Enhancement of NAPL bioavailability by induction of cell-surface hydrophobicity in Exiguobacterium aurantiacum and Burkholderia cepacia

Abstract

Induction of cell surface hydrophobicity in bacterial cultures can facilitate the direct interfacial uptake of non-aqueous phase liquids (NAPLs). This study explores bioavailability of NAPLs for Exiguobacterium aurantiacum and Burkholderia cepacia isolated from oil-contaminated soil and sediments. Surface tension measurements and emulsification activity tests did not provide evidence for release of extracellular biosurfactants/bioemulsifiers. Contact angle measurement on cell layers and bacterial adhesion to hydrocarbon (BATH) assay was conducted for determining the cell surface hydrophobicity. While the surfaces of cultures grown on soluble substrate, dextrose, were not hydrophobic, higher water contact angle and greater adherence to n-hexadecane/diesel revealed the highly hydrophobic nature of the cell surfaces for cultures grown on NAPLs (n-hexadecane and diesel), thus providing evidence for induction in cell surface hydrophobicity. Positive results in the carbocyanine assay indicating release of lipopolysaccharides/extracellular polysaccharides was observed over the log growth phase only for the NAPL-grown cells. Transmission electron microscopy (TEM) revealed an abundance of intracellular electron transparent globules within the NAPL-grown cells. Light microscopy and TEM images together revealed differences in cell surface characteristics of E. aurantiacum and B. cepacia, which was also affected by the growth substrate.