RESUMEN
Pink disease of pineapple, caused by Pantoea citrea, is characterized by a dark coloration on fruit slices after autoclaving. This coloration is initiated by the oxidation of glucose to gluconate, which is followed by further oxidation of gluconate to as yet unknown chromogenic compounds. To elucidate the biochemical pathway leading to pink disease, we generated six coloration-defective mutants of P. citrea that were still able to oxidize glucose into gluconate. Three mutants were found to be affected in genes involved in the biogenesis of c-type cytochromes, which are known for their role as specific electron acceptors linked to dehydrogenase activities. Three additional mutants were affected in different genes within an operon that probably encodes a 2-ketogluconate dehydrogenase protein. These six mutants were found to be unable to oxidize gluconate or 2-ketogluconate, resulting in an inability to produce the compound 2,5-diketogluconate (2,5-DKG). Thus, the production of 2,5-DKG by P. citrea appears to be responsible for the dark color characteristic of the pink disease of pineapple.
Asunto(s)
Frutas/microbiología , Genes Bacterianos , Magnoliopsida/microbiología , Pantoea/fisiología , Enfermedades de las Plantas/etiología , Compuestos Cromogénicos/metabolismo , Color , Grupo Citocromo c/biosíntesis , Gluconatos/metabolismo , Glucosa/metabolismo , Datos de Secuencia Molecular , Operón/genética , Homología de Secuencia de AminoácidoRESUMEN
Pantoea citrea, the causal agent of pink disease of pineapple, harbors a cryptic plasmid of 5229 bp. designated pUCD5000. On the basis of nucleotide and amino acid sequence analyses, pUCD5000 contains both replication and mobilization loci (bom and mobCABD) that are similar to those in plasmids pSW100 and pSW200 in Pantoea stewartii and pEC3 in Erwinia carotovora subsp. carotovora. The survival of P. citrea on pineapple does not depend on pUCD5000. However, full pink coloration development, which is characteristic of the pink disease, appears to require this plasmid.