Irena B. Ivshina

Microbial surfactants and their use in field studies of soil remediation.

The degree of association of organic and inorganic pollutants is governed by the complex physico-chemical interactions at interfaces. This association involves sorption onto soil constituents, sequestration within the soil matrix (micropores) and partitioning in a nonaqueous phase liquid (NAPL) that will, ultimately, control the fate of the contaminants. NAPL represents organic substances that are relatively insoluble in water providing a long-term source of pollutant. They represent a continuous input into the water phase to replace degraded or dissipating concentrations. As a result the bioavailability of contaminants to biodegradation may be reduced (Ogram et al. 1985; Miller and Alexander 1991). The enhancement of natural biological degradation processes, in what is termed bioremediation, can be a preferred cost-effective method of removing contaminants from soil-contaminated and other contaminated environments. The role of microorganisms has been shown to be essential in the remediation of, at least, organic pollution, and the activity of microbial types naturally present can be enhanced by bioremediation techniques which include increased aeration of the polluted material and nutrient additions (Christofi et al. 1998; Ivshina et al. 1998). Supplementing the source of microorganisms capable of degrading particular pollutants (bioaugmentation) and the enhancement of the desorption of pollutants from particulates using surfactants can increase hydrocarbon degradation (Deschenes et al. 1995; Thibault et al. 1996; Christofi et al. 1998; Ivshina et al. 1998). It is only 10–15 years that the use of surfactants in increasing the availability of hydrophobic pollutants in soils and other environments has been considered (Vigon and Rubin 1989). Previous studies have revealed that surfactants can enhance pollutant desorption and availability (Oberbremer et al. 1990; Zang and Miller 1992; Volkering et al. 1995; Rahman et al. 2002). They have been applied in oil washing for secondary oil recovery and to clean oil pipes and oil reservoirs (Osipow 1962). In desorption, both synthetic and natural (biological) surfactants have been used. However, it is not always the case that increasing the bioavailability of nonpolar organic substances through the use of surfactants leads to increased degradation or removal. Synthetic surfactants have also been shown to decrease organic degradation (Bruheim et al. 1999) possibly through, for example, the toxic effects of the surfactant (Rouse et al. 1994). It can also be assumed that increasing bioavailability of a pollutant can lead to an increasing toxicity to degrading microorganisms. It has been shown that sorption of toxicants is one major factor controlling bioavailability and toxicity (Welp

Alkanotrophic Rhodococcus ruber as a biosurfactant producer

Abstract. In this report we examined the structure and properties of surface-active lipids of Rhodococcus ruber. Most historical interest has been in the glycolipids of Rhodococcus erythropolis, which have been extensively characterised. R. erythropolis has been of interest due to its great metabolic diversity. Only recently has the metabolic potential of R. ruber begun to be explored. One major difference in the two species is that most R. ruber strains are able to oxidise the gaseous alkanes propane and butane. In preparation for investigation of the effects of gas metabolism on biosurfactant production, we set out to characterise the biosurfactants produced during growth on liquid n-alkanes and to compare these with R. erythropolis glycolipids.

Oil desorption from mineral and organic materials using biosurfactant complexes produced by Rhodococcus species

Rhodococcus strains from the culture collection at the Institute of Ecology and Genetics of Microorganisms, Perm, Russia were examined for biosurfactant production during growth on n-alkanes and the ability to remove oil associated with contaminated sands and oil shale cuttings. Members of the genus, particularly R. ruber, were shown to produce low toxicity surfactants effective in removing oil from surfaces. The extent of desorption was inversely related to the concentration of high molecular weight hydrocarbons, namely asphaltenes and resins. In addition, crude surfactant complexes enhanced the degradation of crude oil, in the short term, when added to contaminated agricultural soil during bioremediation studies utilizing biopiling technology.

Application of Rhodococcus in Bioremediation of Contaminated Environments

Environmental pollution with anthropogenic organic compounds is the global problem of our planet. Bioremediation has a great potential to effectively restore polluted environments by using biodegradative activities of microorganisms. The genus Rhodococcus is a promising group of bacteria suitable for biodegradation of recalcitrant contaminants, such as petroleum hydrocarbons, chlorinated, nitrogenated, and other complex organics. Rhodococcus species are ubiquitous in pristine and contaminated environments, survive under harsh environmental conditions, compete successfully in complex bacterial populations, and therefore could be efficiently used in bioremediation applications. Some success in bioremediation of contaminated soils, waters, and air has been achieved using rhodococci either as bioaugmentation agents or members of indigenous microbial communities stimulated by nutrient and oxygen amendments. Laboratory and field-scale studies on Rhodococcus application in cleanup technologies are reviewed relating to in-situ subsurface and groundwater remediation, on site treatments of contaminated soils, sludges, wastewaters, and waste gases.

