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Microbial Rhamnolipids as Environmentally Friendly Biopesticides: Congener Composition Produced, Adsorption in Soil, and Effects on Phytophthora sojae

Soltani Dashtbozorg, Soroosh
http://rave.ohiolink.edu/etdc/view?acc_num=akron1438175115

Abstract Details

2015, Doctor of Philosophy, University of Akron, Chemical Engineering.
ABSTRACT Production of microbial biosurfactants as an alternative to synthetic surfactants has attracted much attention during the last decades. Many types of biosurfactants have been recognized. Rhamnolipids are among the most promising biosurfactants. It has a wide range of applications in bioremediation, antimicrobial, anti-biofouling, agriculture and pharmaceutical industries. A Gram-negative bacterium known as pseudomonas aeruginosa is the most effective rhamnolipid producer. Use of rhamnolipids as potential biopestcides has been considered. However, the interaction of rhamnolipids with soil, an important factor for field applications, has not been studied in details. In this work, the effectiveness of rhamnolipids in controlling phytophthora sojae was studied. P. sojae is a plant pathogen, which causes severe damage to crops and causes enormous economic loss worldwide. P. sojae specifically attacks soybean plant. The long-term goal of this research is controlling the p. sojae to improve the soybean production. Three aspects were examined in this project. In this phase, both mycelia and zoospores of p. sojae, two forms during its lifecycle, were considered. Results showed that rhamnolipids are very effective against the zoospores, causing lysis in less than a minute. In addition, the efficiency of different rhamnolipid structures was studied separately. The rhamnolipid adsorption on soil was studied. The primary objective of this phase was to determine the rhamnolipid-soil interaction for the future field studies. Rhamnolipids are pH-sensitive molecules and, depending on the soil pH, the adsorption phenomena might be different. In this study, the effects of soil pH, rhamnolipid congener structure, and concentration were examined. Adsorptive partitioning of different rhamnolipids were obtained at pH 6.5 and 4.5. Moreover, the adsorption isotherm at pH 6.5 and 4.5 were obtained. The adsorption isotherm at pH 6.5 showed a multistage profile over a broad range of rhamnolipid concentration. The less hydrophilic congeners adsorbed more preferentially. Adsorptive selectivity of congeners was reduced with increasing the bulk concentration. Isotherms and changes in congener selectivity were interpreted with aggregate formation in solutions and on soil surface. Cost estimate was made with the adsorption results to supported the economic feasibility of applying rhamnolipids as an antizoosporic biopesticide in soil. In addition, rhamnolipid production and purification was conducted to supply the sufficient rhamnolipid for different aspects of the project. In this phase, several fermentations were performed to produce the rhamnolipid. In addition to providing The rhamnolipid, effect of different carbon source on final product composition was evaluated. Produced rhamnolipid has different composition which is affected by different factors such as carbon sources and feeding strategies. The objective of this phase was to understand how rhamnolipid composition might be altered for producing rhamnolipids more effective in controlling the plant pathogen. High-pressure liquid chromatography coupled with mass spectroscopy techniques was used to identify structures of different rhamnolipid congeners produced. Evaporating light scattering detecting method was used for rhamnolipid quantification. Eight rhamnolipid structures were detected. All had two joined ß-hydroxyl fatty acid residues as the lipid moiety, which was linked to a sugar moiety of either one or two rhamnose residues. Results showed that the dominant rhamnolipids were always those with two ß-hydroxydecanoic acids (C10C10). The abundance of rhamnolipids with longer fatty acid chains such as C10C12 was comparatively higher in the mixtures obtained with oleic acid or soybean oil as the fermentation carbon source. Rhamnolipids with the shorter fatty acid chains such as C8C10 were more seen in the fermentation with glycerol as the carbon source.
Lu-Kwang Ju, Dr. (Advisor)
Steven Chuang, Dr. (Committee Member)
Gang Cheng, Dr. (Committee Member)
Christopher Miller, Dr. (Committee Member)
John Senko, Dr. (Committee Member)
163 p.
Chemical Engineering
Rhamnolipid; Biopesticide; Adsorption; Phytophthora sojae; fermentation; purification; Pseudomonas aeruginosa; Mass Spectroscopy; Chromatography

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Citations

  • Soltani Dashtbozorg, S. (2015). Microbial Rhamnolipids as Environmentally Friendly Biopesticides: Congener Composition Produced, Adsorption in Soil, and Effects on Phytophthora sojae [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1438175115

    APA Style (7th edition)

  • Soltani Dashtbozorg, Soroosh. Microbial Rhamnolipids as Environmentally Friendly Biopesticides: Congener Composition Produced, Adsorption in Soil, and Effects on Phytophthora sojae. 2015. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1438175115.

    MLA Style (8th edition)

  • Soltani Dashtbozorg, Soroosh. "Microbial Rhamnolipids as Environmentally Friendly Biopesticides: Congener Composition Produced, Adsorption in Soil, and Effects on Phytophthora sojae." Doctoral dissertation, University of Akron, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1438175115

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.