Advances in sophorolipid-producing strain performance improvement and fermentation optimization technology

Application of Biosurfactants in Medical Sciences

Biosurfactants derived from microorganisms have attracted widespread attention in scientific research due to their unique surface activity, low toxicity, biodegradability, antibacterial properties, and stability under extreme conditions. Biosurfactants are widely used in many fields, such as medicine, agriculture, and environmental protection. Therefore, this review aims to comprehensively review and analyze the various applications of biosurfactants in the medical field. The central roles of biosurfactants in crucial medical areas are explored, like drug delivery, induction of tumor cell differentiation or death, treating bacterial and viral effects, healing wounds, and immune regulation. Moreover, a new outlook is introduced on optimizing the capabilities of biosurfactants through modification and gene recombination for better use in medicine. The current research challenges and future research directions are described, aiming to provide valuable insights for continuous study of biosurfactants in medicine.

Updated component analysis method for naturally occurring sophorolipids from Starmerella bombicola

Sophorolipids (SLs) are promising glycolipid biosurfactants as they are easily produced and functional. SLs from microorganisms are comprised of mixtures of multiple derivatives that have different structures and properties, including well-known acidic and lactonic SL (ASLs and LSLs, respectively). In this study, we established a method for analyzing all SL derivatives in the products of Starmerella bombicola, a typical SL-producing yeast. Detailed component analyses of S. bombicola products were carried out using reversed-phase high-performance liquid chromatography and mass spectrometry. Methanol was used as the eluent as it is a good solvent for all SL derivatives. With this approach, it was possible to not only quantify the ratio of the main components of ASL, LSL, and SL glycerides but also confirm trace components such as SL mono-glyceride and bola-form SL (sophorose at both ends); notably, this is the first time these components have been isolated and identified successfully in naturally occurring SLs. In addition, our results revealed a novel SL derivative in which a fatty acid is bonded in series to the ASL, which had not been reported previously. Using the present analysis method, it was possible to easily track compositional changes in the SL components during culture. Our results showed that LSL and ASL are produced initially and that SL glycerides accumulate from the middle stage during the fermentation process. KEY POINTS: • An easy and detailed component analysis method for sophorolipids (SLs) is introduced. • Multiple SL derivatives were identified different from known SLs. • A novel hydrophobic acidic SL was isolated and characterized.

Synergistic antifungal activity and potential mechanism of action of a glycolipid-like compound produced by Streptomyces blastmyceticus S108 against Candida clinical isolates

AIM

The present study aimed to investigate a novel antifungal compound produced by Streptomyces blastmyceticus S108 strain. Its effectiveness against clinical isolates of Candida species and its synergistic effect with conventional antifungal drugs were assessed, and its molecular mechanism of action was further studied against Candida albicans.

METHODS AND RESULTS

A newly isolated strain from Tunisian soil, S. blastmyceticus S108, showed significant antifungal activity against Candida species by well diffusion method. The butanolic extract of S108 strain supernatant exhibited the best anti-Candida activity with a minimal inhibitory concentration (MIC) value of 250 μg ml-1, determined by the microdilution method. The bio-guided purification steps of the butanolic extract were performed by chromatographic techniques. Among the fractions obtained, F13 demonstrated the highest level of activity, displaying a MIC of 31.25 μg ml-1. Gas chromatography-mass spectrometry and electrospray ionization mass spectrometry analyses of this fraction (F13) revealed the glycolipidic nature of the active molecule with a molecular weight of 685.6 m/z. This antifungal metabolite remained stable to physicochemical changes and did not show hemolytic activity even at 4MIC corresponding to 125 µg ml-1 toward human erythrocytes. Besides, the glycolipid compound was combined with 5-flucytosine and showed a high synergistic effect with a fractional inhibitory concentration index value 0.14 against C. albicans ATCC 10231. This combination resulted in a decrease of MIC values of 5-flucytosine and the glycolipid-like compound by 8- and 64-fold, respectively. The examination of gene expression in treated C. albicans cells by quantitative polymerase chain reaction (qPCR) revealed that the active compound tested alone or in combination with 5-flucytosine blocks the ergosterol biosynthesis pathway by downregulating the expression of ERG1, ERG3, ERG5, ERG11, and ERG25 genes.

