Trehalose lipid biosurfactants produced by the actinomycetes Tsukamurella spumae and T. pseudospumae

Biosurfactant-mediated transport of tetracycline antibiotics in saturated porous media: Combined effects of the chemical properties of contaminants and solution chemistry conditions

The mobility of tetracycline antibiotics (TCs) in saturated aquifers is possibly affected by the presence of biosurfactants, which are widespread in the aquatic/soil environments. This study investigated the mobility characteristics of various tetracyclines-specifically tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)-within quartz sand columns in the presence of rhamnolipid, a common biosurfactant. Exogenous rhamnolipid significantly inhibited the transport of the three TCs over the pH range of 5.0-9.0 (e.g., the mass of retained TC, OTC, and CTC increased from 32.6 %, 26.9 %, and 39.2 % (in the absence rhamnolipid) to 39.4 %, 38.9 %, and 51.7 % (in the presence of rhamnolipid), respectively). This observation could be attributed to the bridging effects of this biosurfactant. Specifically, the hydrophilic head of rhamnolipid molecules is likely associated with the surfaces of sand grains through surface complexation and/or hydrogen bonding interactions. Accordingly, the hydrophobic moieties of the deposited rhamnolipid molecules (i.e., the aliphatic chains) interact with the hydrophobic groups of TCs molecules via hydrophobic interactions. Interestingly, the extent of the inhibitory effect on CTC mobility was greater than that on OTC and TC, which was related to the different hydrophobic characteristics of the three antibiotics. Furthermore, the inhibitory effect of rhamnolipid on the transport of TCs diminished as the pH of the background solution increased. This observation was attributed to the weakened bridging effects, resulting from the reduced deposition of the biosurfactant on the sand surfaces. Additionally, the cation-bridging mechanism involved in the retention of TCs in the addition of rhamnolipid when the background electrolyte was Ca2+ (i.e., Ca2+ ions served as bridging agents between the deposited rhamnolipid molecules and TCs). The insightful findings enhance our understanding of the critical roles of biosurfactants in influencing the environmental dynamics and ultimate fate of conventional antibiotic pollutants within groundwater systems.

Glycolipids biosurfactants production using low-cost substrates for environmental remediation: progress, challenges, and future prospects

The production of renewable materials from alternative sources is becoming increasingly important to reduce the detrimental environmental effects of their non-renewable counterparts and natural resources, while making them more economical and sustainable. Chemical surfactants, which are highly toxic and non-biodegradable, are used in a wide range of industrial and environmental applications harming humans, animals, plants, and other entities. Chemical surfactants can be substituted with biosurfactants (BS), which are produced by microorganisms like bacteria, fungi, and yeast. They have excellent emulsifying, foaming, and dispersing properties, as well as excellent biodegradability, lower toxicity, and the ability to remain stable under severe conditions, making them useful for a variety of industrial and environmental applications. Despite these advantages, BS derived from conventional resources and precursors (such as edible oils and carbohydrates) are expensive, limiting large-scale production of BS. In addition, the use of unconventional substrates such as agro-industrial wastes lowers the BS productivity and drives up production costs. However, overcoming the barriers to commercial-scale production is critical to the widespread adoption of these products. Overcoming these challenges would not only promote the use of environmentally friendly surfactants but also contribute to sustainable waste management and reduce dependence on non-renewable resources. This study explores the efficient use of wastes and other low-cost substrates to produce glycolipids BS, identifies efficient substrates for commercial production, and recommends strategies to improve productivity and use BS in environmental remediation.

Sustainable trehalose lipid production by Rhodotorula sp.: a promising bio-based alternative

Global environmental concerns drive research toward the development of new eco-friendly compounds to replace pollutant chemicals. This study focuses on optimizing the production of trehalose lipids (TLs), which are glycolipid biosurfactants (BS) with various applications like antimicrobial or surface tension reduction. New microorganism sources, growth conditions, medium composition, purification conditions, and physicochemical properties of TLs are studied. Addressing a microscale approach, TLs production was successfully achieved using Rhodotorula sp. and Rhodococcus erythropolis to compare, with different media compositions including glucose-based and salt media supplemented with glycerol, glucose, n-hexadecane, n-dodecane. Liquid-liquid extraction using ethyl acetate and methanol was employed for compound extraction, followed by characterization using analytical methods such as Thin layer chromatography (TLC), High performance liquid chromatography (HPLC), and UHPLC. The produced TLs exhibited a minimum surface tension of 47 mN/m and a critical micellar concentration of 4.4 mg/mL. This study also identified Rhodotorula sp. as a new sustainable producer of TLs with improved productivity.

