While the results ofmass spectroscopy revealed that some strains of
B. subtilis give a high value on 9th d in their culture medium which is
14.02 μMoL/50 mL (Fig. 4). According to Srinivasan et al. [27] the
different strains of Bacillus showed significant difference in the
amount of IAA varying from 0.40 to 4.88 μg/mL, for the quantification
of IAA they used thin-layer chromatography, high-performance liquid
chromatography, gas chromatography, mass spectrometry, and the
Avena Coleoptile bioassay. In our results the greater amount of IAA
produced by these endophytes in 20 mL LB broth is because of
L-tryptophan which was incubated at 30 ± 2°C in shaking incubator
at 200 rpm for one week. Auxin production by Bacillus spp. in L-broth
medium supplemented with 1000 μg mL-1 L-tryptophan ranges from
0.60 to 3.0 μg IAA Ml-1 as revealed by gas chromatography and mass
spectrometric (GC-MS) analysis [1]. While the results of Idris et al. [5]
also showed that IAA secretion can be increased up to fivefold by
providing 5 mM of tryptophan in the culture medium