Conjugative Plasmid in Corynebacterium flaccumfaciens subsp. oortii That Confers Resistance to Arsenite, Arsenate, and Antimony(III)

Complete Genome Sequencing Provides Novel Insight Into the Virulence Repertories and Phylogenetic Position of Dry Beans Pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens

Bacterial wilt of dry beans (family Fabaceae) caused by the actinobacterial agent Curtobacterium flaccumfaciens pv. flaccumfaciens is one of the most important diseases threatening edible legume production around the globe. Despite the economic losses due to the bacterial wilt disease, the pathogen has not so far been investigated for its genomic features, pathogenicity determinants, and virulence strategies. Here we present the first complete genome sequence of a highly virulent bacteriocin-producing C. flaccumfaciens pv. flaccumfaciens strain P990. The bacterium has a circular chromosome consisting of 3,736 kbp with the G+C% content of 71.0%. Furthermore, a 147-kbp circular plasmid (pCff1) with 66.1% G+C% content as well as two circular plasmid-like DNAs with sizes of 25 and 22 kbp were detected within the genomic contents of C. flaccumfaciens pv. flaccumfaciens. Phylogenetic analyses revealed that only a few number of Curtobacterium sp. strains deposited in the public databases could be classified within the species C. flaccumfaciens. Comparative genomics of C. flaccumfaciens pv. flaccumfaciens using the genome sequences of actinobacterial plant pathogens revealed the presence of a set of unique low G+C% content genomic islands in the C. flaccumfaciens pv. flaccumfaciens genome. Homologs of pathogenicity-determinant loci capable of producing 1,4-beta-xylanase (xysA), pectate lyase (pelA1 and pelA2), serine protease (chpC, chpG, and pat-1), and sortase (srtA) were detected in C. flaccumfaciens pv. flaccumfaciens genome. The genomic data presented here extend our understanding of the C. flaccumfaciens pv. flaccumfaciens genomic features and pave the ways of research on functional and interaction genetics to combat the risk of bacterial wilt disease in the 21st century's dry bean industry.

Bacterial wilt of dry beans caused by Curtobacterium flaccumfaciens pv. flaccumfaciens: A new threat from an old enemy

Bacterial wilt and tan spot of dry beans (family Fabaceae), caused by Curtobacterium flaccumfaciens pv. flaccumfaciens, is an important emerging disease threatening the edible legume industry around the globe. The management of bacterial wilt has been a major problem since its original description in 1922. This is in part due to the seedborne nature of the pathogen allowing the bacterium to be transmitted long distances via infected seeds, as well as a lack of detailed molecular information concerning the pathogenicity repertoires and virulence determinates of the pathogen. Identification can also be difficult owing to the presence of five different colony colour variants (i.e., yellow, orange, pink, purple, and red) on culture media. In this review, we provide an overview of the aetiology, epidemiology, and management strategies of bacterial wilt disease. First, a comprehensive and comparative symptomology of the disease on different dry bean species is described. Then, the taxonomic history of the causal agent and utility of high-throughput sequencing-based approaches in the precise characterization of the pathogen is explained. Furthermore, we provide an updated outline on the global distribution of the pathogen, highlighting expansion of the causal agent into the areas with no history of the disease until the beginning of the current century. Finally, because there are limited options for use of conventional pesticides against the pathogen, we highlight the use of integrated pest management strategies, for example quarantine inspections, resistant cultivars, and crop sanitation, to combat the risk of bacterial wilt disease in the dry bean industry.

DISEASE SYMPTOMS

Interveinal chlorosis on leaflets leading to necrotic areas and systemic wilt. Seed discolouration to yellow, orange, pink, or purple is seen in white-seeded cultivars.

HOST RANGE

Causes bacterial wilt and tan spot disease on edible dry beans in the Fabaceae family, including common bean (Phaseolus vulgaris), cowpea (Vigna unguiculata), mungbean (Vigna radiata), soybean (Glycine max), as well as a number of weed species.

TAXONOMIC STATUS OF THE PATHOGEN

Bacteria; phylum Actinobacteria; order Actinomycetales; suborder: Micrococcineae; family Microbacteriaceae; genus Curtobacterium; species Curtobacterium flaccumfaciens.

SYNONYMS

Corynebacterium flaccumfaciens subsp. flaccumfaciens; Corynebacterium flaccumfaciens pv. flaccumfaciens, Corynebacterium flaccumfaciens, Phytomonas flaccumfaciens, Bacterium flaccumfaciens.

MICROBIOLOGICAL PROPERTIES

Multicoloured (yellow, orange, pink, purple, and red), gram-positive, aerobic, curved rod, nonspore-forming, polar flagellated, motile cells.

DISTRIBUTION

Widespread in America (Brazil, Canada, and the USA), Australia, and Iran. Restricted occurrence in Africa and Europe.

PHYTOSANITARY CATEGORIZATION

EPPO A2 list no. 48, EU Annex II⁄B.

