Adjuvant Pluronic F68 Is Compatible with a Plant Root-Colonizing Probiotic, Pseudomonas chlororaphis O6

Abstract

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.