We have determined the nucleotide sequence of IS 427 , an insertion sequence from Agrobacterium tumefaciens T37. IS 427 is 1271 bp long, contains 16-bp imperfect terminal inverted repeats, and generates a 2-bp target sequence duplication. It is present at three sites in the pTiT37 plasmid and is absent from the chromosome of A. tumefaciens T37. Each of the IS 427 elements sequenced was near a site with sequence homology to integration host factor (IHF)-binding sites which suggested that IHF may be involved in IS 427 transposition.

Bacteria of the genus Azospirillum are diazotrophs associated with the root zone of grasses (for review see Döbereiner and Pedrosa 1987). The molecular genetic analysis of Azospirillum plant interaction is hampered by the lack of plant root differentiation at the site of interaction. The identification of bacterial genes possibly involved in Azospirillum rhizocoenoses has therefore been approached either by molecular hybridization with cloned genes from other rhizosphere bacteria (Fogher et al 1985; Waelkens et al 1987) or by genetic complementation of characterized mutants of Rhizobium meliloti with gene libraries of A. brasilense (Michiels et al 1988). By genetic complementation we initially isolated two A. brasilense Sp7 DNA fragments that correct R. meliloti exoB and exoC mutants respectively. These fragments are located on the p90 plasmid DNA of A. brasilense Sp7 (Michiels et al 1989b). In this paper we report a more extensive inventory of A. brasilense loci that are involved in exopolysaccharide synthesis. Furthermore we describe some experiments to study the nature and regulation of these genes, and finally we focus on the genetic map of the p90 plasmid of A. brasilense strain Sp7.

Bacteria of the genus Azospirillum (1) are free-living diazotrophs that can readily be isolated from the rhizosphere and roots of grasses (2). No differentiated structures are formed following colonization of the root zone. Bacteria are thightly attached to the root surface and pictures of root hair deformation were reported (for review, see (3) Numerous field experiments, carried out since 1975, have demonstrated that Azospirillum inoculations can promote crop yield under certain environmental and soil conditions. Biochemical and physiological studies on Azospirillum in laboratory conditions suggest that processes like biological nitrogen fixation and plant hormones production might contribute to plant growth responses upon inoculation (3, 4) Until now little is known about the genetics of these bacteria or the molecular biology of their association with plants (5). Most progress has been made in the biochemistry and molecular genetics of nitrogen fixation (6, 7, 8). Recently, efforts to develop tools for the genetic analysis of Azospirillum were reinforced, and research programs to identify bacterial genes in the Azospirillum-plant interaction process were initiated.

Journal Article Similarities between nucleotide sequences of insertion elements of Agrobacterium tumefaciens and Pseudomonas savastanoi in relation to Agrobacterium tumefaciens TC-DNA Get access Catherine De Meirsman, Catherine De Meirsman Search for other works by this author on: Oxford Academic PubMed Google Scholar Jos Desair, Jos Desair Search for other works by this author on: Oxford Academic PubMed Google Scholar Jos Vanderleyden, Jos Vanderleyden * *To whom correspondence should be addressed at Search for other works by this author on: Oxford Academic PubMed Google Scholar August P.van Gool, August P.van Gool Search for other works by this author on: Oxford Academic PubMed Google Scholar Geroge C. Jen Geroge C. Jen 1CIBA-Geigy Biotechnology FacilityPO Box 12257, Research Triangle Park, NC 27709, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Nucleic Acids Research, Volume 15, Issue 24, 23 December 1987, Page 10591, https://doi.org/10.1093/nar/15.24.10591 Published: 23 December 1987 Article history Accepted: 13 November 1987 Published: 23 December 1987

Bacteria of the genus Azospirillum (Tarrand et al 1978) are. free-living diazotrophs that can readily be isolated from the rhizosphere and roots of grasses. Little is known about the genetics of these bacteria or the molecular biology of their association with plants (for reviews, see Elmerich, 1984; Okon 1985).

Azospirillum is probably the best studied example of beneficial plant rhizosphere bacteria. Studies in our laboratory focus on the identification of bacterial genes and gene products that are of importance in the physical and metabolic interaction of Azospirillum brasilense with plant roots. Here we report for Azospirillum brasilense, flagellation, motility, the physical interaction with plant roots, the synthesis of indole-3-acetic acid, the expression of nif genes in plant-root associated bacteria, and the induction of gene expression with plant root exudates.