Estudo químico de Xanthomonas citri subsp. citri e sua influência no perfil químico de Citrus sinensis

Abstract

Citrus canker, caused by the bacteria Xanthomonas axonopodis pv. citri (Xac), is a disease that causes serious problems to the global citrus industry, especially to orange(Citrus sinensis). In this regard, this thesis describes the development of new methodologies for the diagnosis of citrus canker by volatile biomarkers or macromolecules produced by the C. sinensis-Xac association, as well, performed the chemical study of the wild strain of bacteria Xac searching to isolate and/or identify chemical compounds that may be associated to pathogenicity. The methods for diagnosis of citrus canker involved: dynamic headspace-GC-MS, HS-SPME/GC-MS and MALDI-TOF/MS. The main volatile biomarker identified by dynamic headspace-GC-MS was isoamyl benzoate and by HS-SPME/GC-MS aromatic compounds (benzaldehyde, phenyl methanol, methyl benzoate, 2-phenyl ethanol, benzyl acetate and ethyl benzoate) when N2 was used in the sample preparation, while without N2, benzothiazole and 2-ethylhexyl benzoate were the main biomarkers. The MALDI-TOF/MS technique was effective to differentiate statistically macromolecules produced by the healthy leaves of C. sinensis when in comparation to symptomatic leaves of citrus canker. The chemical study of Xac allowed the isolation or identification of 15 substances, some of them acting as signaling molecules in other bacteria with genomic similarity. Among the substances are: cyclo (Pro-Leu), cyclo (Pro-Val) and two diastereoisomers of cyclo (Pro-Phe), for which the relative configurations were determined, cyclo (Phe-Phe), quinolin-4-carboxaldehyde, fatty acid amides (octadecanamide, cis-9-octadecenamide, cis-13-docosenamide) and cis-11-methyl-2-dodecenoic acid (signaling molecule in X. campestris pv. campestris). According to several studies in literature, some of these compounds are involved in cell communication of some microorganisms or can be phytoxins released by the bacteria into the plant.