Extracellular Polysaccharides of Rhodococcus rhodochrous S-2 Stimulate the Degradation of Aromatic Components in Crude Oil by Indigenous Marine Bacteria

Rhodococcus rhodochrous S-2 produces extracellular polysaccharides (S-2 EPS) containing d-glucose, d-galactose, d-mannose, d-glucuronic acid, and lipids, which is important to the tolerance of this strain to an aromatic fraction of (AF) Arabian light crude oil (N. Iwabuchi, N. Sunairi, H. Anzai, M. Nakajima, and S. Harayama, Appl. Environ. Microbiol. 66:5073-5077, 2000). In the present study, we examined the effects of S-2 EPS on the growth of indigenous marine bacteria on AF. Indigenous bacteria did not grow significantly in seawater containing AF even when nitrogen, phosphorus, and iron nutrients were supplemented. The addition of S-2 EPS to seawater containing nutrients and AF resulted in the emulsification of AF, promotion of the growth of indigenous bacteria, and enhancement of the degradation of AF by the bacteria. PCR-denaturing gradient gel electrophoresis analyses show that addition of S-2 EPS to the seawater containing nutrients and AF changed the composition of the bacterial populations in the seawater and that bacteria closely related to the genus Cycloclasticus became the major population. These results suggest that Cycloclasticus was responsible for the degradation of hydrocarbons in AF. The effects of 15 synthetic surfactants on the degradation of AF by indigenous marine bacteria were also examined, but enhancement of the degradation of AF was not significant. S-2 EPS was hence the most effective of the surfactants tested in promoting the biodegradation of AF and may thus be an attractive agent to use in the bioremediation of oil-contaminated marine environments

Role of Interfacial Tensions in the Translocation of Rhodococcus erythropolis during Growth in a Two Phase Culture

Rhodococcus erythropolis PR4 is an alkane-degrading bacterium, which grows well in media containing high concentrations of alkanes. These properties give the organism potential in the bioremediation of various environments contaminated by alkanes. In this study, we report the translocation of R. erythropolis PR4 from an aqueous phase to an alkane phase during growth in a two phase culture medium. When the alkane chain length was between C10 and C12, PR4 was located at the aqueous-alkane interface, but when the alkane chain length was above C14, PR4 translocated into the alkane phase. Complete translocation into alkane phase was accompanied by normal growth, whereas interfacial localization hampered growth, indicating that localization among other possible factors, play an important role in the growth of R. erythropolis PR4 in two phase cultures. The PR4 cell surface was physico-chemically characterized in terms of its cell surface charge and surface free energy. Contact angles were measured on bacterial lawns, followed by thermodynamic analyses of Gibbs free energies for localization of PR4 in the aqueous or alkane phase or at the interface. Although entry into the alkane phase of PR4 grown in the presence of both C12 and C19 was thermodynamically favorable, translocation from the inside of the alkane phase to the interface was only favorable for PR4 grown in the presence of C12. In line with these thermodynamic analyses, two phase partitioning showed that PR4 grown in the presence of C12 and C19 were more hydrophobic than PR4 grown in the presence of lower alkanes, while C12 grown bacteria were less lipophilic than C19 grown bacteria. In conclusion, the localization of R. erythropolis PR4 in a two phase culture medium is thermodynamically driven to facilitate its optimal growth