Predominant role of hydrocarbon solubilization in the microbial uptake of hydrocarbons

Abstract

Using EDTA and proteolytic enzymes to suppress hydrocarbon solubilization, direct evidence is presented in support of the mechanism of liquid hydrocarbon uptake by microbial cells predominantly from the solubilized or accommodated substrate. EDTA (2-5mM) strongly inhibited growth of three yeast species and one bacterial species on n-hexadecane and the inhibition was removed by surfactant-emulsified and surfactant-solubilized alkane and also by excess addition of Ca(2+). EDTA had no inhibitory effect on the growth of the organisms on soluble substrates such as sodium acetate and nutrient broth or on n-pentane, a volatile alkane which was primarily transported by diffusion from gas phase. EDTA was shown to have no significant effect on the adsorption of cells on alkane drops. EDTA inhibition of growth was considered to be due to suppression of alkane solubilization, brought about by the solubilizing factor(s) produced by cells. It was shown that this chelating agent did not inhibit the growth of yeast on solubilized alkane but strongly inhibited its growth on alkane drops. It was demonstrated that adherent capacity of microbial cell to oil phase was closely related to the state of hydrocarbon emulsification and had no relationship to the ability of organisms to grow on hydrocarbon. Certain proteolytic enzymes inhibited the growth of yeast on alkane, presumably by digesting the alkane solubilizing protein, but not on glucose, and the inhibition was removed by a supply of surfactant-emulsified and surfactant-solubilized alkane. Specific solubilization of various hydrocarbon types during growth of the prokaryotic bacterial strain was demonstrated. The specific solubilization of hydrocarbon was strongly inhibited strain was demonstrated. The specific solubilization of hydrocarbon was strongly inhibited by EDTA, and the inhibition was removed by excess Ca(2+). It was concluded that specific solubilization of hydrocarbons is an important mechanism in the microbial uptake of hydrocarbons.

Hydrophobic Interactions: Role in Bacterial Adhesion

“…In the open environment, adhesion to oil is frequently observed (e.g., Wyndham and Casterton, 1982); however, emulsification of oil droplets in the open waters would allow them to diffuse away from the cells. Some investigators (working primarily with Pseudomonas strains) have argued that adhesion is not an important factor in growth on oil (Reddy et al, 1982;Chakravarty et al, 1975). This may well be true in the case of growth on aromatic hydrocarbons, which are generally more water-soluble and more toxic than paraffins.…”

Emulsification and utilization of high-speed diesel by a Brevibacterium species isolated from hydraulic oil

“…Requirement of internalization followed by degradation by intra or extra-cellular enzymes was considered important by various investigators (Ratledge 1980;Reddy et al 1982). The process of internalization is reported to be mediated through specific microbial bio-surfactants and bio-emulsifiers.…”

Microbial Bioremediation of Fuel Oil Hydrocarbons in Marine Environment

“…Requirement of internalisation followed by degradation by intra-or extra-cellular enzymes was considered important by various investigators 35,58,59 . The process of internalisation is reported to be mediated through specific microbial biosurfactants and bioemulsifiers.…”

“…The process of internalisation is reported to be mediated through specific microbial biosurfactants and bioemulsifiers. It is reported that hydrocarbon internalisation is mediated by the formation of microemulsion, presumably by lowering interfacial tension 59 . Although, literature on the effect of surfactant on oil utilisation ability shows varying results, majority of reports indicate its important role in effective dispersion and degradation of pollutant oil in marine environment [60][61][62][63] .…”