Diversity and Classification of Microbial Surfactants

Biosurfactant research and development, as well as the commercialization of biosurfactants, have witnessed a dramatic acceleration over the last years. Microorganisms produce many different and in several cases unique amphiphilic metabolites displaying a considerable structural diversity. Besides methods of classification common for surfactants in general, there are different approaches to classify microbial biosurfactants, such as by structural similarities, size, charge, hydrophobicity, degree of modifications, and other physical and chemical properties. Many of the advantages of microbial surfactants trend toward the additional benefits compared with merely the reduction of surface tension. This combined effect of bioactivity and interfacial activity, which strongly depends on structure and composition of each individual molecule, leads to a particularly interesting potential in pharmaceutical, agricultural, environmental, and other applications that remains to be explored for the overwhelming majority of biosurfactant structures. Besides the most prominent examples of glycolipids and lipopeptides, there are many additional classes, structures, and combinations of structures among microbial biosurfactants. This chapter provides an overview of the diversity and classification of microbial biosurfactants by presenting both prominent and well-investigated examples, as well as examples where, as of today, little is known on production or potential for application.