Biochemical, Catabolic, and PGP Activity of Microbial Communities and Bacterial Strains from the Root Zone of Baccharis linearis in a Mediterranean Mine Tailing

The management of mine tailings (MT) is commonly workload heavy, intrusive, and expensive. Phytostabilization offers a promising approach for MT management; however, it poses challenges due to the unfavorable physicochemical properties of these wastes. Nevertheless, native microorganisms capable of supporting plant growth and development could enhance the efficacy of phytostabilization. This study assesses the biological activity of microbial communities from the root zone of Baccharis linearis, which is naturally present in MT, in order to evaluate their biotechnological potential for phytostabilization. The root zone and bulk samples were collected from B. linearis plants located within a MT in the Mediterranean zone of Chile. Enzyme activities related to the cycling of C, N, and P were assessed. The community-level physiological profile was evaluated using the MicroRespTM system. Bacterial plant growth-promoting (PGP) traits and colony forming units (CFU) were evaluated through qualitative and microbiological methods, respectively. CFU, enzyme activities, and CLPP were higher in the root zone compared with the bulk samples. Five bacterial strains from the root zone exhibited PGP traits such as P solubilization and N acquisition, among others. The presence of microbial communities in the root zone of B. linearis with PGP traits suggests their potential to enhance the ecological management of MT through phytostabilization programs.

Microbial surfactants: characteristics, production and broader application prospects in environment and industry

Microbial surfactants are green molecules with high surface activities having the most promising advantages over chemical surfactants including their ability to efficiently reducing surface and interfacial tension, nontoxic emulsion-based formulations, biocompatibility, biodegradability, simplicity of preparation from low cost materials such as residual by-products and renewable resources at large scales, effectiveness and stabilization under extreme conditions and broad spectrum antagonism of pathogens to be part of the biocontrol strategy. Thus, biosurfactants are universal tools of great current interest. The present work describes the major types and microbial origin of surfactants and their production optimization from agro-industrial wastes in the batch shake-flasks and bioreactor systems through solid-state and submerged fermentation industries. Various downstream strategies that had been developed to extract and purify biosurfactants are discussed. Further, the physicochemical properties and functional characteristics of biosurfactants open new future prospects for the development of efficient and eco-friendly commercially successful biotechnological product compounds with diverse potential applications in environment, industry, biomedicine, nanotechnology and energy-saving technology as well.

Novel trehalose-based excipients for stabilizing nebulized anti-SARS-CoV-2 antibody

COVID-19 is caused by the infection of the lungs by SARS-CoV-2. Monoclonal antibodies, such as sotrovimab, showed great efficiency in neutralizing the virus before its internalization by lung epithelial cells. However, parenteral routes are still the preferred route of administration, even for local infections, which requires injection of high doses of antibody to reach efficacious concentrations in the lungs. Lung administration of antibodies would be more relevant requiring lower doses, thus reducing the costs and the side effects. But aerosolization of therapeutic proteins is very challenging, as the different processes available are harsh and trigger protein aggregation and conformational changes. This decreases the efficiency of the treatment, and can increase its immunogenicity. To address those issues, we developed a series of new excipients composed of a trehalose core, a succinyl side chain and a hydrophobic carbon chain (from 8 to 16 carbons). Succinylation increased the solubility of the excipients, allowing their use at relevant concentrations for protein stabilization. In particular, the excipient with 16 carbons (C₁₆TreSuc) used at 5.6 mM was able to preserve colloidal stability and antigen-binding ability of sotrovimab during the nebulization process. It could also be used as a cryoprotectant, allowing storage of sotrovimab in a lyophilized form during weeks. Finally, we demonstrated that C₁₆TreSuc could be used as an excipient to stabilize antibodies for the treatment against COVID-19, by in vitro and in vivo assays. The presence of C₁₆TreSuc during nebulization preserved the neutralization capacity of sotrovimab against SARS-CoV-2 in vitro; an increase of its efficacy was even observed, compared to the non-nebulized control. The in vivo study also showed the wide distribution of sotrovimab in mice lungs, after nebulization with 5.6 mM of excipient. This work brings a solution to stabilize therapeutic proteins during storage and nebulization, making pulmonary immunotherapy possible in the treatment of COVID-19 and other lung diseases.

