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A Gram-negative, non-sporulating, rod-shaped, motile bacterium, with a single polar flagellum, designated strain PsJN T , was isolated from surface-sterilized onion roots. This isolate proved to be a highly effective plant-beneficial bacterium, and was able to establish rhizosphere and endophytic populations associated with various plants. Seven related strains were recovered from Dutch soils. Based on 16S rRNA gene sequence data, strain PsJN T and the Dutch strains were identified as representing a member of the genus Burkholderia, as they were closely related to Burkholderia fungorum (98?7 %) and Burkholderia phenazinium (98?5 %). Analysis of whole-cell protein profiles and DNA-DNA hybridization experiments confirmed that all eight strains belonged to a single species. Strain PsJN T had a DNA G+C content of 61?0 mol%. Only low levels of DNA-DNA hybridization to closely related species were found. Qualitative and quantitative differences in fatty acid composition between strain PsJN T and closely related species were identified. The predominant fatty acids in strain PsJN T were 16 : 0, 18 : 1v7c and summed feature 3 (comprising 16 : 1v7c and/or iso-15 : 0 2-OH). Isolate PsJN T showed high 1-aminocyclopropane-1-carboxylate deaminase activity and is therefore able to lower the ethylene level in a developing or stressed plant. Production of the quorum-sensing signal Abbreviations: ACC, 1-aminocyclopropane-1-carboxylate; GFP, green fluorescent protein; NAHL, N-acyl-homoserine lactone.The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of B. phytofirmans strains PsJN T , G44-5 and G6-5 are AY497470, AY836218 and AY836219.A neighbour-joining tree showing the position of B. phytofirmans sp. nov. within the genus Burkholderia, a dendrogram derived from the protein patterns of the strains studied and cross-sections showing chickpea roots with strain PsJN T

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The ability of endophytic bacteria to influence Erwinia carotovora var. atroseptica (Eca) growth and disease development was examined in potatoes. Bacterial populations isolated from within the tubers of five potato (Solanum tuberosum L.) cultivars (Kennebec, Butte, Green Mountain, Russet Burbank and Sebago) showed antibiosis toward Eca in an in vitro assay. Sebago was host to the highest percentage of bacterial isolates inhibiting Eca growth in vitro (49.5%), followed by Green Mountain (33.3%), Kennebec (29.3%), Russet Burbank (12.9%) and Butte (1.8%). Of these, Curtobacterium luteum was the most common species. Few endophytic bacteria from Butte were inhibitory to Erwinia; all were from Pantoea agglomerans. Significantly higher populations of Erwinia-inhibiting bacteria were recovered from Kennebec (1.89 x 106 cfu fresh weight tuber tissue) as compared to the other cultivars; the lowest populations were recovered from Butte (0.01 x 106 cfu per g fresh weight tuber tissue). Published levels of cultivar disease resistance to blackleg did not correspond to actual bacterial soft rot development (induced by Eca) in an in vivo (tuber) assay. However, bacterial soft rot development was negatively correlated with the density of tuber populations of endophytic bacteria found able to inhibit Eca growth in vitro (R = -0.879, p = 0.05).