Volatile-Mediated Killing of Arabidopsis thaliana by Bacteria Is Mainly Due to Hydrogen Cyanide

Abstract

The volatile-mediated impact of bacteria on plant growth is well documented, and contrasting effects have been reported ranging from 6-fold plant promotion to plant killing. However, very little is known about the identity of the compounds responsible for these effects or the mechanisms involved in plant growth alteration. We hypothesized that hydrogen cyanide (HCN) is a major factor accounting for the observed volatile-mediated toxicity of some strains. Using a collection of environmental and clinical strains differing in cyanogenesis, as well as a defined HCN-negative mutant, we demonstrate that bacterial HCN accounts to a significant extent for the deleterious effects observed when growing Arabidopsis thaliana in the presence of certain bacterial volatiles. The environmental strain Pseudomonas aeruginosa PUPa3 was less cyanogenic and less plant growth inhibiting than the clinical strain P. aeruginosa PAO1. Quorumsensing deficient mutants of C. violaceum CV0, P. aeruginosa PAO1, and P. aeruginosa PUPa3 showed not only diminished HCN production but also strongly reduced volatile-mediated phytotoxicity. The double treatment of providing plants with reactive oxygen species scavenging compounds and overexpressing the alternative oxidase AOX1a led to a significant reduction of volatile-mediated toxicity. This indicates that oxidative stress is a key process in the physiological changes leading to plant death upon exposure to toxic bacterial volatiles.Bacteria interact with plants in many different ways. Over the past few years, the significance of volatile compounds as mediators of bacterium-plant interactions has become increasingly evident (14,18,33,46,50,54). Using compartmental petri dish assays with a bacterial culture on one side and Arabidopsis plants on the other, bacterial volatiles have been shown to either promote the growth of plants (14,36) or to reduce it (16,18,43,46). Despite the strong effects observed, very little is known at present about the identity of the compounds involved in this volatile-mediated impact of bacteria on plants. In addition to carbon dioxide (17), 2,3-butanediol and its precursor acetoin are, to our knowledge, the only organic volatiles which have been put forward as candidates to explain the beneficial effects of bacterial volatiles on plants (14,36). Likewise, the compounds responsible for the "killing" effect of some bacterial strains on Arabidopsis thaliana are yet to be discovered.In the course of a study to assess the volatile-mediated impact of a collection of rhizosphere bacterial isolates on the model plant A. thaliana, we observed contrasting effects, ranging from 6-fold growth promotion to plant killing. We noticed that the most virulent strains were known producers of hydrogen cyanide (e.g., Pseudomonas or Chromobacterium species). We therefore hypothesized that hydrogen cyanide (HCN), a potent inhibitor of cytochrome c oxidase and of other metalcontaining enzymes, might be responsible for the observed plant-killing effects.Few bacterial species are known to produc...

Functional Diversity of Soil Bacteria from Organic Agro Ecosystem

“…Contrary to the role of HCN as abiocontrol agent, several researchers concluded that HCN is hardly a universal biocontrol agent and even caused phytotoxic effects in most in vitro experiments (Alström and Burns, 1989;Pal et al, 2000;Kremer and Souissi, 2001;Rudrappa et al, 2008;Blom et al, 2011). In a recent study by Rijavec and Lapanje (2016) have shown that there is no correlation between the amount of HCN produced by a particular strain and its ability to inhibit the growth of phytopathogenic bacteria or fungi.…”

Dimethyl Disulfide Produced by the Naturally Associated Bacterium Bacillus sp B55 Promotes Nicotiana attenuata Growth by Enhancing Sulfur Nutrition

“…The PGP effects were largely attributed to two volatiles, namely, 3-hydroxybutan-2-one (acetoin) and 2,3-butanediol. Several other studies have examined bacterial bioactive volatile compounds that promote or suppress plant growth (Farag et al, 2006;Splivallo et al, 2007;Vespermann et al, 2007;Kai et al, , 2010Gutiérrez-Luna et al, 2010;Zou et al, 2010;Blom et al, 2011aBlom et al, , 2011bVelazquez-Becerra et al, 2011;Weise et al, 2012;Yu and Lee, 2013), but the underlying mechanisms of these effects remain largely unknown (Wenke et al, 2012b). Profiling studies in Arabidopsis seedlings provided the first insights into changes in the transcriptome and proteome elicited by exposure to bacterial VOCs (Zhang et al, 2007;Kwon et al, 2010) and revealed the importance of hormone signaling, particularly that of indole-3-acetic acid and abscisic acid (Zhang et al, 2007(Zhang et al, , 2008.…”

Pseudomonas Strains Naturally Associated with Potato Plants Produce Volatiles with High Potential for Inhibition of Phytophthora infestans

“…The research carried out to understand the nature of this volatile-mediated interaction of bacteria with plants and with other bacteria has focused so far on model organisms (e.g., Arabidopsis thaliana and Escherichia coli) and has enabled identification of some of the active compounds involved in the respective interactions, such as indole, 2,3-butanediol, dimethyl disulfide, hydrogen sulfide, and ammonia. The research on model organisms has also contributed to understanding of the mechanisms underlying the observed phenotypic changes of increased (13)(14)(15) or decreased (16,17) plant biomass and increased antibiotic resistance in bacteria (2)(3)(4)18).…”