Abstract

---

Phenol tolerant bacteria were isolated from sewage treatment site. Sixteen bacterial colonies were isolated and tested in 100-500 mg/L of 2,4-Dichlorophenol (2,4-DCP). After screening, two isolates which showed high phenol resistances were selected. Both isolates, XC, and N3 were able to tolerate 200 mg/L of 2,4-DCP but isolate N3 tolerated 400 mg/L of 2,4-DCP. Isolate N3 was identified as Bacillus pasteurii while isolate XC was identified as Aeromonas hyrophila. Bacillus pasteurii was selected for further studies and was subjected to plasmid curing experiment which confirmed that 2,4-DCP resistant trait was mediated by a single plasmid of approximately 22kb. Amendment with organic nitrogen sources, to enhance the tolerance of 2,4-DCP by Bacillus pasteurii showed that the maximum 2,4-DCP tolerance level of 300mg/L at an optical density(OD) of 0.35 which was 133% higher than that obtained for control was achieved at 0.5mg/L of peptone. Similarly, a maximum 2.4-DCP tolerance level of 300mg/L at an GD of 0.24 which was 60% higher than that obtained for control was achieved at 0.5 mg/L of yeast extract. A maximum 2,4-DCP tolerance level of 300mg/L at an optical density of 0.19 which was 26% higher than that obtained for control was achieved at 0.5mg/L of tryptone. In all experiments, it was observed that the decrease in inhibition capability of 2,4-DCP and the increase in the tolerance capacity of the strains are synonymous. Among the nitrogen sources tested, peptone showed a significantly (P < 0.05, Student's t-Test) higher level of enhancement of 2,4-DCP tolerance by Bacillus pasteurii.

Keywords: 2,4-dichlorophenol, phenol tolerant, organic nitrogen sources, plasmid DNA, Bacillus pasteurii