starchless mutant STL-P1 possesses novel physiological and phytochemical properties distinct from the 82T cells: their cells were deficient in starch synthesis and showed higher growth rates and productivity than 82T cells.

Systems-Level Analysis of Nitrogen Starvation-Induced Modifications of Carbon Metabolism in a Chlamydomonas reinhardtii Starchless Mutant

“…It is assumed that this occurs because carbon flow to storage carbohydrate is blocked (Ramazanov and Ramazanov, 2006;Wang et al, 2009;Li et al, 2010aLi et al, , 2010bWork et al, 2010;Fan et al, 2011Fan et al, , 2012Sanjaya et al, 2011). The increased yield of TAG in acetate-supplemented N-starved sta6 is not inconsistent with this model (Goodson et al, 2011;Ramanan et al, 2013).…”

Increased Lipid Accumulation in the Chlamydomonas reinhardtii sta7-10 Starchless Isoamylase Mutant and Increased Carbohydrate Synthesis in Complemented Strains

“…Our results regarding the sta6 mutant are consistent with the results reported in those studies and further extend the characterization of lipid overaccumulation to the sta7-10 mutant, which under our culturing conditions accumulates even more cellular lipid than the sta6 mutant. Increased levels of lipid accumulation have also been observed in a starchless mutant of the alga Chlorella pyrenoidosa (42). The study by Li et al used light intensities 4-fold higher than those used here during acclimation to nitrogen deprivation and reports a 10-fold increase in triacylglycerol (TAG) content relative to that in the control strain, CC1690 (26), as a function of dry weight, which is a consequence of both increased TAG synthesis and loss of carbohydrate mass.…”

Genetic Engineering of Algae for Enhanced Biofuel Production

“…Wang et al (197), as well as unpublished results from our laboratory, have shown that these mutants accumulate increased levels of TAG during nitrogen deprivation. Another starchless mutant of Chlorella pyrenoidosa has also been shown to have elevated polyunsaturated fatty acid content (154).…”