Aquatic toxicity and biodegradability of a surfactant produced by Bacillus subtilis ICA56

ABSTRACT

In this work, the environmental compatibility of a biosurfactant produced by a Bacillus subtilis strain isolated from the soil of a Brazilian mangrove was investigated. The biosurfactant, identified as surfactin, is able to reduce surface tension (ST) to 31.5 ± 0.1 mN m⁻¹ and exhibits a lowcritical micelle concentration (CMC) value (0.015 ± 0.003 g L⁻¹). The highest crude biosurfactant concentration (224.3 ± 1.9 mg L⁻¹) was reached at 72 h of fermentation. Acute toxicity tests, carried out with Daphnia magna, Vibrio fischeri and Selenastrum capricornutum indicated that the toxicity of the biosurfactant is lower than that of its chemically derived counterparts. The results of the biodegradability tests demonstrated that the crude surfactin extract was degraded by both Pseudomonas putida and a mixed population from a sewage-treatment plant, in both cases the biodegradation efficiency being dependent on the initial concentration of the biosurfactant. Finally, as the biodegradation percentages obtained fall within the acceptance limits established by the Organization for Economic Co-operation and Development (Guidelines for Testing of Chemicals, OECD 301E), crude surfactin can be classified as a “readily” biodegradable compound.

KEYWORDS:

• Biosurfactant
• environmental compatibility
• OECD guidelines
• saponin
• surfactin

Funding

The authors acknowledge the financial support of the Brazilian and Spanish Governments through project PHB2012-0277-PC, and of the Andalusian Regional Government through project P10-TEP-6550. D.W.F.O. They also acknowledge CNPq (Brazil) for the award of a scholarship and financial support.