Identification and characterisation of a diuron-degrading bacterium

Abstract.

Isolate D47 has previously been shown to degrade a range of urea-based herbicides. The DNA encoding the16 S rRNA gene of this strain was amplified by polymerase chain reaction (PCR) and sequenced. Database similarity searches indicated the gene was similar to those present in Arthrobacter species. The 16S rRNA gene sequence was compared to eight full-length sequences that have been obtained from related strains in this cluster by both distance and parsimony methods. The analyses confirmed the inferred relationship between D47 and Arthrobacter oxydans-type strains within the Arthrobacter globiformis group. Biochemical tests confirmed this result. Studies with ¹⁴C-carbonyl-labelled diuron indicated that D47 hydrolysed the urea side chain at the carbonyl group. Loss of the parent compound was accompanied by an equal accumulation of 3,4-dichloroaniline and loss of [¹⁴C]-CO₂. Cell-free extracts of D47 indicated a broad temperature optimum for degradative activity between 15°C and 30°C, a broad pH optimum of 6.5–8.0 and a decline in activity with increasing salt concentration beyond 50 mM. This information sets the basic characteristics of the strain and the enzyme for cloning and expression of the gene(s) encoding this activity in a heterologous host.