Complete Genome Sequence of Pseudomonas amygdali pv. tabaci Strain 6605, a Causal Agent of Tobacco Wildfire Disease

Pseudomonas amygdali pv. tabaci strain 6605 is the bacterial pathogen causing tobacco wildfire disease that has been used as a model for elucidating virulence mechanisms. Here, we present the complete genome sequence of P. amygdali pv. tabaci 6605 as a circular chromosome from reads using a PacBio sequencer.

Guttation fluids containing Pseudomonas amygdali pv. lachrymans are a potential source of secondary infection in cucumber

Guttation is a common feature of cucumber leaves under high relative humidity conditions; however, little is known about the role of guttation in the transmission of Pseudomonas amygdali pv. lachrymans (Pal), which is the pathogen of cucumber angular leaf spot (ALS) disease. In this study, experimental evidence for the transmission of Pal inside cucumber plants and through guttation was provided, and the results proved that Pal can be transmitted from the bottom leaf to the upper leaves inside the plant and excreted from the upper leaves through guttation. After that, the third leaf of cucumber was inoculated with Pal bacterial suspension, Pal was detected on the fifth leaf, the petiole, and the stem and in guttation drops. Healthy cucumber seedlings were infected by Pal in the guttation droplets, indicating that guttation fluids containing Pal could become a potential source of secondary infection. The results from this study verified the hypothesis that guttation is a potential route for Pal excretion from cucumber plants and may be a source of secondary transmission under high relative humidity conditions.

Two Homologues of the Global Regulator Csr/Rsm Redundantly Control Phaseolotoxin Biosynthesis and Virulence in the Plant Pathogen Pseudomonas amygdali pv. phaseolicola 1448A

The widely conserved Csr/Rsm (carbon storage regulator/repressor of stationary-phase metabolites) post-transcriptional regulatory system controls diverse phenotypes involved in bacterial pathogenicity and virulence. Here we show that Pseudomonas amygdali pv. phaseolicola 1448A contains seven rsm genes, four of which are chromosomal. In RNAseq analyses, only rsmE was thermoregulated, with increased expression at 18 °C, whereas the antagonistic sRNAs rsmX1, rsmX4, rsmX5 and rsmZ showed increased levels at 28 °C. Only double rsmA-rsmE mutants showed significantly altered phenotypes in functional analyses, being impaired for symptom elicitation in bean, including in planta growth, and for induction of the hypersensitive response in tobacco. Double mutants were also non-motile and were compromised for the utilization of different carbon sources. These phenotypes were accompanied by reduced mRNA levels of the type III secretion system regulatory genes hrpL and hrpA, and the flagellin gene, fliC. Biosynthesis of the phytotoxin phaseolotoxin by mutants in rsmA and rsmE was delayed, occurring only in older cultures, indicating that these rsm homologues act as inductors of toxin synthesis. Therefore, genes rsmA and rsmE act redundantly, although with a degree of specialization, to positively regulate diverse phenotypes involved in niche colonization. Additionally, our results suggest the existence of a regulatory molecule different from the Rsm proteins and dependent on the GacS/GacA (global activator of antibiotic and cyanide production) system, which causes the repression of phaseolotoxin biosynthesis at high temperatures.

Nature of the Dutch elm disease: new aspects of diagnostics, pathogenesis, and etiology

