of Rhamnolipids by Pseudomonas chlororaphis, a Nonpathogenic
Nereus W. Gunther IV,* Alberto Nunez,
William Fett, and Daniel K. Y. Solaiman
Eastern Regional Research Center, Agricultural Research
Service, U.S. Department of
Agriculture, 600 East Mermaid Lane, Wyndmoor, PA 19038-8598.
Rhamnolipids, naturally occurring biosurfactants
constructed of rhamnose sugar molecules and -hydroxyalkanoic
acids, have a wide range of potential commercial applications.
In the course of a survey of 33 different bacterial isolates,
we have identified, using a phenotypic assay for rhamnolipid
production, a strain of the nonpathogenic bacterial species
Pseudomonas chlororaphis that is capable of producing
rhamnolipids. Rhamnolipid production by P. chlororaphis
was achieved by growth at room temperature in static cultures
of a mineral salts medium containing 2% glucose. We obtained
yields of roughly 1 g/liter of rhamnolipids, an amount comparable
to the production levels reported in Pseudomonas aeruginosa
grown with glucose as the carbon source. The rhamnolipids
produced by P. chlororaphis appear to be exclusively
the mono-rhamnolipid form. The most prevalent molecular species
had one monounsaturated hydroxy fatty acid of 12 carbons and
one saturated hydroxy fatty acid of 10 carbons. P. chlororaphis,
a nonpathogenic saprophyte of the soil, is currently employed
as a biocontrol agent against certain types of plant fungal
diseases. The pathogenic nature of all bacteria previously
known to produce rhamnolipids has been a major obstacle to
commercial production of rhamnolipids. The use of P. chlororaphis
therefore greatly simplifies this matter by removing
the need for containment systems and stringent separation
processes in the production of rhamnolipids.
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