Biosurfactant production by Rhodococcus ALDO1 isolated from olive mill wastes

Abstract

Rhodococcus is a genus of Gram-positive bacteria that are widely distributed in soil, water, and plants. They have a versatile metabolism that produces different kinds of compounds like biosurfactants, lipids and carotenoids, and therefore are promising for biotechnological applications. In this work, we aimed to characterize the ability of the strain Rhodococcus ALDO1 isolated from alperujo, a complex residue from the olive oil industry, to produce biosurfactants. Growing was determined by counting the number of cells and by dry weight determination Biosurfactant production was followed by xylose equivalents (μg/ml Xylose Eq.), the perimeter obtained in the oil spreading assay and the emulsification index at 24 h (E24). We found that this strain grew in different media like glucose, oil, and glycerol, and produced a biosurfactant of a glycolipid nature as suggested by FT-IR spectrum. The maximal amount of biosurfactant (18.8 ± 2.0 μg/ml Xylose Eq., perimeter = 4.17 ± 0.17 cm, and E24 = 63.1 ± 4.1 %) was obtained when Rhodococcus ALDO1 grew in the media with oil 3% + glucose 1 %. Glycerol was also a suitable substrate for biosurfactant production (8.3 ± 1.0 μg/ml Xylose Eq., perimeter = 2.84 ± 0.07 cm, and E24 = 35.7 ± 2.9 %). The biosurfactant activity is stable at salt concentrations up to 5 g/L, temperatures up to 60 °C and pHs above 9. The thermal degradation started at 220 °C which suggested that the biosurfactant is suitable for various industrial applications. These results indicated that Rhodococcus ALDO1 is a strain to be considered as a source of biocompounds with possible industrial applications obtained from cheap substrates.