Cell secreted molecules analysis by electroanalytical techniques

Author(s)

André Guimarães de Oliveira

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2012-12-21

Examining board members

Lucio Angnes; Mauro Bertotti; Alexandre Zatkovskis Carvalho

• Advisor: Lucio Angnes

Abstract

Cis-11-methyl-2-dodecenoic acid, also known as DSF (autoinducer of the Quorum Sensing system used by the bacteria Xanthomonas axonopodis pv. citri) was explored as a study model for the cell secreted molecules analysis by electroanalytical techniques. Cell cultures from three different cell lines of the bacteria Xanthomonas axonopodis pv. citri were used for this study. A wild type (WT), which produced DSF in naturally observed quantities and two genetically modified ones. One of the lines (ΔC) had a genetic modification that resulted in an elevated production of DSF, and the other (ΔF) had a modification that stopped DSF production. Main analytical techniques used were: cyclic voltammetry, capillary electrophoresis and liquid chromatography (with UV-Vis detection and coupled with mass spectrometry), this last one was used with comparison purposes. Liquid-liquid extractions with organic solvents were realized as sample pre-treatment steps aiming the reduction of interfering species and analyte pre-concentration. Three main methodologies were adopted. One based in the differentiation of cell cultures analyzing or the cell culture supernatants or the resulting extracts from the pre-treatment steps. The main focus was the identification of a differential signal between the cultures that corresponded to the DSF quantities, in other words, null for the ΔF line, high intensity for the ΔC line and a an intermediary intensity for the WT line. The second methodology was based in experiments with a model molecule to obtain some data such as physical-chemistry parameters. Lauric acid (dodecanoic acid) was chosen for its structural similarity and easily acquisition. Calibration curves and similar structure molecules separation experiments were realized using capillary electrophoresis. Third and last methodology was developed using standard cis-11-methyl-2-dodecenoic acid (DSF). Calibration curves were obtained with the isolated standard showing great linearities using both capillary electrophoresis and liquid chromatography with UV-Vis detection. Experiments of standard addiction to the samples were also realized. Experiments using the samples did not show the expected results. Problems found were mainly associated with high amount of interfering species and low analyte concentration at the cultures, extraction methods used were not enough to solve this. The failures with the cyclic voltammetric techniques were associated to electrode poisoning, due to the high amount of organic compounds present at the sample, and DSF lack of electroactivity. Difficulties found with capillary electrophoresis were associated with the samples high ionic strength, presence of interfering species and low analyte concentration. Even liquid chromatography coupled with mass spectrometry experiments didn\'t attended the expectations. Making it difficult to elucidate the problems and not allowing the development of a methodology that could achieve the proposed objectives. (AU)

• FAPESP's process: 10/04540-1 - ANALYSIS OF MOLECULES RELEASED FROM LIVING CELLS USING ELETROANALYTICAL TECHNIQUES AND MINIATURIZED SYSTEMS
• Grantee: André Guimarães de Oliveira
• Support Opportunities: Scholarships in Brazil - Master