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Plant probiotic bacteria are being increasingly used to maximize both the productivity and quality of field crops. Pseudomonas chlororaphis O6 (PcO6) is a plant root colonizer with probiotic activities. This bacterium produces an array of metabolites, including a group of phenazines that are functional in plant protection. The paper reports responses of PcO6 to a nonionic triblock copolymer surfactant, Pluronic F68. This Pluronic exhibits membrane "healing" activity and improves cryopreservation recovery in eukaryotic cells. The product is FDA-approved and is applied as an adjuvant in formulations used in agriculture, medicine, and biotechnology. Growth of PcO6 on lysogeny broth at 25 °C was unhindered by 0.1 and 1.0 g/L F68, reduced at 10 g/L, and with significant inhibition at 100 g/L F68; micelle formation could account for inhibited growth at higher doses. Phenazine production was not changed by F68, whereas the surfactant activity of F68 induced the spread of bacterial colonization on 0.5% agar. Exposure of cells to fluorescein-labeled F68 resulted in intense fluorescence, stable to washing, showing a direct association of the Pluronic with the bacterium. However, neither protection nor harm was found for PcO6 cells suspended in either 0.1% or 1% F68 after three freeze (−20 °C)/thaw cycles. These findings suggest that F68 could be compatible for use in agricultural formulations with little effect on probiotics such as PcO6. [ABSTRACT FROM AUTHOR]

Formulations that include nanoparticles of CuO and ZnO are being considered for agricultural applications as fertilizers because they act as sources of Cu or Zn. Currently, few studies of the effects of these nanoparticles (NPs) consider the three-way interactions of NPs with the plant plus its microbiome. At doses that produced root shortening by both nanoparticles (NPs), CuO NPs induced the proliferation of elongated root hairs close to the root tip, and ZnO NPs increased lateral root formation in wheat seedlings (Triticum aestivum L.). These responses occurred with roots colonized by a beneficial bacterium, Pseudomonas chlororaphis O6 (PcO6), originally isolated from roots of wheat grown under dryland farming in calcareous soils. The PcO6-induced tolerance to drought stress in wheat seedlings was not impaired by the NPs. Rather, growth of the PcO6-colonized plants with NPs resulted in systemic increases in the expression of genes associated with tolerance to water stress. Increased expression in the shoots of other genes related to metal stress was consistent with higher levels of Cu and Zn in PcO6-colonized shoots grown with the NPs. This work demonstrates that plants grown with CuO or ZnO NPs showed cross-protection from different challenges such as metal stress and drought. Key words: beneficial bacterium, drought stress response, nanoparticles, root colonization. Des formules qui comportent du CuO et du ZnO a l'echelle nanometrique sont actuellement envisagees en vue d'applications agricoles comme fertilisant car elles agissent comme sources de Cu ou de Zn. En ce moment, peu d'etudes portant sur les effets de ces nanoparticules (NP) ont considere les interactions tripartites des NP avec la plante et son microbiome. A des doses qui provoquent un raccourcissement des racines par les deux types de nanoparticules, les NP de CuO induisaient une proliferation des poils racinaires allonges a proximite du bout de la racine et les NP de ZnO accroissaient la formation de racines laterales chez les jeunes pousses de ble (Triticum aestivum L.). Ces reponses survenaient avec des racines colonisees par une bacterie benefique, Pseudomonas chlororaphis O6 (PcO6), isolee a l'origine des racines de ble cultive en aridoculture dans des sols calcaires. La tolerance au stress de secheresse induite par PcO6 chez les jeunes pousses de ble n'etait pas diminuee par les NP. La croissance des plants colonises par PcO6 en presence de NP s'accompagnait plutot d'accroissements systemiques de l'expression de genes associes a la tolerance au stress hydrique. L'expression accrue d'autres genes relies au stress provoque par les metaux etait coherente avec les niveaux plus eleves de Cu et de Zn chez les pousses colonisees par PcO6 cultivees en presence de NP. Ce travail demontre que les plants cultives en presence de NP de CuO ou de ZnO presentent une protection croisee envers le stress provoque par les metaux et la secheresse. [Traduit par la Redaction] Mots-cles : bacterie benefique, reponse au stress de secheresse, nanoparticules, colonisation racinaire., Introduction Food security is a major factor addressing the world where population size, climate variability, urbanization of land, and water quality and supply are problematic. Drought is one of the [...]

Mutants of Pseudomonas putida lacking the superoxide dismutases were more sensitive to oxidative stress when cultured on glucose or components from bean root surfaces. The iron-superoxide dismutase is more critical in preventing oxidative stress than the manganese-superoxide dismutase.

The pseudomonas putida bacteria responsible for enhancing plant growth produces A, B and C catalases in stationary-phase cells. The catC gene from a genomic clone of p. putida had a 2,133-bp open reading frame similar to the stationary-phase-specific E. coli katE. Catalase C-deficient cell ability to colonize roots of bean or wheat plants under sterile conditions was not impaired.

The katB gene which codes for one catalese gene of Pseudomonas aeruginosa was cloned on a 5.4-kb EcoRI fragment which encodes 513 amino acids. The katB gene was located in the 71- to 75-min region of the P. aeruginosa chromosome. The katB mutant was 50% more sensitive to hydrogen peroxide than the wild-type bacteria. The findings indicated that KatB is needed by P. aeruginosa to maximize resistance to exogenous hydrogen peroxide.