Uranium binding by emulsan and emulsanosols

Exploring fungal bioemulsifiers: insights into chemical composition, microbial sources, and cross-field applications

The demand for emulsion-based products is crucial for economic development and societal well-being, spanning diverse industries such as food, cosmetics, pharmaceuticals, and oil extraction. Formulating these products relies on emulsifiers, a distinct class of surfactants. However, many conventional emulsifiers are derived from petrochemicals or synthetic sources, posing potential environmental and human health risks. In this context, fungal bioemulsifiers emerge as a compelling and sustainable alternative, demonstrating superior performance, enhanced biodegradability, and safety for human consumption. From this perspective, the present work provides the first comprehensive review of fungal bioemulsifiers, categorizing them based on their chemical nature and microbial origin. This includes polysaccharides, proteins, glycoproteins, polymeric glycolipids, and carbohydrate-lipid-protein complexes. Examples of particular interest are scleroglucan, a polysaccharide produced by Sclerotium rolfsii, and mannoproteins present in the cell walls of various yeasts, including Saccharomyces cerevisiae. Furthermore, this study examines the feasibility of incorporating fungal bioemulsifiers in the food and oil industries and their potential role in bioremediation events for oil-polluted marine environments. Finally, this exploration encourages further research on fungal bioemulsifier bioprospecting, with far-reaching implications for advancing sustainable and eco-friendly practices across various industrial sectors.

Microbial Extracellular Polymeric Substances (EPSs) in Ocean Systems

Microbial cells (i.e., bacteria, archaea, microeukaryotes) in oceans secrete a diverse array of large molecules, collectively called extracellular polymeric substances (EPSs) or simply exopolymers. These secretions facilitate attachment to surfaces that lead to the formation of structured 'biofilm' communities. In open-water environments, they also lead to formation of organic colloids, and larger aggregations of cells, called 'marine snow.' Secretion of EPS is now recognized as a fundamental microbial adaptation, occurring under many environmental conditions, and one that influences many ocean processes. This relatively recent realization has revolutionized our understanding of microbial impacts on ocean systems. EPS occur in a range of molecular sizes, conformations and physical/chemical properties, and polysaccharides, proteins, lipids, and even nucleic acids are actively secreted components. Interestingly, however, the physical ultrastructure of how individual EPS interact with each other is poorly understood. Together, the EPS matrix molecules form a three-dimensional architecture from which cells may localize extracellular activities and conduct cooperative/antagonistic interactions that cannot be accomplished efficiently by free-living cells. EPS alter optical signatures of sediments and seawater, and are involved in biogeomineral precipitation and the construction of microbial macrostructures, and horizontal-transfers of genetic information. In the water-column, they contribute to the formation of marine snow, transparent exopolymer particles (TEPs), sea-surface microlayer biofilm, and marine oil snow. Excessive production of EPS occurs during later-stages of phytoplankton blooms as an excess metabolic by product and releases a carbon pool that transitions among dissolved-, colloidal-, and gel-states. Some EPS are highly labile carbon forms, while other forms appear quite refractory to degradation. Emerging studies suggest that EPS contribute to efficient trophic-transfer of environmental contaminants, and may provide a protective refugia for pathogenic cells within marine systems; one that enhances their survival/persistence. Finally, these secretions are prominent in 'extreme' environments ranging from sea-ice communities to hypersaline systems to the high-temperatures/pressures of hydrothermal-vent systems. This overview summarizes some of the roles of exopolymer in oceans.

Emulsifying and metal ion binding activity of a glycoprotein exopolymer produced by Pseudoalteromonas sp. strain TG12

In this study, we describe the isolation and characterization of a new exopolymer that exhibits high emulsifying activities against a range of oil substrates and demonstrates a differential capacity to desorb various mono-, di-, and trivalent metal species from marine sediment under nonionic and seawater ionic-strength conditions. This polymer, PE12, was produced by a new isolate, Pseudoalteromonas sp. strain TG12 (accession number EF685033), during growth in a modified Zobell's 2216 medium amended with 1% glucose. Chemical and chromatographic analysis showed it to be a high-molecular-mass (>2,000 kDa) glycoprotein composed of carbohydrate (32.3%) and protein (8.2%). PE12 was notable in that it contained xylose as the major sugar component at unusually high levels (27.7%) not previously reported for a Pseudoalteromonas exopolymer. The polymer was shown to desorb various metal species from marine sediment-a function putatively conferred by its high content of uronic acids (28.7%). Seawater ionic strength (simulated using 0.6 M NaCl), however, caused a significant reduction in PE12's ability to desorb the sediment-adsorbed metals. These results demonstrate the importance of electrolytes, a physical parameter intrinsic of seawater, in influencing the interaction of microbial exopolymers with metal ions. In summary, PE12 may represent a new class of Pseudoalteromonas exopolymer with a potential for use in biotechnological applications as an emulsifying or metal-chelating agent. In addition to the biotechnological potential of these findings, the ecological aspects of this and related bacterial exopolymers in marine environments are also discussed.

