Molecular Identification and Characterization of Bacillus sp. NIGAB-1 for Phenol Degradation Under Saline Conditions

Phenol is an aromatic pollutant in industrial wastes that in combination with salts is highly toxic for all forms of life. Phenol elimination is the foremost challenge to meet the goal of pollutant-free environment.

The present study was carried out to isolate phenol degrading bacteria which can degrade phenol under saline conditions and to identify the isolated strains using 16S rRNA gene sequence analysis.

Sediment samples were collected from Rawal Lake, Islamabad, Pakistan and enriched in mineral salt medium (MSM) containing phenol (150 mg.L^-1). Isolated strains were identified on the basis of 16S rRNA gene sequence analysis. Growth of strains were tested at different pH, NaCl concentrations and temperature using Tryptic Soy Agar (TSA). Tolerance to phenol (0-750 mg.L^-1) was checked at 5% NaCl and phenol degrading experiment was performed at 4% NaCl, pH 7 and 30 oC. In both, phenol tolerance and degradation study, phenol was used a sole source of carbon and energy.

Thirteen bacterial strains were isolated after enrichment among which, NIGAB-1 was found capable of degrading phenol in saline conditions. This strain was identified as Bacillus sp. NIGAB-1 on the basis of 16S rRNA gene sequence analysis and the closest match was Bacillus marisflavi with 99.71% sequence identity. The Bacillus sp. NIGAB-1 exhibited best growth at 30 oC at pH 7 with 10% NaCl. The optimum phenol concentration for growth was recorded as 300 mg.L^-1. This strain degraded 300 mg.L-1 of phenol at 4% NaCl in 120 hours with the average degradation rate of 2.63 mg.L^-1.h.

These findings suggest that this strain could be efficient in phenol degradation at adverse environmental conditions and helpful in remediation of phenol where the salt concentration is high.