subsp.
Pcc (formerly
subsp.
) PC1 causes soft-rot disease in a wide variety of plant species by secreting multiple pathogenicity-related traits. In this study, regulatory mechanism of
ir-
iquid (AL) ...biofilm formation was studied using a
homolog gene deletion mutant (Δ
) of Pcc PC1. Compared to the wild type (Pcc PC1), the Δ
mutant produced fragile and significantly (
< 0.001) lower amounts of AL biofilm on
alt-
ptimized
roth plus 2%
lycerol (SOBG), yeast peptone dextrose adenine, and also on King's B at 27°C after 72 h incubation in static condition. The wild type also produced significantly higher quantities of AL biofilm on SOBGMg
(magnesium deprived) containing Cupper (Cu
), Zinc (Zn
), Manganese (Mn
), Magnesium (Mg
), and Calcium (Ca
) compared to the Δ
mutant. Moreover, the wild type was produced higher amounts of biofilms compared to the mutant while responding to pH and osmotic stresses. The Δ
(encoding flagellin),
::Tn5 (encoding a master regulator) and Δ
(a membrane protein essential for flagellar rotation) mutants produced a lighter and more fragile AL biofilm on SOBG compared to their wild counterpart. All these mutants resulted in having weak bonds with the cellulose specific dye (Calcofluor) producing lower quantities of cellulose compared to the wild type. Gene expression analysis using mRNA collected from the AL biofilms showed that Δ
mutant significantly (
< 0.001) reduced the expressions of multiple genes responsible for cellulose production (
, and
), motility (
, and
) and type III secretion system (
, and
) compared to the wild type. The CytR homolog was therefore, argued to be able to regulate the AL biofilm formation by controlling cellulose production, motility and T3SS in Pcc PC1. In addition, all the mutants exhibited poorer attachment to radish sprouts and AL biofilm cells of the wild type was resistant than stationary-phase and planktonic cells to acidity and oxidative stress compared to the same cells of the Δ
mutant. The results of this study therefore suggest that CytR homolog is a major determinant of Pcc PC1's virulence, attachment and its survival mechanism.
KdgR has been reported to negatively regulate the genes involved in degradation and metabolization of pectic acid and other extracellular enzymes in soft-rotting Erwinia spp. through direct binding ...to their promoters. The possible involvement of a KdgR orthologue in virulence by affecting the expression of extracellular enzymes in Xanthomonas oryzae pv. oryzae, the causal agent of rice blight disease, was examined by comparing virulence and regulation of extracellular enzymes between the wild type (WT) and a strain carrying a mutation in putative kdgR (ΔXoo0310 mutant). This putative kdgR mutant of X. oryzae pv. oryzae showed increased pathogenicity on rice without affecting the regulation of extracellular enzymes, such as amylase, cellulase, xylanase, and protease. However, the mutant carrying a mutation in an ortholog of xpsL, which encodes the functional secretion machinery for the extracellular enzymes, showed a dramatic decrease in pathogenicity on rice. Both mutants of kdgR and of xpsL orthologs showed higher expression of two major hrp regulatory genes, hrpG and hrpX, and the genes in the hrp operons when grown in hrp-inducing medium. Thus, both genes were shown to be involved in repression of hrp genes. The kdgR ortholog was thought to suppress virulence mainly by repressing the expression of hrp genes without affecting the expression of extracellular enzymes, unlike findings for the kdgR gene in soft-rotting Erwinia spp. On the other hand, xpsL was confirmed to be involved in virulence by promoting the secretion of extracellular enzymes in spite of repressing the expression of the hrp genes.
ITALIC! Pectobacterium carotovorumsubsp. ITALIC! carotovorumand its lytic bacteriophage PPWS1 were isolated from a Japanese horseradish rhizome with soft rot. Sequencing of the phage genomic DNA ...suggested that PPWS1 is a new species of the family ITALIC! Podoviridaeand has high similarity to the bacteriophage Peat1 infectious to ITALIC! P. atrosepticum.
