Biodegradability of 3-Methyl-4-Nitrophenol by 4-Nitrophenol-Degrading Bacteria

Abstract

The organophosphorous pesticide fenitrothion has been used to control harmful insects in agriculture and for the maintenance of plants in gardens, golf courses, and forests. This pesticide was easily degraded into 3-methyl-4-nitrophenol (3M4NP) by activated sludge and soil bacteria, but 3M4NP then accumulated in the cultures. Although the degradation mechanisms of 4-nitrophenol (4NP) have been well characterized, little is known regarding 3M4NP. The biodegradability of 3M4NP was evaluated using twelve 4NP-degrading bacteria isolated from India and the USA. The 4NP-degrading bacteria were tentatively classified into five genera based on the 16S rRNA gene sequences: Arthrobacter, Pseudomonas, Nocardioides, Micrococcus, and Staphylococcus. Only three strains of the Arthrobacter genus were able to grow on 3M4NP. Testing the degradation of 3M4NP and 4NP by these isolates revealed that most isolates were less able to degrade 3M4NP than 4NP primary due to the lack or weak activity of enzymes for initial 3M4NP degradation. One of the isolates, strain 425 could degrade 3M4NP as efficiently as 4NP, but methylhydroquinone accumulated quantitatively from 3M4NP, indicating that this strain can partially contribute to 3M4NP degradation. These results suggested that 4NP-degrading bacteria do not play a major role in 3M4NP degradation but can aid its metabolism in the environment.