Bacillus subtilis Colonization of Arabidopsis thaliana Roots Induces Multiple Biosynthetic Clusters for Antibiotic Production.

Harsh Maan,Ilana Kolodkin-Gal,Ziv Porat,Omri Gilhar

doi:10.3389/fcimb.2021.722778

Harsh Maan, Ilana Kolodkin-Gal + Show 2 more

Open Access

https://doi.org/10.3389/fcimb.2021.722778

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Abstract

Beneficial and probiotic bacteria play an important role in conferring immunity of their hosts to a wide range of bacterial, viral, and fungal diseases. Bacillus subtilis is a Gram-positive bacterium that protects the plant from various pathogens due to its capacity to produce an extensive repertoire of antibiotics. At the same time, the plant microbiome is a highly competitive niche, with multiple microbial species competing for space and resources, a competition that can be determined by the antagonistic potential of each microbiome member. Therefore, regulating antibiotic production in the rhizosphere is of great importance for the elimination of pathogens and establishing beneficial host-associated communities. In this work, we used B. subtilis as a model to investigate the role of plant colonization in antibiotic production. Flow cytometry and imaging flow cytometry (IFC) analysis supported the notion that Arabidopsis thaliana specifically induced the transcription of the biosynthetic clusters for the non-ribosomal peptides surfactin, bacilysin, plipastatin, and the polyketide bacillaene. IFC was more robust in quantifying the inducing effects of A. thaliana, considering the overall heterogeneity of the population. Our results highlight IFC as a useful tool to study the effect of association with a plant host on bacterial gene expression. Furthermore, the common regulation of multiple biosynthetic clusters for antibiotic production by the plant can be translated to improve the performance and competitiveness of beneficial members of the plant microbiome.

Highlights

Rhizobacteria can promote plant growth directly by colonization of the root and exert beneficial effects on plant growth and development (Kloepper et al, 2004)
As the transcriptional regulation of the biosynthetic clusters for antibiotics is diverse, this hypothesis needs to be evaluated experimentally. To address this question systematically, we considered the overall effect of the plant host in regulating the transcription from four distinct promoters for B. subtilis antibiotics: surfactin, bacillaene, bacilysin, and plipastatin
Our results indicated that the attachment with the root can enhance antibiotic production and may affect the competitiveness of root-associated bacteria compared with their free-living counterparts

Summary

Introduction

Rhizobacteria can promote plant growth directly by colonization of the root and exert beneficial effects on plant growth and development (Kloepper et al, 2004). Various PGPR have been isolated, including various Bacillus species, Burkholderia cepacia, and Pseudomonas fluorescens These beneficial rhizobacteria can confer fitness on their hosts by activating their immune system. The antimicrobial activity of B. subtilis has so far been demonstrated against bacterial, viral, and fungal soil-borne plant pathogens (Kloepper et al, 2004; Nagorska et al, 2007) This activity is mediated largely by antibiotic production: approximately 5% of the B. subtilis genome is dedicated to the synthesis of antimicrobial molecules by non-ribosomal peptide synthetases (NRPSs) or polyketide synthases (PKSs) (Stein, 2005; Ongena and Jacques, 2008; Kinsella et al, 2009; Caulier et al, 2019). In vitro and in planta studies have indicated the importance of four antibiotics for plant protection: surfactin, bacilysin, plipastatin, and bacillaene (Stein, 2005; Hou and Kolodkin-Gal, 2020; Arnaouteli et al, 2021; Ngalimat et al, 2021)

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