Biosurfactants
- PDF / 317,604 Bytes
- 16 Pages / 539 x 751 pts Page_size
- 23 Downloads / 155 Views
CHAPTER 3.7 s tna t ca f ruso iB“
Biosurfactants EUGENE ROSENBERG
Introduction Microorganisms are specialists. In any particular ecological niche, one microorganism or a limited number of strains dominates. These microorganisms have evolved the ability to survive in this niche for long periods when growth is impossible, and then when nutrients become available, they can outgrow their competitors. The fast growth of microorganisms depends largely on their high surface-to-volume ratio, which allows for the efficient uptake of nutrients and release of waste products. The price that the microorganism pays for the high surface-to-volume ratio is that it is totally exposed. All the components outside of the cell must function under the specific conditions of the ecological niche. Probably for this reason, the diversity of the microbial world is best expressed on the outside of the cell. In any heterogenous system, boundaries are of fundamental importance to the behavior of the system as a whole. Therefore, it is not surprising that microorganisms, having a large surface-tovolume ratio, produce a variety of surface active agents (surfactants) that adsorb to and alter the conditions prevailing at interfaces. Surfactants concentrate at interfaces because they are amphipathic, i.e., they contain both hydrophobic and polar groups. Biosurfactants can be divided into low molecular weight molecules that efficiently reduce surface and interfacial tensions and high molecular weight polymers that bind tightly to surfaces. Table 1 and Table 2 list some microbially produced surfactants that have been studied. During the last few years, numerous reviews have examined various aspects of biosurfactants such as their role in bacterial adhesion (Neu, 1996) and in growth of bacteria on hydrocarbons (Rosenberg and Ron, 1996), surface active polymers from the genus Acinetobacter (Rosenberg and Ron, 1998), biochemistry of surfactin (Peypoux et al., 1999), microbial surfactants (Rosenberg and Ron, 1999), biosurfactant assay (Lin, 1996), surfactants from Rhodococci (Land and Philp, 1998), production (Wang and Wand, 1990), molecular genetics (Sullivan, 1998), and
commercial applications (Fiechter, 1992), including enhanced oil recovery (Banat, 1995) and bioemulsans (Rosenberg and Ron, 1997). In this review we will present some of the chemical and surface properties of biosurfactants and the genetics and regulation of their production, and then we will discuss what functions they may play for the producing strains and what their potential is for commercial application. When considering the natural roles and potential applications of biosurfactants, it is important to emphasize that a wide variety of diverse microorganisms (only some of which are shown in Table 1 and Table 2) make these molecules and that biosurfactants have very different chemical structures and surface properties. It is therefore reasonable to assume that different groups of biosurfactants have different natural roles in the growth of the producing microorganisms. Similarly, si
Data Loading...
