From Laboratory to Applications: Challenges and Progress with in vitro Dual Cultures of Potato and Beneficial Bacteria

Induction of endophytic colonization in rice (Oryza sativa L.) tissue culture plants by Azorhizobium caulinodans

Endophytic colonization in rice was induced using rhizobia. Dehusked seeds of rice hybrid, CORH2, were used as explants for induction of calli. MS medium was modified with 2,4-D (2.5 mg l(-1)) and kinetin (0.2 mg l(-1)) for callus induction. Well-developed calli were inoculated with Azorhizobium caulinodans strains ORS 571 and AA-SK-5 by means of imbibition. All treated calli had significant increases in protein content, total nitrogen and nitrogenase activity. Imbibition of ORS 571 had significant biochemical effect on the developing calli than AA-SK-5. The crop response study from the regenerated plantlets showed a positive correlation in yield than uninoculated control. The endophytic colonization was observed in all parts of the plants analyzed. Further, colonization was also confirmed by microtome sectioning.

Burkholderia phytofirmans sp. nov., a novel plant-associated bacterium with plant-beneficial properties

A Gram-negative, non-sporulating, rod-shaped, motile bacterium, with a single polar flagellum, designated strain PsJNT, 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 PsJNT 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 PsJNT 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 PsJNT and closely related species were identified. The predominant fatty acids in strain PsJNT were 16 : 0, 18 : 1ω7c and summed feature 3 (comprising 16 : 1ω7c and/or iso-15 : 0 2-OH). Isolate PsJNT 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 compound 3-hydroxy-C8-homoserine lactone was detected. Based on the results of this polyphasic taxonomic study, strain PsJNT and the seven Dutch isolates are considered to represent a single, novel species, for which the name Burkholderia phytofirmans sp. nov. is proposed. The type strain is strain PsJNT (=LMG 22146T=CCUG 49060T).