Complete Genome Sequence of the N2-Fixing Broad Host Range Endophyte Klebsiella pneumoniae 342 and Virulence Predictions Verified in Mice

We report here the sequencing and analysis of the genome of the nitrogen-fixing endophyte, Klebsiella pneumoniae 342. Although K. pneumoniae 342 is a member of the enteric bacteria, it serves as a model for studies of endophytic, plant-bacterial associations due to its efficient colonization of plant tissues (including maize and wheat, two of the most important crops in the world), while maintaining a mutualistic relationship that encompasses supplying organic nitrogen to the host plant. Genomic analysis examined K. pneumoniae 342 for the presence of previously identified genes from other bacteria involved in colonization of, or growth in, plants. From this set, approximately one-third were identified in K. pneumoniae 342, suggesting additional factors most likely contribute to its endophytic lifestyle. Comparative genome analyses were used to provide new insights into this question. Results included the identification of metabolic pathways and other features devoted to processing plant-derived cellulosic and aromatic compounds, and a robust complement of transport genes (15.4%), one of the highest percentages in bacterial genomes sequenced. Although virulence and antibiotic resistance genes were predicted, experiments conducted using mouse models showed pathogenicity to be attenuated in this strain. Comparative genomic analyses with the presumed human pathogen K. pneumoniae MGH78578 revealed that MGH78578 apparently cannot fix nitrogen, and the distribution of genes essential to surface attachment, secretion, transport, and regulation and signaling varied between each genome, which may indicate critical divergences between the strains that influence their preferred host ranges and lifestyles (endophytic plant associations for K. pneumoniae 342 and presumably human pathogenesis for MGH78578). Little genome information is available concerning endophytic bacteria. The K. pneumoniae 342 genome will drive new research into this less-understood, but important category of bacterial-plant host relationships, which could ultimately enhance growth and nutrition of important agricultural crops and development of plant-derived products and biofuels

Basal Resistance of Plants Against Bacteria: from Discovery to Molecular Characterisation

Basal resistance (BR, a local resistance against pathogens induced by general elicitors) is a multi-faceted defence mechanism appearing in many shapes and with many given names, such as induced (acquired) resistance (protection, defence), as well as a part of innate immunity. Here, we give a historical overview of concepts, present results and an outlook associated with bacteriological studies in the Plant Protection Institute (PPI). The topics on BR briefly covered are its elicitors, light and temperature dependence, changes in plant physiology, transcription and protein expression during it and its effect on bacteria. We emphasize the importance and relevance of its quick form, early BR, which might be a plant defence mechanism in nature against all kinds of pathogenic and saprophytic bacteria

Low temperature delay and inhibition of a plant defence mechanism: early basal resistance in tobacco

The development of local early basal resistance (EBR), is a form of non-specific general defence response of plants to bacteria, greatly depending on temperature. This symptomless defence mechanism is easily detected by its inhibitory action on the hypersensitive response (HR) caused by a subsequent incompatible pathogenic bacterium. Both EBR and HR were investigated at different temperatures ranging from 30 °C to 5 °C. At normal temperatures (30-20 °C) both heat-killed Pseudomonas syringae pv. syringae 61 (polyvirulent to many plants) and Pseudomonas savastanoi pv. phaseolicola S21 (pathogenic to bean) induced EBR in tobacco leaves within a few hours, but below 10 °C it was greatly delayed and at 5 °C usually no EBR response could be detected within 2-3 days. The time required for development of EBR did not depend on the bacterial pathovars or strains. However, the induction time of HR was not as sensitive to low temperatures as that of EBR, instead, it depended on the bacterial pathovars used

Isolation of in planta-Induced Genes of Pseudomonas viridiflava

Pseudomonas viridiflava is an opportunistic, post-harvest pathogenic bacterium that causes soft rot of fruits and vegetables. In vivo expression technology was used to identify genes that participate in the pathogenicity of P. viridiflava. Genetic loci that are induced in planta were identified. Ten such loci were partially sequenced and annotated. Here we describe five of them, which influence the pathogen's stress tolerance in planta. Three of the identified ORFs that show sequence identity to known genes encode membrane proteins, the remaining two encode enzymes in catabolic pathways

Efficient transposon mutagenesis in a wide range of phytopathogenic gram-negative bacteria

Compared to the known method of conjugation the frequency of transposon mutagenesis following conjugation was enhanced 11-fold by two hours of pre-incubation of recipient Pseudomonas viridiflava 1 on conjugation media. The increased frequency was ƒ = 1.3 × 10−4 . In other species of Pseudomonas, Pectobacteira and Xanthomonas high rates of transposon mutants were similarly obtained; however, in these strains the increased frequency was less than 5-fold