Xylella fastidiosa

A Microbial Biorealm page on the genus Xylella fastidiosa

Classification

Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Xanthomonadales; Xanthomonadaceae

Species

NCBI: Taxonomy

Xylella fastidiosa

Description and significance

Xylella fastidiosa is pathogenic bacterium that infects plants, causing a variety of diseases in over 100 plants species, including grapevine, citrus, almonds, and many other species of economic importance. Among the diseases it causes are Pierce's Disease (PD) in grapevine, citrus variegated chlorosis (CVC) in oranges, and leaf scorch diseases in almond, coffee, and oleander. It was first discovered associated with Pierce's Disease of Southern California grapevines in 1973, and first grown in culture in 1978. It was then identified as the agent that causes CVC in 1993, a disease first noticed in Brazil in 1987. X. fastidiosa exclusively colonizes the xylem, the water-conducting systems of plants, forming biofilms, and is transmitted from plant to plant by xylem-feeding leafhopper insects, including the glassy-winged sharpshooter. It poses a serious agricultural and economic threat, as it is responsible for major crop losses globally, and is included in the Federal government's Agricultural Select Agent list. Because of is public importance as an agricultural threat, genomic studies of different host plant stains have been underway in an attempt to gain insight into virulence factors, and consequently the development of microbiological control and disease management strategies.

Genome structure

The genome sequences of four strains of X. fastidiosa have been sequenced to date: X. fastidiosa 9a5c, X. fastidiosa Ann-1, X. fastidiosa Dixon, and X. fastidiosa Temecula-1. There are 1,579 homologous genes in all four strains, accounting for approximately 76.2% of the genome size. All possess pathogenicity-related genes involved in the colonization of their plant host, including a 7kb conserved gene cluster encoding proteins associated with pili biogenesis, functioning in attachment to the host, as well as genes for the type II secretion system, which is involved in exporting exoenzymes that degrade plant cell walls, allowing them to colonize. X. fastidiosa also possesses a gene whose protein product is an exopolysaccharide similar to the xantham gum produced by Xanthomonas campestris. At least 83 genes are bacteriophage-derived, and include virulence-associated genes.

The genome of X. fastidiosa 9a5c, first isolated in 1992 from infected twigs derived from Valencia oranges from Brazil and the cause of citrus variegated chlorosis in oranges, consists of a circular chromosome that is 2,679,306 base pairs long. It has 2,766 protein-coding regions. It also contains two circular plasmids: pXF1.3, and pXF51. pXF1.3 is 1,286 base pairs long, with 2 protein-coding regions. pXF51 is 51,158 base pairs long, with 64 protein-coding regions. Most of the genes on the pXF51 plasmid aid in metabolism, but it does contain 1 virulence-associated protein.

The genome of X. fastidiosa Ann-1, a strain associated with oleander leaf scorch disease, consists of a linear chromosome that is 5,115,342 base pairs long, with 4,660 protein-coding regions. It has no plasmids.

The genome of X. fastidiosa Dixon, a strain that causes almond leaf scorch, consists of a linear chromosome that is 2,622328 base pairs long, with 2,358 protein-coding regions. It has no plasmids.

The genome of X. fastidiosa Temecula-1, first isolated in 1998 from an infected California grapevine and the cause of Pierce's disease of grapevines, consists of a circular chromosome that is 2,519,802 base pairs long. It has 2,034 protein-coding regions. It also contains 1 circular plasmid, pXFPD1.3, which is 1,346 base pairs long, and has 2 protein-coding regions.

Two strains of X. fastidiosa, M12 and M23, are currently being sequenced for comparative genome analysis.

