Seeking faster, alternative methods for glycolipid biosurfactant characterization and purification

Recent advances and discoveries of microbial-based glycolipids: Prospective alternative for remediation activities

Surfactants have always been a prominent chemical that is useful in various sectors (e.g., cleaning agent production industry, textile industry and painting industry). This is due to the special ability of surfactants to reduce surface tension between two fluid surfaces (e.g., water and oil). However, the current society has long omitted the harmful effects of petroleum-based surfactants (e.g., health issues towards humans and reducing cleaning ability of water bodies) due to their usefulness in reducing surface tension. These harmful effects will significantly damage the environment and negatively affect human health. As such, there is an urgency to secure environmentally friendly alternatives such as glycolipids to reduce the effects of these synthetic surfactants. Glycolipids is a biomolecule that shares similar properties with surfactants that are naturally synthesized in the cell of living organisms, glycolipids are amphiphilic in nature and can form micelles when glycolipid molecules clump together, reducing surface tension between two surfaces as how a surfactant molecule is able to achieve. This review paper aims to provide a comprehensive study on the recent advances in bacteria cultivation for glycolipids production and current lab scale applications of glycolipids (e.g., medical and waste bioremediation). Studies have proven that glycolipids are effective anti-microbial agents, subsequently leading to an excellent anti-biofilm forming agent. Heavy metal and hydrocarbon contaminated soil can also be bioremediated via the use of glycolipids. The major hurdle in the commercialization of glycolipid production is that the cultivation stage and downstream extraction stage of the glycolipid production process induces a very high operating cost. This review provides several solutions to overcome this issue for glycolipid production for the commercialization of glycolipids (e.g., developing new cultivating and extraction techniques, using waste as cultivation medium for microbes and identifying new strains for glycolipid production). The contribution of this review aims to serve as a future guideline for researchers that are dealing with glycolipid biosurfactants by providing an in-depth review on the recent advances of glycolipid biosurfactants. By summarizing the points discussed as above, it is recommended that glycolipids can substitute synthetic surfactants as an environmentally friendly alternative.

3D-printed biosurfactant-chitosan antibacterial coating for the prevention of silicone-based associated infections

Infections associated with the surfaces of medical devices represent a critical problem due to biofilm formation and the growing resistance towards antibacterial drugs. This is particularly relevant in commonly used invasive devices such as silicone-based ones where a demand for alternative antibiofilm surfaces is increasing. In this work, an antimicrobial chitosan-biosurfactant hydrogel mesh was produced by 3D-printing. The 3D structure was designed to coat polydimethylsiloxane-based medical devices for infection prevention. Additionally, the porous 3D structure allows the incorporation of customized bioactive components. For this purpose, two biosurfactants (surfactin and sophorolipids) were biosynthesized and tested for their antimicrobial activity. In addition, the printing of surfactant-chitosan-based coatings was optimized, and the resulting 3D structures were characterized (i.e., wettability, FTIR-ATR, antimicrobial activity, and biocompatibility). Compared with surfactin, the results showed a better yield and higher antibacterial activity against Gram-positive bacteria for sophorolipids (SLs). Thus, SLs were used to produce chitosan-based 3D-printed coatings. Overall, the SLs-impregnated coatings showed the best antibacterial activity against Staphylococcus aureus planktonic bacteria (61 % of growth inhibition) and antibiofilm activity (2 log units reduction) when compared to control. Furthermore, concerning biocompatibility, the coatings were cytocompatible towards human dermal fibroblasts. Finally, the coating presented a mesh suitable to be filled with a model bioactive compound (i.e., hyaluronic acid), paving the way to be used for customized therapeutics.

Glycolipid Biosurfactants in Skincare Applications: Challenges and Recommendations for Future Exploitation

The 21st century has seen a substantial increase in the industrial applications of glycolipid biosurfactant technology. The market value of the glycolipid class of molecules, sophorolipids, was estimated to be USD 409.84 million in 2021, with that of rhamnolipid molecules projected to reach USD 2.7 billion by 2026. In the skincare industry, sophorolipid and rhamnolipid biosurfactants have demonstrated the potential to offer a natural, sustainable, and skin-compatible alternative to synthetically derived surfactant compounds. However, there are still many barriers to the wide-scale market adoption of glycolipid technology. These barriers include low product yield (particularly for rhamnolipids) and potential pathogenicity of some native glycolipid-producing microorganisms. Additionally, the use of impure preparations and/or poorly characterised congeners as well as low-throughput methodologies in the safety and bioactivity assessment of sophorolipids and rhamnolipids challenges their increased utilisation in both academic research and skincare applications. This review considers the current trend towards the utilisation of sophorolipid and rhamnolipid biosurfactants as substitutes to synthetically derived surfactant molecules in skincare applications, the challenges associated with their application, and relevant solutions proposed by the biotechnology industry. In addition, we recommend experimental techniques/methodologies, which, if employed, could contribute significantly to increasing the acceptance of glycolipid biosurfactants for use in skincare applications while maintaining consistency in biosurfactant research outputs.

