Enhanced Lycopene Content in Blakeslea trispora by Effective Mutation-Screening Method

Advances in engineering the production of the natural red pigment lycopene: A systematic review from a biotechnology perspective

BACKGROUND

Lycopene is a natural red compound with potent antioxidant activity that can be utilized both as pigment and as a raw material in functional food, and so possesses good commercial prospects. The biosynthetic pathway has already been documented, which provides the foundation for lycopene production using biotechnology.

AIM OF REVIEW

Although lycopene production has begun to take shape, there is still an urgent need to alleviate the yield of lycopene. Progress in this area can provide useful reference for metabolic engineering of lycopene production utilizing multiple approaches. Key scientific concepts of review Using conventional microbial fermentation approaches, biotechnologists have enhanced the yield of lycopene by selecting suitable host strains, utilizing various additives, and optimizing culture conditions. With the development of modern biotechnology, genetic engineering, protein engineering, and metabolic engineering have been applied for lycopene production. Extraction from natural plants is the main way for lycopene production at present. Based on the molecular mechanism of lycopene accumulation, the production of lycopene by plant bioreactor through genetic engineering has a good prospect. Here we summarized common strategies for optimizing lycopene production engineering from a biotechnology perspective, which are mainly carried out by microbial cultivation. We reviewed the challenges and limitations of this approach, summarized the critical aspects, and provided suggestions with the aim of potential future breakthroughs for lycopene production in plants.

Heterologous Lactate Synthesis in Synechocystis sp. Strain PCC 6803 Causes a Growth Condition-Dependent Carbon Sink Effect

Cyanobacteria are considered promising hosts for product synthesis directly from CO₂ via photosynthetic carbon assimilation. The introduction of heterologous carbon sinks in terms of product synthesis has been reported to induce the so-called “carbon sink effect,” described as the release of unused photosynthetic capacity by the introduction of additional carbon. This effect is thought to arise from a limitation of carbon metabolism that represents a bottleneck in carbon and electron flow, thus enforcing a downregulation of photosynthetic efficiency. It is not known so far how the cellular source/sink balance under different growth conditions influences the extent of the carbon sink effect and in turn product formation from CO₂, constituting a heterologous carbon sink. We compared the Synechocystis sp. strain PCC 6803 wild type (WT) with an engineered lactate-producing strain (SAA023) in defined metabolic states. Unexpectedly, high-light conditions combined with carbon limitation enabled additional carbon assimilation for lactate production without affecting biomass formation. Thus, a strong carbon sink effect only was observed under carbon and thus sink limitation, but not under high-sink conditions. We show that the carbon sink effect was accompanied by an increased rate of alternative electron flow (AEF). Thus, AEF plays a crucial role in the equilibration of source/sink imbalances, presumably via ATP/NADPH balancing. This study emphasizes that the evaluation of the biotechnological potential of cyanobacteria profits from cultivation approaches enabling the establishment of defined metabolic states and respective quantitative analytics. Factors stimulating photosynthesis and carbon fixation are discussed.

IMPORTANCE Previous studies reported various and differing effects of the heterologous production of carbon-based molecules on photosynthetic and growth efficiency of cyanobacteria. The typically applied cultivation in batch mode, with continuously changing growth conditions, however, precludes a clear differentiation between the impact of cultivation conditions on cell physiology and effects related to the specific nature of the product and its synthesis pathway. In this study, we employed a continuous cultivation system to maintain defined source/sink conditions and thus metabolic states. This allowed a systematic and quantitative analysis of the effect of NADPH-consuming lactate production on photosynthetic and growth efficiency. This approach enables a realistic evaluation of the biotechnological potential of engineered cyanobacterial strains. For example, the quantum requirement for carbon production was found to constitute an excellent indicator of the source/sink balance and thus a key parameter for photobioprocess optimization. Such knowledge is fundamental for rational and efficient strain and process development.

