The role of the com system in biofilm development mediated by the type IV pilus in Xanthomonas citri subsp. citri

• Grant number: 18/08822-3
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• Start date: August 10, 2018
• End date: February 09, 2019
• Field of knowledge: Biological Sciences - Biochemistry - Biochemistry of Microorganisms
• Principal Investigator: Shaker Chuck Farah
• Grantee: Shaker Chuck Farah
• Visiting researcher: Ricardo German Dunger
• Visiting researcher institution: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 17/17303-7 - Structure and function of bacterial secretion systems, AP.TEM

Abstract

Xanthomonas citri subsp citri is a bacterial phytopathogen that causes citrus canker disease, one of significant economic importance around the world. X. citri spreads from affected plants to healthy plants mainly through rain and wind and has the ability to survive for long periods on different surfaces usually due to the formation of biofilms. The bacterial biofilm is a highly regulated community of bacteria embedded in a polymer matrix composed of polysaccharides, proteins and extracellular DNA (eDNA) that provide physical support and protection against biotic and abiotic stresses. X. citri has been observed to produce a more robust mature biofilm in host plants than in non-host plants. Furthermore, the type IV pilus (T4P) plays an important role in the formation of biofilms, which highlights its importance in the bacterial life cycle. T4Ps are long, flexible filament located on the bacterial surface involved in a variety of important behaviors including twitching motility, surface adhesion, natural transformation, chemotaxis and biofilm formation. T4P have a complex regulatory system that has not yet been fully elucidated, but in X. citri involves the regulatory proteins PilZ and FimX as well as the hexameric ATPase PilB. In some bacteria, T4P carry out the additional function of incorporating of eDNA into the cell by a mechanism coupled to the natural competence (com) system. In addition to the main components involved in T4P biogenesis and regulation, the X. citri genome also carries the com genes predicted to be involved in the internalization of exogenous DNA: comEA (XAC2951), comEC (XAC2084) and comF (XAC0389). The main objective of this project is to investigate the interplay of the T4P, the com system and eDNA in regulation of X. citri motility and the formation of biofilms. We will study the mechanism of absorption of eDNA by the X. citri cells, the participation of the T4P in this process, and generate a map of interactions between the T4P and com system components. Progress in this area will provide information of great interest for the understanding the phenomenon of T4P- and com-mediated eDNA uptake and signaling in biofilm formation; both mechanisms being involved in infection, horizontal gene transfer and bacterial dissemination and persistence. (AU)