Genome Insights of the Plant-Growth Promoting Bacterium Cronobacter muytjensii JZ38 With Volatile-Mediated Antagonistic Activity Against Phytophthora infestans.

Maged M. Saad,Heribert Hirt,Intikhab Alam,Laure Weisskopf,Salim Bougouffa,Floriane L’Haridon,Vladimir B. Bajic,Abdul Aziz Eida

doi:10.3389/fmicb.2020.00369

Abstract

Salinity stress is a major challenge to agricultural productivity and global food security in light of a dramatic increase of human population and climate change. Plant growth promoting bacteria can be used as an additional solution to traditional crop breeding and genetic engineering. In the present work, the induction of plant salt tolerance by the desert plant endophyte Cronobacter sp. JZ38 was examined on the model plant Arabidopsis thaliana using different inoculation methods. JZ38 promoted plant growth under salinity stress via contact and emission of volatile compounds. Based on the 16S rRNA and whole genome phylogenetic analysis, fatty acid analysis and phenotypic identification, JZ38 was identified as Cronobacter muytjensii and clearly separated and differentiated from the pathogenic C. sakazakii. Full genome sequencing showed that JZ38 is composed of one chromosome and two plasmids. Bioinformatic analysis and bioassays revealed that JZ38 can grow under a range of abiotic stresses. JZ38 interaction with plants is correlated with an extensive set of genes involved in chemotaxis and motility. The presence of genes for plant nutrient acquisition and phytohormone production could explain the ability of JZ38 to colonize plants and sustain plant growth under stress conditions. Gas chromatography–mass spectrometry analysis of volatiles produced by JZ38 revealed the emission of indole and different sulfur volatile compounds that may play a role in contactless plant growth promotion and antagonistic activity against pathogenic microbes. Indeed, JZ38 was able to inhibit the growth of two strains of the phytopathogenic oomycete Phytophthora infestans via volatile emission. Genetic, transcriptomic and metabolomics analyses, combined with more in vitro assays will provide a better understanding the highlighted genes’ involvement in JZ38’s functional potential and its interaction with plants. Nevertheless, these results provide insight into the bioactivity of C. muytjensii JZ38 as a multi-stress tolerance promoting bacterium with a potential use in agriculture.

Highlights

The dramatic increase in the human population and the increasingly negative effects of climate change pose a serious threat to global food security, with a number of severe social and economic problems (FAO, 2017)
JZ38 was highlighted as a plant growth promoting bacteria from a collection isolated from the root endosphere of the desert plant Tribulus terrestris (Eida et al, 2018)
The exhibited phenotype and salinity stress tolerance promoting (SSTP) ability of JZ38 was quantitatively confirmed on Arabidopsis thaliana as a model plant

Summary

Introduction

The dramatic increase in the human population and the increasingly negative effects of climate change pose a serious threat to global food security, with a number of severe social and economic problems (FAO, 2017). Models have predicted a significant decrease in the percentage of soil moisture and an increase in drought-experiencing surfaces on Earth by the end of the 21st century (Burke et al, 2006; Dai, 2012) Another major abiotic stress that adversely affects plant growth and crop yields is soil salinity which affects approx. Biological inoculants containing beneficial microbes are emerging as part of the 2nd green revolution technology to tackle biotic and abiotic stresses in a sustainable, environmentallyfriendly and chemical-free manner and as a more rapid and cost-efficient alternative to time-consuming crop breeding (BaezRogelio et al, 2017; de Zélicourt et al, 2018) These beneficial microbes, including plant growth promoting bacteria (PGPB), can establish symbiotic associations and protect plants against biotic stresses, such as fungal pathogens, or promote tolerance to abiotic stresses, such as salinity or drought stress (Hardoim et al, 2008; Eida et al, 2019). Bacteria can produce volatiles (e.g., volatile organic compounds/VOCs, sulfurcontaining compounds, or indole) that are used to communicate with other microbes (Weisskopf et al, 2016) or to promote growth and/or stress tolerance (Bailly et al, 2014; Liu and Zhang, 2015; Ledger et al, 2016)

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Results

Conclusion