Microbial synthesis and extraction of value-added metabolites by Rhodotorula toruloides from waste stream: a sustainable approach

Abstract

Rhodotorula toruloides (R. toruloides) has shown great potential for the microbiological synthesis of useful substances, including lipids and carotenoids. Through interconnected metabolic pathways, this oleaginous yeast can synthesize various carotenoids and accumulate significant amounts of lipids. The mevalonate pathway plays a crucial role in the production of these substances. R. toruloides can utilize diverse carbon sources, including waste-derived and sustainable substrates. The product yields are significantly influenced by the optimization of stress factors and culture conditions. Lipid and carotenoid extraction methods have advanced from traditional approaches to more sophisticated techniques, such as enzyme-assisted extraction, ultrasound-assisted extraction, and supercritical fluid extraction. These modern techniques aim to minimize environmental impact while maximizing efficiency and selectivity. Genetic engineering has played a pivotal role in enhancing lipid and carotenoid accumulation in R. toruloides. These strategies involve overexpressing key biosynthetic genes, modifying regulatory elements, and introducing heterologous pathways. Such approaches have expanded the range of chemical synthesis and led to significant improvements in product yields. This study provides a comprehensive insight into the metabolic linkages between lipid and carotenoid biosynthesis, highlighting how stress factors, genetic engineering, and waste-derived substrates influence productivity. Furthermore, present review uniquely explores the role of R. toruloides in environmental bioremediation and wastewater treatment, emphasizing its potential for sustainable waste valorization. Due to its ability to synthesize valuable chemicals from a wide array of carbon sources, R. toruloides is a promising candidate for commercial applications in the feed, food, cosmetic, and biofuel industries.

Keywords: Carotenoids; Extraction methods; Genetic engineering; Lipids metabolic pathways and sustainable carbon sources.

Fig. 1

Schematic representation of the TCA cycle and the Mevalonate (MVA) pathway leading to carotenoid biosynthesis. Glucose-derived pyruvate enters the TCA cycle that generates intermediates and acetyl-CoA, which feeds into the MVA pathway for the bio synthesis of carotenoids in R. toruloides (substrates involved: HMG-CoA-3-hydroxy-3-methylglutaryl-CoA, IPP-Isopentenyl diphosphate, GPP-Geranyl diphosphate) (Products: 2 ATP, 8 NADH, 2 FADH2, 6 CO2) (Created with Bio render)

Fig. 2

Biosynthesis of lipids—schematic representation of fatty acid and triacylglycerol (TAG) synthesis pathways. Acetyl-CoA derived from the TCA cycle is converted into malonyl-CoA for fatty acid biosynthesis, followed by TAG assembly through a series of enzymatic steps involving GPAT, LPAAT, LPAT, and DGAT in R. toruloides (Enzymes involved in various stages of fatty acid and triacylglycerol biosynthesis in R. toruloides -ACCase: acetyl-CoA carboxylase, MAT: malonyl-CoA ACP transacylase, KAS: ketoacyl-ACP synthase, KAR: ketoacyl-ACP reductase, HD: hydroxyacyl-ACP dehydratase, ENR: enoyl-ACP reductase, FAT: fatty acyl-ACP thioesterase, GPAT: glycerol-3-phosphate acyltransferase, LPAAT: lysophosphatidic acid, acyltransferase, LPAT: lysophosphatidic acid acyltransferase (same as LPAAT), DGAT: diacylglycerol acyltransferase) (Created with Bio render)

Fig. 3

Interconnected metabolic pathways for lipid and carotenoid biosynthesis in R. toruloides. The diagram illustrates the TCA cycle, acetyl-CoA synthesis, MVA pathway, Kennedy pathway for lipid formation, and beta-oxidation, showing the metabolic flow toward triacylglycerol and carotenoid production. (Enzymes involved: PSY- Phytoene synthase, CAR 1- Phytoene desaturase, CAR 2 -Lycopene cyclase, FAS-Fatty acid synthase, G3P—Glyceraldehyde-3-phosphate (Created with Bio render)

Fig. 4

Schematic overview of biomass processing for microbial pigment and lipid production Renewable plant biomass undergoes pretreatment, hydrolysis, and fermentation by yeast cells to produce microbial pigments (β-carotene, torulene, torularhodin) and microbial lipids (linoleic acid, oleic acid, palmitoleic acid, and stearic acid), followed by downstream processing for recovery (Created with Bio render)

Fig. 5

Workflow for extraction and analysis of microbial lipids and carotenoids. The process involves cell harvesting, centrifugation, cell disruption (via high-pressure homogenization or chemical methods), solvent extraction, separation of organic and aqueous phases, and downstream analysis using various techniques