Towards commercial production of microbial surfactants Soumen Mukherjee, Palashpriya Das and Ramkrishna Sen Department of Biotechnology, Indian Institute of Technology, Kharagpur, West Bengal–721302, India. Biosurfactants or microbial surfactants are surface- active biomolecules that are produced by a variety of microorganisms. Biosurfactants have gained importance in the fields of enhanced oil recovery, environmental bioremediation, food processing and pharmaceuticals owing to their unique properties – higher biodegradability, lower toxicity, and effective- ness at extremes of temperature, pH and salinity. However, large-scale production of these molecules has not been realized because of low yields in production processes and high recovery and purification costs. This article describes some practical approaches that have been adopted to make the biosurfactant production process economically attractive: these include the use of cheaper raw materials, optimized and efficient bio- processes and overproducing mutant and recombinant strains for obtaining maximum productivity. The appli- cation of these strategies in biosurfactant production processes, particularly those using hyper-producing recombinant strains in the optimally controlled environ- ment of a bioreactor, might lead towards the successful commercial production of these valuable and versatile biomolecules in near future. Microbial surfactants Microbial surfactants are surface-active metabolites produced by microorganisms when grown on water mis- cible or oily substrates: they either remain adherent to microbial cell surfaces or are secreted in the culture broth. They possess the characteristic property of reducing the surface and interfacial tensions using the same mechan- isms as chemical surfactants. Microbial surfactants con- stitute a diverse group of surface-active molecules and are known to occur in a variety of chemical structures, such as glycolipids, lipopeptides and lipoproteins, fatty acids, neu- tral lipids, phospholipids, and polymeric and particulate structures. The features that make them commercially promising alternatives to chemically synthesized surfac- tants are their lower toxicity, higher biodegradability and, hence, greater environmental compatibility, better foam- ing properties (useful in mineral processing), and stable activity at extremes of pH, salinity and temperature [1]. Unlike chemical surfactants, which are mostly derived from petroleum feedstock, these molecules can be produced by microbial fermentation processes using cheaper agro- based substrates and waste materials. In various indus- trial processes, they are potentially useful surface-active agents for emulsion polymerization, wetting, foaming, phase dispersion, emulsification and de-emulsification [1]. They have also been found to possess several properties of therapeutic and biomedical importance: they have anti- bacterial, antifungal and antiviral properties; they inhibit fibrin clot formation; and they have anti-adhesive action against several pathogenic microorganisms etc. [2–4]. During the past few years, the biosurfactant production by various microorganisms has been studied extensively, and now we have a good amount of data regarding their production, types and properties. Despite possessing many commercially attractive properties and clear advantages compared with their synthetic counterparts, the produc- tion of microbial surfactants on a commercial scale has not been realized because of their low yields and high produc- tion costs – for such purposes, it is necessary that they are produced and recovered profitably on a large scale. The production economy of every microbial metabolite is gov- erned by three basic factors: (i) initial raw material costs; (ii) availability of suitable and economic production and recovery procedures; and (iii) the product yield of the producer microorganisms. Thus, in light of the economic constraints associated with biosurfactant production, three basic strategies were adopted worldwide to make this process cost-competitive: (i) the use of cheaper and waste substrates to lower the initial raw material costs involved in the process; (ii) development of efficient bio- processes, including optimization of the culture conditions and cost-effective separation processes for maximum bio- surfactant production and recovery; and (iii) development and use of overproducing mutant or recombinant strains for enhanced biosurfactant yields. The first two strategies have been explored to a greater extent and have been reported to be effective in substantially increasing the production of biosurfactants. However, the third approach, using recombinant hyperproducing strains, has still not been properly tested, despite the fact that the hyperpro- ducers have been reported to increase yields several fold. This area of biosurfactant research is still in its infancy. Although, various aspects of biosurfactants, such as their biomedical and therapeutic properties [2–4], their natural roles [5], their production on cheap alternative substrates [6–8] and their commercial potential [1,9], have been recently reviewed, no attempt has been made, to the best of our knowledge, to describe the R&D strategies of making biosurfactant production process cheaper and commercially attractive. The present article focuses on such studies, with special emphasis on the development and use of mutant and recombinant hyperproducers of Review TRENDS in Biotechnology Vol.24 No.11 Corresponding author: Sen, R. (rksen@yahoo.com). Available online 25 September 2006. www.sciencedirect.com 0167-7799/$ – see front matter ß 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tibtech.2006.09.005