Engineering a filamentous fungus for l-rhamnose extraction

l-Rhamnose is a high value rare sugar that is used as such or after chemical conversions. It is enriched in several biomass fractions such as the pectic polysaccharides rhamnogalacturonan I and II and in naringin, hesperidin, rutin, quercitrin and ulvan. We engineered the filamentous fungus Aspergillus niger to not consume l-rhamnose, while it is still able to produce the enzymes for the hydrolysis of l-rhamnose rich biomass. As a result we present a strain that can be used for the extraction of l-rhamnose in a consolidated process. In the process the biomass is hydrolysed to the monomeric sugars which are consumed by the fungus leaving the l-rhamnose.