A chromosomal linkage map of Agrobacterium tumefaciens and a comparison with the maps of Rhizobium spp

A 13.1-kb DNA fragment carrying Pseudomonas denitrificans cob genes has been sequenced. The nucleotide sequence and genetic analysis revealed that this fragment contained five different cob genes named cobN to cobQ and cobW. Based on the similarity of NH2-terminal sequences and molecular weights of the purified Cob proteins, CobQ was identified as cobyric acid synthase, CobP was identified as a bifunctional enzyme exhibiting both cobinamide kinase and cobinamide phosphate guanylyltransferase activities, and CobO was identified as cob(I)alamin adenosyltransferase. CobN is proposed to play a role in cobalt insertion reactions. Four other open reading frames were identified on the 13.1-kb fragment, but their chromosomal inactivation did not lead to a cobalamin-minus phenotype.The cobalamin biosynthetic pathway probably involves 20 to 30 different enzymatic steps (Fig. 1) consisting of (i) formation of uroporphyrinogen III (urogen III), which is the common intermediate for the synthesis of hemes, chlorophylls, cobalamins, F430, and sirohemes; (ii) conversion of urogen III into cobyrinic acid by three successive methylations at C-2, C-7, and C-20 followed by five other methylations at C-17, C-11, C-1, C-5, and C-15, decarboxylation of the acetic acid side chain at C-12, elimination of C-20, NADPH-dependent reduction of the macrocycle, methyl migration from C-11 to C-12, and insertion of cobalt; (iii) formation of cobinamide from cobyrinic acid (Fig. 1) by amidation of the peripheral carboxyl groups a, b, c, d, e, and g and insertion of (R)-l-amino-2-propanol at position f; and (iv) conversion of cobinamide into coenzyme B12 (for reviews on cobalamin synthesis, see references 4, 5, 23, 34, and 40). In addition, the central cobalt atom is adenosylated to form the coenzyme derivatives. We have described elsewhere the cloning of Pseudomonas denitrificans genes involved in cobalamin synthesis (cob genes) (12) from urogen III. These genes are grouped into four genomic loci that correspond to four distinct complementation groups (from A to D). We have reported the nucleotide sequence and the results of genetic analysis of a 5.4-kb DNA fragment from complementation group C carrying five cob genes (cobA to cobE) elsewhere (16). This fragment is located on the right end of the complementation group C restriction map (Fig. 2). cobA and cobB are the structural genes for S-adenosyl-L-* Corresponding author. t Present address: 5 bis rue Pierre Curie,

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“…4). All the mutants for which the insertion was within ORF1 (i.e., insertions 19,32,24,27,37,39,26,11, and 14; Fig. 4 (12).…”

Section: Resultsmentioning

confidence: 99%

Nucleotide sequence and genetic analysis of a 13.1-kilobase-pair Pseudomonas denitrificans DNA fragment containing five cob genes and identification of structural genes encoding Cob(I)alamin adenosyltransferase, cobyric acid synthase, and bifunctional cobinamide kinase-cobinamide phosphate guanylyltransferase

Crouzet¹,

Lévy-Schil²,

Cameron³

et al. 1991

J Bacteriol

122

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“…A third type of chromosomal avirulent mutation has been described, chvE (9). In these mutants, vir gene induction by acetosyringone is strongly reduced (8). The three mutations described in this paper, like chvE, reduce the induction of vir genes by acetosyringone.…”

Section: Methodsmentioning

confidence: 76%

Characterization of three Agrobacterium tumefaciens avirulent mutants with chromosomal mutations that affect induction of vir genes

et al. 1991

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Three Agrobacterium tumefaciens mutants with chromosomal mutations that affect bacterial virulence were isolated by transposon mutagenesis. Two of the mutants were avirulent on all hosts tested. The third mutant, Ivr-211, was a host range mutant which was avirulent on BryophyUum diagremontiana, Nicotiana tabacum, N. Infection of susceptible dicotyledonous plants by Agrobacterium tumefaciens results in crown gall tumor formation. The mechanism by which the bacterium infects the plant is not fully understood. An early step in tumor formation involves the attachment of the bacterium to host plant cells (12). Once attached to the plant, the bacterium begins a process that results in the movement of tumor-inducing (Ti) plasmid DNA sequences from the bacterium into the plant host genome (2, 28). Depicker et al. have identified the DNA sequences transferred and termed them T-DNA (5). Without successful transfer of the T-DNA from the bacterium to the plant, tumor formation cannot occur. This paper examines the properties of three avirulent TnS insertion mutants of A. tumefaciens,. These TnS insertions are contained within the chromosome of the bacterium; thus, the insertions have no direct affect on the vir region of the Ti plasmid which is responsible for T-DNA transfer. The only previously identified chromosomal genes required for virulence are chvA and chvB (6), att (16), pscA (27) (also called exoC [1]), chvD (32), and chvE (9). Mutations in each of the first four genes listed result in the inability of the bacteria to attach to host cells and the consequent loss of bacterial virulence. Mutations in chvD result in reduced virulence on Bryophyllum diagremontiana (visible tumors were still formed) and reduced induction of virG by acetosyringone (32). Transposon insertions in chvE result in a * Corresponding author.

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“…This is also true for g. lecmminosarum (Kondorosi et al, 1980) and Aarobacterium (Hooykaas et al, 1982). In B. iaponicum.…”

mentioning

confidence: 58%

“…Rhizobiaceae at the genetic level, genetic maps (Meade and Signer, 1977;Casadeus and Olivares, 1979;Hooykaas et al, 1982;Martin and Long, 1984;Beringer et al, 1987) are of very low resolution for most regions of the genome. This is also true for g. lecmminosarum (Kondorosi et al, 1980) and Aarobacterium (Hooykaas et al, 1982).…”

mentioning

confidence: 99%

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Pulsed-field gel electrophoresis studies of Rhizobiaceae

Sobral

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A chromosomal linkage map of Agrobacterium tumefaciens and a comparison with the maps of Rhizobium spp

Cited by 56 publications

References 24 publications

Characterization of three Agrobacterium tumefaciens avirulent mutants with chromosomal mutations that affect induction of vir genes

Pulsed-field gel electrophoresis studies of Rhizobiaceae

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