Discovery of the dual polysaccharide composition of emulsan and the isolation of the emulsion stabilizing component

Emulsan has been reported as an emulsion stabilizing amphipathic lipoheteropolysaccharide secreted by the oil-degrading bacterium Acinetobacter venetianus RAG-1. Previously, emulsan was regarded as a single polymer. As a result of developing a new purification process, we have discovered that emulsan is a complex of approximately 80% (w/w) lipopolysaccharide (LPS) and 20% (w/w) high molecular weight exopolysaccharide (EPS). The EPS was purified to 98% (w/w) using tangential flow filtration, Triton X-114 phase extraction, ammonium sulfate precipitation, and hydrophobic interaction chromatography. Several previously reported physical properties of emulsan can be attributed to the LPS fraction, such as charge, fatty acid profile, and solution behavior, while the EPS is responsible for the emulsion stabilization activity. The EPS is believed to be cationic in nature, thus providing an electrostatic binding mechanism for the formation of the emulsan complex.

Protein engineering of wzc to generate new emulsan analogs

Acinetobacter venetianus Rag1 produces an extracellular, polymeric lipoheteropolysaccharide termed apoemulsan. This polymer is putatively produced via a Wzy-dependent pathway. According to this model, the length of the polymer is regulated by polysaccharide-copolymerase (PCP) protein. A highly conserved proline and glycine motif was identified in all members of the PCP family of proteins and is involved in regulation of polymer chain length. In order to control the structure of apoemulsan, defined point mutations in the proline-glycine-rich region of the apoemulsan PCP protein (Wzc) were introduced. Modified wzc variants were introduced into the Rag1 genome via homologous recombination. Stable chromosomal mutants were confirmed by Southern blot analysis. The molecular weight of the polymer was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Five of the eight point mutants produced polymers having molecular weights higher than the molecular weight of the polymer produced by the wild type. Moreover, four of these five polymers had modified biological properties. Replacement of arginine by leucine (R418L) resulted in the most significant change in the molecular weight of the polymer. The R418L mutant was the most hydrophilic mutant, exhibiting decreased adherence to polystyrene, and inhibited biofilm formation. The results described in this report show the functional effect of Wzc modification on the molecular weight of a high-molecular-weight polysaccharide. Moreover, in the present study we developed a genetic system to control polymerization of apoemulsan. The use of selective exogenous fatty acid feeding strategies, as well as genetic manipulation of sugar backbone chain length, is a promising new approach for bioengineering emulsan analogs.

Biosurfactants: evolution and diversity in bacteria

In summary, biosurfactants are an example of a class of microbial natural products that has coevolved among many genera. But whereas the biosurfactants produced in the bacterial and archaeal domains are convergent in function (suggesting that they are very important), they have developed in parallel with respect to genotype and phenotype (the surfactants are not related genetically or in terms of molecular structure). Because of this parallel evolution, currently available molecular screening techniques are of little use for the discovery of new biosurfactants. Development of such techniques will continue to be problematic because there is no relationship between the surfactants produced by different microbial genera and even species. Yet, the potential for application of biosurfactants and other natural products is great due to growing demand for biodegradable and environmentally friendly analogues for synthetic chemicals.

Natural roles of biosurfactants. Minireview

Microorganisms produce a variety of surface-active agents (or surfactants). These can be divided into low-molecular-weight molecules that lower surface and interfacial tensions efficiently and high-molecular-weight polymers that bind tightly to surfaces. These surfactants, produced by a wide variety of microorganisms, have very different chemical structures and surface properties. It is therefore reasonable to assume that different groups of biosurfactants have different natural roles in the growth of the producing microorganisms. Moreover, as their chemical structures and surface properties are so different, each emulsifier probably provides advantages in a particular ecological niche. Several bioemulsifiers have antibacterial or antifungal activities. Other bioemulsifiers enhance the growth of bacteria on hydrophobic water-insoluble substrates by increasing their bioavailability, presumably by increasing their surface area, desorbing them from surfaces and increasing their apparent solubility. Bioemulsifiers also play an important role in regulating the attachment-detachment of microorganisms to and from surfaces. In addition, emulsifiers are involved in bacterial pathogenesis, quorum sensing and biofilm formation. Recent experiments indicate that a high-molecular-weight bioemulsifier that coats the bacterial surface can be transferred horizontally to other bacteria, thereby changing their surface properties and interactions with the environment.

