INTERACTIONS BETWEEN 2,4-DB AND ROOT-NODULE BACTERIA OF LOTUS CORNICULATUS

Growth of Lotus nodule bacteria (Strain LC 296) was temporarily suppressed in a yeast-extract mineral-salts medium containing 2,4-DB at 50 and 100 μg/ml. However, the 2,4-DB concentration needed to completely suppress the growth of the bacteria appeared to be above 500 μg/ml. When added during the logarithmic phase of growth 2,4-DB at 50 and 100 μg/ml did not inhibit the growth of the cells, so that the growth-inhibiting effect of the herbicide apparently was directed primarily against lag phase cells. Pre-incubation of rhizobia in a medium containing 2,4-DB at concentrations up to 10 μg/ml did not affect the capacity of the bacteria to effectively nodulate their host plant. Attempts to induce the rhizobia to utilize 2,4-DB as a sole carbon source failed. Nevertheless, when the Lotus nodule bacteria (LC 296) were grown in a medium containing 2,4-DB-1-C14, C14O2 was released. Similar results were obtained with other strains of the Lotus rhizobia and other species of Rhizobium. C14O2 evolution was also demonstrated when radioactive 2,4-DB was added to both intact (excised) and crushed trefoil nodules. The results indicate that the nodule bacteria are capable of degrading 2,4-DB; although the mechanism is still obscure it does not appear to be via cleavage of the ether link. © 1969 Martinus Nijhoff.