Differential Effects of 2,4-D on Aerobic, Anaerobic, and Facultative Anaerobic Microorganisms

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Abstract
Organisms were divided into 3 groups depending on O2 requirement. Solns. of 2,4-D were diluted to concns. of 5, 1; 0.1, 0.01, and 0.001% and autoclaved. Varying amts. were measured into tubes of agars used to give a final vol. of 5 ml. of agar-2,4-D soln./tube. The final concns. of 2,4-D were 2, 1, 0.2, 0.02, 0.002, and 0.0002%/5 ml. of diluent. The number of grams of 2,4-D/5 ml. of agar were 0.1, 0.5, 0.25, 0.001, 0.0001, and 0.00001. The organisms were subcultured on agar slants, washed with 0.85% saline, and streaked on plates. Each organism was tested against the 2,4-D concns. and on control plates. The aerobes were left at room temp., and the facultative anaerobes were incubated. The amt. of growth was read at 24-, 48-, and 72-hr. intervals. All anaerobes were inhibited by 2,4-D, particularly in the higher concns. There was no inhibition with the facultative anaerobes, and in the lower concns. there was an increase in growth over that of the controls. The response of Clostrid-ium tetani resembled that of the facultative anaerobes in that there was an increase in growth with the lower concns. and no inhibition at higher concns.