Abstract
BackgroundOxidation and peroxidation of lipids in microorganisms result in increased levels of intracellular reactive oxygen species (ROS) and reactive aldehydes, and consequent reduction of cell growth and lipid accumulation.ResultsTo reduce oxygen-mediated cell damage and increase lipid and docosahexaenoic acid (DHA) production in Schizochytrium sp., we strengthened the oxidative stress defense pathways. Overexpression of the enzymes thioredoxin reductase (TRXR), aldehyde dehydrogenase (ALDH), glutathione peroxidase (GPO), and glucose-6-phosphate dehydrogenase (ZWF) strongly promoted cell growth, lipid yield, and DHA production. Coexpression of ZWF, ALDH, GPO, and TRXR enhanced ROS-scavenging ability. Highest values of dry cell weight, lipid yield, and DHA production (50.5 g/L, 33.1 g/L, and 13.3 g/L, respectively) were attained in engineered strain OaldH-gpo-trxR by shake flask fed-batch culture; these were increases of 18.5%, 80.9%, and 114.5% relative to WT values.ConclusionsOur findings demonstrate that engineering of oxidative stress defense pathways is an effective strategy for promoting cell robustness, lipid yield, and DHA production in Schizochytrium.
Highlights
Oxidation and peroxidation of lipids in microorganisms result in increased levels of intracellular reactive oxygen species (ROS) and reactive aldehydes, and consequent reduction of cell growth and lipid accumulation
Oxidation and peroxidation of lipids result in increased intracellular levels of ROS and reactive aldehydes, which affect cell growth and lipid accumulation [16]
The results indicated that the increase of dry cell weight (DCW), lipid production and Docosahexaenoic acid (DHA) yields in the overexpression strains was due to overexpression of the oxidative stress defense genes
Summary
Oxidation and peroxidation of lipids in microorganisms result in increased levels of intracellular reactive oxygen species (ROS) and reactive aldehydes, and consequent reduction of cell growth and lipid accumulation. Docosahexaenoic acid (DHA) has received increasing research attention during the past two decades because of its beneficial effects on human health. Oxygen supply plays a key role in cell proliferation and lipid accumulation of Schizochytrium sp. High oxygen supply shortens fermentation period and increases dry cell weight (DCW). Polyunsaturated fatty acids (PUFAs), are highly susceptible to free radical attack. Acyl-CoA oxidase catalyzes the first step of β-oxidation of fatty acyl-CoA and generates hydrogen peroxide [15], and hydroxyl radical (·OH) and oxygen induce oxidation of unsaturated fatty acids and generate lipid peroxide [16]. Autolysis of resulting lipid peroxide generates a variety of lipid-derived aldehydes
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