Rapid screening of surfactant and biosurfactant surface cleaning performance

Microbial surfactants: A journey from fundamentals to recent advances

Microbial surfactants are amphiphilic surface-active substances aid to reduce surface and interfacial tensions by accumulating between two fluid phases. They can be generically classified as low or high molecular weight biosurfactants based on their molecular weight, whilst overall chemical makeup determines whether they are neutral or anionic molecules. They demonstrate a variety of fundamental characteristics, including the lowering of surface tension, emulsification, adsorption, micelle formation, etc. Microbial genera like Bacillus spp., Pseudomonas spp., Candida spp., and Pseudozyma spp. are studied extensively for their production. The type of biosurfactant produced is reliant on the substrate utilized and the pathway pursued by the generating microorganisms. Some advantages of biosurfactants over synthetic surfactants comprise biodegradability, low toxicity, bioavailability, specificity of action, structural diversity, and effectiveness in harsh environments. Biosurfactants are physiologically crucial molecules for producing microorganisms which help the cells to grasp substrates in adverse conditions and also have antimicrobial, anti-adhesive, and antioxidant properties. Biosurfactants are in high demand as a potential product in industries like petroleum, cosmetics, detergents, agriculture, medicine, and food due to their beneficial properties. Biosurfactants are the significant natural biodegradable substances employed to replace the chemical surfactants on a global scale in order to make a cleaner and more sustainable environment.

Characteristics and pH-Responsiveness of SDBS–Stabilized Crude Oil/Water Nanoemulsions

Nanoemulsions are colloidal systems with a wide spectrum of applications in several industrial fields. In this study, crude oil-in-water (O/W) nanoemulsions were formulated using different dosages of the anionic sodium dodecylbenzenesulfonate (SDBS) surfactant. The formulated nanoemulsions were characterized in terms of emulsion droplet size, zeta potential, and interfacial tension (IFT). Additionally, the rheological behavior, long-term stability, and on-demand breakdown of the nanoemulsions via a pH-responsive mechanism were evaluated. The obtained results revealed the formation of as low as 63.5 nm average droplet size with a narrow distribution (33–142 nm). Additionally, highly negative zeta potential (i.e., −62.2 mV) and reasonably low IFT (0.45 mN/m) were obtained at 4% SDBS. The flow-ability of the nanoemulsions was also investigated and the obtained results revealed an increase in the nanoemulsion viscosity with increasing the emulsifier content. Nonetheless, even at the highest SDBS dosage of 4%, the nanoemulsion viscosity at ambient conditions never exceeded 2.5 mPa·s. A significant reduction in viscosity was obtained with increasing the nanoemulsion temperature. The formulated nanoemulsions displayed extreme stability with no demulsification signs irrespective of the emulsifier dosage even after one-month shelf-life. Another interesting and, yet, surprising observation reported herein is the pH-induced demulsification despite SDBS not possessing a pH-responsive character. This behavior enabled the on-demand breakdown of the nanoemulsions by simply altering their pH via the addition of HCl or NaOH; a complete and quick oil separation can be achieved using this simple and cheap demulsification method. The obtained results reveal the potential utilization of the formulated nanoemulsions in oilfield-related applications such as enhanced oil recovery (EOR), well stimulation and remediation, well-bore cleaning, and formation fracturing.

Effect of acid-alkali treatment on serum protein adsorption and bacterial adhesion to porous titanium

Modification of the titanium (Ti) surface is widely known to influence biological reactions such as protein adsorption and bacterial adhesion in vivo, ultimately controlling osseointegration. In this study, we sought to investigate the correlation of protein adsorption and bacterial adhesion with the nanoporous structure of acid-alkali-treated Ti implants, shedding light on the modification of Ti implants to promote osseointegration. We fabricated nontreated porous Ti (NTPT) by powder metallurgy and immersed it in mixed acids and NaOH to obtain acid-alkali-treated porous Ti (AAPT). Nontreated dense sample (NTDT) served as control. Our results showed that nanopores were formed after acid-alkali treatment. AAPT showed a higher specific surface area and became much more hydrophilic than NTPT and NTDT (p < 0.001). Compared to dense samples, porous samples exhibited a lower zeta potential and higher adsorbed protein level at each time point within 120 min (p < 0.001). AAPT formed a thicker protein layer by serum precoating than NTPT and NTDT (p < 0.001). The main adsorbed proteins on AAPT and NTPT were albumin, α1 antitrypsin, transferrin, apolipoprotein A1, complement C3 and haptoglobin α1 chain. The amounts of bacteria adhering to the serum-precoated samples were lower than those adhering to the nonprecoated samples (p < 0.05). Lower-molecular-weight proteins showed higher affinity to porous Ti. In conclusion, acid-alkali treatment facilitated protein adsorption by porous Ti, and the protein coating tended to prevent bacteria from adhering. These findings may be utilized for Ti implant modification aimed at reducing bacterial adhesion and enhancing osseointegration. Graphical abstract.

