Carbon and nitrogen optimization in solid-state fermentation for sustainable sophorolipid production using industrial waste

The use of alternative feedstocks such as industrial or food waste is being explored for the sustainable production of sophorolipids (SLs). Microbial biosurfactants are mainly produced via submerged fermentation (SmF); however, solid-state fermentation (SSF) seems to be a promising alternative for using solid waste or byproducts that could not be exploited by SmF. Applying the advantages that SSF offers and with the aim of revalorizing industrial organic waste, the impact of carbon and nitrogen sources on the relationship between yeast growth and SL production was analyzed. The laboratory-scale system used winterization oil cake as the solid waste for a hydrophobic carbon source. Pure hydrophilic carbon (glucose) and nitrogen (urea) sources were used in a Box-Behnken statistical design of experiments at different ratios by applying the response surface methodology. Optimal conditions to maximize the production and productivity of diacetylated lactonic C18:1 were a glucose:nitrogen ratio of 181.7:1.43 (w w-1 based on the initial dry matter) at a fermentation time of 100 h, reaching 0.54 total gram of diacetylated lactonic C18:1 with a yield of 0.047 g per gram of initial dry mass. Moreover, time course fermentation under optimized conditions increased the SL crude extract and diacetylated lactonic C8:1 production by 22% and 30%, respectively, when compared to reference conditions. After optimization, industrial wastes were used to substitute pure substrates. Different industrial sludges, OFMSW hydrolysate, and sweet candy industry wastewater provided nitrogen, hydrophilic carbon, and micronutrients, respectively, allowing their use as alternative feedstocks. Sweet candy industry wastewater and cosmetic sludge are potential hydrophilic carbon and nitrogen sources, respectively, for sophorolipid production, achieving yields of approximately 70% when compared to the control group.

Heterologous Synthesis and Secretion of Ricinoleic Acid in Starmerella bombicola with Sophorolipid as an Intermediate

Ricinoleic acid (RA) is a long-chain hydroxy fatty acid produced from castor bean that is used in the manufacturing of a variety of industrial products. The demand for RA keeps increasing due to its broad applications. However, due to the presence of a potent toxin ricin, the native oilseed plant is not an ideal source for hydroxy fatty acid production. Although there have been significant efforts on engineering different microorganisms for heterologous production of RA, all had very limited success. The main reason for this is the exhibited toxicity of the intracellularly accumulated RA. To avoid this issue, we genetically modified a Starmerella bombicola strain by engineering its native sophorolipid production pathway to direct the synthesized RA bound with sophorolipid to be secreted out of the cell, followed by acid hydrolysis to recover RA. The engineered S. bombicola strain expressing the heterologous codon-optimized oleate hydroxylase-encoding gene from ergot fungus Claviceps purpurea resulted in a record production titer of RA at about 2.96 g/L. Thus, this work highlights a new strategy to produce a high level of hydroxy fatty acids in engineered yeast through a sophorolipid intermediate, enabling a new biocatalysis platform for the future.

A multi-omics study to boost continuous bolaform sophorolipid production

Biodegradable and biobased surface active agents are renewable and environmentally friendly alternatives to petroleum derived or oleochemical surfactants. However, they are accompanied by relatively high production costs. In this study, the aim was to reduce the production costs for an innovative type of microbial biosurfactant: bolaform sophorolipids, produced by the yeast Starmerella bombicola ΔsbleΔat. A novel continuous retentostat set-up was performed whereby continuous broth microfiltration retained the biomass in the bioreactor while performing an in situ product separation of bolaform sophorolipids. Although a mean volumetric productivity of 0.56 g L^-1 h^-1 was achieved, it was not possible to maintain this productivity, which collapsed to almost 0 g L^-1 h^-1. Therefore, two process adaptations were evaluated, a sequential batch strategy and a phosphate limitation alleviation strategy. The sequential batch set-up restored the mean volumetric productivity to 0.66 g L^-1 h^-1 for an additional 132 h but was again followed by a productivity decline. A similar result was obtained with the phosphate limitation alleviation strategy where a mean volumetric productivity of 0.54 g L^-1 h^-1 was reached, but a productivity decline was also observed. Whole genome variant analysis uncovered no evidence for genomic variations for up to 1306 h of retentostat cultivation. Untargeted metabolomics analysis identified 8-hydroxyguanosine, a biomarker for oxidative RNA damage, as a key metabolite correlating with high bolaform sophorolipid productivity. This study showcases the application of a retentostat to increase bolaform sophorolipid productivity and lays the basis of a multi-omics platform for in depth investigation of microbial biosurfactant production with S. bombicola.