The application of biotechnology to the treatment of wastes produced from the nuclear fuel cycle: biodegradation and bioaccumulation as a means of treating radionuclide-containing streams

Recent concerns on the radiotoxicity and longevity of nuclides have prompted the development of new technologies for their removal from wastes produced from nuclear power programs and nuclear fuel reprocessing activities. Alongside developments from traditional chemical treatment processes, interest has also centered on the application of biotechnology for efficient waste treatment. Many biological techniques have relied on empirical approaches in simple model systems, with scant regard to the nature and volume of actual target wastes; such considerations may limit the application of the new technologies in practice. This review aims to identify some of the likely problems, to discuss the various approaches under current consideration, and to evaluate ways in which either the target waste or the detoxifying biomass may be modified or presented for the most efficient treatment.

Production of exopolysaccharides by Acinetobacter strains in a controlled fed-batch fermentation process using soap stock oil (SSO) as carbon source

The production of two extracellular capsular heteropolysaccharides by two different Acinetobacter strains has been studied in separate controlled fermentation processes with a view to their industrial applications as specific dispersing agents. The first, emulsan, is an extracellular polyanionic amphipathic heteropolysaccharide (MW 10(6) D) made by A. calcoaceticus RAG-1. It forms and stabilizes oil in water emulsions. The other, biodispersan (PS-A2), is another extracellular zwitterionic heteropolysaccharide (MW 51 kD) made by A. calcoaceticus A2. This polysaccharide disperses big solid limestone granules forming micron-size water suspension. Both polysaccharides are synthesized within the cells, exported to their outer surface to form an extracellular cell-associated capsule and released subsequently into the growth medium. The polymers were produced in a computer-controlled fed-batch intensively aerated fermentation process. A commercially available and cheap fatty acids mixture (soap stock oil) served as the carbon source, and was fed in coordination with the required nitrogen. The coordinated feed of carbon and nitrogen was operated on the basis of two metabolic correlations: The first correlation related the cell protein produced and the ammonium nitrogen consumed with the outcoming coeffients of 24 and 21 mM NH3/g protein for the emulsan and the biodispersan fermentations respectively. The second correlation linked the consumption of the fatty acids with that of the nitrogen source dictating the appropriate C/N ratio of the feed into the operating fermentor. These ratios were 7.7 g C/g N for the emulsan fermentation and 8.5 gC/g N in the case of the biodispersan production process.(ABSTRACT TRUNCATED AT 250 WORDS)

Reconstitution of emulsifying activity of Acinetobacter calcoaceticus BD4 emulsan by using pure polysaccharide and protein

Acinetobacter calcoaceticus BD4 and BD413 produce extracellular emulsifying agents when grown on 2% ethanol medium. For emulsifying activity, both polysaccharide and protein fractions were required, as demonstrated by selective digestion of the polysaccharide with a specific bacteriophage-borne polysaccharide depolymerase, deproteinization of the extracellular emulsifying complex with hot phenol, and reconstitution of emulsifier activity with pure polysaccharide and a polysaccharide-free protein fraction. Chemical modification of the carboxyl groups in the polysaccharide resulted in a loss of activity. The protein required for reconstitution of emulsifying activity was purified sevenfold. The BD4 emulsan apparently derives its amphipathic properties from the association of an anionic hydrophilic polysaccharide with proteins.

Structural studies of the capsular polysaccharide of Acinetobacter calcoaceticus BD4

Compositional analysis of the intact and carboxyl-reduced capsular polysaccharide of Acinetobacter calcoaceticus BD4 (PS-4) showed it to consist of L-rhamnose, D-glucose, D-glucuronic and D-mannose in molar ratios of 4:1:1:1. 13C-nuclear magnetic resonance spectroscopy, methylation analysis, oligosaccharide analysis and base-catalyzed beta-elimination were used to elucidate the primary structure. Oligosaccharides were obtained by enzymatic depolymerization with a specific bacteriophage-induced depolymerase and by partial acid hydrolysis. Form the results it is concluded that PS-4 consists of repeating units of the heptasaccharide (Formula: see text). The bacteriophage-induced depolymerase was found to be an endo-beta-D-glucosidase that hydrolyzed the bond beta-D-Glc-(1----3)-L-Rha to generate a heptasaccharide in 40% yield.

Uptake of Metal Ions by Rhizopus arrhizus Biomass

Rhizopus arrhizus biomass was found to absorb a variety of different metal cations and anions but did not absorb alkali metal ions. The amount of uptake of the cations was directly related to ionic radii of La 3+ , Mn 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Ba 2+ , Hg 2+ , Pb 2+ , UO 2 2+ , and Ag + . The uptake of all the cations is consistent with absorption of the metals by sites in the biomass containing phosphate, carboxylate, and other functional groups. The uptake of the molybdate and vanadate anions was strongly pH dependent, and it is proposed that the uptake mechanism involves electrostatic attraction to positively charged functional groups.