Potential of Enterococcus faecium LM5.2 for lipopeptide biosurfactant production and its effect on the growth of maize (Zea mays L.).

This study characterized the lipopeptide biosurfactants produced by lactic acid bacteria isolated from milk and milk products, in addition to their effect on maize plant growth. The oil displacement test was performed as a primary screening method to select the BS producing bacteria. The strain LM5.2 had the maximum emulsification index of 45.1 ± 3, reduced the surface tension to 32.98 ± 0.23% among all the isolates, and efficiently produced 945.26 ± 4.62 mg/l of biosurfactants within 48 h in MRS broth under the optimum conditions. The isolate LM5.2 was identified using physiochemical tests and 16S rRNA gene sequencing as E. faecium. The biosurfactant was purified by TLC and identified as lipopeptide-like iturins and surfactins based on Rf values. Mass spectroscopy, NMR, and FTIR analysis also confirmed the biosurfactant's identity as the derivatives of iturin and surfactin. In vitro biosurfactant application significantly enhanced seedling growth at an optimal concentration of 450 µg/ml. Plant treatment (pot experiment) with E. faecium LM5.2 significantly promoted Zea mays growth compared to the control. To the best of our knowledge, this is the first report of lipopeptide biosurfactant production by E. faecium. Moreover, the study also showed that the biosurfactant and biosurfactant-producing E. faecium LM5.2 could be an eco-friendly plant growth-promoting agent.

Influence of biosurfactant producing Bacillus tequilensis LK5.4 isolate of kinema, a fermented soybean, on seed germination and growth of maize (Zea mays L.).

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.