Microbial biosurfactant research: time to improve the rigour in the reporting of synthesis, functional characterization and process development

The demand for microbially produced surface-active compounds for use in industrial processes and products is increasing. As such, there has been a comparable increase in the number of publications relating to the characterization of novel surface-active compounds: novel producers of already characterized surface-active compounds and production processes for the generation of these compounds. Leading researchers in the field have identified that many of these studies utilize techniques are not precise and accurate enough, so some published conclusions might not be justified. Such studies lacking robust experimental evidence generated by validated techniques and standard operating procedures are detrimental to the field of microbially produced surface-active compound research. In this publication, we have critically reviewed a wide range of techniques utilized in the characterization of surface-active compounds from microbial sources: identification of surface-active compound producing microorganisms and functional testing of resultant surface-active compounds. We have also reviewed the experimental evidence required for process development to take these compounds out of the laboratory and into industrial application. We devised this review as a guide to both researchers and the peer-reviewed process to improve the stringency of future studies and publications within this field of science.

Biosurfactants’ Potential Role in Combating COVID-19 and Similar Future Microbial Threats

During 2020, the world has experienced extreme vulnerability in the face of a disease outbreak. The coronavirus disease 2019 (COVID-19) pandemic discovered in China and rapidly spread across the globe, infecting millions, causing hundreds of thousands of deaths, and severe downturns in the economies of countries worldwide. Biosurfactants can play a significant role in the prevention, control and treatment of diseases caused by these pathogenic agents through various therapeutic, pharmaceutical, environmental and hygiene approaches. Biosurfactants have the potential to inhibit microbial species with virulent intrinsic characteristics capable of developing diseases with high morbidity and mortality, as well as interrupting their spread through environmental and hygiene interventions. This is possible due to their antimicrobial activity, ability to interact with cells forming micelles and to interact with the immune system, and compatibility with relevant processes such as nanoparticle synthesis. They, therefore, can be applied in developing innovative and more effective pharmaceutical, therapeutics, sustainable and friendly environmental management approaches, less toxic formulations, and more efficient cleaning agents. These approaches can be easily integrated into relevant product development pipelines and implemented as measures for combating and managing pandemics. This review examines the potential approaches of biosurfactants as useful molecules in fighting microbial pathogens both known and previously unknown, such as COVID-19.

Properties of novel surfactin-derived biosurfactants obtained through solid-phase synthesis

Eight molecules, four peptides (SPs) and four lipopeptides (LPs) derived by rational design from surfactin, a well-known secreted biosurfactant from Bacillus subtilis, were produced employing Fmoc-based solid-phase synthesis. These new peptides were tested to evaluate their potential biosurfactant and biological activities, aiming at possible applications in industrial, biological, pharmaceutical, and medical use. Five molecules (SP1, SP2, SP4, LP5, and LP8) presented potential for medical uses, mainly due to their drug delivery properties as suggested by their synergistic activity with the antibiotic vancomycin against Staphylococcus aureus. All synthetic peptides showed low toxicity against Vero cell cultures, in assays of hemolysis, and in different cytotoxicity assays. In addition, we found that three peptides (SP1, LP6, and LP7) had potential technological and industrial use because of their emulsifying capacity, low toxicity, and ability to physically stabilize solutions. These novel molecules retained some properties of the parental molecule (surfactin, which was originally obtained through nonribosomal synthesis in Bacillus subtilis) but have the advantage of being linear peptides, which can be produced at large scales through the use of conventional heterologous protein expression protocols.

Biosurfactants and surfactants interacting with membranes and proteins: Same but different?