CONCLUSION AND IMPACT OF THE STUDY

The new glycolipid-like compound, produced by Streptomyces S108 isolate, could be a promising drug for medical use against pathogenic Candida isolates.

Precise fermentation coupling with simultaneous separation strategy enables highly efficient and economical sophorolipids production

Sophorolipids (SLs) represent highly promising biosurfactants. However, its widespread production and application encounter obstacles due to the significant costs involved. Here, an intelligent and precise regulation strategy was elucidated for the fermentation process coupled with in-situ separation production mode, to achieve cost-effective SLs production. Firstly, a mechanism-assisted data-driven model was constructed for "on-demand feeding of cells". Moreover, a strategy of step-wise oxygen supply regulation based on the demand for cell metabolic capacity was developed, which accomplished "on-demand oxygen supply of cells", to optimize the control of energy consumption. Finally, a systematic approach was implemented by integrating a semi-continuous fermentation mode with in-situ separation technology for SLs production. This strategy enhanced SLs productivity and yield, reaching 2.30 g/L/h and 0.57 g/g, respectively. These values represented a 40.2% and 18.7% increase compared to fed-batch fermentation. Moreover, the concentration of crude SLs after separation reached 793.12 g/L, facilitating downstream separation and purification processes.

Efficient Biosynthesis of Acidic/Lactonic Sophorolipids and Their Application in the Remediation of Cyanobacterial Harmful Algal Blooms

Cyanobacterial harmful algal blooms (CyanoHABs) pose significant threats to human health and natural ecosystems worldwide, primarily caused by water eutrophication, increased surface water temperature, and co-occurring microorganisms. Urgent action is needed to develop an eco-friendly solution to effectively curb the proliferation of CyanoHABs. Sophorolipids (SLs) are fully biodegradable biosurfactants synthesized by Starmerella bombicola. They can be classified into lactone and acid types. The lactone type displays strong antimicrobial activity, while the acid type exhibits good solubility, which make them ideal agents for mitigating CyanoHABs. Nevertheless, the broad utilization of SLs are hindered by their expensive production costs and the absence of effective genetic editing tools in the native host. In this study, we constructed recombinant strains capable of producing either acidic or lactonic SLs using the CRISPR-Cas9 gene editing system. The yields of acidic and lactonic SLs reached 53.64 g/L and 45.32 g/L in a shaking flask, respectively. In a 5 L fermenter, acidic SLs reached 129.7 g/L using low-cost glucose and rapeseed oil as substrates. The addition of 5 mg/L lactonic SLs effectively degraded cyanobacteria within 30 min, and a ratio of 8.25:1.75 of lactonic to acidic SLs showed the highest degradation efficiency. This study offers a safe and promising solution for CyanoHABs treatment.

Sophorolipids: A comprehensive review on properties and applications

Sophorolipids are surface-active glycolipids produced by several non-pathogenic yeast species and are widely used as biosurfactants in several industrial applications. Sophorolipids provide a plethora of benefits over chemically synthesized surfactants for certain applications like bioremediation, oil recovery, and pharmaceuticals. They are, for instance less toxic, more benign and environment friendly in nature, biodegradable, freely adsorb to different surfaces, self-assembly in hydrated solutions, robustness for industrial applications etc. These miraculous properties result in valuable physicochemical attributes such as low critical micelle concentrations (CMCs), reduced interfacial surface tension, and capacity to dissolve non-polar components. Moreover, they exhibit a diverse range of physicochemical, functional, and biological attributes due to their unique molecular composition and structure. In this article, we highlight the physico-chemical properties of sophorolipids, how these properties are exploited by the human community for extensive benefits and the conditions which lead to their unique tailor-made structures and how they entail their interfacial behavior. Besides, we discuss the advantages and disadvantages associated with the use of these sophorolipids. We also review their physiological and functional attributes, along with their potential commercial applications, in real-world scenario. Biosurfactants are compared to their man-made equivalents to show the variations in structure-property correlations and possible benefits. Those attempting to manufacture purported natural or green surfactant with innovative and valuable qualities can benefit from an understanding of biosurfactant features structured along the same principles. The uniqueness of this review article is the detailed physico-chemical study of the sophorolipid biosurfactant and how these properties helps in their usage and detailed explicit study of their applications in the current scenario and also covering their pros and cons.

