Biosurfactant

What is a biosurfactant?

A biosurfactant is a surfactant that a microorganism makes. Like any surfactant, it has a water-attracting part and an oil-attracting part, so it gathers at interfaces and lowers surface tension and interfacial tension. What sets it apart is where it comes from: the molecule is assembled by the cell’s own metabolism and usually released into the surrounding liquid, rather than built in a chemical reactor.

Commercially, biosurfactants are produced by large-scale fermentation, in which the producing organism is grown on sugars, plant oils or a combination of the two, and the surfactant is then recovered from the fermentation broth.

Biosurfactants, bio-based surfactants and synthetic surfactants

These three terms are often confused. The difference is how the molecule is made, not only what it is made from.

	Synthetic surfactant	Bio-based surfactant	Biosurfactant
Feedstock	Petroleum or plant oils	Renewable feedstocks, such as plant oils and sugars	Sugars and oils consumed by microorganisms
How the molecule is made	Chemical synthesis	Chemical synthesis	Produced by a microorganism during fermentation
Examples	Linear alkylbenzene sulfonate, alcohol ethoxylates	Alkyl polyglucosides, some coconut-derived surfactants	Sophorolipids, rhamnolipids, surfactin

A bio-based surfactant can therefore be entirely renewable in origin and still be a synthetic molecule. A biosurfactant is always a product of biology.

Main classes of biosurfactants

• Glycolipids: a sugar head group joined to a fatty acid tail. This is the most commercially developed class. It includes sophorolipids, made mainly by the yeast Starmerella bombicola; rhamnolipids, made mainly by Pseudomonas bacteria; mannosylerythritol lipids; and trehalolipids.
• Lipopeptides: a short peptide ring joined to a fatty acid. Surfactin, produced by Bacillus species, is the best known.
• Polymeric biosurfactants: larger molecules such as emulsan, which are especially effective emulsifiers.
• Phospholipids and fatty acids produced by microorganisms, which also show surface activity.

How biosurfactants are produced

Production follows the general pattern of industrial fermentation. A selected microbial strain is grown in a controlled vessel with a carbon source and nutrients. The organism produces the biosurfactant, often in response to the carbon source it is fed, and releases it into the broth. The product is then separated, concentrated and purified. The strain, the feedstock and the process conditions all determine which molecular forms are made and in what proportions, which is why processes described as precision fermentation put so much weight on strain selection and process control.

Properties and limitations

Many biosurfactants have low critical micelle concentrations, meaning they reach their full effect at low concentrations, and many are reported to tolerate a range of pH, temperature and salinity. They are generally described as biodegradable. These are properties of individual molecules rather than of biosurfactants as a group, so claims about any particular product should be checked against its own data, for example a standardized biodegradation test such as OECD 301.

The long-standing obstacle to wider use has been cost: fermentation, recovery and purification have historically been more expensive per kilogram than petrochemical surfactant production, which limited biosurfactants to specialty uses until production volumes grew.

Where biosurfactants are used

Biosurfactants are used, or being developed, in cleaning products, agricultural formulations, personal care, oil production and enhanced oil recovery, mineral processing and environmental remediation. In oil production specifically, microbial enhanced oil recovery relies on biosurfactants and other microbial products to help mobilize trapped oil.

Biosurfactants at Locus

Locus Fermentation Solutions produces glycolipid biosurfactants by fermentation at commercial scale in Solon, Ohio, and supplies them into agriculture, oil and gas, mining and industrial formulations.

Frequently asked questions