Diversity of bacterial strains degrading hexadecane in relation to the mode of substrate uptake

The relative distribution of the modes of hydrocarbon uptake, used by bacte ria 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, biosurfact ant-mediated transfer, cell contact takes place with hydrocarbons emulsifie d or solubilized by biosurfactants, Sixty-one strains growing on hexadecane were isolated from polluted and non-polluted soils and identified. The maj ority (61%) belonged to the Corynebacterium-Mycobacterium-Nocardia group. C riteria selected for characterizing hexadecane uptake were cell hydrophobic ity, interfacial and surface tensions and production of glycolipidic extrac ellular biosurfactants, These properties were determined in flask cultures on an insoluble (hexadecane) and on a soluble (glycerol or succinate) carbo n source for a subset of 23 representative strains. Exclusive direct interf acial 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 micella r transfer were made for 11% of the isolated strains, and of biosurfactant- enhanced interfacial uptake for 42%.