Cell structure and metabolism

Xylella fastidiosa is a gram-negative, biofilm-forming, rod-shaped bacterium with dimensions of 0.25 to 0.35 µm in radius and 0.9 to 3.5 µm in length. It possesses two types of polar pili: type I pili 0.4 to 1.0 µm in length, and type IV pili 1 to 6 µm in length. Both types of pili are positioned at the same pole, and aid in xylem attachment, biofilm formation, and twitching motility. X. fastidiosa is a nutritionally fastidious aerobe that grows in the highly specialized environment of the xylem fluid, which contains the lowest concentration of organic energy sources of all plant tissues. This nutritionally poor environment does, however, contain amino acids, organic acids, and inorganic ions that are essential nutrient sources for the bacterium, allowing it to efficiently produce energy and grow. Because of its nutrient-poor environment, it has special mechanisms to concentrate and absorb nutrients. It is believed that it possess extracellular glycocayx-like fibers that may funtion in ion-exchange, nutrient binding, and concentrating digestive enzymes released by the bacterium.

Ecology

Although xylem-limited, 'X. fastidiosa' is able to colonize over 100 species of plants, and its host range continues to expand (Schuenzel et al.). It can cause a wide variety of wilt diseases in its plant hosts, however, disease is not produced in most plants. Its residency in the xylem appears to be the main criteria for survival, as it can survive in symptomless hosts, but can accumulate and produce disease symptoms if the host becomes weakened or susceptible. Strains causing Pierce's Disease in California, for example, appear to kill susceptible grapevines in restricted areas called "hot spots", near permanent water sources where leafhopper vectors are present (Hopkins).

'X. fastidiosa' forms aggregated biofilms upon colonization of the xylem. In fact, biofilm formation appears to be important for its survival and pathogenicity, and thus there is a connection between aggregation and virulence (Hopkins). Its polar pili and secreted exopolysaccharides are involved in both plant-bacterium and bacterium-bacterium interactions, allowing them them adhere to one another and the xylem wall (Simpson). Colonization of the xylem also seems to be dependent on movement of the bacterium between xylem vessels, which is mediated by twitching motility using its type IV pili, which allow downward migration in the plant (Li), as well as degradation of the pit membranes (primary cell walls) protecting the xylem by bacterial enzymes (Simpson).

Survival of 'X. fastidiosa' is dependent on its interaction with xylem sap-feeding insect vectors, as well these insect vectors interaction with plants (Newman), as the insect vectors are necessary for their transmittance to new host plants (Newman). Upon feeding from an infected plant, bacteria enter the insect vector, attaching to the lining of the foregut, where they multiply and form biofilms (Purcell). They are then transferred to the xylem of another host plant by the force of pumping action during feedingof the insect vector, which dislogdes some of the bacteria (Hopkins).

'X. fastidiosa' can cause widespread disease and crop damage to affected areas, and thus has a negative impact on the environment.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required

References

Bhattacharyya, A., Stilwagen, S., Ivanova, N., D'Souza, M., Bernal, A., Lykidis, A., Kapatral, V., Anderson, I., Larsen, N., Los, T., Reznik, G., Selkov, E.G., Walunas, T.L., Feil, H., Feil, W.S., Purcell, A., Lassez, J., Hawkins, T.L., Haselkorn, R., Overbeek, R., Predki, P.F., Kyrpides, N.C. "Whole-genome comparative analysis of three phytopathogenic Xylella fastidiosa strains". Proceedings of the National Academy of Sciences of the U.S.A. 2002. Volume 99. p.12403-12408.

De La Fuente, L., Montanes, E., Meng, Y., Li, Y., Burr, T.J., Hoch, H.C., Wu, M. "Assessing adhesion forces of type I and type IV pili of Xylella fastidiosa bacteria by use of a microfluidic flow chamber". Applied and Environmental Microbiology. 2007. Volume 73. p. 2690-2696.

Doddapaneni, H., Yao, J. Lin, H., Walker, M.A., and Civerolo, E.L. "Analysis of the genome wide variations among multiple strains of the plant pathogenic bacterium Xylella fastidiosa". BMC Genomics. 2006. Volume 7. p.225

Entrez Genome Database: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=genomeprj&cmd=Retrieve&dopt=Overview&list_uids=13864

Hopkins, D.L. "Xylella fastidiosa: xylem-limited bacterial pathogen of plants". Annual Review of Phytopathology. 1989. Volume 27. p. 271-90.

