The concentrations of hexadecane and inorganic nutrients modulate the production of extracellular membrane-bound vesicles, soluble protein, and bioemulsifier by Acinetobacter venetianus RAG-1 and Acinetobacter sp. strain HO1-N.

In the present study, we addressed the possibility that the production of both bioemulsifiers and membrane-bound vesicles may be a common feature of the growth of Acinetobacter spp. on alkanes, and we determined the extent to which the release of extracellular products by these organisms is regulated by the concentrations of the alkane substrate and inorganic nutrients. To accomplish this objective, we grew Acinetobacter venetianus RAG-1 and Acinetobacter sp. strain HO1-N with different concentrations of nutrients and assayed for extracellular products. The results indicated that the release of vesicles, soluble protein, and bioemulsifier was promoted in various degrees by higher concentrations of hexadecane and inorganic nutrients, while the specific activities of the bioemulsifiers were enhanced with lower nutrient concentrations. Based on our findings, we propose that under conditions of nutrient excess, these strains produce membrane-bound vesicles to function in "luxury uptake" of the alkane substrate for delivery and storage in the form of inclusions. Under the same conditions, soluble bioemulsifier and protein may perform auxiliary roles in cell desorption and (or) alkane uptake. With low concentrations of nutrients, the decreased production of vesicles, protein, and bioemulsifier and the increased activity of the emulsifier may represent a mechanism for reducing biosynthetic demands and conserving cellular material.