Application of the knowledge-based approach to strain selection for a bioaugmentation process of phenanthrene- and Cr(VI)-contaminated soil.

AIMS: The objective of this study was to apply the knowledge-based approach to the selection of an inoculum to be used in bioaugmentation processes to facilitate phenanthrene degradation in phenanthrene- and Cr(VI)-co-contaminated soils. METHODS AND RESULTS: The bacterial community composition of phenanthrene and phenanthrene- and Cr(VI)-co-contaminated microcosms, determined by denaturing gradient gel electrophoresis analysis, showed that members of the Sphingomonadaceae family were the predominant micro-organisms. However, the Cr(VI) contamination produced a selective change of predominant Sphingomonas species, and in co-contaminated soil microcosms, a population closely related to Sphingomonas paucimobilis was naturally selected. The bioaugmentation process was carried out using the phenanthrene-degrading strain S. paucimobilis 20006FA, isolated and characterized in our laboratory. Although the strain showed a low Cr(VI) resistance (0·250 mmol l⁻¹); in liquid culture, it was capable of reducing chromate and degrading phenanthrene simultaneously. CONCLUSION: The inoculation of this strain managed to moderate the effect of the presence of Cr(VI), increasing the biological activity and phenanthrene degradation rate in co-contaminated microcosm. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, we have applied a novel approach to the selection of the adequate inoculum to enhance the phenanthrene degradation in phenanthrene- and Cr(VI)-co-contaminated soils.

Effects of the inoculant strain Sphingomonas paucimobilis 20006FA on soil bacterial community and biodegradation in phenanthrene-contaminated soil.

The effects of the inoculant strain Sphingomonas paucimobilis 20006FA (isolated from a phenanthrene-contaminated soil) on the dynamics and structure of microbial communities and phenanthrene elimination rate were studied in soil microcosms artificially contaminated with phenanthrene. The inoculant managed to be established from the first inoculation as it was evidenced by denaturing gradient gel electrophoresis analysis, increasing the number of cultivable heterotrophic and PAH-degrading cells and enhancing phenanthrene degradation. These effects were observed only during the inoculation period. Nevertheless, the soil biological activity (dehydrogenase activity and CO(2) production) showed a late increase. Whereas gradual and successive changes in bacterial community structures were caused by phenanthrene contamination, the inoculation provoked immediate, significant, and stable changes on soil bacterial community. In spite of the long-term establishment of the inoculated strain, at the end of the experiment, the bioaugmentation did not produce significant changes in the residual soil phenanthrene concentration and did not improve the residual effects on the microbial soil community.