Ralstonia solanacearum is a devastating, soil-borne plant pathogen with a global distribution and an unusually wide host range. It is a model system for the dissection of molecular determinants governing pathogenicity. We present here the complete genome sequence and its analysis of strain GMI1000. The 5.8-megabase (Mb) genome is organized into two replicons: a 3.7-Mb chromosome and a 2.1-Mb megaplasmid. Both replicons have a mosaic structure providing evidence for the acquisition of genes through horizontal gene transfer. Regions containing genetically mobile elements associated with the percentage of G+C bias may have an important function in genome evolution. The genome encodes many proteins potentially associated with a role in pathogenicity. In particular, many putative attachment factors were identified. The complete repertoire of type III secreted effector proteins can be studied. Over 40 candidates were identified. Comparison with other genomes suggests that bacterial plant pathogens and animal pathogens harbour distinct arrays of specialized type III-dependent effectors.

/pdf/genome-sequence-of-the-plant-pathogen-ralstonia-solanacearum-5fwrv1o7aq.pdf

Genome sequence of the plant pathogen Ralstonia solanacearum

Large plasmids of molecular weight varying from 90 to around 200×106 have earlier been detected in most Rhizobium meliloti strains using an alkaline denaturation-phenol extraction procedure With a less destructive method (Eckhardt 1978) it was possible additionally to detect one plasmid of molecular weight clearly greater than 300×106 (=megaplasmid) in all of twenty-seven R meliloti strains of various geographical origins and nodulation groupings investigated Four strains (RCR 2011, A145, S26 and CC2013) were found to carry one megaplasmid and no smaller plasmids Hybridization experiments with Klebsiella pneumoniae and R meliloti cloned nitrogenase structural genes D and H showed that these genes are located on the megaplasmid and not on the smaller plasmids

Genes controlling early and late functions in symbiosis are located on a megaplasmid in Rhizobium meliloti

A simple gel technique is described for the detection of large, covalently closed, circular DNA molecules in eucaryotic cells. The procedure is based on the electrophoretic technique of Eckhardt (T. Eckhardt, Plasmid 1:584-588, 1978) for detecting bacterial plasmids and has been modified for the detection of circular and linear extrachromosomal herpesvirus genomes in mammalian cells. Gentle lysis of suspended cells in the well of an agarose gel followed by high-voltage electrophoresis allows separation of extrachromosomal DNA from the bulk of cellular DNA. Circular viral DNA from cells which carry the genomes of Epstein-Barr virus, Herpesvirus saimiri, and Herpesvirus ateles can be detected in these gels as sharp bands which comigrate with bacterial plasmid DNA of 208 kilobases. Epstein-Barr virus producer cell lines also show a sharp band of linear 160-kilobase DNA. The kinetics of the appearance of this linear band after induction of viral replication after temperature shift parallels the known kinetics of Epstein-Barr virus production in these cell lines. Hybridization of DNA after transfer to filters shows that the circular and linear DNA bands are virus specific and that as little as 0.25 Epstein-Barr virus genome per cell can be detected. The technique is simple, rapid, and sensitive and requires relatively low amounts of cells (0.5 X 10(6) to 2.5 X 10(6)).

Detection of circular and linear herpesvirus DNA molecules in mammalian cells by gel electrophoresis

Studies of root nodule bacteria isolated from Galega orientalis and Galega officinalis are reviewed, and as a result a new species, Rhizobium galegae, is proposed. The type strain of the species is R. galegae HAMBI 540 (= ATCC 43677), which forms nitrogen-fixing root nodules on G. orientalis. Deoxyribonucleic acid homology distinguishes R. galegae from other rhizobia, whereas nodulation of Galega sp. and sensitivity to phage gal 1/R phenotypically separate the strains currently included in the species from other members of the genus Rhizobium. Other criteria supporting the formation of a new species include ribosomal ribonucleic aciddeoxyribonucleic acid homology data, protein and lipopolysaccharide patterns, serological properties, and numerical taxonomy data.

/pdf/rhizobium-galegae-a-new-species-of-legume-root-nodule-4nqg9if2de.pdf

Rhizobium galegae, a new species of legume root nodule bacteria

Ralstonia solanacearum is a devastating plant pathogen with a global distribution and an unusually wide host range. This bacterium can also be free-living as a saprophyte in water or in the soil in the absence of host plants. The availability of the complete genome sequence from strain GMI1000 provided the basis for an integrative analysis of the molecular traits determining the adaptation of the bacterium to various environmental niches and pathogenicity toward plants. This review summarizes current knowledge and speculates on some key bacterial functions, including metabolic versatility, resistance to metals, complex and extensive systems for motility and attachment to external surfaces, and multiple protein secretion systems. Genome sequence analysis provides clues about the evolution of essential virulence genes such as those encoding the Type III secretion system and related pathogenicity effectors. It also provided insights into possible mechanisms contributing to the rapid adaptation of the bacterium to its environment in general and to its interaction with plants in particular.

Lessons learned from the genome analysis of ralstonia solanacearum.

Using analytical and preparative methods, we demonstrated the presence of megaplasmids with molecular weight larger than 450 x 10(6) in the two plant-associated bacteria Rhizobium meliloti and Pseudomonas solanacearum. Such giant plasmids were found in 8 of 9 P. solanacearum strains tested and in all of the 18 R. meliloti strains tested.

Megaplasmids in the plant-associated bacteria Rhizobium meliloti and Pseudomonas solanacearum.

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Megaplasmids in the plant-associated bacteria Rhizobium meliloti and Pseudomonas solanacearum.