Phenol biodegradation by halophilic archaea

•Phenol can be used as a sole carbon and energy source by halophilic archaea.•Phenol or toluene acclimatized cells degrade the phenol two or more times higher than non-acclimatized.•Phenol degradation achieve by catechol 2,3-dioxygenase and meta-cleavage pathway.

Phenol is a toxic aromatic compound produced as a by-product of industrial activities. Biological treatment of highly saline wastewaters containing phenol can be performed through halophilic microorganisms. In this study, the ability of halophilic archaeal isolates to degrade phenol was investigated. Among 103 tested isolates, the strain designated A235 was identified as having the highest phenol degradation capacity on solid and liquid media containing 20% (w/v) NaCl and phenol as the sole carbon and energy source. The strain was adapted sequentially to increasing phenol concentrations. The removal of phenol via cross-toluene adaptation was increased by 14% in the medium. The growth kinetics of strain A235 during growth on phenol was found to fit the Monod model. The values of μmax and Ks were calculated to be 0.015 h−1 and 71.4 g l−1, respectively. For an initial phenol concentration of 100 ppm, the biodegradation by A235 was found to be optimal at pH 7.5, 37 °C and 200 rpm when the culture contained 20% (w/v) NaCl, 0.025% yeast extract and the inoculum size was set at 10%. A preliminary enzyme screening indicated that the degradation of phenol was achieved through a meta-cleavage pathway involving a catechol 2,3-dioxygenase. Catechol 2,3-dioxygenase displayed its highest catalytic activity at 42 °C, 2 M KCl, and pH 8. To the best of our knowledge, this is the first report showing the ability an extremely halophilic archaeon to metabolize phenol at higher salt concentrations.