Juan Carlos Caicedo

By Juan Carlos Caicedo, Sonia Villamizar and Jesus Aparecido Ferro

Xanthomonas citri subsp. citri (Xcc) is the etiological agent of citrus canker, a disease that affects almost all types of citrus crops. Production of Xcc virulence factors is controlled by a gene cluster rpf, which encodes elements of a cell-cell communication system called quorum sensing (QS). Perturbation of cell-cell signaling systems either by signal degradation or by overproduction significantly reduces symptoms and thereby the severity of the disease. Pathogenicity assays in Citrus sinensis showed that some bacterial species natural inhabitants of citrus phyllosphera have the strong ability to disturb QS system mediated by diffusible signal factor (DSF) molecule in Xcc and to reduce disease severity. The lessening of symptoms was associated with alteration in bacterial attachment and biofilm formation. These factors are known to contribute to Xcc virulence in the early stages of disease. The aim of this chapter is to review QS system in Xcc, the virulence factors affected by QS disturbing, as well as the main secretion systems that participate actively in virulence and its effect on the symptomatology of citrus canker.

Part of the book: Citrus Pathology

By Sonia Villamizar and Juan Carlos Caicedo

Citrus canker is a disease that affects the major types of commercial citrus crops. Xanthomonas citri subsp. citri, the etiological agent, reaches to mesophyll tissue through the stomata and afterward induces cell hyperplasia. Disease management has been based on both tree eradication and copper spray treatment. Overuse of copper for control of bacterial citrus canker has led to the development and prevalence of copper-resistant strains of Xcc. Several genera of both soil- and plant-associated bacteria became powerful tools in sustainable agriculture for control of Xcc and reduction of citrus canker disease severity. In this chapter we present bacteria able to interfere with quorum sensing as well to display antibacterial activity against Xcc by production of secondary metabolite. These bacteria may represent a highly valuable tool in the process of biological control and offer an alternative to the traditional copper treatment currently used for the treatment of citrus canker disease, with significant environmental, economic, and health implications worldwide.

Part of the book: Plant Diseases

By Juan Carlos Caicedo and Sonia Villamizar

The infectious process of plant by bacteria is not a simple, isolated and fortuitous event. Instead, it requires a vast collection of molecular and cell singularities present in bacteria in order to reach target tissues and ensure successful cell thriving. The bacterium Xanthomonas citri ssp. citri is the etiological agent of citrus canker, this disease affects almost all types of commercial citrus crops. In this chapter we review the main structural and functional bacterial features at phenotypical and genotypical level that are responsible for the symptomatology and disease spread in a susceptible host. Biological features such as: bacterial attachment, antagonism, effector production, quorum sensing regulation and genetic plasticity are the main topics of this review.

Part of the book: Citrus

By Juan Carlos Caicedo and Sonia Villamizar

A group of particular acidophiles microorganisms (bacteria and archaea) known as chemolithoautotrophs are capable of using minerals as fuel. Its oxidation generates electrons to obtain energy and carbon that is obtained by fixing CO2 from the air. During this aerobic mineral oxidation, metals are solubilized or biodegraded. Metal bioleaching usually is used in biomining and urban biomining approaches to recovery metals such as copper, gold and zinc. Several species of bacterial genus Acidithiobacillus display a great bioleaching activity. Bacterial attachment and biofilm formation are the initial requirements to begin a successful bioleaching process. Biofilm formation in Acidithiobacillus bacteria is strongly regulated by cell to cell communication system called Quorum Sensing. The goal of this chapter is to review the Quorum Sensing system mediated by the autoinducer N-acyl- homoserine-lactones in the Bacterium Acidiothiobacillus ferroxidans, in order to enhance and to boost the bioleaching technologies based in the use of this bacterium. The main applications of the cell-to-cell communication system concepts in A. ferrooxidans are reviewed in this chapter. It is that the addition of synthetic autoinducers molecules, which act as agonist of quorum sensing system, especially those with long acyl chains, both as single molecules (C12-AHL, 3-hydroxy-C12-AHL, C14-AHL, and 3-hydroxy-C14-AHL) or as a mixture (C14-AHL/3- hydroxy-C14-AHL/3-oxo-C14-AHL) increased the adhesion to sulfur and pyrite and enhance the metal bioleaching in urban biomining approaches.

Part of the book: Acidophiles

By Juan Carlos Caicedo and Sonia Villamizar

Cell-to-cell communication system quorum sensing (QS) denotes the ability of bacteria to track the population density, in order to coordinate its phenotypic traits to successfully establish and thrive in new ecological niches. Different citrus phytopathogenic bacteria such as: Xanthomonas citri spp. citri, Xillela fastidiosa and Pseudomonas syringae pv. syringae regulate several pathogenicity factors through well-established quorum sensing DSF (Diffusible Signal Factor) and AHL (AcylHomoserine Lactone) pathways. The goal of this chapter is to review exophytic and endophytic bacteria able to disrupt quorum sensing communication system in these bacteria in order to reduce the symptomatology of citrus canker, citrus variegated chlorosis and citrus blast. The quorum quenching of phytopathogen bacteria could afford new tools for disease control, thus reducing the overuse of antimicrobial drug and decrease its environmental accumulation, thus relieving the selection pressure of resistant bacterial populations.

Part of the book: Citrus Research