Effect of beta-indolylacetic acid on the growth and the auxin catabolism of Lactobacillus bulgaricus.

Abstract

ENDOGENOUS auxin may act in the regulation of bacteria growth1, although its precise role is as yet poorly understood2. For example, Lactobacillus can grow without auxin3; however, in the presence of β-indolylacetic acid (IAA), its multiplication can be strongly modified4. In the following experiments, Lactobacillus bulgaricus (strain 1416, Liebefeld Institute of Dairy Research) was used and the medium was Lactobacillus broth AOAC (Difco). For each series of growth measurements, tubes containing 10 ml. of medium (with IAA) were inoculated with 1 ml. of a young culture of Lactobacillus (standard: 0.416 ml. of protein). The cultures were incubated at 37° C and the growth was measured after 6 and 12 h. Two methods were found most satisfactory for the growth determinations. The first is related to a direct measurement of the increase in turbidity5, using the ‘Lumetron 402 E’ with a double photoelectric cell. The second is based on the analysis of the total protein content6. The protein was determined by precipitating the washed bacteria cells with trichloroacetic acid. Comparing the turbidity with a series of standard solutions of serum-albumin, precipitated with trichloroacetic acid, a good correlation was found. Further examination of this technique will be discussed elsewhere.