Microbial biosurfactant

Lang, S. (2002). Biological amphiphiles (microbial biosurfactants), Curr. Opin. Coll. Interf. Sci., 1, 12-20. 

Finnerty, W. R. Singer, M. E. (1984). A microbial biosurfactant physiology, biochemistry and applications. Developments in Industrial Microbiology, 25, 311-40. 

Transparency Market Research. Microbial biosurfactants market (Rhamnolipids, sophorolipids, mannosylerythri-tol lipids (MEL) and other) for household detergents, industrial institutional cleaners, personal care, oilfield chemicals, agricultural chemicals, food processing, textile and other applications. Global Industry Analysis, Size, Share, Growth, Trends and Forecast 2014. 2014—2020. 

In this chapter, I would like to give an overview (1) on the first generation microbial biosurfactants (detected between 1950 and 1990), but focusing on recent developments in production and new application potentials, and (2) on the last decade microbial biosurfactants (found during the last 10 years), their physicochemical properties, as well as some of their other properties. 

TABLE 4 Essential Data on Minimal Surface Tension Values (omir.) of Aqueous Solutions of Microbial Biosurfactants... 

Hommel RK (1994) Formation and function of biosurfactants for degradation of water-insoluble substrates. In Biochemistry of Microbial Degradation (Ed C Rattledge), pp. 63-87. Kluwer Academic Publishers, Dordrecht, The Netherlands. 

The B. licheniformis JF-2 strain produces a very effective surfactant under conditions typical of oil reservoirs. The partially purified biosurfactant from JF-2 was shown to be the most active microbial surfactant found, and it gave an interfacial tension against decane of 0.016 mN/m. An optimal production of the surfactant was obtained in cultures grown in the presence of 5% NaCl at a temperature of 45° C and pH of 7. TTie major endproducts of fermentation were lactic acid and acetic acid, with smaller amounts of formic acid and acetoin. The growth and biosurfactant formation were also observed in anaerobic cultures supplemented with a suitable electron acceptor, such as NaNO3[1106]. 

S. C. Lin, J. C. Goursaud, P. J. Kramer, G. Georgiou, and M. M. Sharma. Production of biosurfactant by Bacillus licheniformis strain JF-2. In E. C. Donaldson, editor. Microbial enhancement of oil recovery recent advances Proceedings of the 1990 International Conference on Microbial Enhancement of Oil Recovery, volume 31 of Developments in Petroleum Science, pages 219-226. Elsevier Science Ltd, 1991. 

Surfactants are used widely in industry, agriculture and medicine. The materials currently in use are produced primarily by chemical synthesis, or as by-products of industrial processes. For a microbial surfactant to penetrate the market, it must provide a clear advantage over the existing competing materials. The major considerations are (1) safety, i.e., low toxicity and biodegradability (2) cost (3) selectivity and (4) specific surface modifications. Biosurfactants exhibit low toxicity and good biodegradability, properties that are essential if the surfactant is to be released into the environment. 

Microbially produced biosurfactants can also have important effects on increasing bioavailability and biodegradation (Zhang Miller, 1992). A new PCB-degrading strain was recently isolated and found to produce a bio-emulsifier (Rothmel et al., 1993). Experiments show that the bio-emulsifier stimulates the extent of PCB degradation well beyond the levels seen before with other Type strains of its class, and that the bio-emulsifier can stimulate the extent of PCB biodegradation of added co-cultures as well. 

Although their role in nature is still not clear, there are extracellular microbial products, such as biosurfactants, bioemulsifiers and siderophores, that complex or chelate metals quite efficiently. Examples of these compounds are shown in Figure 10.1. 

Among the microbial surfactant producers, Bacillus subtilis strains generate a lipopeptide called surfactin, one of the most effective biosurfactants known. This biomolecule is usually a cyclic compound consisting of seven amino acids bonded to a lipid moiety. Surfactin is effective in lowering the surface tension of water to <30 dyn/cm (17), which is comparable with the values obtained by conventional synthetic surfactants. Additionally, surfactin preparations have other interesting characteristics, including antibiotic and antiviral properties (18). In fact, surfactin is one of the few biosurfactants that has found commercial use (19). 

The maximum biosurfactant production was verified at pH 7.0 and 8.0. The addition of EDTA and microsalts favored microbial synthesis of surface-active compounds. On the other hand, the addition of yeast extract stimulated cell growth to the detriment of biosurfactant production. The most suitable concentration of commercial sucrose for biosurfactant synthesis was 10 g/L. Biosurfactant production occurred in the late-exponential phase, achieving its maximum value at the early stationary phase of growth. The values of surface tension that we obtained compare favorably with those obtained with commercial synthetic surfactants. 

Many organisms growing on hydrocarbons are able to produce substances that lower the interfacial tension of the growth medium, and may serve to emulsify oil in water (30, 38-41). Such biosurfactant production is believed to facilitate microbial uptake of hydrocarbon by increasing the substrate surface area via emulsification. Thus, it permits greater contact between hydrocarbon and bacteria and enhances the substrate dissolution rate. Alternatively, biosurfactant production may increase the solubility of the hydrocarbons, which are utilized only in solution. 

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