Biosurfactants (BS) are surface-active molecules produced by microorganisms. For several decades they have attracted interest as promising alternatives to current petroleum-based surfactants. Aside from their green profile, they have remarkably low critical micelle concentrations, reduce the air/water surface tension to very low levels and are excellent emulsifiers, all of which make them comparable or superior to their synthetic counterparts. These remarkable physical properties derive from their more complex chemical structures in which hydrophilic and hydrophobic regions are not as clearly separated as chemical surfactants but have a more mosaic distribution of polarity as well as branched or circular structures. This allows the lipopeptide surfactin to adopt spherical structures to facilitate dense packing at interfaces. They are also more complex. Glycolipid BS, e.g. rhamnolipids (RL) and sophorolipids, are produced biologically as mixtures which vary in the size and saturation of the hydrophobic region as well as modifications in the hydrophilic headgroup, such as the number of sugar groups and different levels of acetylation, leading to variable surface-active properties. Their amphiphilicity allows RL to insert easily into membranes at sub-cmc concentrations to modulate membrane structure and extract lipopolysaccharides, leading to extensive biofilm remodeling in vivo, sometimes in collaboration with hydrophobic RL precursors. Thanks to their mosaicity, even anionic BS like RL only bind weakly to proteins and show much lower denaturing potency, even supporting membrane protein refolding. Nevertheless, they can promote protein degradation by proteases e.g. by neutralizing positive charges, which together with their biofilm-combating properties makes them very promising detergent surfactants. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.

Review lipopeptides biosurfactants: Mean classes and new insights for industrial, biomedical, and environmental applications

Lipopeptides are microbial surface active compounds produced by a wide variety of bacteria, fungi, and yeast. They are characterized by high structural diversity and have the ability to decrease the surface and interfacial tension at the surface and interface, respectively. Surfactin, iturin, and fengycin of Bacillus subtilis are among the most popular lipopeptides. Lipopepetides can be applied in diverse domains as food and cosmetic industries for their emulsification/de-emulsification capacity, dispersing, foaming, moisturizing, and dispersing properties. Also, they are qualified as viscosity reducers, hydrocarbon solubilizing and mobilizing agents, and metal sequestering candidates for application in environment and bioremediation. Moreover, their ability to form pores and destabilize biological membrane permits their use as antimicrobial, hemolytic, antiviral, antitumor, and insecticide agents. Furthermore, lipopeptides can act at the surface and can modulate enzymes activity permitting the enhancement of the activity of certain enzymes ameliorating microbial process or the inhibition of certain other enzymes permitting their use as antifungal agents. This article will present a detailed classification of lipopeptides biosurfactant along with their producing strain and biological activities and will discuss their functional properties and related applications.

Benchmarking the Self-Assembly of Surfactin Biosurfactant at the Liquid-Air Interface to those of Synthetic Surfactants

The adsorption of surfactin, a lipopeptide biosurfactant, at the liquid–air interface has been investigated in this work. The maximum adsorption density and the nature and the extent of lateral interaction between the adsorbed surfactin molecules at the interface were estimated from surface tension data using the Frumkin model. The quantitative information obtained using the Frumkin model was also compared to those obtained using the Gibbs equation and the Langmuir–Szyszkowski model. Error analysis showed a better agreement between the experimental and the calculated values using the Frumkin model relative to the other two models. The adsorption of surfactin at the liquid–air interface was also compared to those of synthetic anionic, sodium dodecylbenzenesulphonate (SDBS), and nonionic, octaethylene glycol monotetradecyl ether (C₁₄E₈), surfactants. It has been estimated that the area occupied by a surfactin molecule at the interface is about 3- and 2.5-fold higher than those occupied by SDBS and C₁₄E₈ molecules, respectively. The interaction between the adsorbed molecules of the anionic biosurfactant (surfactin) was estimated to be attractive, unlike the mild repulsive interaction between the adsorbed SDBS molecules.

Microbial biosurfactants production, applications and future potential

Microorganisms synthesise a wide range of surface-active compounds (SAC), generally called biosurfactants. These compounds are mainly classified according to their molecular weight, physico-chemical properties and mode of action. The low-molecular-weight SACs or biosurfactants reduce the surface tension at the air/water interfaces and the interfacial tension at oil/water interfaces, whereas the high-molecular-weight SACs, also called bioemulsifiers, are more effective in stabilising oil-in-water emulsions. Biosurfactants are attracting much interest due to their potential advantages over their synthetic counterparts in many fields spanning environmental, food, biomedical, and other industrial applications. Their large-scale application and production, however, are currently limited by the high cost of production and by limited understanding of their interactions with cells and with the abiotic environment. In this paper, we review the current knowledge and the latest advances in biosurfactant applications and the biotechnological strategies being developed for improving production processes and future potential.