Response of Azospirillum brasilense to the pesticides bromopropylate and methidathion on chemically defined media and dialysed-soil media

The effects of 10, 50, 100, 200 and 300 ìg mlÿ1 of bromopropylate and methidathion were investigated in the cells of Azospirillum brasilense grown in chemically de®ned media and dialysed-soil media. The insecticide bromopropylate did not affect microbial growth, the levels of ATP and dinitrogen ®xation of A. brasilense in either chemically de®ned media or dialysedsoil media. Methidathion signi®cantly reduced dinitrogen ®xation, the intracellular levels of ATP and growth in cells grown in chemically de®ned media. However, these negative effects were not signi®cant in cells grown in dialysed-soil media, showing that A. brasilense can tolerate high concentrations (300 ìg mlÿ1) of methidathion under the present experiment conditions.