Biosurfactant production by a rhizosphere bacteria Bacillus altitudinis MS16 and its promising emulsification and antifungal activity

Generally, most of the biosurfactant producing microbes are the common inhabitants of hydrocarbon contaminated sites. However, there are a very few literatures that report the existence of biosurfactant producing microbes in rhizosphere soil of plants involved in remediation of pesticide laden agricultural soil and in general welfare of the plants indicating the necessity of further research. A total of twenty three morphologically distinct rhizosphere strains were isolated and were screened for biosurfactant production through preliminary biosurfactant screening assays. Based on the screening results, MS16 was selected as the most efficient and potential biosurfactant producer and was identified as Bacillus altitudinis MS16. Biosurfactant production was indicated by a sharp reduction in the surface tension (ST) of the culture medium from 72.8 to 32.3 +/- 0.1 mN/m after 48 h of incubation with a maximum yield of 3.8 g/L. The biosurfactant exhibited excellent emulsifying activity (E-24) of 95.4% and emulsion stability of 95.8% against crude oil after an incubation period of 28 days with striking stability over a wide range of temperature (20 - 120 degrees C, 30 min each), pH (4 - 12) and salinity (2 - 12% NaCl, w/v). The produced biosurfactant was extracted with ethyl acetate and was subjected to compositional analyses revealing it to be a mixed lipopeptide. Furthermore, the biosurfactant exhibited significant antifungal activity showing 42.8% inhibition against Colletotrichum gloeosporioides followed by 41.2% inhibition against Sclerotinia sclerotiorum. To our knowledge, the study reports for the first time biosurfactant producing ability of a novel rhizosphere bacteria Bacillus altitudinis.