Glycolipid Biosurfactant Production from Waste Cooking Oils by Yeast: Review of Substrates, Producers and Products

Biosurfactants are a microbially synthesized alternative to synthetic surfactants, one of the most important bulk chemicals. Some yeast species are proven to be exceptional biosurfactant producers, while others are emerging producers. A set of factors affects the type, amount, and properties of the biosurfactant produced, as well as the environmental impact and costs of biosurfactant’s production. Exploring waste cooking oil as a substrate for biosurfactants’ production serves as an effective cost-cutting strategy, yet it has some limitations. This review explores the existing knowledge on utilizing waste cooking oil as a feedstock to produce glycolipid biosurfactants by yeast. The review focuses specifically on the differences created by using raw cooking oil or waste cooking oil as the substrate on the ability of various yeast species to synthesize sophorolipids, rhamnolipids, mannosylerythritol lipids, and other glycolipids and the substrate’s impact on the composition, properties, and limitations in the application of biosurfactants.

Valorization of waste-cooking oil into sophorolipids and application of their methyl hydroxyl branched fatty acid derivatives to produce engineering bioplastics

Waste-cooking oil (WCO) is defined as vegetable oil that has been used to fry food at high temperatures. The annual global generation of WCO is 41-67 million tons. Without proper treatment, most WCO is abandoned in sinks and the solid residue of WCO is disposed of in landfills, resulting in serious environmental problems. Recycling and valorizing WCO have received considerable attention to reduce its negative impact on ecosystems. To convert WCO into a high value-added compound, we aimed to produce sophorolipids (SLs) that are industrially important biosurfactants, using WCO as a hydrophobic substrate by the fed-batch fermentation of Starmerella bombicola. The SLs concentration was increased ~3.7-fold compared with flask culture (315.6 vs. 84.8 g/L), which is the highest value ever generated from WCO. To expand the applications of SLs, we prepared methyl hydroxy branched fatty acids (MHBFAs) from SLs, which are important chemicals for various industries yet difficult to produce by chemical methods, using a bio-chemical hybrid approach. We synthesized bio-based plastics using MHBFAs as co-monomers. Compared with the control polymer without MHBFAs, even the incorporation of 1 mol% into polymer chains improved mechanical properties (such as ultimate tensile strength, 1.1-fold increase; toughness, 1.3-fold increase). To the best of our knowledge, this is the first attempt to apply MHBFAs from SLs derived from WCO to building blocks of plastics. Thus, we extended the valorization areas of WCO to one of the world's largest industries.

ROS-Mediated Necrosis by Glycolipid Biosurfactants on Lung, Breast, and Skin Melanoma Cells

Cancer is one of the major leading causes of death worldwide. Designing the new anticancer drugs is remained a challenging task due to ensure complexicity of cancer etiology and continuosly emerging drug resistance. Glycolipid biosurfactants are known to possess various biological activities including antimicrobial, anticancer and antiviral properties. In the present study, we sought to decipher the mechanism of action of the glycolipids (lactonic-sophorolipd, acidic-sophorolipid, glucolipid, and bolalipid) against cancer cells using lung cancer cell line (A549), breast cancer cell line (MDA-MB 231), and mouse skin melanoma cell line (B16F10). Scratch assay and fluorescence microscopy revealed that glycolipids inhibit tumorous cell migration possibly by inhibiting actin filaments. Fluorescence activated cell sorter (FACS) analysis exhibited that lactonic sophorolipid and glucolipid both induced the reactive oxygen species, altered the mitochondrial membrane potential (ΔΨ) and finally led to the cell death by necrosis. Furthermore, combinatorial effect of lactonic-sophorolipd and glucolipid demonstrated synergistic interaction on A549 cell line whereas additive effect on MDA-MB 231 and B16F10 cell lines. Our study has highlighted that lactonic-sophorolipd and glucolipid could be useful for developing new anticancer drugs either alone or in combination.

