Production of Trehalolipid Biosurfactants by Rhodococcus

An Insightful Overview of Microbial Biosurfactant: A Promising Next-Generation Biomolecule for Sustainable Future

Microbial biosurfactant is an emerging vital biomolecule of the 21st century. They are amphiphilic compounds produced by microorganisms and possess unique properties to reduce surface tension activity. The use of microbial surfactants spans most of the industrial fields due to their biodegradability, less toxicity, being environmentally safe, and being synthesized from renewable sources. These would be highly efficient eco-friendly alternatives to petroleum-derived surfactants that would open up new approaches to research on the production of biosurfactants. In the upcoming era, biobased surfactants will become a dominating multifunctional compound in the world market. Research on biosurfactants ranges from the search for novel microorganisms that can produce new molecules, structural and physiochemical characterization of biosurfactants, and fermentation process for enhanced large-scale productivity and green applications. The main goal of this review is to provide an overview of the recent state of knowledge and trends about microbially derived surfactants, various aspects of biosurfactant production, definition, properties, characteristics, diverse advances, and applications. This would lead a long way in the production of biosurfactants as globally successful biomolecules of the current century.

Biosurfactants: Secondary Metabolites Involved in the Process of Bioremediation and Biofilm Removal

The search for environmentally friendly methods to remove persistent substances such as organic pollutants and sessile communities such as biofilms that severely affect the environment and human health resulted in biosurfactant discovery. Owing to their low level of toxicity and high biodegradability, biosurfactants are increasingly preferred to be used for removal of pollutants from nature. These amphipathic molecules can be synthesized inexpensively, employing cheap substrates such as agricultural and industrial wastes. Recent progress has been made in identifying various biosurfactants that can be used to remove organic pollutants and harmful microbial aggregates, as well as novel microbial strains that produce these surface-active molecules to survive in a hydrocarbon-rich environment. This review focuses on the identification and understanding the role of biosurfactants and the microorganisms involved in the removal of biofilms and remediation of xenobiotics and various types of hydrocarbons such as crude oil, aromatic hydrocarbons, n-alkanes, aliphatic hydrocarbons, asphaltenes, naphthenes, and other petroleum products. This property of biosurfactant is very important as biofilms are of great concern due to their impact on the environment, public health, and industries worldwide. This work also includes several advanced molecular methods that can be used to enhance the production of biosurfactants by the microorganisms studied.

A comprehensive review on production of bio-surfactants by bio-degradation of waste carbohydrate feedstocks: an approach towards sustainable development

The advancement of science and technology demands chemistry which is safer, smarter and green by nature. The sustainability of science thus requires well-behaved alternates that best suit the demand. Bio-surfactants are surface active compounds, established to affect surface chemistry. In general, microbial bio-surfactants are a group of structurally diverse molecules produced by different microbes. A large number of bio-surfactants are produced during hydrocarbon degradation by hydrocarbonoclistic microorganisms during their own growth on carbohydrates and the production rate is influenced by the rate of degradation of carbohydrates. The production of such biological surfactants is thus of greater importance. This write up is a dedicated review to update the existing knowledge of inexpensive carbohydrate sources as substrates, microorganisms and technologies of biosurfactant production. This is an economy friendly as well as sustainable approach which will facilitate achieving some sustainable development goals. The production is dependent on the fermentation strategies, different factors of the microbial culture broth and downstream processing; these all have been elaborately presented in this article.

Biotechnological potential of microbial bio-surfactants, their significance, and diverse applications

Globally, there is a huge demand for chemically available surfactants in many industries, irrespective of their detrimental impact on the environment. Naturally occurring green sustainable substances have been proven to be the best alternative for reducing reliance on chemical surfactants and promoting long-lasting sustainable development. The most frequently utilized green active biosurfactants, which are made by bacteria, yeast, and fungi, are discussed in this review. These biosurfactants are commonly originated from contaminated sites, the marine ecosystem, and the natural environment, and it holds great potential for environmental sustainability. In this review, we described the importance of biosurfactants for the environment, including their biodegradability, low toxicity, environmental compatibility, and stability at a wide pH range. In this review, we have also described the various techniques that have been utilized to characterize and screen the generation of microbial biosurfactants. Also, we reviewed the potential of biosurfactants and its emerging applications in the foods, cosmetics, pharmaceuticals, and agricultural industries. In addition, we also discussed the ways to overcome problems with expensive costs such as low-cost substrate media formulation, gravitational techniques, and solvent-free foam fractionation for extraction that could be employed during biosurfactant production on a larger scale.

Characterization of trehalolipid biosurfactant produced by the novel marine strain Rhodococcus sp. SP1d and its potential for environmental applications

BACKGROUND

Biosurfactants are surface-active compounds with environmental and industrial applications. These molecules show higher biocompatibility, stability and efficiency compared to synthetic surfactants. On the other hand, biosurfactants are not cost-competitive to their chemical counterparts. Cost effective technology such as the use of low-cost substrates is a promising approach aimed at reducing the production cost. This study aimed to evaluate the biosurfactant production and activity by the novel strain Rhodococcus sp. SP1d by using different growth substrates. Therefore, to exploit the biosurfactant synthesized by SP1d for environmental applications, the effect of this compound on the bacteria biofilm formation was evaluated. Eventually, for a possible bioremediation application, the biosurfactant properties and its chemical characteristics were investigated using diesel as source of carbon.

RESULTS

Rhodococcus sp. SP1d evidence the highest similarity to Rhodococcus globerulus DSM 43954^T and the ability to biosynthesize surfactants using a wide range of substrates such as exhausted vegetable oil, mineral oil, butter, n-hexadecane, and diesel. The maximum production of crude biosurfactant after 10 days of incubation was reached on n-hexadecane and diesel with a final yield of 2.38 ± 0.51 and 1.86 ± 0.31 g L^- 1 respectively. Biosurfactants produced by SP1d enhanced the biofilm production of P. protegens MP12. Moreover, the results showed the ability of SP1d to produce biosurfactants on diesel even when grown at 10 and 18 °C. The biosurfactant activity was maintained over a wide range of NaCl concentration, pH, and temperature. A concentration of 1000 mg L^- 1 of the crude biosurfactant showed an emulsification activity of 55% towards both xylene and olive oil and a reduction of 25.0 mN m^- 1 of surface tension of water. Eventually, nuclear magnetic resonance spectroscopy indicated that the biosurfactant is formed by trehalolipids.

CONCLUSIONS

The use of low-cost substrates such as exhausted oils and waste butter reduce both the costs of biosurfactant synthesis and the environmental pollution due to the inappropriate disposal of these residues. High production yields, stability and emulsification properties using diesel and n-hexadecane as substrates, make the biosurfactant produced by SP1d a sustainable biocompound for bioremediation purpose. Eventually, the purified biosurfactant improved the biofilm formation of the fungal antagonistic strain P. protegens MP12, and thus seem to be exploitable to increase the adherence and colonization of plant surfaces by this antagonistic strain and possibly enhance antifungal activity.

Biosynthesis and Characterization of Gold Nanoparticles Produced Using Rhodococcus Actinobacteria at Elevated Chloroauric Acid Concentrations

The growing industrial and medical use of gold nanoparticles (AuNPs) requires environmentally friendly methods for their production using microbial biosynthesis. The ability of actinobacteria of the genus Rhodococcus to synthesize AuNPs in the presence of chloroauric acid (HAuCl₄) was studied. The effect of elevated (0.8–3.2 mM) concentrations of HAuCl₄ on bacterial viability, morphology, and intracellular accumulation of AuNPs by different Rhodococcus species was shown. An increase in surface roughness, a shift of the zeta potential to the positive region, and the formation of cell aggregates of R. erythropolis IEGM 766 and R. ruber IEGM 1135 during nanoparticle synthesis were revealed as bacterial adaptations to toxic effects of HAuCl₄. The possibility to biosynthesize AuNPs at a five times higher concentration of chloroauric acid compared to chemical synthesis, for example, using the citrate method, suggests greater efficiency of the biological process using Rhodococcus species. The main parameters of biosynthesized AuNPs (size, shape, surface roughness, and surface charge) were characterized using atomic force microscopy, dynamic and electrophoretic light scattering, and also scanning electron microscopy in combination with energy-dispersive spectrometry. Synthesized by R. erythropolis spherical AuNPs have smaller (30–120 nm) dimensions and are positively (12 mV) charged, unlike AuNPs isolated from R. ruber cells (40–200 nm and −22 mV, respectively). Such differences in AuNPs size and surface charge are due to different biomolecules, which originated from Rhodococcus cells and served as capping agents for nanoparticles. Biosynthesized AuNPs showed antimicrobial activity against Gram-positive (Micrococcus luteus) and Gram-negative (Escherichia coli) bacteria. Due to the positive charge and high dispersion, the synthesized by R. erythropolis AuNPs are promising for biomedicine, whereas the AuNPs formed by R. ruber IEGM 1135 are prone to aggregation and can be used for biotechnological enrichment of gold-bearing ores.

