In the present study, eight kinds plant growth regulators—salicylic acid (SA), 1-naphthaleneacetic acid (NAA), gibberellic acid (GA₃), 6-benzylaminopurine (6-BA), 2, 4-epi-brassinolide (EBR), abscisic acid (ABA), ethephon (ETH), and spermidine (SPD)—were used to investigate the impact on microalgal biomass, lipid, total soluble protein, carotenoids, and polyunsaturated fatty acids (PUFAS) production of Chlorella pyrenoidosa ZF strain. The results showed the quickest biomass enhancement was induced by 50 mg·L⁻¹ NAA, with a 6.3-fold increase over the control; the highest protein content was increased by 0.005 mg·L⁻¹ ETH, which produced 3.5-fold over the control; total carotenoids content was induced most effectively by 1 mg·L⁻¹ NAA with 3.6-fold higher production than the control; the most efficient elicitor for lipid production was 5 mg·L⁻¹ GA₃ at 1.9-fold of the control; 0.2 mg·L⁻¹ ETH induced the abundant production of 1.82 ± 0.23% linoleic acid; 0.65 ± 0.01% linolenic acid was induced by 1 mg·L⁻¹ NAA; 2.53 ± 0.15% arachidonic acid and 0.44 ± 0.05% docosahexaenoic acid were induced by 5 mg·L⁻¹ GA₃. Transcriptional expression levels of seven lipid-related genes, including ACP, BC, FAD, FATA, KAS, MCTK, and SAD, were studied by real-time RT-q-PCR. 5 mg·L⁻¹ GA₃ was the most effective regulator for transcriptional expressions of these seven genes, producing 23-fold ACP, 31-fold BC, 25-fold FAD, 6-fold KAS, 12-fold MCTK compared with the controls, respectively.

Background: Biological α-olefins can be used as both biofuels and high value-added chemical precursors to lubricants, polymers, and detergents. The prototypic CYP152 peroxygenase family member OleT_JE from Jeotgalicoccus sp. ATCC 8456 catalyzes a single-step decarboxylation of free fatty acids (FFAs) to form α-olefins using H₂O₂ as a cofactor, thus attracting much attention since its discovery. To improve the productivity of α-olefins, significant efforts on protein engineering, electron donor engineering, and metabolic engineering of OleT_JE have been made. However, little success has been achieved in obtaining α-olefin high-producer microorganisms due to multiple reasons such as the tight regulation of FFA biosynthesis, the difficulty of manipulating multi-enzyme metabolic network, and the poor catalytic performance of OleT_JE. Results: In this study, a novel enzyme cascade was developed for one-pot production of α-olefins from low-cost triacylglycerols (TAGs) and natural oils without exogenous H₂O₂ addition. This artificial biocatalytic route consists of a lipase (CRL, AOL or Lip2) for TAG hydrolysis to produce glycerol and free fatty acids (FFAs), an alditol oxidase (AldO) for H₂O₂ generation upon glycerol oxidation, and the P450 fatty acid decarboxylase OleT_JE for FFA decarboxylation using H₂O₂ generated in situ. The multi-enzyme system was systematically optimized leading to the production of α-olefins with the conversion rates ranging from 37.2 to 68.5%. Furthermore, a reaction using lyophilized CRL/OleT_JE/AldO enzymes at an optimized ratio (5 U/6 μM/30 μM) gave a promising α-olefin yield of 0.53 g/L from 1500 μM (~1 g/L) coconut oil. Conclusions: The one-pot enzyme cascade was successfully established and applied to prepare high value-added α-olefins from low-cost and renewable TAGs/natural oils. This system is independent of exogenous addition of H₂O₂, thus not only circumventing the detrimental effect of H₂O₂ on the stability and activity of involved enzymes, but also lower the overall costs on the TAG-to-olefin transformation. It is anticipated that this biotransformation system will become industrially relevant in the future upon more engineering efforts based on this proof-of-concept work.

Haematococcus pluvialis accumulates a large amount of astaxanthin under various stresses, e.g., blue light and salicylic acid (SA). However, the metabolic response of H. pluvialis to blue light and SA is still unclear. We investigate the effects of blue light and SA on the metabolic response in H. pluvialis using both transcriptomic and proteomic sequencing analyses. The largest numbers of differentially expressed proteins (DEPs; 324) and differentially expressed genes (DEGs; 13,555) were identified on day 2 and day 7 of the treatment with blue light irradiation (150 μmol photons m⁻²s⁻¹), respectively. With the addition of SA (2.5 mg/L), a total of 63 DEPs and 11,638 DEGs were revealed on day 2 and day 7, respectively. We further analyzed the molecular response in five metabolic pathways related to astaxanthin synthesis, including the astaxanthin synthesis pathway, the fatty acid synthesis pathway, the heme synthesis pathway, the reactive oxygen species (ROS) clearance pathway, and the cell wall biosynthesis pathway. Results show that blue light causes a significant down-regulation of the expression of key genes involved in astaxanthin synthesis and significantly increases the expression of heme oxygenase, which shows decreased expression by the treatment with SA. Our study provides novel insights into the production of astaxanthin by H. pluvialis treated with blue light and SA.

Microalgae produce a variety of high-value products. Enhancing product contents in microalgal cells is one of the efficient ways to decrease production costs. Improved germplasm and heterotrophic cultivation may enhance microalgae biomass and lipid content. In this study, we investigated the effect of three types of laser irradiation and heterotrophic cultivation on lipid productivity, lipid content, and biomass of two Chlorella strains (i.e., FACHB 9 and FACHB 31). Results showed that the highest biomasses of 4.81 g/L (15.03-fold) and 4.66 g/L (7.32-fold) were obtained in the third generation of FACHB 9 and FACHB 31 induced by a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for 8 min and 12 min, respectively. The highest lipid contents were 525.6 mg/g (1.67-fold) dry weight (DW) and 780.0 mg/g DW (2.20-fold) in the third and the first generations of FACHB 9 and FACHB 31 induced by Nd:YAG for 8 min and by a helium–neon (He–Ne) laser for 4 min, respectively. The highest lipid productivities of 69.82 ± 3.29 mg/L/d (19.7-fold) and 30.71 ± 3.77 mg/L/d (3.1-fold) were obtained in FACHB 9 and FACHB 31 treated by a semiconductor (SC) laser for 4 min and by a He–Ne laser for 12 min, respectively. Our study suggested that laser mutagenesis is a potential method for screening economically important oleaginous microalgae strains.

Cold stress causes changes in the lipid composition of Mortierella alpina. In order to investigate the molecular mechanisms of M. alpina in response to cold stress, transcriptome analyses were performed on three groups of M. alpina cultured at (1) 25 °C, (2) 15 °C, and (3) first at 25 °C for 2 days and then 15 °C for 7 days, respectively. The results of a gas chromatography–mass spectrometry (GC–MS) analysis suggested that, compared with 25 °C conditions, dry weight and lipid production were significantly decreased in M. alpina grown at 15 °C, with a total of 1552 differentially expressed genes (DEGs) identified in response to cold stress. The quantitative real-time PCR (qRT-PCR) analysis was conducted to verify the expression patterns of six DEGs involved in lipid metabolism. Results of the enrichment analyses of the DEGs based on the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases showed that fatty acid compositions were regulated by genes involved in the glycolysis pathway, fatty acid synthesis, the pentose phosphate pathway, the glycerolipid pathway, the tricarboxylic acid (TCA) cycle, and the glycerophospholipid pathway. Our study provided solid experimental evidence and novel insights into the metabolic engineering and the molecular mechanisms regulating the response to cold stress in M. alpina.