Mangotoxin Production Research Articles

Turning a bacterial gaseous virulence trigger off.

Recently, Sieber et al. discovered the new diazeniumdiolate volatile signaling molecule, leudiazen. They confirmed that inactivation of leudiazen by KMnO4 can reduce the production of mangotoxin. This alleviates the pathogenicity of Pseudomonas syringae pv. syringae on mango trees, providing a new strategy for plant protection, compatible with organic farming.

CHARACTERIZATION OF PSEUDOMONAS SYRINGAE pv. SYRINGAE ISOLATED FROM MANGO IN SICILY AND OCCURRENCE OF COPPER-RESISTANT STRAINS

Mango (Mangifera indica) is grown throughout a wide range of frost-free climates and is one of the world’s most important fruit crops. During 2010-2014, severe symptoms of bacterial apical necrosis (BAN) caused by Pseudomonas syringae pv. syringae (Pss) were observed on mango plants throughout all mango-growing areas in Sicily (southern Italy). The causal agent was identified based on phenotypic, genotypic and pathogenicity tests. The genetic variability of strains obtained from different areas and cultivars were assessed by rep- PCR and allowed clear differentiation of the Pss strains isolated from mango from other representative strains of the pathovar. In addition, the respective production of syringomycin, syringopeptin and mangotoxin was checked by in vitro tests and PCR detection. All tested strains showed the presence of mgoA and mgoB of the mangotoxin operon. Some copper- resistant Pss strains showing cusCBA genes were also found in some orchards. This feature could explain the failure of the disease control using copper compounds. Among 71 strains tested using in vitro assay, no copper-sensitive strains were detected, whereas 44 strains (62%) had high resistance, 16 strains (22.5%) were resistant and 11 strains (15.5%) had low resistance to copper sulfate. To our knowledge, this is the first report of copper resistance among Pss strains causing BAN on mango in Sicily.

Mangotoxin production of Pseudomonas syringae pv. syringae is regulated by MgoA.

BackgroundThe antimetabolite mangotoxin is a key factor in virulence of Pseudomonas syringae pv. syringae strains which cause apical necrosis of mango trees. Previous studies showed that mangotoxin biosynthesis is governed by the mbo operon. Random mutagenesis led to the identification of two other gene clusters that affect mangotoxin biosynthesis. These are the gacS/gacA genes and mgo operon which harbors the four genes mgoBCAD.ResultsThe current study shows that disruption of the nonribosomal peptide synthetase (NRPS) gene mgoA resulted in loss of mangotoxin production and reduced virulence on tomato leaves. Transcriptional analyses by qPCR and promoter reporter fusions revealed that mbo expression is regulated by both gacS/gacA and mgo genes. Also, expression of the mgo operon was shown to be regulated by gacS/gacA. Heterologous expression under the native promoter of the mbo operon resulted in mangotoxin production in non-producing P. syringae strains, but not in other Pseudomonas species. Also introduction of the mbo and mgo operons in nonproducing P. protegens Pf-5 did not confer mangotoxin production but did enhance transcription of the mbo promoter.ConclusionsFrom the data obtained in this study, we conclude that both mbo and mgo operons are under the control of the gacS/gacA two-component system and that the MgoA product acts as a positive regulator of mangotoxin biosynthesis.

A Pseudomonas syringae Diversity Survey Reveals a Differentiated Phylotype of the Pathovar syringae Associated with the Mango Host and Mangotoxin Production

Pseudomonas syringae pv. syringae, the causal agent of bacterial apical necrosis (BAN) in mango crops, has been isolated in different mango-producing areas worldwide. An extensive collection of 87 P. syringae pv. syringae strains isolated from mango trees affected by BAN from different countries, but mainly from Southern Spain, were initially examined by repetitive sequence-based polymerase chain reaction (rep-PCR) to analyze the genetic diversity with an epidemiological aim. rep-PCR was powerful in assessing intrapathovar distribution and also allowing clustering of the P. syringae pv. syringae strains isolated from mango, depending on the isolation area. A clear pattern of clustering was observed for all the P. syringae pv. syringae strains isolated from mango distinct from strains from other hosts, including strains for the same geographical regions as the mango isolates. For this reason, a representative group of 51 P. syringae pv. syringae strains isolated from mango and other hosts, as well as some P. syringae strains from other pathovars, were further characterized to determine their possible genetic, phenotypic, and phylogenetic relationships. Similar to the rep-PCR results, the randomly amplified polymorphic DNA PCR (RAPD-PCR) and catabolic diversity analysis using the Biolog GN2 profile grouped 90% of the mango isolates together in a unique cluster. Interestingly, the majority of P. syringae pv. syringae strains isolated from mango produced mangotoxin. The analysis of the phylogenetic distribution using the multilocus sequence typing analysis strongly supports the existence of a differentiated phylotype of the pathovar syringae mainly associated with the mango host and characterized by the mangotoxin production.

