Mechanisms of membrane toxicity of hydrocarbons.

Many microorganisms, especially bacteria, produce biosurfactants when grown on water-immiscible substrates. Biosurfactants are more effective, selective, environmentally friendly, and stable than many synthetic surfactants. Most common biosurfactants are glycolipids in which carbohydrates are attached to a long-chain aliphatic acid, while others, like lipopeptides, lipoproteins, and heteropolysaccharides, are more complex. Rapid and reliable methods for screening and selection of biosurfactant-producing microorganisms and evaluation of their activity have been developed. Genes involved in rhamnolipid synthesis (rhlAB) and regulation (rhlI and rhlR) in Pseudomonas aeruginosa are characterized, and expression of rhlAB in heterologous hosts is discussed. Genes for surfactin production (sfp, srfA, and comA) in Bacillus spp. are also characterized. Fermentative production of biosurfactants depends primarily on the microbial strain, source of carbon and nitrogen, pH, temperature, and concentration of oxygen and metal ions. Addition of water-immiscible substrates to media and nitrogen and iron limitations in the media result in an overproduction of some biosurfactants. Other important advances are the use of water-soluble substrates and agroindustrial wastes for production, development of continuous recovery processes, and production through biotransformation. Commercialization of biosurfactants in the cosmetic, food, health care, pulp- and paper-processing, coal, ceramic, and metal industries has been proposed. However, the most promising applications are cleaning of oil-contaminated tankers, oil spill management, transportation of heavy crude oil, enhanced oil recovery, recovery of crude oil from sludge, and bioremediation of sites contaminated with hydrocarbons, heavy metals, and other pollutants. Perspectives for future research and applications are also discussed.

Microbial production of surfactants and their commercial potential.

Environmental applications for biosurfactants

Principles of microbial PAH-degradation in soil.

Bioremediation of soil contaminated with polynuclear aromatic hydrocarbons (PAHs): A review

The hydrocarbon degradation rate could be doubled by the addition of sophorose lipids as biosurfactants in a model system containing 10% soil and a 1.35% hydrocarbon mixture of tetradecane, pentadecane, hexadecene, 1,2,4-trimethylcyclohexane, pristane (2,6,10,14-tetramethylpentadecane) phenyldecane and naphthalene suspended in mineral salts medium. The adaptation phases for two degradation phases were shortened, and the extent of degradation and final biomass were increased. The added biosurfactants were degraded after they had facilitated degradation of all hydrocarbon components.

Effect of the addition of microbial surfactants on hydrocarbon degradation in a soil population in a stirred reactor.

Using a model system containing 10% soil and a 1.35% hydrocarbon mixture of tetradecane, pentadecane, hexadecene, pristane (2,6,10,14-tetramethylpentadecane), trimethylcyclohexane, phenyldecane and naphthalene suspended in a mineral salts medium, the hydrocarbon degradation rate by a soil population was 25.7 g model oil per kg soil dry weight per day under non-limited conditions within two degradation phases. During the first degradation phase only the most water-soluble naphthalene was degraded, while the other components could only be metabolized when the interfacial tension was lowered by the production of surfactants at the beginning of the second degradation phase. This second degradation phase ended when 89% of the hydrocarbons were metabolized.

Aerobic stepwise hydrocarbon degradation and formation of biosurfactants by an original soil population in a stirred reactor

The purpose of this investigation was to show whether or no employing a starter culture of the bacterium Rhodococcus erythropolis that produces 6,6-trehalosedicorynomycolates could replace the addition of purified biosurfactant known to accelerate hydrocarbon degradation by an original soil population in a stirred reactor. The rate of degradation, degree of elimination of hydrocarbons, mineralization and degree of oxidation were determined in order to assess the extent of degradation. In comparison with degradation by soil microorganisms only an acceleration of utilization of the hydrocarbons was observed in cultivations of growing cells of R. erythropolis, although the effect of purified trehalosedicorynomycolates is not reached. Except for a higher degree of oxidation a sufficient amount of trehalosedicorynomycolates bound to autoclaved biomass of R. erythropolis does not have any effect.

Influence of the glycolipid-producing bacterium Rhodococcus erythropolis on the degradation of a hydrocarbon mixture by an original soil population

The degradation of a model oil in submerged culture with a content of 10% of soil under optimum conditions (T,pH,oxygen supply, mineral salts medium) is accelerated by adding biosurfactants (1,2,3). Because of high costs of production of these glycolipids it was now examined whether or not the same effect could be reached by adding microorganisms which produce the appropriate surfactants. A criterion for the bacteria to be chosen was that they had to produce the biosurfactants under the conditions of hydrocarbon degradation. Accordingly, Rhodococcus erythropolis was chosen, which -as opposed to most of the other biosurfactant producing bacteria — produces cell associated trehalose dicorynomycolates during its growth (4). Furthermore Pseudomonas spec. DSM 2874 was added, which is able to produce the extracellular rhamnolipids at a neutral pH value (5).

Influence of Biosurfactant Producing Microorganisms on the Degradation of a Model Oil by an Original Soil Population

Der Abbau eines Modellols in Submerskultur mit 10% Bodenanteil unter optimalen Bedingungen(T, pH, Sauerstoffversorgung, Mineralsalzmedium) wird durch Zusatz von Biotensiden beschleunigt (1, 2, 3). Aufgrund hoher Produktionskosten fur Biotenside wurde nun untersucht, ob durch Zusatz der entsprechenden, Biotensid produzierenden Mikroorganismen der gleiche Effekt erreicht werden kann. Ein Kriterium fur die Auswahl der Bakterien war, das das Biotensid auch unter Bedingungen des KW-Abbaus gebildet werden muste. Demnach wurde Rhodococcus erythropolis ausgewahlt, der zeilassoziierte Trehalosedicorynomycolate im Gegensatz zu den meisten Biotensidbildnern wahrend des Wachstums uberproduziert (4). Weiterhin wurde Pseudomonas spec. DSM 2874 zugesetzt, der die extrazellularen Rhamnolipide bei pH-Werten im Neutralbereich bilden kann (5).

R. Müller-Hurtig

Papers

Effect of the addition of microbial surfactants on hydrocarbon degradation in a soil population in a stirred reactor.

Aerobic stepwise hydrocarbon degradation and formation of biosurfactants by an original soil population in a stirred reactor

Influence of the glycolipid-producing bacterium Rhodococcus erythropolis on the degradation of a hydrocarbon mixture by an original soil population

Influence of Biosurfactant Producing Microorganisms on the Degradation of a Model Oil by an Original Soil Population

Einfluss von Tensidproduzierenden Mikroorganismen auf den Abbau Eines Modellöls durch eine Ursprüngliche Bodenpopulation