Pseudomonas alliivorans sp. nov., a plant-pathogenic bacterium isolated from onion foliage in Georgia, USA

ABSTRACTToxin-antitoxin (TA) systems are genetic elements composed of a protein toxin and a counteracting antitoxin that is either a noncoding RNA or protein. In type I TA systems, the antitoxin is a noncoding small RNA (sRNA) that base pairs with the cognate toxin mRNA interfering with its translation. Although type I TA systems have been extensively studied inEscherichia coliand a few human or animal bacterial pathogens, they have not been characterized in plant-pathogenic bacteria. In this study, we characterized a chromosomal locus in the plant pathogenErwinia amylovoraEa1189 that is homologous to thehok-soktype I TA system previously identified in theEnterobacteriaceae-restricted plasmid R1. Phylogenetic analysis indicated that the chromosomal location of thehok-soklocus is, thus far, unique toE. amylovora. We demonstrated that ectopic overexpression ofhokis highly toxic toE. amylovoraand that the sRNAsokreversed the toxicity ofhokthroughmok, a reading frame presumably translationally coupled withhok. We also identified the region that is essential for maintenance of the main toxicity of Hok. Through ahok-sokdeletion mutant (Ea1189Δhok-sok), we determined the contribution of thehok-soklocus to cellular growth, micromorphology, and catalase activity. Combined, our findings indicate that thehok-sokTA system, besides being potentially self-toxic, provides fitness advantages toE. amylovora.IMPORTANCEBacterial toxin-antitoxin systems have received great attention because of their potential as targets for antimicrobial development and as tools for biotechnology.Erwinia amylovora, the causal agent of fire blight disease on pome fruit trees, is a major plant-pathogenic bacterium. In this study, we identified and functionally characterized a unique chromosomally encodedhok-soktoxin-antitoxin system inE. amylovorathat resembles the plasmid-encoded copies of this system in otherEnterobacteriaceae. This study of a type I toxin-antitoxin system in a plant-pathogenic bacterium provides the basis to further understand the involvement of toxin-antitoxin systems during infection by a plant-pathogenic bacterium. The new linkage between thehok-soktoxin-antitoxin system and the catalase-mediated oxidative stress response leads to additional considerations of targeting this system for antimicrobial development.

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The use of fluorescent probes to assess viability of the plant pathogenic bacterium Clavibacter michiganensis subsp. michiganensis by flow cytometry

Fitopatologia Brasileira ◽

10.1590/s0100-41582006000400004 ◽

2006 ◽

Vol 31 (4) ◽

pp. 349-356 ◽

Cited By ~ 5

Author(s):

Luiz G. Chitarra ◽

Peter Breeuwer ◽

Tjakko Abee ◽

Ruud W. Bulk

Keyword(s):

Flow Cytometry ◽

Fluorescent Probes ◽

Membrane Integrity ◽

Pathogenic Bacterium ◽

Plant Pathogenic Bacterium ◽

Clavibacter Michiganensis ◽

Clavibacter Michiganensis Subsp ◽

Alternatives Assessment ◽

Heat Treated ◽

Calcein Am

Determination of the viability of bacteria by the conventional plating technique is a time-consuming process. Methods based on enzyme activity or membrane integrity are much faster and may be good alternatives. Assessment of the viability of suspensions of the plant pathogenic bacterium Clavibacter michiganensis subsp. michiganensis (Cmm) using the fluorescent probes Calcein acetoxy methyl ester (Calcein AM), carboxyfluorescein diacetate (cFDA), and propidium iodide (PI) in combination with flow cytometry was evaluated. Heat-treated and viable (non-treated) Cmm cells labeled with Calcein AM, cFDA, PI, or combinations of Calcein AM and cFDA with PI, could be distinguished based on their fluorescence intensity in flow cytometry analysis. Non-treated cells showed relatively high green fluorescence levels due to staining with either Calcein AM or cFDA, whereas damaged cells (heat-treated) showed high red fluorescence levels due to staining with PI. Flow cytometry also allowed a rapid quantification of viable Cmm cells labeled with Calcein AM or cFDA and heat-treated cells labeled with PI. Therefore, the application of flow cytometry in combination with fluorescent probes appears to be a promising technique for assessing viability of Cmm cells when cells are labeled with Calcein AM or the combination of Calcein AM with PI.

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Microbial Conversion of Tomato by a Plant Pathogenic Bacterium Pectobacterium atrosepticum: A Plant-Microbial Approach to Control Pathogenic Candida Species

Natural Product Communications ◽

10.1177/1934578x1200700124 ◽

2012 ◽

Vol 7 (1) ◽

pp. 1934578X1200700

Author(s):

Vivek K. Bajpai ◽

Sun Chul Kang ◽

Soon-Gu Lee ◽

Kwang-Hyun Baek

Keyword(s):

Candida Species ◽

Fungal Pathogens ◽

Pharmaceutical Preparations ◽

Pathogenic Bacterium ◽

Plant Pathogenic Bacterium ◽

Microbial Conversion ◽

Pectobacterium Atrosepticum ◽

Minimum Fungicidal Concentration ◽

Therapeutic Uses

This study was carried out to produce bioconverted products by microbial fermentation of tomato using a plant pathogenic bacterium Pectobacterium atrosepticum and to evaluate their in vitro antimycotic effect against pathogenic Candida species. The bioconverted products (500 μg/disc) provoked promising antimycotic effects against pathogenic isolates of Candida species as shown by the diameters of zones of inhibition (9 ± 0.6 to 14 ± 0.4 mm), along with their respective minimum inhibitory and minimum fungicidal concentration values, which increased from 250 to 1000 and 250 to 2000 μg/mL, respectively. With the viable counts of the tested fungal pathogens, exposure of the bioconverted products revealed a remarkable antimycotic effect. In addition, the morphology of a clinical isolate of C. glabrata KBN06P00368, visualized by scanning electron microscopy, showed a severe detrimental effect produced by the bioconverted products at the minimum inhibitory concentration (250 μg/mL). The bioconverted products significantly inhibited the in vitro growth of all the tested clinical and pathogenic laboratory isolates of Candida species. This study confirmed the potent antimycotic efficacy of the bioconverted products of tomato, hence justifying the therapeutic uses of bioconverted products in pharmaceutical preparations as an alternative approach to support the antifungal activity of conventional antimycotics.

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