Microbially produced rhamnolipid as a source of rhamnose.

The sugar L-rhamnose (6-deoxy-~-mannose) is used as a fine chemical in scientific and industrial settings, as a component in chemical reactions, and as a starting material in the synthesis of organic compounds. Present methods for the commercial preparation of rhamnose require extraction of quercitrin from oak bark, naringin from citrus peels, or rutin (quercetin-3-rutinoside) from oak bark or a variety of plants, such as buckwheat.’.‘ Quercitrin is a glycoside made up of the aromatic aglycone quercetine and rhamnose, whereas naringin and rutin are glycosides containing a glucose moiety in addition to rhamnose and the aglycone. Rhamnose is recovered by the hydrolysis of these molecules. Several disadvantages accompany the labor-intensive processes for production of rhamnose from quercitrin, naringin, and rutin, including the production of large quantities of potentially toxic, aromatic waste products and the need for toxic or corrosive chemicals in the extraction process. Furthermore, the bulky raw materials used for extraction must be harvested and then either transported at some expense to the extraction facility, or the processing plant must be located in proximity to the raw materials. Another potential source of rhamnose is rhamnosecontaining polysaccharides produced by plants or microorganisms. Certain polysaccharides (i.e., gelrite) are characterized by gelling or thickening proper tie^,^ while others may be used as emulsifier^.^.^ The growth of certain microorganisms results in the production of extracellular polysaccharides.6 These extracellular polysaccharides may be present as a capsule around the outside of the cell or may be released into the growth medium as slime, or may be present in both capsular and released form. For instance, production of a Pseudornonas elodea polysaccharide containing 30% rhamnose was reported at yields of 1.5% “gel” from growth in 3% glucose.’ Fermentation of Acinetobacter calcoaceticus has also been reported to yield 0.5 g/L polysaccharide containing 80% rhamnose.’ Yields as much as 3.5 g/L rhamnose have recently been reported