Review on sophorolipids – a promising microbial bio-surfactant

Surfactants are amphiphilic molecules used primarily for cleaning. Petroleum-based surfactants have a high production rate, but are non-biodegradable and destructive to the environment. Environmentally friendly biosurfactants are therefore becoming increasingly important. In addition to not being toxic; they are environmentally safe and mild to the skin. Depending on their structure, there are different types of biosurfactants. One of the types are the glycolipids, they are low molecular weight biosurfactants, and consist of sophorolipids. Sophorolipids are getting more attention as alternative to petroleum-based surfactants due to excellent stability at various pH levels, temperatures, and salinities. In addition to being anti-microbial, they have excellent wetting and foaming abilities and act as emulsifiers. There are numerous applications of sophorolipids in food, agriculture, biomedicine, cosmetics and personal care.

Surfactin Shows Relatively Low Antimicrobial Activity against Bacillus subtilis and Other Bacterial Model Organisms in the Absence of Synergistic Metabolites

Surfactin is described as a powerful biosurfactant and is natively produced by Bacillus subtilis in notable quantities. Among other industrially relevant characteristics, antimicrobial properties have been attributed to surfactin-producing Bacillus isolates. To investigate this property, stress approaches were carried out with biotechnologically established strains of Corynebacterium glutamicum, Bacillus subtilis, Escherichia coli and Pseudomonas putida with the highest possible amounts of surfactin. Contrary to the popular opinion, the highest growth-reducing effects were detectable in B. subtilis and E. coli after surfactin treatment of 100 g/L with 35 and 33%, respectively, while P. putida showed no growth-specific response. In contrast, other antimicrobial biosurfactants, like rhamnolipids and sophorolipids, showed significantly stronger effects on bacterial growth. Since the addition of high amounts of surfactin in defined mineral salt medium reduced the cell growth of B. subtilis by about 40%, the initial stress response at the protein level was analyzed by mass spectrometry, showing induction of stress proteins under control of alternative sigma factors σB and σW as well as the activation of LiaRS two-component system. Overall, although surfactin is associated with antimicrobial properties, relatively low growth-reducing effects could be demonstrated after the surfactin addition, challenging the general claim of the antimicrobial properties of surfactin.

Sophorolipids bioproduction in the yeast Starmerella bombicola: Current trends and perspectives

Sophorolipids are highly active green surfactants (glycolipid biosurfactants) getting tremendous appreciation worldwide due to their low toxicity, biodegradability, broad spectrum of applications, and significant biotechnological potential. Sophorolipids are mainly produced by an oleaginous budding yeast Starmerella bombicola using low-cost substrates. Therefore, the recent state-of-art literature information about S. bombicola yeast is hereby provided, especially the underlying production pathways, biosynthetic gene cluster, and regulatory enzymes. Moreover, the S. bombicola offers flexibility for regulating the structural diversity of sophorolipids, either genetically or by varying fermentative conditions. The emergence of advanced technologies like 'Omics and CRISPR/Cas have certainly boosted rational engineering research for designing high-performing platform strains. Therefore, currently available genetic engineering tools in S. bombicola were reviewed, thereby opening up exciting new possibilities for improving the overall bioproduction titers, structural variability, and stability of sophorolipids. Finally, some technical perspectives to address the current challenges were discussed.

