Salt-tolerant phenol-degrading microorganisms isolated from Amazonian soilsamples

Two phenol-degrading microorganisms were isolated from Amazonian rain fores t soil samples after enrichment in the presence of phenol and a high salt c oncentration. The yeast Candida tropicalis and the bacterium Alcaligenes fa ecalis were identified using several techniques, including staining, morpho logical observation and biochemical tests, fatty acid profiles and 16S/18S rRNA sequencing. Both isolates, A. faecalis and C. tropicalis, were used in phenol degradation assays, with Rhodococcus erythropolis as a reference ph enol-degrading bacterium, and compared to microbial populations from wastew ater samples collected from phenol-contaminated environments. C. tropicalis tolerated higher concentrations of phenol and salt (16 mM and 15%, respect ively) than A. faecalis (12 mM and 5.6%). This yeast also tolerated a wider pH range (3-9) during phenol degradation than A. faecalis (pH 7-9). Phenol degradation was repressed in C. tropicalis by acetate and glucose, but not by lactate. Glucose and acetate had little effect, while lactate stimulate d phenol degradation in A. faecalis. To our knowledge, these soils had neve r been contaminated with man-made phenolic compounds and this is the first report of phenol-degrading microorganisms from Amazonian forest soil sample s. The results support the idea that natural uncontaminated environments co ntain sufficient genetic diversity to make them valid choices for the isola tion of microorganisms useful in bioremediation.