Mutant breeding of Starmerella bombicola by atmospheric and room-temperature plasma (ARTP) for improved production of specific or total sophorolipids

To enhance specific or total sophorolipids (SLs) production by Starmerella bombicola for specific application, mutant library consisting of 106 mutants from 7 batches was constructed via atmospheric and room-temperature plasma (ARTP). When compared to the wild strain, 11, 36 and 12 mutants performed increases over 30% in lactonic, acidic or total SLs production. Genetic stability investigation showed that 8, 7, and 4 mutants could maintain the improved SLs production capacity. Mutants of A6-9 and A2-8 were selected out for enhanced specific SLs and total SLs production in fed-batch cultivation in flask. Without optimization, A6-9 obtained the highest reported lactonic SLs production of 51.95 g/l and A2-8 performed comparable acidic and total SLs production of 68.75 g/l and 100.33 g/l with all the reported stains. The structural composition of the obtained SLs was analyzed by HPLC and LC/MS, and the results confirmed the enhancement of SLs and certain SL components. These mutants would be important in industrial applications because the production and purification costs of SLs could be greatly reduced. Besides, the acquisition of these mutants also provided materials for the investigation of regulation mechanism of SLs biosynthesis for further genetic engineering of S. bombicola. Furthermore, critical micelle concentration (CMC), minimum surface tension (ST_min) and hydrophilic-lipophilic balance (HLB) of the SLs obtained from the wild and mutant strains were also examined and compared. These results demonstrated the feasibility of obtaining SLs with different properties from different strains and the high efficiency of mutation breeding of S. bombicola by ARTP.

Production of long-chain hydroxy fatty acids by Starmerella bombicola

To decrease our dependency for the diminishing source of fossils resources, bio-based alternatives are being explored for the synthesis of commodity and high-value molecules. One example in this ecological initiative is the microbial production of the biosurfactant sophorolipids by the yeast Starmerella bombicola. Sophorolipids are surface-active molecules mainly used as household and laundry detergents. Because S. bombicola is able to produce high titers of sophorolipids, the yeast is also used to increase the portfolio of lipophilic compounds through strain engineering. Here, the one-step microbial production of hydroxy fatty acids by S. bombicola was accomplished by the selective blockage of three catabolic pathways through metabolic engineering. Successful production of 17.39 g/l (ω-1) linked hydroxy fatty acids was obtained by the successive blockage of the sophorolipid biosynthesis, the β-oxidation and the ω-oxidation pathways. Minor contamination of dicarboxylic acids and fatty aldehydes were successfully removed using flash chromatography. This way, S. bombicola was further expanded into a flexible production platform of economical relevant compounds in the chemical, food and cosmetic industries.

Exploring magnetic and imprinted cross-linked enzyme aggregates of rhamnopyranosidase in microbioreactors

The goal of this work was the development of magnetic cross link enzyme aggregates (mCLEAs) of rhamnopyranosidase (Rhmnase), prepared by chemical cross-linking with functionalized magnetite nanoparticles for glycompounds biosynthesis in microbioreactors (specially design 24-well microplate and mini-packed bed). Rhamnopyranosidase (EC number 3.2.1.40) present high potential in glycocompounds production, with applications in food and pharmaceutical industries. The influence of precipitants, cross-linkers, temperature and time on (m)CLEAs@Rhmnase development were optimized. Biocatalyst activity was accessed in the hydrolysis of 4',5,7-trihydroxyflavanone-7-rhamnoglucoside and kinetic constants in the deglycosylation reaction were evaluated. Rhmnase operational stability was enhanced in mCLEAs, retaining almost 90% initial activity after 7 cycles of 24 h each. In a mini-packed bed bioreactor a maximum volumetric productivity of 140 μmol/L.h was attained. In this bioreactor the operational stability of mCLEAs@Rhmnase were evaluated at a flow rate of 5 mL/h during 5 days and a residual activity of 95% was observed.

Enantiocomplementary Yarrowia lipolytica Oxidoreductases: Alcohol Dehydrogenase 2 and Short Chain Dehydrogenase/Reductase

Enzymes of the non-conventional yeast Yarrowia lipolytica seem to be tailor-made for the conversion of lipophilic substrates. Herein, we cloned and overexpressed the Zn-dependent alcohol dehydrogenase ADH2 from Yarrowia lipolytica in Escherichia coli. The purified enzyme was characterized in vitro. The substrate scope for YlADH2 mediated oxidation and reduction was investigated spectrophotometrically and the enzyme showed a broader substrate range than its homolog from Saccharomyces cerevisiae. A preference for secondary compared to primary alcohols in oxidation direction was observed for YlADH2. 2-Octanone was investigated in reduction mode in detail. Remarkably, YlADH2 displays perfect (S)-selectivity and together with a highly (R)-selective short chain dehydrogenase/ reductase from Yarrowia lipolytica it is possible to access both enantiomers of 2-octanol in >99% ee with Yarrowia lipolytica oxidoreductases.