Assuring the Biofunctionalization of Silicone Covalently Bonded to Rhamnolipids: Antibiofilm Activity and Biocompatibility

Silicone-based medical devices composed of polydimethylsiloxane (PDMS) are widely used all over the human body (e.g., urinary stents and catheters, central venous catheters stents) with extreme clinical success. Nevertheless, their abiotic surfaces, being prone to microorganism colonization, are often involved in infection occurrence. Improving PDMS antimicrobial properties by surface functionalization with biosurfactants to prevent related infections has been the goal of different works, but studies that mimic the clinical use of these novel surfaces are missing. This work aims at the biofunctional assessment of PDMS functionalized with rhamnolipids (RLs), using translational tests that more closely mimic the clinical microenvironment. Rhamnolipids were covalently bonded to PDMS, and the obtained surfaces were characterized by contact angle modification assessment, ATR-FTIR analysis and atomic force microscopy imaging. Moreover, a parallel flow chamber was used to assess the Staphylococcus aureus antibiofilm activity of the obtained surfaces under dynamic conditions, and an in vitro characterization with human dermal fibroblast cells in both direct and indirect characterization assays, along with an in vivo subcutaneous implantation assay in the translational rabbit model, was performed. A 1.2 log reduction in S. aureus biofilm was observed after 24 h under flow dynamic conditions. Additionally, functionalized PDMS lessened cell adhesion upon direct contact, while supporting a cytocompatible profile, within an indirect assay. The adequacy of the biological response was further validated upon in vivo subcutaneous tissue implantation. An important step was taken towards biofunctional assessment of RLs-functionalized PDMS, reinforcing their suitability for medical device usage and infection prevention.

Transcription-Associated Fluorescence-Activated Droplet Sorting for Di-rhamnolipid Hyperproducers

Rhamnolipids (RLs) are biosurfactants with great economic significance that have been used extensively in multiple industries. Pseudomonas aeruginosa is a promising microorganism for sustainable RL production. However, current CTAB-MB based screening of RL-producing strains is time-consuming, labor-intensive, and unable to distinguish mono- and di-RL. In this study, we developed a novel transcription-associated fluorescence-activated droplet sorting (FADS) method to specifically target the di-RL hyperproducers. We first investigated critical factors associated with this method, including the specificity and sensitivity for discriminating di-RL overproducers from other communities. Validation of genotype-phenotype linkage between the GFP intensity, rhlC transcription, and di-RL production showed that rhlC transcription is closely correlated with di-RL production, and the GFP intensity is responsive to rhlC transcription, respectively. Using this platform, we screened out ten higher di-RL producing microorganisms, which produced 54-208% more di-RL than the model P. aeruginosa PAO1. In summary, the droplet-based microfluidic platform not only facilitates a more specific, reliable, and rapid screening of P. aeruginosa colonies with desired phenotypes, but also shows that intracellular transcription-associated GFP intensity can be used to measure the yield of di-RL between populations of droplets containing different environmental colonies. This method also can be integrated with transposon mutation libraries to target P. aeruginosa mutants.

Fighting S. aureus catheter-related infections with sophorolipids: Electing an antiadhesive strategy or a release one?

Staphylococcus aureus medical devices related-infections, such as blood stream catheter are of major concern. Their prevention is compulsory and strategies, not prone to the development of resistance, to prevent S. aureus biofilms on catheter surfaces (e.g. silicone) are needed. In this work two different approaches using sophorolipids were studied to prevent S. aureus biofilm formation on medical grade silicone: i) an antiadhesive strategy through covalent bond of sophorolipids to the surface; ii) and a release strategy using isolated most active sophorolipids. Sophorolipids produced by Starmerella bombicola, were characterized by UHPLC-MS and RMN, purified by automatic flash chromatography and tested for their antimicrobial activity towards S. aureus. Highest antimicrobial activity was observed for C18:0 and C18:1 diacetylated lactonic sophorolipids showing a MIC of 50 μg mL^-1. Surface modification with acidic or lactonic sophorolipids when evaluating the anti-adhesive or release strategy, respectively, was confirmed by contact angle, FTIR-ATR and AFM analysis. When using a mixture of acidic sophorolipids covalently bonded to silicone surface as antiadhesive strategy cytocompatible surfaces were obtained and a reduction of 90 % on biofilm formation was observed. Nevertheless, if a release strategy is adopted with purified lactonic sophorolipids a higher effect is achieved. Most promising compound was C18:1 diacateylated lactonic sophorolipid that showed no cellular viability reduction when a concentration of 1.5 mg mL^-1 was selected and a reduction on biofilm around 5 log units. Results reinforce the applicability of these antimicrobial biosurfactants on preventing biofilms and disclose that their antimicrobial effect is imperative when comparing to their antiadhesive properties.