Abstract
Biosurfactants, a wide group of compounds produced by different microorganisms, generally have less toxicity and are more biodegradable than synthetic surfactants. Biosurfactant-producing bacteria can be found in contaminated environments, such as soils receiving pesticide applications constantly, or in pesticides treatment systems where microorganisms are adapted to biodegrading pesticides. Five pesticide-tolerant bacteria previously isolated from a pesticide biopurification system were evaluated as biosurfactant-producers. Pseudomonas rhodesiae C4, Rhodococcus jialingiae C8 and Pseudomonas marginalis C9 strains were positive in qualitative tests. Biosurfactant production by these strains using Bushnell-Haas medium with olive oil at 2% (w/v) was evaluated as emulsification index, oil displacement, droplet collapse test and surface tension. After 144 h, these strains showed a similar emulsification index of >55%. The two Pseudomonas (C4 and C9) strains showed lower superficial tension compared with Rhodococcus strain (C8)—34.47, 37.44 and 47.55 mN/m for strains C4, C9 and C8, respectively. The chemical characterization of the biosurfactants revealed the presence of glycolipids in P. rhodesiae (C4) and glycopeptides in P. marginalis (C9). The degradation of chlorpyrifos increased from 39.2% to 51.6% when biosurfactants produced by P.rhodesiae (C4) were added (10%) with respect to the control. Therefore, biopurification systems are a relevant source of biosurfactant-producing bacteria with environmental biotechnology applications.
Highlights
Biosurfactants are a broad group of diverse compounds produced by various microorganisms that have low toxicity, great biodegradability and environmental compatibility, enabling a wide range of industrial applications [1,2,3]
Desorption or solubilization of hydrophobic pollutants tightly bound to soil particles can be accelerated by biosurfactants, which are very crucial for bioremediation processes, especially enhancing the degradation of pesticides when they are accumulated in agricultural soils [6,7,8]
The bacteria A. deleyi strain C7 and A. kerstersii strain C10 were negative with respect to the cetyltrimethylammonium bromide (CTAB) analysis and C10 strain did not produce drop-collapse or olive oil displacement
Summary
Biosurfactants are a broad group of diverse compounds produced by various microorganisms that have low toxicity, great biodegradability and environmental compatibility, enabling a wide range of industrial applications [1,2,3]. These compounds each have a hydrophilic region formed by amino acids—peptides (anions or cations), or mono and polysaccharides—in addition to a hydrophobic region consisting of saturated and unsaturated fatty acids [4]. The efficacy of biosurfactants is due to the solubilization capacity of the hydrophobic pesticides, which reduces the surface tension and interfacial bonding between liquids, solids and gases. Diverse microorganisms have been reported to be biosurfactant producers [5,6,7,8]
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