ABSTRACT
Pectobacterium species are necrotrophic bacterial pathogens that cause soft rot diseases in potatoes and several other crops worldwide. Gene expression data identified Pectobacterium carotovorum subsp. carotovorum budB, which encodes the α-acetolactate synthase enzyme in the 2,3-butanediol pathway, as more highly expressed in potato tubers than potato stems. This pathway is of interest because volatiles produced by the 2,3-butanediol pathway have been shown to act as plant growth promoting molecules, insect attractants, and, in other bacterial species, affect virulence and fitness. Disruption of the 2,3-butanediol pathway reduced virulence of P. c. subsp. carotovorum WPP14 on potato tubers and impaired alkalinization of growth medium and potato tubers under anaerobic conditions. Alkalinization of the milieu via this pathway may aid in plant cell maceration since Pectobacterium pectate lyases are most active at alkaline pH.
Subject(s)
Acetoin/metabolism , Biosynthetic Pathways , Pectobacterium carotovorum/metabolism , Pectobacterium carotovorum/pathogenicity , Acetoin/pharmacology , Alkalies , Biosynthetic Pathways/drug effects , Butylene Glycols/pharmacology , Culture Media/pharmacology , Gene Expression Profiling , Gene Expression Regulation, Bacterial/drug effects , Genes, Bacterial/genetics , Hydrogen-Ion Concentration/drug effects , Mutation/genetics , Operon/genetics , Pectobacterium carotovorum/genetics , Pectobacterium carotovorum/growth & development , Plant Stems/drug effects , Plant Stems/microbiology , Plant Tubers/drug effects , Plant Tubers/microbiology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Solanum tuberosum/drug effects , Solanum tuberosum/microbiology , Tissue Culture Techniques , Virulence/drug effectsABSTRACT
Pectobacterium species cause disease worldwide in many crop and ornamental plants, including potato. A new Pectobacterium subspecies, P. carotovorum subsp. brasiliensis was recently described in Brazil and later found in the United States, Israel, and South Africa. Its virulence traits and host range remain unknown. A comparison of three taxa commonly found on potato showed that both P. carotovorum subsp. carotovorum and subsp. brasiliensis are more aggressive in causing tuber and stem soft rot than P. atrosepticum. Also, despite bacterial growth inhibition in vitro of P. carotovorum subsp. carotovorum and P. atrosepticum strains by P. carotovorum subsp. brasiliensis, this new subspecies and P. carotovorum subsp. carotovorum are able to co-colonize in the same infected tissue. Both subspecies were motile in lesions. Pathogenesis assays showed that host ranges of all three overlap, but are not identical. The host ranges of individual strains of P. carotovorum subsp. carotovorum and subsp. brasiliensis are limited, whereas P. atrosepticum can macerate many plant species in addition to potato. There was high variability in virulence assays with potato tuber; thus physiological factors were investigated. Tuber size, maturity, and field location had significant effects on susceptibility to soft rot, with larger, more mature tubers being more susceptible.
