RESUMO
In this study, the lipopeptide biosurfactant was extracted, purified and characterized from the Bacillus isolate LK5.4 obtained from kinema samples of Sikkim. Plant growth-promoting property of the biosurfactant producing bacterium was also evaluated. Out of fifty-seven isolates, only ten were biosurfactant producer as determined by the oil displacement test. Bacillus isolate LK5.4 showed the maximum emulsification index (52.3 ± 0.02), reduced surface tension up to 40% and produced 754 mgL-1 biosurfactant in the nutrient broth. Based on 16S rRNA gene sequencing, the isolate LK5.4 was identified as B. tequilensis. Biosurfactant was purified by Thin Layer Chromatography (TLC). Evaluation of the chemical characteristics by TLC, Liquid Chromatography-Mass Spectrometry, Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance Spectroscopy identified the biosurfactant as surfactin. The effect of different concentration of biosurfactant in maize seed germination was evaluated under in vitro condition. It showed the fastest growth of seedlings at 300 µg/ml biosurfactant solution. Similar results were shown by the potted plant experiment, where the soil was directly treated with biosurfactant producing bacterium LK5.4. The LK5.4 treated plants showed a mean height of 29.17 ± 0.47 cm and mean leaf length of 18.42 ± 0.17 cm while the mean height and mean length of the leaf were 15.48 ± 0.98 cm and 11.12 ± 0.40 cm respectively in the control plants. The treated plants had higher moisture content (68.48 ± 2.79%) than the control plants (50.53 ± 1.63%), which is because of higher bioadsorption in the treated plants. These results provided indirect evidence of plant growth-promoting property of the biosurfactant.
