PARAQUAT-INDUCED CHANGES IN SELECTED RHIZOBIA AND AGROBACTERIA

Abstract

Adaptations of eight strains of rhizobia from seven cross-inoculation groups and of two agrobacteria from two species to paraquat, in concentrations up to 20 000 μg∙mL−1, affected 11 of the 40 properties studied, including carbohydrate, nitrogen, sulfur, and other metabolism. The number of characteristics altered varied among the bacteria without species or group affiliation. Of the total of 18 changes, 13 occurred in Rhizobium meliloti 22 and R. trifolii 7 and 42, while R. leguminosarum 56, R. lupini 112, R. japonicum 80, cowpea strain 131, and Agrobacterium tumefaciens A6-K1 had only one. Rhizobium phaseoli 95 and A. radiobacter R-590 remained unaffected. Generally, the adapted organisms produced lower nephelometric growth and manometric respiration rates at 0 and 200 μg of paraquat∙mL−1, relative to the herbicide-free parent controls. Tolerance of R. trifolii 7 to NaCl increased from 1% to 5% (wt/vol). The findings suggest that paraquat may have affected cell permeability, adaptive and/or constitutive enzymes in these bacteria. Key words: Rhizobia, agrobacteria, adaptations, physiology, paraquat and herbicides