A team of researchers have identified two enzymes that improve the productivity of medium-chain triacylglycerol production in microalgae.
In a new study by researchers from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences (CAS), it was revealed that industrial marine microalga has enzymes that can produce medium-chain triacylglycerols, which is a type of plant oil with a number of health benefits.
Triacylglycerols are biological oils that are the main form of energy storage in cells and are present in all animal fats and vegetable oils. However, not all triacylglycerols are created equal.
Three fatty acid moieties are attached to a glycerol scaffold to form one triacylglycerol molecule. Each molecule can be characterised as either a long-chain triacylglycerol (LCTG) or a medium-chain triacylglycerol (MCT), which differ in terms of application area, economic worth, and market potential.
“During digestion, MCTs are converted to medium-chain fatty acids, which bypass fat tissue, lowering the chance of it converting into fat tissue,” said Xu Jian, a professor at Single-Cell Center of QIBEBT. “It also increases energy expenditure, fat oxidation and satiety, and lowers energy and food intake in both lean and obese individuals.”
The problem is with accessibility. Only oils from the palm and coconut plants, which are limited to growth in tropical and subtropical climates, can be used to make MCT oil.
“Moreover, only about 3 per cent of the whole plant mass is stored in the form of oil, so we need a more efficient and versatile feedstock,” said Xin Yi, an associate professor at Single-Cell Center, explaining that the limited availability of MCT has impeded extensive study of the product.
The marine microalgae Nannochloropsis oceania has received a lot of attention from researchers due to its high capacity for photosynthetic growth and rich oil content. Yet, it typically only comprises 0.01 to 0.05 per cent of MCT. Despite this low composition, this microalga has a native MCT-assembling mechanism, according to a previous genetic analysis.
In this study, researchers identified two distinct enzymes in the microalga that are responsible for assembling medium-chain fatty acids. These two enzymes can increase MCT productivity by 64.8-fold at the peak phase of oil production when combined with other enzymes that provide substrates to the specialised MCT-assembly mechanism.
Such functional specialisation of these proteins in determining the chain length of products indicates a previously unknown level of control over cellular triacylglycerol that can be used to produce customisable oils in microalgae.
To further improve MCT production, the researchers plan to genetically modify the molecules to stop fatty acid breakdown, regulate how long fatty acids can be, and increase the total triacylglycerol content.
“Such efforts should further enhance cellular MCT production and accelerate the pace of engineering industrial microalgae into efficient and sustainable feedstock for customisable oils,” said Hu Chunxiu, an associate professor at the Dalian Institute of Chemical Physics (DICP) of CAS.
Source: Xin et al. (2022). Medium-Chain Triglyceride Production in Nannochloropsis via a Fatty Acid Chain Length Discriminating Mechanism. Plant Physiology.