Biocatalytic production of novel glycolipids with cellodextrin phosphorylase

Glycolipids have gained increasing attention as natural surfactants with a beneficial environmental profile. They are typically produced by fermentation, which only gives access to a limited number of structures. Here we describe the biocatalytic production of novel glycolipids with the cellodextrin phosphorylase from Clostridium stercorarium. This enzyme was found to display a broad donor and acceptor specificity, allowing the synthesis of five different products. Indeed, using either α-glucose 1-phosphate or α-galactose 1-phosphate as glycosyl donor, sophorolipid as well as glucolipid could be efficiently glycosylated. The transfer of a glucosyl moiety afforded a mixture of products that precipitated from the solution, resulting in near quantitative yields. The transfer of a galactosyl moiety, in contrast, generated a single product that remained in solution at thermodynamic equilibrium. These glycolipids not only serve as a new class of biosurfactants, but could also have applications in the pharmaceutical and nanomaterials industries.

Identification of suitable ionic liquids for application in the enzymatic hydrolysis of rutin by an automated screening

An automated method in milliliter scale was developed for the screening of process parameters concerning the hydrolysis of the flavonoid rutin catalyzed by the rhamnosidase activity of naringinase from Penicillium decumbens. Besides the effect of additives such as ionic liquids and low molecular salts, the productivity in a multiple phase system as well as the recyclability of the enzyme in repetitive batches were studied. The hydrophobic ionic liquid (IL) trihexyl(tetradecyl)phosphonium bis(trifluormethylsulfonyl)imide [P(h(3))t][Tf(2)N] was identified to combine the most favorable characteristics out of 23 investigated ILs with regard to enzyme compatibility, substrate solubility and enzyme partition coefficient. Also, for the corresponding cations 1-ethyl-3-methylimidazolium [EMIM], 1-butyl-3-methylimidazolium [BMIM], 1-butyl-1-methylpyrrolidinium [BMPL] and 1-octyl-3-methylimidazolium [OMIM], the entity with the [Tf(2)N] anion was best tolerated by the naringinase. With increasing IL content, higher space time yields with up to 1.5 g/(L h) for 80% (v/v) [P(h(3))t][Tf(2)N] were achieved. Enhanced specific enzyme activity was observed in the presence of Ca(2+) ions. By addition of [P(h(3))t][Tf(2)N] and calcium chloride, the reactive aqueous phase was successfully used in three repetitive batches with full conversion.

Cloning and functional characterization of the UDP-glucosyltransferase UgtB1 involved in sophorolipid production by Candida bombicola and creation of a glucolipid-producing yeast strain

Sophorolipids produced by the non-pathogenic yeast Candida bombicola ATCC 22214 are glycolipid biosurfactants applied commercially as biodegradable and eco-friendly detergents. Their low cell toxicity, excellent wetting capability and antimicrobial activity attract the attention of high-value markets, such as the cosmetic and pharmaceutical industries. Although sophorolipid production yields have been increased by the optimization of fermentation parameters and feed sources, the biosynthetic pathway and genetic mechanism behind sophorolipid production still remains unclear. Here we identify a UDP-glucosyltransferase gene, UGTB1, with a key function in this economically important pathway. The protein shows sequence and structural homology to several bacterial glycosyltransferases involved in macrolide antibiotic synthesis. Deletion of UGTB1 in C. bombicola did not affect cell growth and resulted in a yeast producing glucolipids, thereby opening the route for in vivo production of these glycolipid intermediates. Activity assays on cell lysates confirmed that the identified gene is responsible for the second glucosylation step during sophorolipid production and illustrated that sophorolipid production in C. bombicola involves the stepwise action of two independent glucosyltransferases. The complete UGTB1 sequence data have been submitted to the GenBank database (http://www.ncbi.nlm.nih.gov) under Accession No. HM440974.