Enhancement of astaxanthin production in Schizochytrium limacinum B4D1 under ethanol induction

Identification and Functional Analysis of Two Novel Genes-Geranylgeranyl Pyrophosphate Synthase Gene (AlGGPPS) and Isopentenyl Pyrophosphate Isomerase Gene (AlIDI)-from Aurantiochytrium limacinum Significantly Enhance De Novo β-Carotene Biosynthesis in Escherichia coli

Precursor regulation has been an effective strategy to improve carotenoid production and the availability of novel precursor synthases facilitates engineering improvements. In this work, the putative geranylgeranyl pyrophosphate synthase encoding gene (AlGGPPS) and isopentenyl pyrophosphate isomerase encoding gene (AlIDI) from Aurantiochytrium limacinum MYA-1381 were isolated. We applied the excavated AlGGPPS and AlIDI to the de novo β-carotene biosynthetic pathway in Escherichia coli for functional identification and engineering application. Results showed that the two novel genes both functioned in the synthesis of β-carotene. Furthermore, AlGGPPS and AlIDI performed better than the original or endogenous one, with 39.7% and 80.9% increases in β-carotene production, respectively. Due to the coordinated expression of the 2 functional genes, β-carotene content of the modified carotenoid-producing E. coli accumulated a 2.99-fold yield of the initial EBIY strain in 12 h, reaching 10.99 mg/L in flask culture. This study helped to broaden current understanding of the carotenoid biosynthetic pathway in Aurantiochytrium and provided novel functional elements for carotenoid engineering improvements.

Propanol and 1, 3-propanediol enhance fatty acid accumulation synergistically in Schizochytrium ATCC 20888

The effects of propanol and 1, 3-propanediol on fatty acid and biomass accumulation in Schizochytrium ATCC 20888 were explored. Propanol increased the contents of saturated fatty acids and total fatty acids by 55.4 and15.3%, while 1, 3-propanediol elevated the polyunsaturated fatty acids, total fatty acids and biomass contents by 30.7, 17.0, and 6.89%. Although both of them quench ROS to increase fatty acids biosynthesis, the mechanisms are different. The effect of propanol did not reflect on metabolic level while 1, 3-propanediol elevated osmoregulators contents and activated triacylglycerol biosynthetic pathway. The triacylglycerol content and the ratio of polyunsaturated fatty acids to saturated fatty acids were significantly increased by 2.53-fold, which explained the higher PUFA accumulation in Schizochytrium after adding 1, 3- propanediol. At last, the combination of propanol and 1, 3-propanediol further elevated total fatty acids by approximately 1.2-fold without compromising cell growth. These findings are valuable for scale-up production of designed Schizochytrium oil for various application purposes.

Elucidation of sterol biosynthesis pathway and its co-regulation with fatty acid biosynthesis in the oleaginous marine protist Schizochytrium sp

Sterols constitute vital structural and regulatory components of eukaryotic cells. In the oleaginous microorganism Schizochytrium sp. S31, the sterol biosynthetic pathway primarily produces cholesterol, stigmasterol, lanosterol, and cycloartenol. However, the sterol biosynthesis pathway and its functional roles in Schizochytrium remain unidentified. Through Schizochytrium genomic data mining and a chemical biology approach, we first in silico elucidated the mevalonate and sterol biosynthesis pathways of Schizochytrium. The results showed that owing to the lack of plastids in Schizochytrium, it is likely to use the mevalonate pathway as the terpenoid backbone pathway to supply isopentenyl diphosphate for the synthesis of sterols, similar to that in fungi and animals. In addition, our analysis revealed a chimeric organization of the Schizochytrium sterol biosynthesis pathway, which possesses features of both algae and animal pathways. Temporal tracking of sterol profiles reveals that sterols play important roles in Schizochytrium growth, carotenoid synthesis, and fatty acid synthesis. Furthermore, the dynamics of fatty acid and transcription levels of genes involved in fatty acid upon chemical inhibitor-induced sterol inhibition reveal possible co-regulation of sterol synthesis and fatty acid synthesis, as the inhibition of sterol synthesis could promote the accumulation of fatty acid in Schizochytrium. Sterol and carotenoid metabolisms are also found possibly co-regulated, as the inhibition of sterols led to decreased carotenoid synthesis through down-regulating the gene HMGR and crtIBY in Schizochytrium. Together, elucidation of the Schizochytrium sterol biosynthesis pathway and its co-regulation with fatty acid synthesis lay the essential foundation for engineering Schizochytrium for the sustainable production of lipids and high-value chemicals.

Transcriptome analysis of malate-induced Schizochytrium sp. FJU-512 reveals a novel pathway for biosynthesis of docosahexaenoic acid with enhanced expression of genes responsible for acetyl-CoA and NADPH accumulation

Schizochytrium is one of the few oleaginous microalgae that produce docosahexaenoic acid (DHA)-rich lipids. In this study, global changes in gene expression levels of Schizochytrium sp. FJU-512 cultured with malate in a 15 l-bioreactor was analyzed using comparative transcriptomics. The changes were found mainly in the genes involved in oxidative phosphorylation, β-oxidation, and pentose phosphate pathways. Consequently, the global changes in genes associated with the pathways could lead to an increase in the influx throughputs of pyruvate, branched-chain amino acids, fatty acids, and vitamin B6. Our transcriptome analysis indicated pyruvate dehydrogenase E2 component and acetolactate synthase I/II/III large subunit as major contributors to acetyl-CoA biosynthesis, whereas glucose-6-phosphate dehydrogenase was indicated as the major contributor to the biosynthesis of NADPH. An increase in DHA titer of up to 22% was achieved with the addition of malate to the fed-batch culture of Schizochytrium sp. FJU-512. This study provides an alternate method to enhance DHA production in Schizochytrium sp. FJU-512 through malate induced upregulation of genes responsible for acetyl-CoA and NADPH biosynthesis.

Sustainable production of astaxanthin in microorganisms: the past, present, and future

Astaxanthin (3,3'-dihydroxy-4,4'-diketo-β-carotene) is a type of C40 carotenoid with remarkable antioxidant characteristics, showing significant application prospects in many fields. Traditionally, the astaxanthin is mainly obtained from chemical synthesis and natural acquisition, with both approaches having many limitations and not capable of meeting the growing market demand. In order to cope with these challenges, novel techniques, e.g., the innovative cell engineering strategies, have been developed to increase the astaxanthin production. In this review, we first elaborated the biosynthetic pathway of astaxanthin, with the key enzymes and their functions discussed in the metabolic process. Then, we summarized the conventional, non-genetic strategies to promote the production of astaxanthin, including the methods of exogenous additives, mutagenesis, and adaptive evolution. Lastly, we reviewed comprehensively the latest studies on the synthesis of astaxanthin in various recombinant microorganisms based on the concept of microbial cell factory. Furthermore, we have proposed several novel technologies for improving the astaxanthin accumulation in several model species of microorganisms.