Phenotypic and Molecular-Phylogenetic Analysis Provide Novel Insights into the Diversity of Curtobacterium flaccumfaciens

A multiphasic approach was used to decipher the phenotypic features, genetic diversity, and phylogenetic position of 46 Curtobacterium spp. strains isolated from dry beans and other annual crops in Iran and Spain. Pathogenicity tests, resistance to arsenic compounds, plasmid profiling and BOX-PCR were performed on the strains. Multilocus sequence analysis (MLSA) was also performed on five housekeeping genes (i.e., atpD, gyrB, ppk, recA, and rpoB) of all the strains, as well as five pathotype strains of the species. Pathogenicity test showed that six out of 42 strains isolated in Iran were nonpathogenic on common bean. Despite no differences found between pathogenic and nonpathogenic strains in their plasmid profiling, the former were resistant to different concentrations of arsenic, while the latter were sensitive to the same concentrations. Strains pathogenic on common bean were polyphyletic with at least two evolutionary lineages (i.e., yellow-pigmented strains versus red/orange-pigmented strains). Nonpathogenic strains isolated from solanaceous vegetables were clustered within either the strains of C. flaccumfaciens pv. flaccumfaciens or different pathovars of the species. The results of MLSA and BOX-PCR analysis were similar to each other and both methods were able to discriminate the yellow-pigmented strains from the red/orange-pigmented strains. A comprehensive study of a worldwide collection representing all five pathovars as well as nonpathogenic strains of C. flaccumfaciens is warranted for a better understanding of the diversity within this phytopathogenic bacterium.

Draft Genome Sequence of Curtobacterium flaccumfaciens Strain UCD-AKU (Phylum Actinobacteria)

Here we present the draft genome of an actinobacterium, Curtobacterium flaccumfaciens strain UCD-AKU, isolated from a residential carpet. The genome assembly contains 3,692,614 bp in 130 contigs. This is the first member of the Curtobacterium genus to be sequenced.

The accidental plant pathologist

This article presents the experiences of a woman in academic plant pathology from the 1950s to today. Topics include the social climate for women in science, personal and professional developments and research discoveries, public policy issues in agriculture and biotechnology affecting plant pathology, and projections for the future of plant pathology.

Transformation of the phytopathogenic bacterium Clavibacter michiganense subsp. michiganense by electroporation and development of a cloning vector

We constructed a cloning vector for use in the plant pathogenic bacterium Clavibacter michiganense subsp. michiganense. The vector pDM100 consists of a 3.2-kb restriction fragment of the Clavibacter plasmid pCM1 joined to a pBR325 derivative carrying the neomycin phosphotransferase of transposon Tn5 and the gentamicin acetyltransferase of Tn1696. Both antibiotic resistance genes are efficiently expressed in C. michiganense subsp. michiganense. Although polyethylene glycol-mediated transfection of spheroplasts with the DNA of the C. michiganense subsp. michiganense-specific bacteriophage CMP1 yielded about 3 x 10(3) transfectants per microgram of DNA, in transformations with plasmid DNA only a very few transformants were obtained. However, the transformation efficiency could be improved by electroporation of intact cells, giving about 2 x 10(3) transformants per microgram of plasmid DNA. Since a transformation procedure and a cloning vector are now available, pathogenicity in C. michiganense subsp. michiganense can now be analyzed genetically.

Conjugative transfer of cadmium resistance plasmids in Rhodococcus fascians strains

The presence of a 138-kilobase plasmid (pD188) correlated with increased resistance to cadmium in Rhodococcus fascians D188. This plasmid could be transferred by a conjugation-like system in matings between R. fascians strains. Transconjugants expressed the cadmium resistance and could be used as donors in subsequent matings. Four other R. fascians strains (NCPPB 1488, NCPPB 1675, NCPPB 2551, and ATCC 12974) could also be used as donors for cadmium resistance in matings. Strain NCPPB 1675 showed a 100% cotransfer of cadmium and chloramphenicol resistance markers.

Homology of pCS1 Plasmid Sequences with Chromosomal DNA in Clavibacter michiganense subsp. sepedonicum : Evidence for the Presence of a Repeated Sequence and Plasmid Integration

Restriction fragments of pCS1, a 50.6-kilobase (kb) plasmid present in many strains of Clavibacter michiganense subsp. sepedonicum (“ Corynebacterium sepedonicum ”), have been cloned in an M13mp11 phage vector. Radiolabeled forms of these cloned fragments have been used as Southern hybridization probes for the presence of plasmid sequences in chromosomal DNA of this organism. These studies have shown that all tested strains lacking the covalently closed circular form of pCS1 contain the plasmid in integrated form. In each case the site of integration exists on a single plasmid restriction fragment with a size of 5.1 kb. Southern hybridizations with these probes have also revealed the existence of a major repeated sequence in C. michiganense subsp. sepedonicum. Hybridizations of chromosomal DNA with deletion subclones of a 2.9-kb plasmid fragment containing the repeated sequence indicate that the size of the repeated sequence is approximately 1.3 kb. One of the copies of the repeated sequence is on the plasmid fragment containing the site of integration.

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High incidence of selenite-resistant bacteria from a site polluted with selenium

The level of selenium-resistant bacteria in water, algal mats, and sediment from Kesterson reservoir, Calif., a site with known selenium pollution, was compared with that in nearby Volta reservoir, a site with low selenium levels. A high percentage (greater than 50%) of all isolates from the Kesterson samples were resistant to 10 mM selenite. In contrast, only a small percentage of the Volta isolates were resistant to this level of selenite. The identity of some selenite-resistant isolates and MICs of selenite, selenate, arsenate, tellurite, and tellurate were determined.

Separate resistances to arsenate and arsenite (antimonate) encoded by the arsenical resistance operon of R factor R773

The arsenical resistance operon of R factor R773 was analyzed by subcloning and insertional inactivation. The operon was found to have two functional regions, the promoter-proximal region encoding resistance to arsenite and antimonate and the promoter-distal region encoding arsenate resistance. A unique 1.6-kilobase fragment was shown to be sufficient to encode arsenate resistance and produce arsenate extrusion from intact cells.