Metabolic Engineering of Different Microbial Hosts for Lycopene Production

As a result of the extensive use of lycopene in a variety of fields, especially the dietary supplement and health food industries, the production of lycopene has attracted considerable interest. Lycopene can be obtained through extraction from vegetables and chemical synthesis. Alternatively, the microbial production of lycopene has been extensively researched in recent years. Various types of microbial hosts have been evaluated for their potential to accumulate a high level of lycopene. Metabolic engineering of the hosts and optimization of culture conditions are performed to enhance lycopene production. After years of research, great progress has been made in lycopene production. In this review, strategies used to improve lycopene production in different microbial hosts and the advantages and disadvantages of each microbial host are summarized. In addition, future perspectives of lycopene production in different microbial hosts are discussed.

Biotechnological production of lycopene by microorganisms

Lycopene is a dark red carotenoid belonging to C40 terpenoids and is widely found in a variety of plants, especially ripe red fruits and vegetables. Lycopene has been shown to reduce the risk of prostate cancer, other cancers, and cardiovascular disease. It is one of the most widely used carotenoids in the healthcare product market. Currently, commercially available lycopene is mainly extracted from tomatoes. However, production of lycopene from plants is costly and environmentally unfriendly. To date, there have been many reports on the biosynthesis of lycopene by microorganisms, providing another route for lycopene production. This review discusses the lycopene biosynthetic pathway and natural and engineered lycopene-accumulating microorganisms, as well as their production of lycopene. The effects of different metabolic engineering strategies on lycopene accumulation are also considered. Furthermore, this work presents perspectives concerning the microbial production of lycopene, especially trends to construct microbial cell factories for lycopene production. KEY POINTS: • Recent achievements in the lycopene biosynthesis in microorganisms. • Review of lycopene biosynthetic metabolism engineering strategy. • Discuss the current challenges and prospects of using microorganisms to produce lycopene.

A Negative Regulator of Carotenogenesis in Blakeslea trispora

As an ideal carotenoid producer, Blakeslea trispora has gained much attention due to its large biomass and high production of β-carotene and lycopene. However, carotenogenesis regulation in B. trispora still needs to be clarified, as few investigations have been conducted at the molecular level in B. trispora In this study, a gene homologous to carotenogenesis regulatory gene (crgA) was cloned from the mating type (-) of B. trispora, and the deduced CrgA protein was analyzed for its primary structure and domains. To clarify the crgA-mediated regulation in B. trispora, we used the strategies of gene knockout and complementation to investigate the effect of crgA expression on the phenotype of B. trispora In contrast to the wild-type strain, the crgA null mutant (ΔcrgA) was defective in sporulation but accumulated much more β-carotene (31.2% improvement at the end) accompanied by enhanced transcription of three structural genes (hmgR, carB, and carRA) for carotenoids throughout the culture time. When the wild-type copy of crgA was complemented into the crgA null mutant, sporulation, transcription of structural genes, and carotenoid production were restored to those of the wild-type strain. A gas chromatography-mass spectrometry (GC-MS)-based metabolomic approach and multivariate statistical analyses were performed to investigate the intracellular metabolite profiles. The reduced levels of tricarboxylic acid (TCA) cycle components and some amino acids and enhanced levels of glycolysis intermediates and fatty acids indicate that more metabolic flux was driven into the mevalonate (MVA) pathway; thus, the increase of precursors and fat content contributes to the accumulation of carotenoids.IMPORTANCE The zygomycete Blakeslea trispora is an important strain for the production of carotenoids on a large scale. However, the regulation mechanism of carotenoid biosynthesis is still not well understood in this filamentous fungus. In the present study, we sought to investigate how crgA influences the expression of structural genes for carotenoids, carotenoid biosynthesis, and other anabolic phenotypes. This will lead to a better understanding of the global regulation mechanism of carotenoid biosynthesis and facilitate engineering this strain in the future for enhanced production of carotenoids.

