Microbial biosurfactants : is mainstream on the horizon?

Microbial biosurfactants have been holding the promise as environmentally friendly alternatives for petrochemical derived surfactants for the last decade. Indeed, across the market (large) companies are investing in these technologies and microbial biosurfactants are already applied in quite some consumer products today. The remaining hurdles for these technologies to really lift off can be summarized as high costs in comparison to the market references and a limited variety in molecular structures to satisfy the plethora of sought for functionalities. Moreover, most of the technologies are still in their infancy, characterized by suboptimal processes often resulting in batch to batch variation, a lack of knowledge and a of scale up evidence. A last issue is the fact that the use of so-called first-generation renewable substrates, such as sugar and vegetable oil, as substrates negatively impacts the LCA for microbial biosurfactants. At BBEPP and InBio.be we focus on all the above-mentioned shortcomings and aim to increase the microbial biosurfactant market segment in the coming years. We apply an integrated approach where microbial strain engineering, process (fermentation and purification) development and -optimization, scale up and application testing are tightly linked and interconnected. We recently succeeded in the development of a battery of Starmerella bombicola yeast strains producing a library of over 20 (new-to-nature) glycolipid biosurfactants and developed sustainable and scalable (continuous) fermentation and purification processes for these biosurfactants. The biosurfactants were screened in high throughput for a range of relevant properties for the industry, such as foaming, rheology, surface tension (and CMC), emulsification, but also biological properties such as anti-microbial and -viral properties. Moreover, efforts were done to develop the bioprocesses starting from waste- and side streams instead of 1G substrates, thus positively impacting the environmental impact of the new microbial biosurfactants. The combination of the described efforts is expected to result in a commercial breakthrough of microbial biosurfactant in the next ten years

Advanced materials from microbial fermentation : the case of glycolipids and nanocellulose

Green chemistry is a recent discipline ruled by twelve founding principles, which include, among others, atom economy, the prevention of pollution via environmentally friendly chemical synthesis methods, such as, for example, the choice of an aqueous medium over organic solvents, but also the development of chemicals and materials derived from plant biomass. In this context, microbial synthesis is a tool to supplant, in some notable cases, syntheses by a standard organic chemistry approach. More recently, attention has begun to be given to the microbial synthesis of polymeric sugars, such as dextran or cellulose, or lipids, such as amphiphilic glycolipids. Although the microbial production of glycosylated compounds can be traced back by several decades, the development of green chemistry is encouraging teams of multidisciplinary researchers to focus on production, diversification, and applications of this class of compounds, thus going beyond the community of researchers in microbiology, historically interested in the development of fermentation products from microorganisms. This article develops the above-mentioned theme by focusing on nanocellulose, representing an important glycosylated polymer, and on biosurfactants, in regards of the glycosylated lipids. The choice of these two systems is justified by the strong development of nanocellulose-based materials but also by the need to replace in part the “conventional” surfactants, a significant source of CO2 emissions worldwide. The main classes of molecules, the classical methods of synthesis, their properties and some examples of notorious applications are presented

Self-assembly mechanism of pH-responsive glycolipids : micelles, fibers, vesicles, and bilayers

A set of four structurally related glycolipids are described: two of them have one glucose unit connected to either stearic or oleic acid, and two other ones have a diglucose headgroup (sophorose) similarly connected to either stearic or oleic acid. The self-assembly properties of these compounds, poorly known, are important to know due to their use in various fields of application from cleaning to cosmetics to medical. At basic pH, they all form mainly small micellar aggregates. At acidic pH, the oleic and stearic derivatives of the monoglucose form, respectively, vesicles and bilayer, while the same derivatives of the sophorose headgroup form micelles and twisted ribbons. We use pH-resolved in situ small angle X-ray scattering (SAXS) under synchrotron radiation to characterize the pH-dependent mechanism of evolution from micelles to the more complex aggregates at acidic pH. By pointing out the importance of the COO-/COOH ratio, the melting temperature, T-m, of the lipid moieties, hydration of the glycosidic headgroup, the packing parameter, membrane rigidity, and edge stabilization, we are now able to draw a precise picture of the full self-assembly mechanism. This work is a didactical illustration of the complexity of the self-assembly process of a stimuli-responsive amphiphile during which many concomitant parameters play a key role at different stages of the process

Weak and saturable protein-surfactant interactions in the denaturation of apo-α-lactalbumin by acidic and lactonic sophorolipid

Biosurfactants are of growing interest as sustainable alternatives to fossil-fuel-derived chemical surfactants, particularly for the detergent industry. To realize this potential, it is necessary to understand how they affect proteins which they may encounter in their applications. However, knowledge of such interactions is limited. Here, we present a study of the interactions between the model protein apo-alpha-lactalbumin (apo-aLA) and the biosurfactant sophorolipid (SL) produced by the yeast Starmerella bombicola. SL occurs both as an acidic and a lactonic form; the lactonic form (lactSL) is sparingly soluble and has a lower critical micelle concentration (cmc) than the acidic form [non-acetylated acidic sophorolipid (acidSL)]. We show that acidSL affects apo-aLA in a similar way to the related glycolipid biosurfactant rhamnolipid (RL), with the important difference that RL is also active below the cmc in contrast to acidSL. Using isothermal titration calorimetry data, we show that acidSL has weak and saturable interactions with apo-aLA at low concentrations; due to the relatively low cmc of acidSL (which means that the monomer concentration is limited to ca. 0-1 mM SL), it is only possible to observe interactions with monomeric acidSL at high apo-aLA concentrations. However, the denaturation kinetics of apo-aLA in the presence of acidSL are consistent with a collaboration between monomeric and micellar surfactant species, similar to RL and non-ionic or zwitterionic surfactants. Inclusion of diacetylated lactonic sophorolipid (lactSL) as mixed micelles with acidSL lowers the cmc and this effectively reduces the rate of unfolding, emphasizing that SL like other biosurfactants is a gentle anionic surfactant. Our data highlight the potential of these biosurfactants for future use in the detergent and pharmaceutical industry

Sophorolipids: Renewable resources for chemical derivatization

C