We investigated pellicle (i.e., the bacterial network formed at the air–liquid interface to block the surface of a standing culture) formation governed by the PhoP–PhoQ two-component system (TCS) and ...its role in susceptibility to harsh environments and virulence of the phytopathogen
Dickeya dadantii
(formerly
Erwinia chrysanthemi
) 3937. Pellicle formation was dramatically reduced in
phoP
and
phoQ
mutants compared to the wild type in low (10 μM) magnesium, but was greater and more robust in high (10 mM) magnesium. Pellicles formed by the wild type and by the mutants in low magnesium were composed of cellulose, but pellicles formed by these mutants at high magnesium condition were composed of cellulose and a cellulase-resistant polymer. In the wild type at low magnesium, expression of
bcsABCD
(cellulose biosynthesis operon),
adrA
(a GGDEF protein) and
fliC
(a flagellar component called flagellin) increased significantly, whereas expression of these genes was elevated in the mutants at high magnesium condition. Thus, PhoP–PhoQ TCS may regulate pellicle formation by transcriptional control of
bcsABCD
,
adrA
and
fliC
. Overall, pellicle-associated bacteria were more tolerant to adverse environmental cues and more virulent than aerobically grown cells. Furthermore, at low magnesium, wild-type bacteria associated with a pellicle were more resistant to stress environments and more virulent than the pellicle-associated cells of the mutants. Intriguingly, the reverse relationship is found at high magnesium. Thus, formation of pellicle may be required for survival and virulence of
D. dadantii
3937.
The genes required for the pathogenicity of plant pathogens can be divided into two groups: those for eliciting virulence and those for establishing host-parasite interactions. Basically, the former ...genes are required for efficient production of the virulence factor(s) leading to the development of symptoms, while the latter genes are needed for well-balanced production of the factors required at each step of the parasitism. To understand the overall picture of plant pathogenicity, we need to understand not only the list of both genes but also how their expressions are regulated. We chose the major virulence genes of soft rot causing Enterobacteriaceae (represented by Pectobacterium carotovorum subsp. carotovorum and Dickeya dadantii) as a model system for dynamic study of the former genes. For the dynamic study of the latter genes, we chose the hrp genes, many of which are responsible for the Type III secretion system (T3SS) and the genes for the T3SS-dependent effectors of xanthomonads. Particularly since the major effector of xanthomonads, the AvrBs3 group or TAL (transcription activator-like) effectors contain NLS (nuclear localization signal) and an acidic activation domain, their studies are also expected to lead us to dynamic analyses of plant genes too.
The first open-reading frame (ORF) of the genus
Capillovirus encodes an apparently chimeric polyprotein containing conserved regions for replicase (Rep) and coat protein (CP), while other viruses in ...the family
Flexiviridae have separate ORFs encoding these proteins. To investigate the role of the full-length ORF1 polyprotein of capillovirus, we generated truncation mutants of ORF1 of apple stem grooving virus by inserting a termination codon into the variable region located between the putative Rep- and CP-coding regions. These mutants were capable of systemic infection, although their pathogenicity was attenuated.
In vitro translation of ORF1 produced both the full-length polyprotein and the smaller Rep protein. The results of
in vivo reporter assays suggested that the mechanism of this early termination is a ribosomal −1 frame-shift occurring downstream from the conserved Rep domains. The mechanism of capillovirus gene expression and the very close evolutionary relationship between the genera
Capillovirus and
Trichovirus are discussed.
In July 2013, black spots were observed on leaves of calanthe in a flowerbed of a park in Tokyo, Japan. The spots were circular to oval and often accompanied by a yellow halo. A bacterium was ...isolated from the lesions and was found to cause the same symptoms on calanthe leaves after inoculation. Based on phylogenetic and bacteriological analyses, the causal bacterium was identified as
Burkholderia andropogonis
. This is the first report of bacterial black spot on calanthe caused by
B. andropogonis
in Japan.
HrpG, a two-component response regulator-like protein, is a key regulator of the type III secretion system (T3SS) in
Xanthomonas
spp. In
X
.
campestris
pv.
vesicatoria
, HrpG with a single amino acid ...substitution (HrpG*) gains the ability to induce the expression of T3SS-related genes even under nutrient-rich conditions. In this study, we investigated the role of HrpG in the synthesis of the secretory protein using HrpG* in strain NA-1 of
X
.
axonopodis
pv.
citri
(Xac NA-1), a causal agent of citrus canker. Eleven proteins secreted via a type II secretion system (T2SS) were induced by HrpG*. In proteomic analyses, six of the 11 proteins were identified as extracellular enzymes, and the others as a fimbrial biogenesis-related protein, a type IV-related protein, two hypothetical proteins, and a conserved hypothetical protein. Further analysis of these proteins revealed that the genes coding all 11 proteins were upregulated by HrpG*, even though they had different expression patterns for HrpXct-dependency. The data indicated that HrpG, a key regulator of T3SS, also acts as a positive regulator of certain proteins secreted via a T2SS in Xac NA-1.
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