Biodegradation of phenmedipham by novel Ochrobactrum anthropi NC-1

An Ochrobactrum anthropi bacterial strain named as NC-1, capable of utilizing phenmedipham (PMP) herbicide as the sole of carbon source and energy for growth was isolated from pesticide-contaminated soil sample by enrichment culture technique. The isolated bacterial strain was identified as Ochrobactrum anthropi NC-1 (MH 796134) based on its morphological, cultural, biochemical characteristics and analysis of 16S rRNA gene sequence. The strain NC-1 could degrade more than 98.5% of PMP (2 mM) within 168 h. The optimal degradation pH and temperature were 7.0 and 30-35 °C, respectively. The strain NC-1 degraded PMP by a pathway involving its initial hydrolysis of their central amide carbamate linkage to yield m-aminophenol via methyl-N-(3-hydroxyphenyl) carbamate and m-toluidine were the major intermediates. However, m-aminophenol was not further metabolized, because they neither supported the growth of organism nor stimulated oxygen uptake. But m-toluidine released by dealkylation was followed by hydrolysis. Further, results also revealed that degradation of 4-methyl catechol proceeded via 2-hydroxy-5-methyl-6-oxohexa-2, 4-dienoate through meta cleavage ring processes. The formation of these compounds was confirmed by UV, TLC, HPLC, IR, NMR, and GC-MS spectral analysis. The cell-free extracts of O. anthropi NC-1 grown on PMP contained the activities of PMP hydrolase, toluidine dioxygenase, and 4-methyl catechol 1, 2-dioxygenase. These results demonstrate the biodegradation of PMP and promote the potential use of strain NC-1 to bioremediate PMP-contaminated environment.