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.