New Glycosylated Secondary Metabolites from Marine-Derived Bacteria

Three new glycosylated secondary metabolites, including a new indole alkaloid, pityriacitrin D (1), and two new trehalose lipids (2 and 3), together with three known compounds (4-6) were isolated from two marine-derived bacterial strains, Bacillus siamensis 168CLC-66.1 and Tsukamurella pseudospumae IV19-045. The structures of 1-3 were determined by extensive analysis and comparison of their spectroscopic data with literature values. The absolute configurations of sugar moieties were determined by chemical derivatization followed by LC-MS analysis. Cytotoxicity of 1-3 against six cancer cell lines was evaluated by SRB assay, and 1 showed moderate activity against all the tested cell lines with GI50 values ranging from 8.0 to 10.9 µM.

S. R, Hameeda B, El Enshasy HA, Hanapi SZ, Sayyed RZ. Biosurfactant producing multifarious Streptomyces puniceus RHPR9 of Coscinium fenestratum rhizosphere promotes plant growth in chilli

The present study involves isolation of Streptomyces spp. from rhizosphere of Coscinium fenestratum Gaertn, an endangered medicinal plant from Western Ghats of Karnataka, India. Four potential isolates were identified by 16S rRNA sequencing as Streptomyces sp. RHPR3, Streptomyces puniceus RHPR9, Streptomyces sp. RHPR14 and Streptomyces mediolani RHPR25. An enrichment culture method was used for the isolation of Streptomyces spp. for biosurfactant activity. Among four potential Streptomyces spp., S. puniceus RHPR9 showed highest Emulsification index (EI) (78±0.2%) and Emulsification assay (EA) (223±0.2 EU mL^-1). Thin layer chromatography, Fourier transform infrared spectroscopy (FTIR) and mass spectrometric analysis revealed that as glycolipid. Further confirmed by presence of fatty acids like hexanoic acid methyl ester, decanoic acid by Gas chromatography mass spectroscopy (GC-MS) analysis. S. puniceus RHPR9 showed a significant IAA production (41μg mL^-1), solubilized P (749.1 μg mL^-1), growth promotion of chilli (Capsicum annuum L.) was evaluated using paper towel method and greenhouse conditions. S. puniceus RHPR9 showed a significant increase in seed vigor index (2047) and increase in plant biomass (65%) when compared to uninoculated control. To our knowledge, this is the first report on epiphytic S. puniceus RHPR9 isolated from an endangered medicinal plant C. fenestratum Gaertn, for biosurfactant production and plant growth promotion activities.

Significance of both alkB and P450 alkane-degrading systems in Tsukamurella tyrosinosolvens: proteomic evidence

The Tsukamurella tyrosinosolvens PS2 strain was isolated from hydrocarbons-contaminated petrochemical sludge as a long chain alkane-utilizing bacteria. Complete genome analysis showed the presence of two alkane oxidation systems: alkane 1-monooxygenase (alkB) and cytochrome P450 monooxygenase (P450) genes with established high homology to the well-known alkane-degrading actinobacteria. According to the comparative genome analysis, both systems have a wide distribution among environmental and clinical isolates of the genus Tsukamurella and other members of Actinobacteria. We compared the expression of different proteins during the growth of Tsukamurella on sucrose and on hexadecane. Both alkane monooxygenases were upregulated on hexadecane: AlkB-up to 2.5 times, P450-up to 276 times. All proteins of the hexadecane oxidation pathway to acetyl-CoA were also upregulated. Accompanying proteins for alkane degradation involved in biosurfactant synthesis and transport of organic and inorganic molecules were increased. The change in the carbon source affected the pathways for the regulation of translation and transcription. The proteomic profile showed that hexadecane is an adverse factor causing activation of general and universal stress proteins as well as shock and resistance proteins. Differently expressed proteins of Tsukamurella tyrosinosolvens PS2 shed light on the alkane degradation in other members of Actinobacteria class. KEY POINTS: • alkB and P450 systems have a wide distribution among the genus Tsukamurella. • alkB and P450 systems have coexpression with the predominant role of P450 protein. • Hexadecane causes significant changes in bacterial proteome.

