title: Microarray profiling of host-extract-induced genes and characterization of the type VI secretion cluster in the potato pathogen Pectobacterium atrosepticum.
abstract: Pectobacterium atrosepticum is a Gram-negative plant-pathogenic bacterium that rots potato stems and tubers. Microarray analysis was used to identify genes that were differentially expressed when host extracts were added to the growth medium. Potato extracts downregulated the expression of ribosomal genes and genes related to uptake and metabolism of nutrients, and upregulated genes needed for nitrate or phosphonate use. Some of the observed changes in gene expression in host-extract-induced cultures are similar to those during attachment of the bacterium to host tissues. Other responses indicated defence against toxic metabolites in the extract. Tuber extract induced a large gene cluster having homology to type VI secretion genes shown to be virulence determinants in many, but not all, animal and human pathogens. Two of the genes in the type VI cluster were found to be expressed during infection in potato tubers and stems, and mutants with knockouts of the corresponding genes had increased virulence on potato. One of the type VI secretion mutants was further characterized and found to grow to higher cell density in culture in the presence of host extract and to produce slightly more extracellular tissue-macerating enzymes than the wild-type strain. Analysis of secreted proteins showed that this type VI mutant was affected in the production of haemolysin-coregulated proteins (Hcps), which have been suggested to be secreted by the type VI pathway in other bacteria. The results suggest that the type VI secretion system of P. atrosepticum is needed for secretion of Hcps but not for virulence on its host plant, potato.
authors.affiliation: Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Mattinen
authors.affiliation: Institute of Biotechnology, PO Box 56, FIN-00014 University of Helsinki, Finland.|Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Panu
authors.initials: P
authors.lastname: Somervuo
authors.affiliation: Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Johanna
authors.initials: J
authors.lastname: Nykyri
authors.affiliation: Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Riitta
authors.initials: R
authors.lastname: Nissinen
authors.affiliation: Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, FIN-20521 Turku, Finland.
authors.forename: Petri
authors.initials: P
authors.lastname: Kouvonen
authors.affiliation: Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, FIN-20521 Turku, Finland.
authors.forename: Garry
authors.initials: G
authors.lastname: Corthals
authors.affiliation: Institute of Biotechnology, PO Box 56, FIN-00014 University of Helsinki, Finland.
authors.forename: Petri
authors.initials: P
authors.lastname: Auvinen
authors.affiliation: Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Marja
authors.initials: M
authors.lastname: Aittamaa
authors.affiliation: Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Jari P T
authors.initials: JPT
authors.lastname: Valkonen
authors.affiliation: Department of Applied Biology, FIN-00014 University of Helsinki, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Pirhonen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions; D008969:Molecular Sequence Data; D005810:Multigene Family; D020411:Oligonucleotide Array Sequence Analysis; D016973:Pectobacterium carotovorum / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology*; D011198:Solanum tuberosum / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins