Isolation and Characterization of 4- tert -Butylphenol-Utilizing Sphingobium fuliginis Strains from Phragmites australis Rhizosphere Sediment

Abstract

ABSTRACT We isolated three Sphingobium fuliginis strains from Phragmites australis rhizosphere sediment that were capable of utilizing 4- tert -butylphenol as a sole carbon and energy source. These strains are the first 4- tert -butylphenol-utilizing bacteria. The strain designated TIK-1 completely degraded 1.0 mM 4- tert -butylphenol in basal salts medium within 12 h, with concomitant cell growth. We identified 4- tert -butylcatechol and 3,3-dimethyl-2-butanone as internal metabolites by gas chromatography-mass spectrometry. When 3-fluorocatechol was used as an inactivator of meta -cleavage enzymes, strain TIK-1 could not degrade 4- tert -butylcatechol and 3,3-dimethyl-2-butanone was not detected. We concluded that metabolism of 4- tert -butylphenol by strain TIK-1 is initiated by hydroxylation to 4- tert -butylcatechol, followed by a meta -cleavage pathway. Growth experiments with 20 other alkylphenols showed that 4-isopropylphenol, 4- sec -butylphenol, and 4- tert -pentylphenol, which have alkyl side chains of three to five carbon atoms with α-quaternary or α-tertiary carbons, supported cell growth but that 4- n -alkylphenols, 4- tert -octylphenol, technical nonylphenol, 2-alkylphenols, and 3-alkylphenols did not. The rate of growth on 4- tert -butylphenol was much higher than that of growth on the other alkylphenols. Degradation experiments with various alkylphenols showed that strain TIK-1 cells grown on 4- tert -butylphenol could degrade 4-alkylphenols with variously sized and branched side chains (ethyl, n -propyl, isopropyl, n -butyl, sec -butyl, tert -butyl, n -pentyl, tert -pentyl, n -hexyl, n -heptyl, n -octyl, tert -octyl, n -nonyl, and branched nonyl) via a meta -cleavage pathway but not 2- or 3-alkylphenols. Along with the degradation of these alkylphenols, we detected methyl alkyl ketones that retained the structure of the original alkyl side chains. Strain TIK-1 may be useful in the bioremediation of environments polluted by 4- tert -butylphenol and various other 4-alkylphenols.