The actinobacterium Tsukamurella paurometabola has a functionally divergent arylamine N-acetyltransferase (NAT) homolog

Actinobacteria in the Tsukamurella genus are aerobic, high-GC, Gram-positive mycolata, considered as opportunistic pathogens and isolated from various environmental sources, including sites contaminated with oil, urban or industrial waste and pesticides. Although studies look into xenobiotic biotransformation by Tsukamurella isolates, the relevant enzymes remain uncharacterized. We investigated the arylamine N-acetyltransferase (NAT) enzyme family, known for its role in the xenobiotic metabolism of prokaryotes and eukaryotes. Xenobiotic sensitivity of Tsukamurella paurometabola type strain DSM 20162^T was assessed, followed by cloning, recombinant expression and functional characterization of its single NAT homolog (TSUPD)NAT1. The bacterium appeared quite robust against chloroanilines, but more sensitive to 4-anisidine and 2-aminophenol. However, metabolic activity was not evident towards those compounds, presumably due to mechanisms protecting cells from xenobiotic entry. Of the pharmaceutical arylhydrazines tested, hydralazine was toxic, but the bacterium was less sensitive to isoniazid, a drug targeting mycolic acid biosynthesis in mycobacteria. Although (TSUPD)NAT1 protein has an atypical Cys-His-Glu (instead of the expected Cys-His-Asp) catalytic triad, it is enzymatically active, suggesting that this deviation is likely due to evolutionary adaptation potentially serving a different function. The protein was indeed found to use malonyl-CoA, instead of the archetypal acetyl-CoA, as its preferred donor substrate. Malonyl-CoA is important for microbial biosynthesis of fatty acids (including mycolic acids) and polyketide chains, and the corresponding enzymatic systems have common evolutionary histories, also linked to xenobiotic metabolism. This study adds to accummulating evidence suggesting broad phylogenetic and functional divergence of microbial NAT enzymes that goes beyond xenobiotic metabolism and merits investigation.

Cell Walls and Membranes of Actinobacteria

Actinobacteria is a group of diverse bacteria. Most species in this class of bacteria are filamentous aerobes found in soil, including the genus Streptomyces perhaps best known for their fascinating capabilities of producing antibiotics. These bacteria typically have a Gram-positive cell envelope, comprised of a plasma membrane and a thick peptidoglycan layer. However, there is a notable exception of the Corynebacteriales order, which has evolved a unique type of outer membrane likely as a consequence of convergent evolution. In this chapter, we will focus on the unique cell envelope of this order. This cell envelope features the peptidoglycan layer that is covalently modified by an additional layer of arabinogalactan . Furthermore, the arabinogalactan layer provides the platform for the covalent attachment of mycolic acids , some of the longest natural fatty acids that can contain ~100 carbon atoms per molecule. Mycolic acids are thought to be the main component of the outer membrane, which is composed of many additional lipids including trehalose dimycolate, also known as the cord factor. Importantly, a subset of bacteria in the Corynebacteriales order are pathogens of human and domestic animals, including Mycobacterium tuberculosis. The surface coat of these pathogens are the first point of contact with the host immune system, and we now know a number of host receptors specific to molecular patterns exposed on the pathogen's surface, highlighting the importance of understanding how the cell envelope of Actinobacteria is structured and constructed. This chapter describes the main structural and biosynthetic features of major components found in the actinobacterial cell envelopes and highlights the key differences between them.

Trehalose Lipid Biosurfactant Reduces Adhesion of Microbial Pathogens to Polystyrene and Silicone Surfaces: An Experimental and Computational Approach

Rhodococcus fascians BD8, isolated from Arctic soil, was found to produce biosurfactant when grown on n-hexadecane as the sole carbon source. The glycolipid product was identified as the trehalose lipid with a molecular mass of 848 g mol^-1. The purified biosurfactant reduced the surface tension of water from 72 to 34 mN m^-1. The critical micelle concentration of trehalose lipid was 0.140 mg mL^-1. To examine its potential for biomedical applications, the antimicrobial and antiadhesive activity of the biosurfactant was evaluated against several pathogenic microorganisms. Trehalose lipid showed antimicrobial activity against resistant pathogens. The largest antimicrobial activities of trehalose lipid were observed against Vibrio harveyi and Proteus vulgaris. The highest concentration tested (0.5 mg mL^-1) caused a partial (11-34%) inhibition of other Gram-positive and Gram-negative bacteria and 30% inhibition of Candida albicans growth. The trehalose lipid also showed significant antiadhesive properties against all of the tested microorganisms to polystyrene surface and silicone urethral catheters. The biosurfactant showed 95 and 70% antiadhesive activity against C. albicans and Escherichia coli, respectively. Finally, the role and application of trehalose lipid as an antiadhesive compound was investigated by the modification of the polystyrene and silicone surfaces. The intermolecular interaction energy calculations were performed for investigated complexes at the density functional level of theory. The results indicate that the presence of aromatic moieties can be substantial in the stabilization of trehalose lipid-surface complexes. The antimicrobial and antiadhesive activities of trehalose lipid make them promising alternatives to synthetic surfactants in a wide range of medical applications. Based on our findings, we propose that, because of its ability to inhibit microbial colonization of polystyrene and silicone surfaces, trehalose lipid can be used as a surface coating agent.