Расхождения по установлению первопричины голландской болезни вязов (ГБВ) возникли сразу после её обнаружения в 1918 г. В разные годы указывали фитопатогенные бактерии (Васillus amylovorus, Miсrососсus ulmi, Рseudomonas lignicola) и гриб Ophiostoma (Ceratostomella) ulmi (Graphium ulmi). В 1937 г. в Краснодарском крае наряду с закупоркой сосудов на вязах описано ядро бактериальной водянки, т. е. уже 80 100 лет назад отмечали смешанную этиологию ГБВ, но бактериозы посчитали недостоверной причиной, возобладала теория грибной моноинфекции. Позже открыли агрессивный патоген Ophiostoma novoulmi, близкие виды O. himalulmi, O. novoulmi subsp. novoulmi, O. novoulmi subsp. americana. Параллельно на вязах выявлены бактериальная водянка (Pectobacterium carotovorum), бактериальный ожог (Erwinia группы Amylovora), Pseudomonas amygdali pv. ulmi, связанная с поражением коры, Xylella fastidiosa, вызывающая ожог листвы. К симптоматике ГБВ причастны виды фитопатогенных бактерий. Анализ факторов патогенности гриба показывает неоднозначность их проявления в симптоматике ГБВ. Агрессивность O. novoulmi проявилась не в патогенезе, а в вытеснении O. ulmi. Продукты метаболизма бактерий (кислота, газ, ферменты) разрушают целлюлозу, лигнин клеточных стенок, срединную пластинку и крахмал, вызывая камедь, мокроту, экссудат, закупорку сосудов, некрозы, мацерацию, растрескивание коры и древесины. Graphium ulmi развивается на подготовленных тканях совместно с бактериями как факультативный паразит, не проявляя антагонизма. Предполагается, что ГБВ имеет либо полифункциональную этиологию смешанного бактериальногрибного происхождения, либо самостоятельную бактериальную. Ареалы ильмовых пород, таксонов комплекса Ophiostoma ulmi и бактериозов имеют зоны перекрытия, что предполагает смешанный или сопряженный патогенез. В проблеме ГБВ на смену теории грибной моноинфекции должна прийти парадигма фитопатологической диагностики с использованием метагеномного анализа. Discordance on establishing the prime cause of the Dutch elm disease (DED) arose soon after its discovery in 1918. Through the years different causes were specified in literature: phytopathogenic bacteria (Bacillus amylovorus, Micrococcus ulmi, Pseudomonas lignicola) and fungi Ophiostoma (Ceratostomella) ulmi (Graphium ulmi). The bacterial dropsy together with obstruction of vessels was described in 1937. Hence, even 80 100 years ago the mixed etiology was noted. However, bacterioses were considered as a doubtful reason. Later on, an aggressive pathogen Ophiostoma novoulmi and close species O. himalulmi, O. novoulmi subsp. novoulmi, O. novoulmi subsp. americana were found. At the same time, bacterial dropsy (Pectobacterium carotovorum), fire blight (Erwinia of group Amylovora), Pseudomonas amygdali pv. ulmi connected to the injuries of bark, and Xylella fastidiosa causing foliage burn, were revealed on elms. Some species of phytopathogenic bacteria are also involved in symptoms of DED. The analysis of factors of pathogenesis of G. ulmi shows ambiguity of their manifestation in DED symptoms. The aggressivity of O. novoulmi was not in pathogenesis, these fungi force another species O. ulmi out. Products of bacteria metabolism (acid, gas, and enzymes) destroy cellulose, lignin cell walls, middle plate, and starch, causing gum, sputum, exudate, blockage of vessels, necrosis, maceration, cracks of bark and wood. Graphiosis settles on the prepared tissues where G. ulmi grows as a facultative parasite together with bacteria without showing any antagonism. It is suggested that DED has polyfunctional etiology of the mixed bacterial and fungi origin or independent bacterial origin. Distribution areas of elms, taxa of the Ophiostoma ulmi complex and the main bacterioses of elms have overlapping zones, that suggests mixed or associated pathogenesis. The theory of fungal monoinfection in a problem of DED requires a change of the paradigm of phytopathological diagnostics and use of metagenomic analysis in the diagnostics.

Control of Pseudomonas amygdali pv. loropetali on Metal, Wood, and Loropetalum chinense Stem Surfaces

Clorox Germicidal Bleach, Cuproxat, Green-Shield II, KleenGrow, Virkon S, and ZeroTol 2.0 were evaluated for their ability to inactivate Pseudomonas amygdali pv. loropetali on stainless steel (SS), pressure-treated wood (PtW), and loropetalum stem sections. Clorox at 11% product and Virkon S at 1.0% product eliminated P. amygdali pv. loropetali on SS surfaces and nearly eliminated it on PtW surfaces. Green-Shield II at 0.5% product and KleenGrow at 0.8% product nearly eliminated the bacterium on SS, while causing a significant reduction without elimination on PtW. Cuproxat and ZeroTol 2.0 were not effective against this bacterium in these applications. Clorox and KleenGrow were evaluated further for their ability to kill P. amygdali pv. loropetali on loropetalum stems, which was used as a preliminary surrogate for vegetative stem cuttings. Only Clorox eliminated bacteria from stem surfaces, but the bacterial inoculum level appeared to affect efficacy. Several disinfestants are commercially available that kill P. amygdali pv. loropetali on production surfaces.