The influence of 2,4‐dichlorophenoxyacetic acid on lactic acid bacteria

Abstract

The effect of 2,4-dichlorophenoxyacetic acid (2,4-D) (4 x 1 0 -5~4 x 10-3~) on the growth and physiological activity of Streptococcus lactis subsp. diacetylactis and Lactobacillus casei has been investigated when cultivated in milk and lactose-peptone media. The concentrations of 2,4-D applied in milk did not cause complete growth inhibition of any of the strains. The degree of inhibition was dependent upon the bacterium species and the herbicide dose. Growth of the tolerant strain-L. casei W-10-was reduced by about 40% (in the presence of 4 x l o -3~ 2,4-D), whereas the the level of lactic acid production remained almost unchanged. Under the sanie conditions, growth of the sensitive strain S. lactissubsp. diacetylactis239 wasreducedby almost 25 times and lactic acid production inhibited by about 40% in comparison with the controls. Cultivation of S. lactis subsp. diacetylactis 239 in lactose-peptone medium with 2 x l o -3~ 2,4-D was characterised by a lengthened lag-phase, lengthened generation time (3 times) and an increased rate of herbicide metabolism. In addition, selective or mutative action of 2,4-D has been shown. Herbicide treatment inhibited the cells of c.f.u. producing the least acid and enhanced the contribution of the active ones. Cells of c.f.u. with activities not found in the control population have also been revealed. Both species of bacteria were capable of metabolism of 2,4-D to 2,4-dichlorophenol.