Isolasi Dan Karakterisasi Bacillus sp. Indigenus Penghasil Asam Indol Asetat Asal Tanah Rizosfer

TIKA WIDAYANTI. Isolation and Characterization of Bacillus sp. Indigenous Producing Indole Acetic Acid from Rhizosphere Soils. Supervised by ARIS TRI WAHYUDI and NISA RACHMANIA MUBARIK. Bacteria belonging to genus Bacillus as plant growth promoting bacteria (PGPB), had been isolated from soil’s rhizosphere of eleven places in Java. Partial characterization shows the bacteria had rod-shaped and Gram positive, endospore structures, and generally positive catalases, except HI-9, SI-2, and PI-8 were negative catalases. These isolates were analysed for indole acetic acid (IAA) production which were assayed colorimetrically using Salkowski’s reagent. IAA production assay showed that 61 from 63 isolates produced IAA, in which HI-2 and TG-1 had the highest concentration of IAA. These isolates produced 67.2 ppm IAA in media supplemented with 0.5 mM L-tryptophan, whereas 47.6 and 38.9 ppm each for HI-2 and TG-1 in media without Ltryptophan. Growth and IAA determination curve were made by using HI-2 as a model. The result showed that IAA production parallel with bacterial growth. IAA concentration in media supplemented with L-tryptophan higher than in media without L-tryptophan. IAA was produced significantly at 8 hour at the end of logaritmic phase, and its concentration increased in the stationer phase. This condition indicated that IAA is secondary metabolite compound of these bacteria. Twelve isolates that produced the highest level of IAA were tested qualitatively in ability for solubilizing inorganic phosphate by plating the bacteria in Pikovskaya’s medium. The highest ability to solubilize P was produced by isolate DM-4 with 55.6 of phosphate solubilization index. The ability to promote the growth of soybean seeds germination of HI-2 and BY-1 were tested. The result of seeds germination promotion test suggested that the effect of IAA-producing bacteria significantly were not different compared with the control regarding to the germination of stem elongation, but its influenced significantly toward the lateral roots proliferation and primary roots elongation. The number of lateral roots branch treated with IAA producing-bacteria higher than that the control. In contrary, the elongation of primary roots was inhibited by the bacteria inoculated. ISOLASI DAN KARAKTERISASI Bacillus sp. INDIGENUS PENGHASIL ASAM INDOL ASETAT ASAL TANAH RIZOSFER