Influence of Gramoxone and paraquat on growth and respiration of Azotobacter vinelandii

Abstract

The influence of the herbicide Gramoxone and its active ingredient paraquat on growth and respiratory activity of Azotobacter vinelandii was studied. The experiments were performed in nitrogen-free medium and in medium with combined nitrogen. Addition of Gramoxone (50 ppm) or paraquat (15 ppm) to the cultures during lag phase caused a total inhibition of growth. However, even after 24 h of incubation in the presence of herbicides the number of viable counts did not decrease. When herbicides were added to exponentially growing cultures, the growth response of the cultures was different. After addition of herbicides only a transient short inhibition period was noted and the length of the inhibition period was dependent on the time of herbicide addition. Neither Gramoxone (50 ppm) nor paraquat (15 ppm) enhanced catalase production. The respiratory activity of paraquat-treated cells in the presence of 1 mM KCN was distinctly reduced (75%), while that of untreated cells did not change.The herbicide Gramoxone is widely used for a variety of crops. Its active ingredient is paraquat (methyl viologen), an aromatic quaternary nitrogen compound. Because of its redox potential paraquat interferes with the respiratory chain (electron transport) and produces superoxide radicals in the presence of oxygen (HASSAN FRIDOVICH 1986). Several strains of rhizobia and agrobacteria are known to tolerate paraquat from 20 to 200ppm and 500 to lOOOppm, respectively (ROSLYCKY 1985). I n the presence of 1 mM paraquat, paraquat-tolerant cells of Saccharomyces cerevisiae developed at normal growth rate (HANSSON and HAGGSTROM 1986).As there is only limited information about the influence of paraquat on N,-fixing free-living microorganisms (SZEGI et al. 1974, JAGNOW et al. 1979, the effects of Gramoxone and paraquat on growth and respiration of Azotobacter vilaelandii were studied. Materials and methodsOrganism: Azotobacter vinelandii (DSM No. 87) was obtained from the German Collection of Microorganisms. The stock culture was maintained on nitrogen-free medium.Conditions of cell cultivation : Cultures were grown either in nitrogen-free medium (NF-medium) or in nutrient broth glucose medium (NBG-medium). NF-medium was prepared as previously described (GADKARI 1987). NBG-medium was composed of nutrient broth (MERCK, No. 5443), 8.0 g; glucose, 10.0 g; tap water, 1000 ml. The pH of both media was adjusted to 6.8. For batch 31 J.

STUDIES ON THE EFFECTS OF THE HERBICIDE SIMAZINE ON MICROFLORA OF FOUR AGRICULTURAL SOILS—Short Communication

“…In many cases, studies of pesticides on soil microflora have been performed by measuring microbial activities such as CO 2 evolution, ammonification, or denitrification [3]. Studies on the effects of pesticides on quantitative changes in microbial composition are limited [4,5]; studies on qualitative changes in broad microbial groups (bacteria, fungi, etc.) in response to applications of pesticides are even more limited [6].…”