Effects of exogenous lipids and cold acclimation on lycopene production and fatty acid composition in Blakeslea trispora

Exogenous lipids serving as stimulators to improve lycopene production in Blakeslea trispora have been widely reported. However, the selection basis of exogenous lipids and their effects on intracellular lipids are not very clear. In this study, five plant oils with different fatty acid compositions were selected to investigate their effects on lycopene production, fatty acid composition and the desaturation degree of intracellular lipids. Among the oils, soybean oil, with a fatty acid composition similar to that of mycelium, exhibited the best stimulating effect on lycopene formation (improvement of 82.1%). The plant oils enhanced the total content of intracellular lipids and the desaturation degree of reserve lipids due to the alteration of fatty acid composition, especially in neutral lipids. Lycopene production was increased with the improved desaturation degree of intracellular lipids, which may be attributed to the enhancement of storage capacity for lycopene in storage lipid, thus reducing the feedback regulation of free lycopene. In addition, the increase of the desaturation degree of reserve lipids through temperature-changing fermentation also enhanced lycopene production. The present study could serve as a basis for a better understanding of the relationship between the fatty acid composition of reserve lipids and lycopene production.

Lycopene Production by Mated Fermentation of Blakeslea trispora

Lycopene is a carotenoid mainly present in red-colored fruits and vegetables. Its value in the pharmaceutical and food industry is linked to its benefits for the human health, including properties against cancer and cardiovascular diseases, and its use as a food colorant. Lycopene can be produced either by synthetic or natural means, but there is a preference for the second, since it is considered a more eco-friendly and less harmful process. Among natural methods for obtaining lycopene, microbial fermentation is a good alternative to extraction from plants that naturally contain lycopene, since it implies obtaining higher and more specific amounts of this carotenoid. This chapter describes lycopene production by fermentation of the fungus Blakeslea trispora, a naturally carotenoid producer, at 30 L scale. This procedure involves separated growth of the two sexual mating types of B. trispora during the vegetative stages and the use of a lycopene cyclase inhibitor to achieve lycopene accumulation during the production stage.

Waste cooking oil: A new substrate for carotene production by Blakeslea trispora in submerged fermentation

The objective of this study was to evaluate a waste, waste cooking oil (WCO) as substrate for carotene production by Blakeslea trispora in shake flask culture. WCO was found to be a useful substrate for carotene production. B. trispora formed only pellets during fermentation. The oxidative stress in B. trispora induced by hydroperoxides and BHT as evidenced by increase of the specific activities of superoxide dismutase (SOD) and catalase (CAT) increased significantly the production of carotenes. The highest concentration of carotenes (2021 ± 75 mg/l or 49.3 ± 0.2 mg/g dry biomass) was obtained in culture grown in WCO (50.0 g/l) supplemented with CSL (80.0 g/l) and BHT (4.0 g/l). In this case the carotenes produced consisted of β-carotene (74.2%), γ-carotene (23.2%), and lycopene (2.6%). The external addition in the above medium glucose, Span 80, yeast extract, casein acid hydrolysate, l-asparagine, thiamine. HCl, KH2PO4, and MgSO4·7H2O did not improve the production of carotenes.

Changing trends in biotechnology of secondary metabolism in medicinal and aromatic plants

Medicinal and aromatic plants are known to produce secondary metabolites that find uses as flavoring agents, fragrances, insecticides, dyes and drugs. Biotechnology offers several choices through which secondary metabolism in medicinal plants can be altered in innovative ways, to overproduce phytochemicals of interest, to reduce the content of toxic compounds or even to produce novel chemicals. Detailed investigation of chromatin organization and microRNAs affecting biosynthesis of secondary metabolites as well as exploring cryptic biosynthetic clusters and synthetic biology options, may provide additional ways to harness this resource. Plant secondary metabolites are a fascinating class of phytochemicals exhibiting immense chemical diversity. Considerable enigma regarding their natural biological functions and the vast array of pharmacological activities, amongst other uses, make secondary metabolites interesting and important candidates for research. Here, we present an update on changing trends in the biotechnological approaches that are used to understand and exploit the secondary metabolism in medicinal and aromatic plants. Bioprocessing in the form of suspension culture, organ culture or transformed hairy roots has been successful in scaling up secondary metabolite production in many cases. Pathway elucidation and metabolic engineering have been useful to get enhanced yield of the metabolite of interest; or, for producing novel metabolites. Heterologous expression of putative plant secondary metabolite biosynthesis genes in a microbe is useful to validate their functions, and in some cases, also, to produce plant metabolites in microbes. Endophytes, the microbes that normally colonize plant tissues, may also produce the phytochemicals produced by the host plant. The review also provides perspectives on future research in the field.