Effect of biosurfactant sophorolipids on Rhizomucor miehei lipase fermentation by Aspergillus oryzae

In this study, the effect of biosurfactant sophorolipids (SLs) on Rhizomucor miehei lipase (RML) fermentation by Aspergillus oryzae was investigated. With the exogenous addition of 0.3% (w/v) SLs in the initial medium, the RML activity reached 430.0 U/mL, an increase of 25.0% compared to the control group. Subsequently, the physiological metabolic responses of A. oryzae to the addition of SLs were further explored. The results showed that though SLs had almost no effect on the RML secretion, it would affect the morphology of the cells. During the late phase of the fermentation, the proportion of middle pellets, which was generally considered as an energetic and stable state for enzyme production was increased with the addition of SLs. Simultaneously, the viscosity of fermentation broth was reduced, which facilitated the increase of oxygen transfer, thereby improving the RML production. Finally, it could be found that the addition of SLs significantly increased the contents of precursor amino acids, especially for those rank first and second of the RML composition, and it could promote the synthesis of RML.

Burkholderia thailandensis E264 as a promising safe rhamnolipids' producer towards a sustainable valorization of grape marcs and olive mill pomace

Within the circular economy framework, our study aims to assess the rhamnolipid production from winery and olive oil residues as low-cost carbon sources by nonpathogenic strains. After evaluating various agricultural residues from those two sectors, Burkholderia thailandensis E264 was found to use the raw soluble fraction of nonfermented (white) grape marcs (NF), as the sole carbon and energy source, and simultaneously, reducing the surface tension to around 35 mN/m. Interestingly, this strain showed a rhamnolipid production up to 1070 mg/L (13.37 mg/g of NF), with a higher purity, on those grape marcs, predominately Rha-Rha C14-C14, in MSM medium. On olive oil residues, the rhamnolipid yield of using olive mill pomace (OMP) at 2% (w/v) was around 300 mg/L (15 mg/g of OMP) with a similar CMC of 500 mg/L. To the best of our knowledge, our study indicated for the first time that a nonpathogenic bacterium is able to produce long-chain rhamnolipids in MSM medium supplemented with winery residues, as sole carbon and energy source. KEY POINTS: • Winery and olive oil residues are used for producing long-chain rhamnolipids (RLs). • Both higher RL yields and purity were obtained on nonfermented grape marcs as substrates. • Long-chain RLs revealed stabilities over a wide range of pH, temperatures, and salinities.

The role of transport proteins in the production of microbial glycolipid biosurfactants

Several microorganisms are currently being used as production platform for glycolipid biosurfactants, providing a greener alternative to chemical biosurfactants. One of the reasons why these processes are commercially competitive is the fact that microbial producers can efficiently export their product to the extracellular environment, reaching high product titers. Glycolipid biosynthetic genes are often found in a dedicated cluster, amidst which genes encoding a dedicated transporter committed to shuttle the glycolipid to the extracellular environment are often found, as is the case for many other secondary metabolites. Knowing this, one can rely on gene clustering features to screen for novel putative transporters, as described and performed in this review. The above strategy proves to be very powerful to identify glycolipid transporters in fungi but is less valid for bacterial systems. Indeed, the genetics of these export systems are currently largely unknown, but some hints are given. Apart from the direct export of the glycolipid, several other transport systems have an indirect effect on glycolipid production. Specific importers dictate which hydrophilic and hydrophobic substrates can be used for production and influence the final yields. In eukaryotes, cellular compartmentalization allows the assembly of glycolipid building blocks in a highly specialized and efficient way. Yet, this requires controlled transport across intracellular membranes. Next to the direct export of glycolipids, the current state of the art regarding this indirect involvement of transporter systems in microbial glycolipid synthesis is summarized in this review. KEY POINTS: • Transporters are directly and indirectly involved in microbial glycolipid synthesis. • Yeast glycolipid transporters are found in their biosynthetic gene cluster. • Hydrophilic and hydrophobic substrate uptake influence microbial glycolipid synthesis.