Identification and characterisation of short chain rhamnolipid production in a previously uninvestigated, non-pathogenic marine pseudomonad

This study aimed to identify and characterise biosurfactant compounds produced by bacteria associated with a marine eukaryotic phytoplankton bloom. One strain, designated MCTG214(3b1), was isolated by enrichment with polycyclic aromatic hydrocarbons and based on 16S rDNA, and gyrB sequencing was found to belong to the genus Pseudomonas, however not related to P. aeruginosa. Cell-free supernatant samples of strain MCTG214(3b1) at stationary phase showed significant reductions in surface tension. HPLC-MS and NMR analysis of these samples indicated the presence of five different rhamnolipid (RL) congeners. Di-rhamnolipids accounted for 87% relative abundance and all congeners possessed fatty acid moieties consisting of 8–12 carbons. PCR screening of strain MCTG214(3b1) DNA revealed homologues to the P. aeruginosa RL synthesis genes rhlA and rhlB; however, no rhlC homologue was identified. Using the Galleria mellonella larvae model, strain MCTG214(3b1) was demonstrated to be far less pathogenic than P. aeruginosa. This study identifies for the first time a significantly high level of synthesis of short chain di-rhamnolipids by a non-pathogenic marine Pseudomonas species. We postulate that RL synthesis in Pseudomonas sp. MCTG214(3b1) is carried out by enzymes expressed from rhlA/B homologues similar to those of P. aeruginosa; however, a lack of rhlC potentially indicates the presence of a second novel rhamnosyltransferase responsible for the di-rhamnolipid congeners identified by HPLC-MS.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Trehalose Contributes to Gamma-Linolenic Acid Accumulation in Cunninghamella echinulata Based on de Novo Transcriptomic and Lipidomic Analyses

Gamma-linolenic acid (GLA) is essential for the well-being of humans and other animals. People may lack GLA because of aging or diseases, and thus, dietary supplements or medical reagents containing GLA-enriched lipids are in demand. Cunninghamella echinulata is a potential GLA-producing strain. Interestingly, we found that the GLA content of C. echinulata FR3 was up to 21% (proportion of total lipids) when trehalose was used as a carbon source, significantly higher than the 13% found when glucose was used. Trehalose is quite common and can be accumulated in microorganisms under stress conditions. However, little information is available regarding the role of trehalose in GLA synthesis and accumulation. Our study aimed to understand how the metabolism of C. echinulata responds to trehalose as a carbon source for GLA and lipid biosynthesis. We profiled the major sugars, fatty acids, phospholipids, and gene transcripts of C. echinulata FR3 grown in trehalose medium with glucose as a control by de novo transcriptomics, lipidomics, and other methods. The results showed that trehalose could influence the expression of desaturases and that the GLA proportion increased because of delta-6 desaturase upregulation. The increased GLA was transferred to the extracellular environment through the active PI ion channel, which prefers polyunsaturated acyl chains. At the same time, trehalose might prevent GLA from peroxidation by forming a trehalose-polyunsaturated fatty acid (PUFA) complex. Our study provides new insights into the functions of trehalose in GLA accumulation.

Current status in biotechnological production and applications of glycolipid biosurfactants

Biosurfactants are natural compounds with surface activity and emulsifying properties produced by several types of microorganisms and have been considered an interesting alternative to synthetic surfactants. Glycolipids are promising biosurfactants, due to low toxicity, biodegradability, and chemical stability in different conditions and also because they have many biological activities, allowing wide applications in different fields. In this review, we addressed general information about families of glycolipids, rhamnolipids, sophorolipids, mannosylerythritol lipids, and trehalose lipids, describing their chemical and surface characteristics, recent studies using alternative substrates, and new strategies to improve of production, beyond their specificities. We focus in providing recent developments and trends in biotechnological process and medical and industrial applications.

