Low-temperature biodegradation of high amounts of phenol by Rhodococcus spp. and basidiomycetous yeasts

Four cold-adapted microbial strains able to degrade high amounts of phenol were isolated from hydrocarbon-contaminated alpine soils. Two of the strains were bacteria identified as Rhodococcus spp., and two strains were basidiomycetous yeasts. One of the yeasts was identified as Trichosporon dulcitum, while the second yeast strain belonged to the Urediniomycetes and probably represents a novel species. This strain was not able to grow at temperatures above 20 degrees C, while the other three strains were cold-tolerant and could grow at temperatures ranging from 1-25 degrees C (T. dulcitum) or 1-30 degrees C (rhodococci). The yeast strains were characterized by a substantially lower optimum temperature for growth and biodegradation compared to the bacteria. The urediniomycete strain degraded 5 mM phenol at 1 degrees C faster than the two bacteria at 10 degrees C. The optimum temperature for phenol degradation was 10 degrees C (novel yeast species), 20 degrees C (T. dulcitum), or 30 degrees C (rhodococci). Using fed-batch cultivation in mineral medium with phenol as the sole carbon source, high amounts of phenol were degraded at 10 degrees C. Both rhodococci degraded up to 12.5 mM phenol, while the two yeast strains even utilized as much as 15 mM phenol.