Hormesis of glyphosate on ferulic acid metabolism and antifungal volatile production in rice root biocontrol endophyte Burkholderia cepacia LS-044.

Glyphosate (GP, N-phosphonomethyl glycine) is one of the most popular organophosphate herbicides widely used in agricultural practices worldwide. There have been extensive reports on the biohazard attributes and hormetic impacts of GP on plant and animal systems. However, the effects of GP on plant growth-promoting microbes and its ecological relevance remain unknown. Here, we show that GP does exert a hormetic impact on Burkholderia cepacia LS-044, a rice (Oryza sativa ssp. japonica cv. Tainung 71) root endophytic isolate. We used increasing doses of ferulic acid (FA, 1-25 mM) and GP (0.5-5 mM) to test the growth and antifungal volatile production in LS-044 by electrochemical, liquid chromatographic, gas chromatographic and spectrophotometric means. GP treatment at a low dose (0.5 mM) increased FA utilization and significantly (P < 0.0001) enhanced antifungal volatile activity in LS-044. Although FA (1 mM) was rapidly utilized by LS-044, no chromatographically detectable utilization of GP was observed at tested doses (0.5-5 mM). LS-044 emitted predominant amounts of tropone in addition to moderate-to-minor amounts of diverse ketones and/or their derivatives (acetone, acetophenone, 2-butanone, 1-propanone, 1-(2-furanyl-ethanone, 1-phenyl-1-propanone and 1-(3-pyridinyl)-1-propanone), d-menthol, 2-methoxy-3-(1-methylethyl)-pyrazine, dimethyl disulfide, pyridine and ammonium carbamate when grown under GP supplement. GP hormesis on LS-044 induced phenotypic variations in O. sativa ssp. japonica cv. Tainan 11 as evident through seed germination assay. Genes involved in the transformation of FA, and a key gene encoding 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) with Gly-94 and Tyr-95 residues localized at active site most likely rendering EPSPS sensitivity to GP, were detected in LS-044. This is the first report on the GP hormesis influencing morphological and metabolic aspects including volatile emission in a biocontrol bacterium that could modulate rice plant phenotype.

Volatile 1-octanol of tea (Camellia sinensis L.) fuels cell division and indole-3-acetic acid production in phylloplane isolate Pseudomonas sp. NEEL19.

Tea leaves possess numerous volatile organic compounds (VOC) that contribute to tea's characteristic aroma. Some components of tea VOC were known to exhibit antimicrobial activity; however, their impact on bacteria remains elusive. Here, we showed that the VOC of fresh aqueous tea leaf extract, recovered through hydrodistillation, promoted cell division and tryptophan-dependent indole-3-acetic acid (IAA) production in Pseudomonas sp. NEEL19, a solvent-tolerant isolate of the tea phylloplane. 1-octanol was identified as one of the responsible volatiles stimulating cell division, metabolic change, swimming motility, putative pili/nanowire formation and IAA production, through gas chromatography-mass spectrometry, microscopy and partition petri dish culture analyses. The bacterial metabolic responses including IAA production increased under 1-octanol vapor in a dose-dependent manner, whereas direct-contact in liquid culture failed to elicit such response. Thus, volatile 1-octanol emitting from tea leaves is a potential modulator of cell division, colonization and phytohormone production in NEEL19, possibly influencing the tea aroma.