Production des biosurfactants par les microorganismes et leurs applications

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Résumé (Français et/ou Anglais) : The majority of commercially available surfactants are made from petroleum and presents a major risk to the environment and by their toxicities and biodégradabilités. The biosurfactants are mainly produced by yeast, fungi, bacteria that grow under aerobic conditions in liquid culture media containing a carbon source such as carbohydrates, oils and hydrocarbons. The present work focused on bacteria that are distinguished by their ability to produce biosurfactants. These biomolecules have a preferred value in several areas including the sectors of environment, industry and medical sciences. Thirty-seven strains has been isolated from various sites in particular polluted lands by hydrocarbons (petrol, diesel, oil) and waste from olive oil mill. After preliminary screening, eight strains present a haemolytic activity on blood agar, reflecting their ability to produce biosurfactants. In the second screening performed by "Drop Collapsing", "Oil Displacement" tests, measurement of emulsification index and surface tension, three strains showed a high production potential of these biomolecules. Following the results of macroscopic, microscopic and biochemical identification, these strains affiliated to the species Pseudomonas aeruginosa, Bacillus subtilis, and Bacillus cereus. The study of the parameters influencing the production of biosurfactants was carried out by fermentation on a mineral salt medium. High rhamnolipids production was observed during the exponential phase with the strain P. aeruginosa NF5 using olive oil (30 g/l) and yeast extract (5 g/l) as carbon and nitrogen sources, and pH 7 with shaking at 150 rpm and a temperature of 30 ° C. Thus, a reduction in surface tension to 3.7 mN/m of the culture medium was observed with B. subtilis ZS1 when using glucose (10 g/l) and ammonium sulfate (0.1 g/l) as carbon and nitrogen sources.
Doctorat en Sciences