Glycolipid biosurfactants: main properties and potential applications in agriculture and food industry

Glycolipids, consisting of a carbohydrate moiety linked to fatty acids, are microbial surface active compounds produced by various microorganisms. They are characterized by high structural diversity and have the ability to decrease the surface and interfacial tension at the surface and interface, respectively. Rhamnolipids, trehalolipids, mannosylerythritol lipids and cellobiose lipids are among the most popular glycolipids. They have received much practical attention as biopesticides for controlling plant diseases and protecting stored products. As a result of their antifungal activity towards phytopathogenic fungi and larvicidal and mosquitocidal potencies, glycolipid biosurfactants permit the preservation of plants and plant crops from pest invasion. Also, as a result of their emulsifying and antibacterial activities, glycolipids have great potential as food additives and food preservatives. Furthermore, the valorization of food byproducts via the production of glycolipid biosurfactant has received much attention because it permits the bioconversion of byproducts on valuable compounds and decreases the cost of production. Generally, the use of glycolipids in many fields requires their retention from fermentation media. Accordingly, different strategies have been developed to extract and purify glycolipids. © 2016 Society of Chemical Industry.

Cold stress promoting a psychrotolerant bacterium Pseudomonas fragi P121 producing trehaloase

A newly isolated Pseudomonas fragi P121 strain in a soil sample taken from the Arctic Circle is able to produce trehalose. The P121 strain was able to grow at temperatures ranging from 4 to 25 °C, had an optimum pH of 6.5, and an optimum salt concentration of 2 %. The P121 strain had a survival rate of 29.1 % after being repeatedly frozen and thawed five times, and a survival rate of 78.9 % when placed in physiological saline for 15 days at 20 °C after cold shock, which is far higher than the type strain Pseudomonas fragi ATCC 4973. The P121 strain could produce 2.89 g/L trehalose, which was 18.6 % of dry cell weight within 52 h in a 25 L fermention tank using the malt extract prepared from barley as medium at 15 °C, while only 11.8 % of dry cell weight at 20 °C. These results suggested that cold stress promoted the strain producing trehalose. It is the first reported cold-tolerant bacterium that produces trehalose, which may protect cells against the cold environment.

Extracellular aromatic biosurfactant produced by Tsukamurella pseudospumae and T. spumae during growth on n-hexadecane

Biosurfactants are surface-active agents produced by microorganisms and show increasing significance in various industrial applications. A great variety of these secondary metabolites are described to occur within actinomycetes, amongst trehalose lipids and oligosaccharide lipids produced by the family Tsukamurellaceae. This study reports on the production of not yet described compounds with surface active behavior by non-pathogenic Tsukamurella pseudospumae and Tsukamurella spumae during growth on hydrophobic carbon sources. Extracts of the purified compounds differ in terms of structure and performance properties to other biosurfactants described within their family. Infrared and nuclear magnetic resonance spectroscopic analysis revealed the presence of aromatic moieties within the surfactant produced, which to date is only known to occur within phenolic glycolipids of some mycobateria.

Surfactants tailored by the class Actinobacteria

Globally the change towards the establishment of a bio-based economy has resulted in an increased need for bio-based applications. This, in turn, has served as a driving force for the discovery and application of novel biosurfactants. The class Actinobacteria represents a vast group of microorganisms with the ability to produce a diverse range of secondary metabolites, including surfactants. Understanding the extensive nature of the biosurfactants produced by actinobacterial strains can assist in finding novel biosurfactants with new potential applications. This review therefore presents a comprehensive overview of the knowledge available on actinobacterial surfactants, the chemical structures that have been completely or partly elucidated, as well as the identity of the biosurfactant-producing strains. Producer strains of not yet elucidated compounds are discussed, as well as the original habitats of all the producer strains, which seems to indicate that biosurfactant production is environmentally driven. Methodology applied in the isolation, purification and structural elucidation of the different types of surface active compounds, as well as surfactant activity tests, are also discussed. Overall, actinobacterial surfactants can be summarized to include the dominantly occurring trehalose-comprising surfactants, other non-trehalose containing glycolipids, lipopeptides and the more rare actinobacterial surfactants. The lack of structural information on a large proportion of actinobacterial surfactants should be considered as a driving force to further explore the abundance and diversity of these compounds. This would allow for a better understanding of actinobacterial surface active compounds and their potential for biotechnological application.