Natural compounds able to inhibit cell division in Xanthomonas citri subsp. citri

Abstract

The bacterium Xanthomonas citri subsp. citri (Xcc) is the causal agent of citrus canker, a severe disease that affects citrus plants worldwide. An effective control for the citrus canker is not available yet, and the elimination of infected plants continues to be the recommended practice to control the disease. Although the genome sequence of Xcc has been available for almost a decade, little is known about its biology, and most importantly, there is a complete lack in the literature of studies concerning chromosome segregation and cell division of this plant pathogen. These essential processes are normally carried out in bacteria with the help of protein factors sharing very low homology to functional analogs encoded by more derived eukaryotes, hence, chromosome segregation and the cell division machine are recognized as excellent targets for drug development aimed to bacterial disease control. The objective of the present proposal is to identify natural chemicals able to block cell division in Xcc, following by the characterization of such compounds to evaluate their potential use as antimicrobial agents in the field. Chemicals to be tested will be obtained from a collection of plant extracts typical of the Brazilian flora (held at the Institute of Chemistry, UNESP, Araraquara). Only samples already in the form of purified fractions and/or isolated chemicals will be evaluated. In addition, compounds isolated from Xcc hosts that exhibit some degree of resistance to bacterial infection will be studied. The ability of such chemicals to inhibit cell division will be measured in three steps: first, we intend to separate chemicals able to promote visible alterations of cell morphology, when supplied in culture, to be detected under microscope analyses (e.g. filamentation); second, those compounds identified in the first screening will be re-evaluated so to identify any of them able to disrupt septum organization (we have recently developed a mutant of Xcc expressing a GFP-fusion of a protein constituent of the division septum that enable us to observe septum development in vivo using fluorescent microscopy), and third, we shall characterize genetically and/or biochemically the points of action of cell division inhibitors into Xcc in order to tentatively use such data to develop new methods of control for the citrus canker. (AU)