3.6. Phytoxicity determination of biosurfactant
Germination test has been employed to measure the phytotoxicity
due to its low execution cost. The test used seed germination
and root elongation of selected vegetable species as a bioindicator
of phytotoxicity of the biosurfactant. A series of experiments was
conducted to assess the level of toxicity of the biosurfactant
against T. aestivum, R. sativus, V. radiate, and B. napus. 100% germination
of the seeds was obtained for the biosurfactant. V. radiate
(185) has the highest growth index (GI) followed by T. aestivum
(158), B. napus (132), and R. sativus (102). A GI of 80% has been used
as a bioindicator to confirm the absence of phytotoxicity of the biosurfactant
[37]. Our results confirm that the biosurfactant from
strain USTBa does not pose any inhibitory effect on seed germination
and root elongation. Interestingly, leaves and secondary root
growth were observed in almost all tested vegetable species. Furthermore,
the USTBa biosurfactant exhibits excellent antibiotic
activity against Gram positive and Gram negative bacteria
(Fig. S3), demonstrating its prospective use in biomedical
applications.