In vitro immunomodulating activity of biosurfactant glycolipid complex from Rhodococcus ruber

The biosurfactant glycolipid complex synthesized by Rhodococcus ruber actinobacteria is not toxic and exhibits no appreciable effect on proliferative activity of peripheral blood leukocytes. In the monocyte fraction, the biosurfactant activates the production of IL-1β and TNF-α cytokines without modifying the production of IL-6. In the mononuclear fraction, the glycolipid biosurfactant exhibited no effects on the production of IL-1β, TNF-α, and IL-6. These results indicate good prospects for further studies of immunomodulating and antitumor activities of biosurfactant drug.

Effect of cell lipid composition on the formation of nonspecific antibiotic resistance in alkanotrophic rhodococci

The antibiotic resistance and lipid composition of rhodococci grown in rich organic media with gaseous or liquidn-alkanes were studied. Hydrocarbon-grown rhodococci exhibited an increased resistance to a wide range of antibiotics (aminoglycosides, linkosamides, macrolides, β-lactams, and aromatic compounds). The enhanced antibiotic resistance of rhodococci grown onn-alkanes correlated with an increased content of total cell lipids (up to 14–28%) and saturated straight-chain fatty acids (C16:0, C18:0, C21:0) and was accompanied by the appearance of cardiolipin and phosphatidylglycerol in cells. These lipid compounds are supposed to promote the formation of nonspecific antibiotic resistance in rhodococci by decreasing the permeability of their cell envelope to antibiotics.

TREHALOLIPID BIOSURFACTANTS FROM NONPATHOGENIC RHODOCOCCUS ACTINOBACTERIA WITH DIVERSE IMMUNOMODULATORY ACTIVITIES

Actinobacteria of the genus Rhodococcus produce trehalolipid biosurfactants with versatile biochemical properties and low toxicity. In recent years, these biosurfactants are increasingly studied as possible biomedical agents with expressed immunological activities. Applications of trehalolipids from Rhodococcus, predominantly cell-bound, in biomedicine are also attractive because their cost drawback could be less significant for high-value products. The review summarizes recent findings in immunomodulatory activities of trehalolipid biosurfactants from nonpathogenic Rhodococcus and related actinobacteria and compares their biomedical potential with well-known immunomodifying properties of trehalose dimycolates from Mycobacterium tuberculosis. Molecular mechanisms of trehalolipid interactions with immunocompetent cells are also discussed.

Assessment of bacterial resistance to organic solvents using a combined confocal laser scanning and atomic force microscopy (CLSM/AFM)

Using combined confocal laser scanning and atomic force microscopy (CLSM/AFM), bacterial viability under organic solvent stress was assessed at single cell level. Solvent-exposed bacteria stained with the LIVE/DEAD BacLight fluoresced green or red, allowing viable and dead cell discrimination. However, with toluene, butanol and acetonitrile, dually fluorescent cells appeared having compromised cell membranes. Changes in size, surface/volume ratio and roughness were revealed as possible resistance mechanisms.

Efficient Uptake of Cesium Ions by Rhodococcus Cells

Bacteria of the genus Rhodococcus were found to be able to accumulate cesium by means of active transport and nonspecific sorption on the cell surface structures. The maximum removal (up to 97%) of cesium from a medium supplemented with ammonium acetate was observed at 28°C, pH 7.8–8.6, and an equimolar content (0.2 mM) of potassium and cesium ions in the medium. The most active cesium-accumulating rhodococcal strains may be useful in biological treatment of industrial wastewaters contaminated with radionuclides.

Modulation of Cytokine Secretion and Oxidative Metabolism of Innate Immune Effectors by Rhodococcus Biosurfactant

The glycolipid biosurfactant complex from Rhodococcus ruber IEGM 231 had a stimulatory effect on the production of IL-12, IL-18, and reactive oxygen species by cells of the innate immunity. This effect depended on the composition of cell cultures and presence of LPS. It was primarily observed in non-stimulated cultures. The glycolipid biosurfactant complex had little effect on IL-10 secretion by monocytes and mononuclear cells.