D. Spasova

Bio: D. Spasova is an academic researcher from Bulgarian Academy of Sciences. The author has contributed to research in topics: Phosphatase & Acid phosphatase. The author has an hindex of 8, co-authored 13 publications receiving 438 citations.

Rhamnolipid-biosurfactant permeabilizing effects on gram-positive and gram-negative bacterial strains.

Abstract: The potential of biosurfactant PS to permeabilize bacterial cells of Pseudomonas aeruginosa, Escherichia coli, and Bacillus subtilis on growing (in vivo) and resting (in vitro) cells was studied. Biosurfactant was shown to have a neutral or detrimental effect on the growth of Gram-positive strains, and this was dependent on the surfactant concentration. The growth of Gram-negative strains was not influenced by the presence of biosurfactant in the media. Cell permeabilization with biosurfactant PS was shown to be more effective with B. subtilis resting cells than with Pseudomonas aeruginosa. Scanning-electron microscopy observations showed that the biosurfactant PS did not exert a disruptive action on resting cells such that it was detrimental to the effect on growing cells of B. subtilis. Low critical micelle concentrations, tender action on nongrowing cells, and neutral effects on the growth of microbial strains at low surfactant concentrations make biosurfactant PS a potential candidate for application in different industrial fields, in environmental bioremediation, and in biomedicine.

Thermostable α-amylase production by immobilized Bacillus licheniformis cells in agar gel and on acrylonitrile/acrylamide membranes

Abstract: Immobilized cells of Bacillus licheniformis 44MB82-G were used for the production of thermostable α-amylase The immobilization was carried out by entrapment in agar gel or by binding to formaldehyde-activated acrylonitrile/acrylamide membranes The α-amylase production after 144 h of cultivation of membrane immobilized cells was 40% higher in comparison with the free cells The respective value for the agar-entrapped cells was 22% Similar trends were observed in the repeated batch fermentations performed with the immobilized cells The scanning electron micrographs (SEM) of the immobilized cells gave additional information about their binding to the respective carriers

Microbial biosurfactants production, applications and future potential

Abstract: 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.

Environmental applications of biosurfactants: Recent advances

Abstract: Increasing public awareness of environmental pollution influences the search and development of technologies that help in clean up of organic and inorganic contaminants such as hydrocarbons and metals. An alternative and eco-friendly method of remediation technology of environments contaminated with these pollutants is the use of biosurfactants and biosurfactant-producing microorganisms. The diversity of biosurfactants makes them an attractive group of compounds for potential use in a wide variety of industrial and biotechnological applications. The purpose of this review is to provide a comprehensive overview of advances in the applications of biosurfactants and biosurfactant-producing microorganisms in hydrocarbon and metal remediation technologies.

Rhamnolipids: diversity of structures, microbial origins and roles

Abstract: Rhamnolipids are glycolipidic biosurfactants produced by various bacterial species. They were initially found as exoproducts of the opportunistic pathogen Pseudomonas aeruginosa and described as a mixture of four congeners: α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-Rha-C10-C10), α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoate (Rha-Rha-C10), as well as their mono-rhamnolipid congeners Rha-C10-C10 and Rha-C10. The development of more sensitive analytical techniques has lead to the further discovery of a wide diversity of rhamnolipid congeners and homologues (about 60) that are produced at different concentrations by various Pseudomonas species and by bacteria belonging to other families, classes, or even phyla. For example, various Burkholderia species have been shown to produce rhamnolipids that have longer alkyl chains than those produced by P. aeruginosa. In P. aeruginosa, three genes, carried on two distinct operons, code for the enzymes responsible for the final steps of rhamnolipid synthesis: one operon carries the rhlAB genes and the other rhlC. Genes highly similar to rhlA, rhlB, and rhlC have also been found in various Burkholderia species but grouped within one putative operon, and they have been shown to be required for rhamnolipid production as well. The exact physiological function of these secondary metabolites is still unclear. Most identified activities are derived from the surface activity, wetting ability, detergency, and other amphipathic-related properties of these molecules. Indeed, rhamnolipids promote the uptake and biodegradation of poorly soluble substrates, act as immune modulators and virulence factors, have antimicrobial activities, and are involved in surface motility and in bacterial biofilm development.

Anti-adhesion activity of two biosurfactants produced by Bacillus spp. prevents biofilm formation of human bacterial pathogens.

Abstract: In this work, two biosurfactant-producing strains, Bacillus subtilis and Bacillus licheniformis, have been characterized Both strains were able to grow at high salinity conditions and produce biosurfactants up to 10% NaCl Both extracted-enriched biosurfactants showed good surface tension reduction of water, from 72 to 26–30 mN/m, low critical micelle concentration, and high resistance to pH and salinity The potential of the two lipopeptide biosurfactants at inhibiting biofilm adhesion of pathogenic bacteria was demonstrated by using the MBEC device The two biosurfactants showed interesting specific anti-adhesion activity being able to inhibit selectively biofilm formation of two pathogenic strains In particular, Escherichia coli CFT073 and Staphylococcus aureus ATCC 29213 biofilm formation was decreased of 97% and 90%, respectively The V9T14 biosurfactant active on the Gram-negative strain was ineffective against the Gram-positive and the opposite for the V19T21 This activity was observed either by coating the polystyrene surface or by adding the biosurfactant to the inoculum Two fractions from each purified biosurfactant, obtained by flash chromatography, fractions (I) and (II), showed that fraction (II), belonging to fengycin-like family, was responsible for the anti-adhesion activity against biofilm of both strains