The mangotoxin biosynthetic operon (mbo) is specifically distributed within Pseudomonas syringae genomospecies 1 and was acquired only once during evolution.

Mangotoxin production was first described in Pseudomonas syringae pv. syringae strains. A phenotypic characterization of 94 P. syringae strains was carried out to determine the genetic evolution of the mangotoxin biosynthetic operon (mbo). We designed a PCR primer pair specific for the mbo operon to examine its distribution within the P. syringae complex. These primers amplified a 692-bp DNA fragment from 52 mangotoxin-producing strains and from 7 non-mangotoxin-producing strains that harbor the mbo operon, whereas 35 non-mangotoxin-producing strains did not yield any amplification. This, together with the analysis of draft genomes, allowed the identification of the mbo operon in five pathovars (pathovars aptata, avellanae, japonica, pisi, and syringae), all of which belong to genomospecies 1, suggesting a limited distribution of the mbo genes in the P. syringae complex. Phylogenetic analyses using partial sequences from housekeeping genes differentiated three groups within genomospecies 1. All of the strains containing the mbo operon clustered in groups I and II, whereas those lacking the operon clustered in group III; however, the relative branching order of these three groups is dependent on the genes used to construct the phylogeny. The mbo operon maintains synteny and is inserted in the same genomic location, with high sequence conservation around the insertion point, for all the strains in groups I and II. These data support the idea that the mbo operon was acquired horizontally and only once by the ancestor of groups I and II from genomospecies 1 within the P. syringae complex.

The mbo operon is specific and essential for biosynthesis of mangotoxin in Pseudomonas syringae.

Mangotoxin is an antimetabolite toxin produced by certain Pseudomonas syringae pv. syringae strains. This toxin is an oligopeptide that inhibits ornithine N-acetyl transferase, a key enzyme in the biosynthesis of ornithine and arginine. Previous studies have reported the involvement of the putative nonribosomal peptide synthetase MgoA in virulence and mangotoxin production. In this study, we analyse a new chromosomal region of P. syringae pv. syringae UMAF0158, which contains six coding sequences arranged as an operon (mbo operon). The mbo operon was detected in only mangotoxin-producing strains, and it was shown to be essential for the biosynthesis of this toxin. Mutants in each of the six ORFs of the mbo operon were partially or completely impaired in the production of the toxin. In addition, Pseudomonas spp. mangotoxin non-producer strains transformed with the mbo operon gained the ability to produce mangotoxin, indicating that this operon contains all the genetic information necessary for mangotoxin biosynthesis. The generation of a single transcript for the mbo operon was confirmed and supported by the allocation of a unique promoter and Rho-independent terminator. The phylogenetic analysis of the P. syringae strains harbouring the mbo operon revealed that these strains clustered together.

Characterisation of the mgo operon in Pseudomonas syringae pv. syringae UMAF0158 that is required for mangotoxin production.

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.

A Nonribosomal Peptide Synthetase Gene (mgoA) of Pseudomonas syringae pv. syringae Is Involved in Mangotoxin Biosynthesis and Is Required for Full Virulence

Pseudomonas syringae pv. syringae, which causes the bacterial apical necrosis of mango, produces the antimetabolite mangotoxin. We report here the cloning, sequencing, and identity analysis of a chromosomal region of 11.1 kb from strain P syringae pv. syringae UMAF0158, which is involved in mangotoxin biosynthesis. This chromosomal region contains six complete open reading frames (ORFs), including a large gene (ORF5) with a modular architecture characteristic of nonribosomal peptide synthetases (NRPS) named mgoA. A Tn5 mutant disrupted in mgoA was defective in mangotoxin production, revealing the involvement of the putative NRPS gene in the biosynthesis of mangotoxin. This derivative strain impaired in mangotoxin production also showed a reduction in virulence as measured by necrotic symptoms on tomato leaflets. Mangotoxin production and virulence were restored fully in the NRPS mutant by complementation with plasmid pCG2-6, which contains an 11,103-bp chromosomal region cloned from the wild-type strain P syringae pv. syringae UMAF0158 that includes the putative NPRS gene (mgoA). The results demonstrate that mgoA has a role in the virulence of P. syringae pv. syringae. The involvement of an NRPS in the production of an antimetabolite toxin from P. syringae inhibiting ornithine acetyltransferase activity is proposed.