RESUMEN

Cellobiose lipids (CL) are glycolipids synthesized by Ustilaginaceae species with potential application as detergents or in cosmetics. This study identified process optimisation potential for CL fermentation based on process modelling and techno-economic analysis. Using a stoichiometric equation based on laboratory data, we calculated the maximum possible CL yield YP/S of 0.45 gCL·gglucose -1 at the biomass yield of 0.10 gBiomass·gglucose -1 with an Ustilago maydis strain. Due to substrate inhibition that may occur at high glucose concentrations, a fed-batch process to increase biomass and CL concentrations was considered in our model. Simulation of different process scenarios showed that the choice of aeration units with high oxygen transfer rates and adaptation of power input to oxygen uptake can significantly decrease electricity consumption. We further assessed scenarios with different fermentation media and CL purification methods, suggesting additional process optimisation potential. Here the omission of vitamins from the fermentation medium proved to be a possible mean to enhance process economy, without compromising CL productivity.

RESUMEN

Wide ranges of microorganisms produce glycosylated lipids (GL), which are characterized by their tensio-active properties. Therefore, they can be used in different industrial applications as biosurfactants, such as food, agriculture, cosmetics, and health products among others. Two GL biosurfactants, rhamnolipids (RL) and sophorolipids (SL), are now commercially available and share a significant part of the biosurfactant market that in 2017 represented about 2.5% of the total surfactants market, estimated at 15 million tons globally.In this chapter, we present a general overview of GL biosurfactants in terms of their diversity and the microorganisms that produce them. Additionally, we focus on the more detailed description of RL, SL, mannosylerythritol lipids (MEL), and cellobiose lipids (CL).Pseudomonas aeruginosa, the ubiquitous opportunistic pathogenic bacterium, is the best RL producer, but other non-pathogenic bacteria like Burkholderia thailandensis and Pseudomonas chlororaphis NRRL B-30761 are also capable of producing them naturally. In addition, Pseudomonas putida has been used as heterologous host to produce RL with good yields. Here we describe the biosynthetic pathway for RL production, the genes involved in its synthesis, and some of the challenges for producing a homogeneous RL product in high quantities that is suitable for specific applications.SL, MEL, and CL are some of the GL biosurfactants produced in high quantities by fungi, like Starmerella bombicola, Moesziomyces aphidis, or Ustilago maydis. We provide an overview of some of their characteristics, insights on the metabolic pathways involved in their synthesis and genetic modifications performed to increase their production, as well as fermentation and purification strategies and some of their applications.

Asunto(s)

Celobiosa , Pseudomonas putida , Celobiosa/metabolismo , Hongos/genética , Hongos/metabolismo , Pseudomonas putida/genética , Tensoactivos/metabolismo

RESUMEN

Cellobiose lipids (CL) are extracellular glycolipids that are produced by many microorganisms from the family Ustilaginaceae. The sugarcane smut fungus Sporisorium scitamineum has been long known as a producer of the glycolipids mannosylerythritol lipids (MEL) and was recently described to additionally secrete CL as a byproduct. In fact, we identified 11 homologous genes in S. scitamineum by in silico analysis sharing a high similarity to the CL biosynthesis gene cluster of Ustilago maydis. We here report the first systematic cultivation of S. scitamineum targeting the synthesis of CL with high product titers and its transfer to the bioreactor. In an initial screening we examined different fermentation media compositions, consisting of a mineral salts solution with vitamins and/or trace elements, three carbon sources (glucose, fructose, sucrose), three pH values (2.5, 4.0, 6.7) and three levels of C/N values (42.2, 83.8, 167.2 molC⋅molN -1) with urea as nitrogen source. A pH of 2.5 proved to result in the highest product titers. An increase of urea concentration from 0.6 to 1.2 g⋅L-1 had a positive effect on biomass formation, however the glycolipid formation was favored at a C/N ratio of 83.8 molC⋅molN -1, using 0.6 g⋅L-1 urea. Amongst the examined carbon sources, sucrose resulted in an increase in the secretion of cellobiose lipids, compared to glucose. Comparing different media compositions, vitamins were identified as not necessary for CL synthesis. We obtained a concentration of cellobiose lipids of 8.3 ± 1.0 g⋅L-1 in shaking flasks. This increased to 17.6 g⋅L-1 in the 1 L bioreactor with additional feeding of carbon source, with a final purity of 85-93%. As a side product, erythritol and mannosylerythritol lipids (MEL) were also synthesized. Via HPTLC coupled MALDI-TOF MS we were able to analyze the secreted CL structures. S. scitamineum produces a mixture of acylated low molecular weight D-glucolipids, linked to a 2,15,16-trihydroxy-hexadecanoic acid via their ω-hydroxyl group (CL-B). The produced cellobiose lipids precipitate as needle like crystals at an acidic pH value of 2.5.