M. BOUCHEZ-NAÏTALI, H. RAKATOZAFY, R. MARCHAL, J.-Y. LEVEAU AND J.-P.V AN DE C AS TE E LE . 1999. The relative distribution of the modes of hydrocarbon uptake, used by bacteria of the environment for the degradation of long-chain alkanes, has been evaluated. The first mode of uptake, direct interfacial accession, involves contact of cells with hydrocarbon droplets. In the second mode, biosurfactant-mediated transfer, cell contact takes place with hydrocarbons emulsified or solubilized by biosurfactants. Sixty-one strains growing on hexadecane were isolated from polluted and non-polluted soils and identified. The majority (61%) belonged to the CorynebacteriumMycobacterium-Nocardia group. Criteria selected for characterizing hexadecane uptake were cell hydrophobicity, interfacial and surface tensions and production of glycolipidic extracellular biosurfactants. These properties were determined in flask cultures on an insoluble (hexadecane) and on a soluble (glycerol or succinate) carbon source for a subset of 23 representative strains. Exclusive direct interfacial uptake was utilized by 47% of studied strains. A large proportion of strains (53%) produced biosurfactants. The data on cellular hydrophobicity suggested the existence of two distinct alkane transfer mechanisms in this group. Accordingly, tentative assignments of biosurfactant-mediated micellar transfer were made for 11% of the isolated strains, and of biosurfactant-enhanced interfacial uptake for 42%.
The production of sophorose lipids from ethyl esters of rapeseed oil fatty acids and glucose by Candida bombicola CBS 6009 was studied. A kinetic description of the fermentation is presented, showing in particular two distinct phases of growth and, following nitrogen limitation, subsequent production of sophorose lipids, which were excluded from the aqueous phase. With the fed-batch fermentation technology used, a high production performance (320 g . l -1 sophorose lipids with a weight yield of 65°7o with respect to the carbon sources) was obtained. Detailed fermentation balances were established and their implications for energy metabolism during glycolipid production are discussed. The variations in the structure of the sophorose lipids during fermentation were also studied. Sophorolipid 1', 4"-lactone 6', 6"-diacetate was the major class compound produced (about 50o/o of the glycolipids). A correlation between the lipidic composition of the products and the nature of the fatty acids of the rapeseed esters was observed.
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