Bioherder Generated by Rhodococcus erythropolis as a Marine Oil Spill Treating Agent

There is an urgent call for contingency planning with effective and eco-friendly oil spill cleanup responses. In situ burning, if properly applied, could greatly mitigate oil in water and minimize the adverse environmental impacts of the spilled oil. Chemical herders have been commonly used along with in situ burning to increase the thickness of spilled oil at sea and facilitate combustion. These chemical surfactant-based agents can be applied to the edges of the oil slick and increase its thickness by reducing the water–oil interfacial tension. Biosurfactants have recently been developed as the next generation of herds with a smaller environmental footprint. In this study, the biosurfactant produced by Rhodococcus erythropolis M25 was evaluated and demonstrated as an effective herding agent. The impact of environmental and operational factors (e.g., temperature, herder dose, spilled oil amount, water salinity, and operation location) on its performance was investigated. A five-factor fractional design was applied to examine the importance of these factors and their impact on herding effectiveness and efficiency. The results of this study showed that higher temperature and a higher dose of herder could result in an increased oil slick thickness changing rate. Differences in water salinity at the same temperature led to the same trend, that is, the herding process effectively goes up with increasing herder–oil ratio (HOR). Further large-scale testing needs to be conducted for evaluating the applicability of the developed bioherder in the field.

Production of mannosylerythritol lipids: biosynthesis, multi-omics approaches, and commercial exploitation

Compilation of resources regarding MEL biosynthesis, key production parameters; available omics resources and current commercial applications, for smut fungi known to produce MELs.

Biosurfactant is a powerful tool for the bioremediation of heavy metals from contaminated soils

Heavy metal toxicity has become a pressing ecological problem that affects the ecosystems through bioaccumulation, representing a serious public health hazard. Many conventional strategies have been developed and applied to decontaminate and restore metal-contaminated areas. However, these conventional approaches are not very suitable and environmentally safe for heavy metal remediation because of their high operational costs, high energy requirements, post-waste disposal problems, and secondary pollutant generation. Thus, biosurfactant-based bioremediation of heavy metals is a sustainable and promising approach because of its biodegradation capability, economic effectiveness, and ecofriendly nature. Pseudomonas sp., Bacillus sp., Citrobacter freundii, and Candida tropicalis have been isolated as potential sources of biosurfactants and produce compounds such as surfactin, rhamnolipids, and sophorolipids. Owing to the severity of heavy metal pollution in certain parts of the environment, biosurfactants have garnered great interest and attention as an emerging multi-functional technology of the new century for successful removal of heavy metal pollutants. The present study describes the role of biosurfactants in the bioremediation of heavy metals from contaminated environments. Moreover, the interaction mechanism underlying biosurfactant-metal complexation and metal remediation are discussed. Based on the review of the literature, further research is warranted to elucidate the mechanistic roles and explore the structural characterization and gene regulation of biosurfactants to improve their productivity and expand their applicability in bioremediation.

Responses to Ecopollutants and Pathogenization Risks of Saprotrophic Rhodococcus Species

Under conditions of increasing environmental pollution, true saprophytes are capable of changing their survival strategies and demonstrating certain pathogenicity factors. Actinobacteria of the genus Rhodococcus, typical soil and aquatic biotope inhabitants, are characterized by high ecological plasticity and a wide range of oxidized organic substrates, including hydrocarbons and their derivatives. Their cell adaptations, such as the ability of adhering and colonizing surfaces, a complex life cycle, formation of resting cells and capsule-like structures, diauxotrophy, and a rigid cell wall, developed against the negative effects of anthropogenic pollutants are discussed and the risks of possible pathogenization of free-living saprotrophic Rhodococcus species are proposed. Due to universal adaptation features, Rhodococcus species are among the candidates, if further anthropogenic pressure increases, to move into the group of potentially pathogenic organisms with "unprofessional" parasitism, and to join an expanding list of infectious agents as facultative or occasional parasites.

Biosurfactants: Production and application prospects in the food industry

There has been considerable interest in the use of biosurfactants due to the diversity of structures and the possibility of production from a variety of substrates. The potential for industrial applications has been growing, as these natural compounds are tolerant to common processing methods and can compete with synthetic surfactants with regards to the capacity to reduce surface and interfacial tensions as well as stabilise emulsions while offering the advantages of biodegradability and low toxicity. Among biosurfactant-producing microorganisms, some yeasts present no risks of toxicity or pathogenicity, making them ideal for use in food formulations. Indeed, the use of these biomolecules in foods has attracted industrial interest due to their properties as emulsifiers and stabilizers of emulsions. Studies have also demonstrated other valuable properties, such as antioxidant and antimicrobial activity, enabling the aggregation of greater value to products and the avoidance of contamination both during and after processing. All these characteristics allow biosurfactants to be used as additives and versatile ingredients for the processing of foods. The present review discusses the potential application of biosurfactants as emulsifying agents in food formulations, such as salad dressing, bread, cakes, cookies, and ice cream. The antioxidant, antimicrobial and anti-adhesive properties of these biomolecules are also discussed, demonstrating the need for further studies to make the use of the natural compounds viable in this expanding sector.