Li, Y., Hao, G., Galvani, C.D., Meng, Y., De La Fuente, L., Hoch, H.C., Burr, T.J. " Type I and type IV pili of Xylella fastidiosa affect twitching motility, biofilm formation and cell–cell aggregation". Microbiology. 2007. Volume 153. p. 719-726.

Newman, K.L., Almeida, R.P.P., Purcell, A.H., Lindow, S.E. "Cell-cell signaling control 'Xylella fastidiosa' interactions with both insects and plants". 'Proceedings of the National Academy of Sciences of the United States of America'. 2004. Volume 101. p. 1737-1742.

Purcell, A.H., and Hopkins, D.L. "Fastidious xylem-limited bacterial plant pathogens". Annual Review of Phytopathology. 1996. Volume 34. p. 131-51.

Schuenzel, E.L., Scally, M., Stouthamer, R., Nunney, L. " A multigene phylogenetic study of clonal diversity and divergence in North American strains of the plant pathogen Xylella fastidiosa". Applied Environmental Microbiology. 2005. Volume 71. p. 3832-3839.

Simpson, A.J., Reinach, F.C., Arruda, P., Abreu, F.A., Acencio, M., Alvarenga, R., Alves, L.M.C., Araya, J.E, Baia, G.S., Baptista, C.S, Barros, M.H., Bonaccorsi, E.D., Bordin, S., Bové, J.M., Briones, M.R.S., Bueno, M.R.P., Camargo, A.A., Camargo, L.E.A., Carraro, D.M., Carrer, H., Colauto, N.B., Colombo, C., Costa, F.F., Costa, M.C.R, Costa-Neto, C.M., Coutinho, L.L., Cristofani, M., Dias-Neto, E., Docena, C., El-Dorry, H., Facincani, A.P., Ferreira, A.J.S., Ferreira, V.C.A., Ferro, J.A., Fraga, J.S., França, S.C., Franco, M.C., Frohme, M., Furlan, L.R., Garnier, M., Goldman, G.H., Goldman, M.H.S., Gomes, S.L., Gruber, A., Ho, P.L., Hoheise, J.D., Junqueira, M.L., Kemper, E.L., Kitajima, J.P., Krieger, J.E., Kuramae, E.E., Laigret, F., Lambais, M.R., Leite, L.C.C., Lemos, E.G.M., Lemos, M.V.F., Lopes, S.A., Lopes, C.R., Machado, J.A., Machado, M.A., Madeira, A.M.B.N., Madeira, H.M.F., Marino, C.L., Marques, M.V., Martins, E.A.L., Martins, E.M.F., Matsukuma, A.Y., Menck, C.F.M., Miracca, E.C., Miyaki, C.Y., Monteiro-Vitorello, C.B., Moon, D.H., Nagai, M.A., Nascimento, A.L.T.O., Netto, L.E.S., Nhani, A., Nobrega, F.G., Nunes, L.R., Oliveira, M.A., de Oliveira, M.C., de Oliveira, R.C., Palmieri, D.A., Paris, A., Peixoto, B.R., Pereira, G.A.G., Pereira, H.A., Pesquero, J.B.Jr., Quaggio, R.B., Roberto, P.G., Rodrigues, V., de M. Rosa, A.J., de Rosa, V.E., de Sá, R.G., Santelli, R.V., Sawasaki, H.E., da Silva, A.C.R., da Silva, A.M., da Silva, F.R., Silva, W.A., da Silveira, J.F., Silvestri, M.L.Z., Siqueira, W.J., de Souza, A.A., de Souza, A.P., Terenzi, M.F., Truffi, D., Tsai, S.M., Tsuhako, M.H., Vallada, H., Van Sluys, M.A., Verjovski-Almeida, S., Vettore, A.L., Zago, M.A., Zatz, M., Meidanis, J., and Setuba, J.C. "The genome sequence of the plant pathogen Xylella fastidiosa". Nature. 2000. Volume 406. p. 151-157.

Xylella fastidiosa Genome Project: http://aeg.lbi.ic.unicamp.br/xf/

Edited by Kathryn Thompson, student of Rachel Larsen and Kit Pogliano, UCSD