Isolation and Characterization of Indole Acetic Acid Producing Halophilic Bacteria from Salt Affected Soil of Rice–Shrimp Farming System in the Mekong Delta, Vietnam

The main aim of this study was to deal with isolation, characterization and identification IAA producing bacteria from paddy rice cultivated soil samples collected in rice–shrimp farming system in salt affected areas of the Mekong Delta of Vietnam. Fifteen soil samples collected from the rice crop in the rice-shrimp farming system of 5 different provinces within the Mekong Delta, Vietnam were used to isolate the IAA producing bacteria. NBRIP media was used to isolate the potentially IAA producing bacteria. Result showed that 213 isolates were obtained from the fifteen different soil samples. Out of 45 indole acetic acid producing isolates, ten were selected as efficient producers. One out of ten, the isolate ST2-1 was identified as the most promising strain as efficient biofertilizer inoculants to promote plant growth. This strain produced 33.13 mg.L-1 as the highest concentration of IAA after 8 days of incubation. As well, this strain stimulated the growth of rice’s roots and dry biomass after 7 days of experiment with Hoagland medium containing 0.3% NaCl in 100 mL glass tube. This strain produced well IAA production in pH variation range of medium between 5 and 9 and this bacterial strain can resist to salinity of environment up to 3% NaCl. However, this bacterial was highly inhibited by not only 3 commonly used antibiotics: Ampicillin, Chloramphenicol and Steptomycin at recommended rates but also 3 plant pathology fungicides: Thiophanate Methyl, Propineb and Mancozed regarding to IAA production ability. The results of the 16S rRNA gene sequence analysis showed that this IAA producer coded as ST2-1 was genetically identified as species of Bacillus megaterium ST2-9 since 99% of its sequence affiliated with Bacillus megaterium. In conclusion, the study suggests the IAA producing bacteria as efficient biofertilizer inoculants to promote plant growth.