Community analysis and metabolic pathway of halophilic bacteria for phenol degradation in saline environment

• The enrichment degraded phenol at concentrations of up to 350 mg/L with widely salinity (1–3 M NaCl).
• The major functional populations in the enrichment consisted of Acidobacteria and Chloroflexi.
• The halophilic bacterial community contained all the known pathways for phenol degradation.
• The enrichment adjusted the osmotic pressure by ectoine and hydroxyectoine as compatible solutes.

A moderately halophilic bacterial enrichment was able to degrade 120 mg/L of phenol in the presence of 1–2 M of NaCl within 3 d or 2.5–3 M of NaCl within 6 d. The optimal degradation was achieved at 1.5 M of NaCl and 350 mg/L of phenol. PCR-DGGE profile of the enrichment showed that the Acidobacterium sp. and Chloroflexus sp. dominated the community. The phenol-biodegradation pathways consisted of an initial oxidative attack by phenol hydroxylase, and subsequent ring fission by catechol 1,2-dioxygenase and catechol 2,3-dioxygenase. Nuclear magnetic resonance (NMR) spectroscopy profiles showed that ectoine and hydroxyectoine were the main compatible solutes to adjust the bacterial osmotic pressure. This study provides further information on the understanding of phenol-degradation over a wide range of salinity and remediation of phenol as a pollutant in the environment.