Pathogenic, phenotypic and molecular characterisation of Xanthomonas nasturtii sp. nov. and Xanthomonas floridensis sp. nov., new species of Xanthomonas associated with watercress production in Florida.

We describe two new species of the genus Xanthomonas, represented by yellow mucoid bacterial strains isolated from diseased leaves of watercress (Nasturtium officinale) produced in Florida, USA. One strain was pathogenic on watercress, but not in other species including a range of brassicas; other strains were not pathogenic in any of the tested plants. Data from Biolog carbon source utilization tests and nucleotide sequence data from 16S and gyrB loci suggested that both pathogenic and non-pathogenic strains were related to, yet distinct from, previously described Xanthomonas species. Multilocus sequence analysis and whole genome-wide comparisons of the average nucleotide identity (ANI) of genomes of two strains from watercress showed that these are distinct and share less than 95 % ANI with all other known species; the non-pathogenic strain WHRI 8848 is close to Xanthomonascassavae (ANI of 93.72 %) whilst the pathogenic strain WHRI 8853 is close to a large clade of species that includes Xanthomonasvesicatoria (ANI ≤90.25 %). Based on these results, we propose that both strains represent new Xanthomonas species named Xanthomonas floridensis sp. nov. (type strain WHRI 8848=ATCC TSD-60=ICMP 21312=LMG 29665=NCPPB 4601) and Xanthomonas nasturtii sp. nov. (type strain WHRI 8853=ATCC TSD-61=ICMP 21313=LMG 29666=NCPPB 4600), respectively. The presence of non-pathogenic Xanthomonas strains in watercress and their interaction with pathogenic strains needs to be further investigated. Although the importance of the new pathogenic species is yet to be determined, the bacterial disease that it causes constitutes a threat to watercress production and its distribution should be monitored.

Public Health Investigation of Two Outbreaks of Shiga Toxin-Producing Escherichia coli O157 Associated with Consumption of Watercress.

An increase in the number of cases of Shiga toxin-producing Escherichia coli (STEC) O157 phage type 2 (PT2) in England in September 2013 was epidemiologically linked to watercress consumption. Whole-genome sequencing (WGS) identified a phylogenetically related cluster of 22 cases (outbreak 1). The isolates comprising this cluster were not closely related to any other United Kingdom strain in the Public Health England WGS database, suggesting a possible imported source. A second outbreak of STEC O157 PT2 (outbreak 2) was identified epidemiologically following the detection of outbreak 1. Isolates associated with outbreak 2 were phylogenetically distinct from those in outbreak 1. Epidemiologically unrelated isolates on the same branch as the outbreak 2 cluster included those from human cases in England with domestically acquired infection and United Kingdom domestic cattle. Environmental sampling using PCR resulted in the isolation of STEC O157 PT2 from irrigation water at one implicated watercress farm, and WGS showed this isolate belonged to the same phylogenetic cluster as outbreak 2 isolates. Cattle were in close proximity to the watercress bed and were potentially the source of the second outbreak. Transfer of STEC from the field to the watercress bed may have occurred through wildlife entering the watercress farm or via runoff water. During this complex outbreak investigation, epidemiological studies, comprehensive testing of environmental samples, and the use of novel molecular methods proved invaluable in demonstrating that two simultaneous outbreaks of STEC O157 PT2 were both linked to the consumption of watercress but were associated with different sources of contamination.

Local ciliate communities associated with aquatic macrophytes

This study, based within the catchment area of the River Frome, an important chalk stream in the south of England, compared ciliated protozoan communities associated with three species of aquatic macrophyte common to lotic habitats: Ranunculus penicillatus subsp. pseudofluitans, Nasturtium officinale and Sparganium emersum. A total of 77 ciliate species were counted. No species-specific ciliate assemblage was found to be typical of any one plant species. Ciliate abundance between plant species was determined to be significantly different. The ciliate communities from each plant species were unique in that the number of species increased with ciliate abundance. The community associated with R. penicillatus subsp. pseudofluitans showed the highest consistency and species richness whereas S. emersum ciliate communities were unstable. Most notably, N. officinale was associated with low ciliate abundances and an apparent reduction in biofilm formation, discussed herein in relation to the plant’s production of the microbial toxin phenethyl isothiocyanate. We propose that the results reflect differences in the quantity and quality of biofilm present on the plants, which could be determined by the different plant morphologies, patterns of plant decay and herbivore defense systems, all of which suppress or promote the various conditions for biofilm growth (AU)

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An efficient protocol for genetic transformation of watercress (Nasturtium officinale) using Agrobacterium rhizogenes.

Watercress (Nasturtium officinale) is a member of the Brassicaceae family and a rich source of glucosinolate, which has been shown to possess anticancer properties. To extract these compounds from N. officinale for study, a method was developed in which Agrobacterium rhizogenes was used to transfer DNA segments into plant genomes in order to produce hairy root cultures, which are a reliable source of plant compounds. The A. rhizogenes strain R1000 had the highest infection frequency and induces the most hairy roots per explant. Polymerase chain reaction and cytohistochemical staining methods were used to validate transgenic hairy roots from N. officinale. Glucosinolate from watercress hairy roots was separated and analyzed using high-performance liquid chromatography coupled to electrospray ionization mass spectrometry. Indolic glucosinolates, including glucobrassicin (0.01-0.02 µmol/g of DW) and 4-methoxyglucobrassicin (0.06-0.18 µmol/g of DW), as well as aromatic glucosinolate (gluconasturtiin) (0.06-0.21 µmol/g of DW), were identified virtually identical or more in transformed than wild type roots of N. officinale. Hairy root culture of watercress is a valuable approach for future efforts in the metabolic engineering of glucosinolate biofortification in plants, particularly, because indolic glucosinolates are the precursors of a potent cancer chemopreventive agent (indole-3-carbinol).

Microbiological and metal contamination of watercress in the Wellington region, New Zealand--2000 survey.

OBJECTIVES: To investigate potential microbiological and metal contamination of watercress and to assess the public health risks associated with harvesting and consumption of watercress. METHOD: During March and April 2000, samples were taken from 11 known or potential watercress collection sites in the Wellington region. Microbiological testing included bacterial counts for presumptive and faecal coliforms (watercress); total coliforms (growing water); and Escherichia coli (E. coli) and presence/absence tests for Campylobacter species (growing water and watercress). Watercress concentrations of a range of metals were also measured. RESULTS: All of the sites showed significant levels of E. coli in samples of both watercress and water. The E. coli levels in water were well above recommended freshwater recreational contact safety guidelines at most sites. Campylobacter was detected in the growing waters at all sites (80% of the samples) and in 11% of the watercress samples. Mean metal concentrations in watercress did not exceed the NZ Food Regulations (1984) levels at any of the sites. However, lead concentrations at the urban sites and one of the semi-urban sites would have exceeded the new Australia New Zealand Food Standards Code maximum levels (2003). CONCLUSIONS AND IMPLICATIONS: The consumption of raw watercress contaminated with enteric pathogens could potentially cause serious gastrointestinal illness (e.g. campylobacteriosis) and people gathering watercress could also be at risk of infection from contact with contaminated surface waters.