Biosurfactant production

Biosurfactants Production Properties Applications, edited by Naim Ko-saric... 

Deziel E, G Paquette, R Villemur, F Lepine, J-G Bisaillon (1996) Biosurfactant production by a soil Pseudomonas strain growing on polycyclic aromatic hydrocarbons. Appl Environ Microbiol 62 1908-1912. 

Defoaming Theory and Industrial Applications, edited by P. R. Garrett Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe Coagulation and Flocculation Theory and Applications, edited by Bohusiav DobiaD Biosurfactants Production Properties Applications, edited by Naim Kosaric Wettability, edited by John C. Berg... 

The alkane rc-tetradecane was found to have significant effect on desulfurization ability, with the rate being 10 times more than that obtained when using glucose for biocatalyst growth. This effect was associated with production of rhamnolipids by the strain. However, the mechanism by which alkane actually enhances desulfurization activity, whether it is by assisting in biosurfactant production or by some other mechanism was not reported. However, this biocatalyst was found to be active for only a short period (4h) during its desulfurization test with oils. 

In addition to desulfurization activity, several other parameters are important in selecting the right biocatalyst for a commercial BDS application. These include solvent tolerance, substrate specificity, complete conversion to a desulfurized product (as opposed to initial consumption/removal of a sulfur substrate), catalyst stability, biosurfactant production, cell growth rate (for biocatalyst production), impact of final desulfurized oil product on separation, biocatalyst separation from oil phase (for recycle), and finally, ability to regenerate the biocatalyst. Very few studies have addressed these issues and their impact on a process in detail [155,160], even though these seem to be very important from a commercialization point of view. While parameters such as activity in solvent or oil phase and substrate specificity have been studied for biocatalysts, these have not been used as screening criteria for identifying better biocatalysts. 

Koch, A. K., Kappeli, O., Fiechter, A. and Reiser, J. (1991). Hydrocarbon assimilation and biosurfactant production in Pseudomonas aeruginosa mutants, J. Bac-... 

Persson, A., Osterberg, E. Dostalek, M. (1988). Biosurfactant production by Pseudomonas fluorescens 378 growthand product characteristics. Applied Microbiology and Biotechnology, 29, 1-4. 

A variety of factors affect the horizontal and vertical migration of PAHs, including contaminant volume and viscosity, temperature, land contour, plant cover, and soil composition (Morgan Watkinson, 1989)- Vertical movement occurs as a multiphase flow that will be controlled by soil chemistry and structure, pore size, and water content. For example, non-reactive small molecules (i.e., not PAHs) penetrate very rapidly through dry soils and migration is faster in clays than in loams due to the increased porosity of the clays. Once intercalated, however, sorbed PAHs are essentially immobilized. Mobility of oily hydrophobic substances can potentially be enhanced by the biosurfactant-production capability of bacteria (Zajic et al., 1974) but clear demonstrations of this effect are rare. This is discussed below in more detail (see Section 5 5). 

Experiments on growth and biosurfactant production were performed on a mineral salt medium (26) containing 2.0 g/L of NaN03,0.1 g/L of KC1,... 

All carbon sources tested have favored extracellular production of active surface agent by B. subtilis ATCC 6633, which was estimated by the reduction in surface tension of the fermented broth. However, except for stillage, there was no relationship between cell growth and biosurfactant production. Similar results were reported by other investigators (21,32,33) not only with B. subtilis strains, but also with other species of bacteria. The... 

Effect of Different Substrates on Growth and Biosurfactant Production by B. subtilis ATCC 6633... 

Biosurfactant production, expressed in terms of CMC b reached maximum values within 48 h, practically the same for all substrate initial concentrations tested (Fig. 4) the corresponding values of surface tension were 28.7 and 29.3 dyn/cm (data not shown). These results are quite satisfactory when compared to values reported for more active biosurfactants, indicating a good performance of the product formed. 

As shown in Fig. 6B, a two-phase pattern occurred for the substrate uptake. It can be observed that during the exponential growth phase, sucrose assimilation by the bacteria was small, corresponding to about 20% of the initial amount introduced into the medium. However, after a 40-h process corresponding to the end of the growth phase, there was a rise in the substrate uptake, suggesting that the carbon source was directed to biosurfactant production, for the conditions tested. It should be emphasized that the fermentative process, when the medium was supplemented with microsalts and EDTA (Fig. 6A), generated a different substrate kinetics in comparison with that obtained for the nonsupplemented medium (Fig. 6B). 

Thompson et al. (24) also verified that the addition of trace minerals to potato process effluents has little effect on surfactinproductionby B. subtilis ATCC 21332. In fact, the addition of com steep liquor had a detrimental effect on biosurfactant production, whereas the addition of trace minerals had no effect on surface tensions. On the other hand, growth rates were marginally higher with added nutrients. 

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. 

Oxygen-controlled Biosurfactant Production in a Bench Scale Bioreactor... 

The cost of biosurfactants production is approximately fiom three to ten times larger than the one of chemical surfactants. Usually, the biosurfactants are produced during the growth of the microorganisms in hydrocarbons, which are usually expensive, increasing the... 

The DO concentration control along the fermentations was initially accomplished manually. However, the difficulty of that control resulted in great variations in the DO concentration value during the fermentations. That variation was not desired, as the objective was to evaluate the influence of the amount of oxygen transferred and also of its concentration in the medium during the biosurfactant production. This fact justified the implementation of a control system with more efficient equipment connected to a PLC. The difference in the DO profile during fermentation with the manual-controlled system and with the use of the new system can be observed in the Fig. 3. It was noticed that the... 

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