In summary, our results indicate that from a bioenergy perspective (i) nitrogen deprivation is advantageous as it represents an effective means to organize cellular metabolites into the two principal biofuels feedstocks, starch and TAG, but a significant drawback of nitrogen deprivation is that it results in attenuated rates of photosynthesis and acetate uptake, as overall anabolic processes are diminished; (ii) the disruption of starch synthesis is an effective means to overaccumulate lipid in the sta6 and sta7-10 starchless mutants during nitrogen deprivation, but this is tempered by decreases in overall anabolic processes (primarily starch accumulation) in comparison to the other strains; and (iii) the isoamylase complemented strains accumulate significantly higher levels of lipids and starch on a cellular basis during nitrogen deprivation, and starch overaccumulation can be achieved in the sta7-10[c5] and sta7-10[c19] strains in nutrient-replete medium while these cells are actively dividing, albeit at a lower rate than the other strains in nitrogen-replete medium.
The single-gene alterations reported here result in dramatic carbon product accumulation phenotypes. The metabolic engineering of algae for improved biofuel productivity is just beginning, and it is noteworthy that the relatively simple genetic manipulations reported here resulted in metabolic alterations that significantly affected the accumulation of starch or lipid, the two most relevant algal bioenergy carriers. As engineering approaches in C. reinhardtii and other algae become more refined, additional advances are likely.
In summary, our results indicate that from a bioenergy perspective (i) nitrogen deprivation is advantageous as it represents an effective means to organize cellular metabolites into the two principal biofuels feedstocks, starch and TAG, but a significant drawback of nitrogen deprivation is that it results in attenuated rates of photosynthesis and acetate uptake, as overall anabolic processes are diminished; (ii) the disruption of starch synthesis is an effective means to overaccumulate lipid in the sta6 and sta7-10 starchless mutants during nitrogen deprivation, but this is tempered by decreases in overall anabolic processes (primarily starch accumulation) in comparison to the other strains; and (iii) the isoamylase complemented strains accumulate significantly higher levels of lipids and starch on a cellular basis during nitrogen deprivation, and starch overaccumulation can be achieved in the sta7-10[c5] and sta7-10[c19] strains in nutrient-replete medium while these cells are actively dividing, albeit at a lower rate than the other strains in nitrogen-replete medium.The single-gene alterations reported here result in dramatic carbon product accumulation phenotypes. The metabolic engineering of algae for improved biofuel productivity is just beginning, and it is noteworthy that the relatively simple genetic manipulations reported here resulted in metabolic alterations that significantly affected the accumulation of starch or lipid, the two most relevant algal bioenergy carriers. As engineering approaches in C. reinhardtii and other algae become more refined, additional advances are likely.
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