Table 5.

Improvement of lipid content in different species of microalgae with genetic engineering methods

Microalgae species or strain	Type of modification	Changes in lipid profile in the microalgal cells	Refs.
Chlamydomonas reinhardtii	Repression of Major lipid droplet protein (MLDP) gene expression	40% increase in the average lipid droplet diameter	[197]
Chlamydomonas reinhardtii	Knockout of citrate synthase gene	TAG level increased up to 169.5%	[198]
Chlamydomonas reinhardtii	Artificial silencing of Diacylglycerol acyltransferase 2–4 gene (CrDGAT2-4)	24%-34% increase in lipid content	[199]
Chlamydomonas reinhardtii (starchless mutant)	Inactivation of Adenosine diphosphoglucose pyrophosphorylase (ADP-glucose pyrophosphorylase)	10-fold increase in TAG	[200]
Chlorella minutissima UTEX 2219	Overexpression of glycerol-3-phosphate aceyltransferease gene, lysophosphatidic acetyltransferase gene and diglyceride acyltransferase	2-fold increase in lipid content	[201]
Scenedesmus obliquus (starchless mutant)	Knockdown of competitive pathways genes	Increase in TAG accumulation of up to 51%	[202]
Phaeodactylum tricornutum	Heterologous gene expression of acyl–acyl carrier protein thioesterases (Acyl-ACP thioesterases)	Increased accumulation of shorter chain length fatty acids	[203]
Synechocystis sp.	Cyanophycin synthetase gene deletion	Fatty acids secretion into the medium	[204]
Synechocystis sp.	Phosphotransacetylase gene deletion	Increase in production of fatty acids	[204]
Phaeodactylum tricornutum	Suppression of TAG lipase gene expression	Increase of the lipid content (0.04 ± 0.01 mg TAG/mg dry weight)	[205]
Scenedesmus obliquus	Successful expression of diacylglycerol acyl-transferase gene	Enhanced 128% of lipid content.	[190]
C. reinhardtii	Knock-down of PEPC enzyme with CRISPRi	Enhanced lipid production up to 94%	[191]
P. tricornutum	Expression of malic enzyme	Enhanced lipid productivity by 2.5 in comparison with wild-type	[192]
P. tricornutum	Overexpression of glucose-6-phosphate dehydrogenase (G6PD)	Increased production of lipids up to 55.7% of dry weight	[186]
T. pseudonana	Knock-down of a multifunctional lipase/phospholipase/acetyltransferase enzyme	Mutant strains produced 2.4- to 3.3-fold higher amounts of lipids in comparison with wild-type	[186]