Enhanced biodegradation of phenanthrene in a biphasic culture system

Abstract

Degradation of phenanthrene by Pseudomonas aeruginosa AK1 was examined in (i) an aqueous mineral salts medium to which phenanthrene particles of varying size (i.e. diameter) were added, and (ii) an aqueous/organic biphasic culture system consisting of mineral salts medium supplemented with 2,2,4,4,6,8,8-heptamethylnonane (HMN) as the phenanthrene-carrying organic phase. In both systems, the rate of phenanthrene biodegradation could be significantly enhanced by manipulations leading to improved phenanthrene mass transfer into the aqueous phase. With crystalline phenanthrene, the rate of biodegradation was found to be directly correlated to the particle surface area, whereas in the biphasic system the rate of biodegradation of the dissolved phenanthrene was mainly governed by the HMN/water interface area. In the latter system, exponential growth with a doubling time td of 6-8 hours has been achieved under conditions of intensive agitation of the medium indicating that phenanthrene degrad ation by strain AK1 is limited mainly by physicochemical parameters. Addition of selected surfactants to the culture medium was found to accelerate phenanthrene degradation by strain AK1 only under conditions of low agitation (in the presence of HMN) and after pretreatment of phenanthrene crystals by ultrasonication (in the absence of HMN). Evidence is presented that the stimulating effect of the surfactants was primarily due to improved dispersion of phenanthrene particle agglomerates (in the aqueous mineral salts medium supplemented with phenanthrene crystals) or of the phenanthrene-carrying lipophilic solvent drops (in the aqueous/organic biphasic culture system) whereas the solubilizing activity towards phenanthrene was neglectible. Under conditions of intensive mixing of the culture medium (i.e. if a high particle surface area of HMN/water interface area, resp., is provided), the addition of surfactants did not enhance phenanthrene biodegradation

The enhancement by surfactants of hexadecane degradation by Pseudomonas aeruginosa varies with substrate availability

“…Presumably, mass transfer of hexadecane from the matrix to the bulk solution is enhanced by mixing, especially for matrices with large pores, but cannot be further enhanced by rhamnolipid or another surfactant under conditions of intense agitation. A similar dependence on hydrodynamic conditions was found for the effect of surfactants on the biodegradation of phenanthrene present as crystals or dissolved in an organic phase by P. aeruginosa (Kö hler et al, 1994). Under conditions of low agitation, surfactant addition stimulated degradation but under conditions of high agitation surfactants failed to further stimulate biodegradation.…”

Chlorinated biphenyl degradation by wild yeasts pre-cultured in biphasic systems

“…These data and the microscopic observations revealed that yeasts grew in Significantly better adaptation was observed in the consortium in relation to each species alone in the biphasic assays; moreover, phenol presence incremented the interfacial associated cells and the biodegradation of hydrophobic organic pollutants as was shown by other authors (Köhler et al 1994;Owen et al 1997). …”

Rhodanobactersp. Strain BPC1 in a Benzo[a]pyrene-Mineralizing Bacterial Consortium

“…It was hypothesized that solubilization of benzo-[a]pyrene was a necessary step in the overall biodegradation process because benzo[a]pyrene bioavailability to the consortium organisms was increased. Increased bioavailability of target hydrophobic compounds to degrading organisms is an integral part of the biodegradation of these compounds, especially PAHs (18,32).…”