Biosurfactants are amphiphilic molecules that have both hydrophilic and hydrophobic moieties which partition preferentially at the interfaces such as liquid/liquid, gas/liquid or solid/liquid interfaces. Such characteristics enable emulsifying, foaming, detergency and dispersing properties. Their low toxicity and environmental friendly nature and the wide range of potential industrial applications in bioremediation, health care, oil and food processing industries makes them a highly sought after group of chemical compounds. Interest in them has also been encouraged because of the potential advantages they offer over their synthetic counterparts in many fields spanning environmental, food, biomedical, petrochemical and other industrial applications. Their large scale production and application however are currently restricted by the high cost of production and by the limited understanding of their interactions with cells and with the abiotic environment. In this paper, we review the current knowledge and latest advances in the search for cost effective renewable agro industrial alternative substrates for their production.

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Polycyclic aromatic hydrocarbon (PAH) contamination of the environment represents a serious threat to the health of humans and ecosystems. Given the human health effects of PAHs, effective and cost-competitive remediation technologies are required. Bioremediation has shown promise as a potentially effective and low-cost treatment option, but concerns about the slow process rate and bioavailability limitations have hampered more widespread use of this technology. An option to enhance the bioavailability of PAHs is to add surfactants directly to soil in situ or ex situ in bioreactors. Surfactants increase the apparent solubility and desorption rate of the PAH to the aqueous phase. However, the results with some synthetic surfactants have shown that surfactant addition can actually inhibit PAH biodegradation via toxic interactions, stimulation of surfactant degraders, or sequestration of PAHs into surfactant micelles. Biosurfactants have been shown to have many of the positive effects of synthetic surfactants but without the drawbacks. They are biodegradable and nontoxic, and many biosurfactants do not produce true micelles, thus facilitating direct transfer of the surfactant-associated PAH to bacteria. The results with biosurfactants to date are promising, but further research to elucidate surfactant-PAH interactions in aqueous environments is needed to lead to predictive, mechanistic models of biosurfactant-enhanced PAH bioavailability and thus better bioremediation design.

The interest in industrial biotechnology and its importance opens up challenging possibilities of research in this area. Surfactants have long been among the most versatile of process chemicals. Their market is extremely competitive and manufacturers will have to expand their arsenal to develop products for the year 2000 and beyond. Biosurfactants are one of the most promising compounds in this regard. A review of the literature reveals that studies on oil-degrading and biosurfactant-producing microorganisms deal almost exclusively with their synthesis in moderate environments. Biosurfactants and the microbes that produce them have numerous industrial, medical and environmental applications, which frequently involve exposure to extremes of temperatures, pressure, ionic strength, pH and organic solvents. Hence, there is a continuing need to isolate microbes that are able to function under extreme conditions. There is an urgent need to explore these extremophiles for their ability to produce biosurfactants that can function suitably under the conditions prevailing when they are applied.

In recent years natural biosurfactants have attracted attention because of their low toxicity, biodegradability, and ecological acceptability. However, for reasons of functionality and production cost, they are not competitive with chemical surfactants. Use of inexpensive substrates can drastically decrease the production cost of biosurfactants. This review describes the use of unconventional carbon sources for biosurfactant production. These sources include urban as well as agroindustrial wastes. With suitable engineering and microbiological modifications, these wastes can be used as substrates for large‐scale production of biosurfactants.