Abstract
BackgroundMangotoxin is an antimetabolite toxin that is produced by strains of Pseudomonas syringae pv. syringae; mangotoxin-producing strains are primarily isolated from mango tissues with symptoms of bacterial apical necrosis. The toxin is an oligopeptide that inhibits ornithine N-acetyl transferase (OAT), a key enzyme in the biosynthetic pathway of the essential amino acids ornithine and arginine. The involvement of a putative nonribosomal peptide synthetase gene (mgoA) in mangotoxin production and virulence has been reported.ResultsIn the present study, we performed a RT-PCR analysis, insertional inactivation mutagenesis, a promoter expression analysis and terminator localisation to study the gene cluster containing the mgoA gene. Additionally, we evaluated the importance of mgoC, mgoA and mgoD in mangotoxin production. A sequence analysis revealed an operon-like organisation. A promoter sequence was located upstream of the mgoB gene and was found to drive lacZ transcription. Two terminators were located downstream of the mgoD gene. RT-PCR experiments indicated that the four genes (mgoBCAD) constitute a transcriptional unit. This operon is similar in genetic organisation to those in the three other P. syringae pathovars for which complete genomes are available (P. syringae pv. syringae B728a, P. syringae pv. tomato DC3000 and P. syringae pv. phaseolicola 1448A). Interestingly, none of these three reference strains is capable of producing mangotoxin. Additionally, extract complementation resulted in a recovery of mangotoxin production when the defective mutant was complemented with wild-type extracts.ConclusionsThe results of this study confirm that mgoB, mgoC, mgoA and mgoD function as a transcriptional unit and operon. While this operon is composed of four genes, only the last three are directly involved in mangotoxin production.
Highlights
Mangotoxin is an antimetabolite toxin that is produced by strains of Pseudomonas syringae pv. syringae; mangotoxin-producing strains are primarily isolated from mango tissues with symptoms of bacterial apical necrosis
The construction and characterisation of insertion mutants derived from Pseudomonas syringae pv. syringae UMAF0158 Each ORF that was cloned into plasmid pCG2-6 (Figure 1) was subjected to insertional inactivation mutagenesis in the P. syringae pv. syringae UMAF0158 chromosome by integration of the appropriately cloned PCR products
The disruption of ORF0 and ORF1 did not affect mangotoxin production. These two genes may belong to another independent gene cluster located close to the mgo operon that is not involved in mangotoxin production
Summary
Mangotoxin is an antimetabolite toxin that is produced by strains of Pseudomonas syringae pv. syringae; mangotoxin-producing strains are primarily isolated from mango tissues with symptoms of bacterial apical necrosis. Mangotoxin is an antimetabolite toxin that is produced by strains of Pseudomonas syringae pv. Syringae; mangotoxin-producing strains are primarily isolated from mango tissues with symptoms of bacterial apical necrosis. The toxin is an oligopeptide that inhibits ornithine N-acetyl transferase (OAT), a key enzyme in the biosynthetic pathway of the essential amino acids ornithine and arginine. Each antimetabolite toxin inhibits a specific step in the glutamine and arginine biosynthesis pathways of the host, enhancing disease symptoms and increasing the virulence of the bacterial. Tabtoxin is a monocyclic b-lactam that inhibits the enzyme glutamine synthetase (GS, EC 6.3.1.2). This toxin is produced by P. syringae pv. Novel ORFs were identified in a portion of the biosynthetic region that is known to be associated with a toxin hypersensitivity phenotype [6]
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