Root Exudate-Induced Alterations in Bacillus cereus Cell Wall Contribute to Root Colonization and Plant Growth Promotion

Swarnalee Dutta,T. Swaroopa Rani,Appa Rao Podile,Raymond Schuch

doi:10.1371/journal.pone.0078369

Abstract

The outcome of an interaction between plant growth promoting rhizobacteria and plants may depend on the chemical composition of root exudates (REs). We report the colonization of tobacco, and not groundnut, roots by a non-rhizospheric Bacillus cereus (MTCC 430). There was a differential alteration in the cell wall components of B. cereus in response to the REs from tobacco and groundnut. Attenuated total reflectance infrared spectroscopy revealed a split in amide I region of B. cereus cells exposed to tobacco-root exudates (TRE), compared to those exposed to groundnut-root exudates (GRE). In addition, changes in exopolysaccharides and lipid-packing were observed in B. cereus grown in TRE-amended minimal media that were not detectable in GRE-amended media. Cell-wall proteome analyses revealed upregulation of oxidative stress-related alkyl hydroperoxide reductase, and DNA-protecting protein chain (Dlp-2), in response to GRE and TRE, respectively. Metabolism-related enzymes like 2-amino-3-ketobutyrate coenzyme A ligase and 2-methylcitrate dehydratase and a 60 kDa chaperonin were up-regulated in response to TRE and GRE. In response to B. cereus, the plant roots altered their exudate-chemodiversity with respect to carbohydrates, organic acids, alkanes, and polyols. TRE-induced changes in surface components of B. cereus may contribute to successful root colonization and subsequent plant growth promotion.

Highlights

Plant roots influence rhizospheric microenvironment through root exudates (REs)
We report that RE-induced changes in B. cereus cell surface have implications in root colonization and consequent growth promotion
Seed bacterization with five bacterial strains improved the growth of tobacco when compared to the non-bacterized control

Summary

Introduction

Plant roots influence rhizospheric microenvironment through root exudates (REs). Selection of bacteria in the root zone depends on niche utilization as well as rhizospheric-processes that reciprocate between the host plant and bacteria. Free oxygen, water, enzymes, mucilage and a diverse array of primary and secondary metabolites in the REs might deter one organism and attract the other. Differences in chemotactic responses of microbes towards amino acids, sugars and organic acids in the REs influence their ability to colonize roots [1]. Root nodulating-rhizobia sense flavonoids and betaines secreted by the host root, and respond by expressing nod genes [2,3]. Components of REs, like acetosyringone, induce the expression of virulence genes in Agrobacterium [4]. The REs, play an important role in plant-microbe interactions

Methods

Results

Discussion

Conclusion