Physicochemical characterization of tensio-active produced by Geobacillus stearothermophilus isolated from petroleum-contaminated soil

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Abstract

Biosurfactants are surface-active agents of microbial origin, and have a property of lowering the interfacial tension between two liquids. They act on the interface and are amphiphathic molecules; in with both hydrophilic and hydrophobic portions are present in the same molecule. However, the economics of producing biosurfactant has limited its commercial applications, and the costs can be reduced using cheap substrates or industrial waste. The present study showed the biosurfactant production using corn steep liquor and palm oil as carbon and nitrogen sources for reduction the costs of production. The biosurfactant production by Geobacillus stearothermophilus UCP 986 was carried out using optimized culture medium constituted by palm oil (7.5%) and corn steep liquor (4.5%) using Bioflo fermentor, at temperature of 45 °C, during 32 h and agitation of 300 rpm. The biosurfactant showed a reduction of the water surface tension of 72–31 mN/m and interfacial tension of 0.3 mN/m. The biosurfactant was obtained from the net metabolic liquid by acetone precipitation corresponding to the yield of 2.3 g/L. The isolate biosurfactant showed a CMC of 2.5% and non-ionic profile. The best emulsification index (E24) obtained was 87% using motor oil burned. The biosurfactant solution (2.5%) used in oil spreading test increases the viscosity of engine burning oil of 149.2% and 138.2% to vegetable fat post-frying, respectively. The gas chromatography–mass spectrometer indicated at 29.52 min a molecular weight of 207 Da and eight peaks by FT-IR identified the chemical structure of the biosurfactant produced by G. stearothermophilus.

Graphical abstract

Contour curves demonstrated the optimization biosurfactant production by Geobacillus stearothermophilus using corn steep liquor of (4.5%) and oil palm (7.5%) medium. The statistical methods were successfully used to optimize a medium and their interactions of the intermediate levels to reduce the surface tension. From the data we observed that the biosurfactant has an excellent ability to reduce the surface tension and lower CMC which characterize its low cost and good surfactant ability.

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Highlights

► Biosurfactant a greener bioprocess. ► The molecule reduced the surface tension. ► We report the detergency phenomenon.

Introduction

The biosurfactants are amphiphilic molecules consisting of hydrophobic and hydrophilic groups produced by bacteria, yeasts and filamentous fungi, and acting on the interfaces between fluid phases with different degrees of polarity (oil/water). The biosurfactants find application in an extremely wide variety of industrial processes involving reduction of the interfacial and surface tensions, emulsification activity, foaming, detergency, wetting, dispersing or solubilization, and de-emulsification [1], [2], [3], [4], [5].

Nowadays, biosurfactants are used in cosmetic, pharmaceutical, chemical, food, agriculture, cleansers, enhanced oil recovery industries, and in bioremediation of oil contaminated sites, considering the advantages and characteristics as thermostability, tolerance to ionic strength, biodegradability and low toxicity [6], [7], [8], [9], [10], [11], [12], [13].

The biosurfactant type and the amount produced depend primarily on the microorganism and influence of carbon and nitrogen sources, nutrient concentration, agitation, aeration and other factors. The use of agro-industrial waste is described as substrates considering the high amounts of carbohydrates or lipids, and those have been used for biosurfactant production [14], [15], [16], [17]. The aim of this investigation was to produce the tensio-active agent by Geobacillus stearothermophilus using agro-industrial substrates, such as carbon (palm oil) and nitrogen (corn steep liquor) sources using bioreactor, and isolation of biosurfactant and physical–chemical characterization, considering the importance of the studies with bioprocess.

Section snippets

Microorganism and culture conditions

G. stearothermophilus strain (UCP 0986) was isolated from the soil contaminated with petroleum of the Port of Recife-Pernambuco, Brazil, deposited at the Culture Collection of the Nucleus of Research in Environmental Sciences (NPCIAMB), Catholic University of Pernambuco, and registered in World Federation Culture for Collection (WFCC). The strain is maintained in Nutrient Agar at 5 °C. The growth was carried out in Luria–Bertani solid medium [10 g/L tryptone, 5 g/L yeast extract, 10 g/L NaCl, and 15

Production of biosurfactant by G. stearothermophilus in bioreactor

The production of biosurfactant by G. stearothermophilus showed excellent reduction of water surface tension 72 mN/m to 31 mN/m, as well the interface tension of 0.3 mN/m in the production medium consisted by 4.5% of corn steep liquor and 7.5% of palm oil. The agitation was the one important parameter (300 rpm), remaining at the same temperature and time of batch submerse fermentation. The biosurfactant produced by G. stearothermophilus yield was 2.3 g/L, two times more than batch fermentation, and

Conclusion

This study for the first time had shown a bioprocess using corn steep liquor and palm oil as medium for non-ionic biosurfactant production by G. stearothermophilus UCP 0986. The biosurfactant is capable of reducing the surface and interfacial tensions of water to significant lower value, and having excellent emulsifier and dispersion properties. These properties are of great importance in bioremediation of hydrophobic molecules, which shows promising application.

Acknowledgements

This work was financially supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

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