Different modes of hydrocarbon uptake by two Pseudomonas species.

The mode of n-hexadecane uptake by two organisms-Pseudomonas M 1 and Pseudomonas N 1-was studied. During the growth of Pseudomonas M 1 on n-hexadecane, no extracellular biosurfactant/bioemulsifier was produced, no significant n-hexadecane pseudosolubilization was observed, and the reduction of surface and interfacial tensions in the cell-free culture broth was negligible. EDTA, a known inhibitor of hydrocarbon pseudosolubilization, did not inhibit the growth of the organism on n-hexadecane. Normal hexadecane-grown cells showed strong surface-active properties and capacity to adhere firmly to hydrocarbon phase. It was concluded that in this organism, surface-active properties of the cells facilitate attachment of cells to the hydrocarbon-water interface generated by agitation, and promote substrate uptake and growth; no hydrocarbon pseudosolubilization or extracellular mediator is involved in the substrate uptake. Pseudomonas N 1 grew on n-hexadecane much faster than Pseudomonas M 1. Growth of this organism on n-hexadecane was associated with the extracellular production of biosurfactant-bioemulsifier and n-hexadecane pseudosolubilizing factor; the growth was strongly inhibited by 5 mM EDTA, indicating that hydrocarbon pseudosolubilization was the dominant factor in substrate uptake. The rate of n-hexadecane pseudosolubilization was high enough to account for the substrate up take rate. Hydrocarbon emulsifying and n-hexadecane pseudosolubilizing factors were isolated and tentatively characterized as lipoprotein and glycoprotein, respectively. Both factors act in a synergistic manner to provide enhanced hydrocarbon transport to cells through pseudosolubilization. It is proposed that this facility of mediated hydrocarbon transport is the basis for the relatively fast rate of growth of Pseudomonas N 1 on hydrocarbon.