Effects of Calcium and Signal Sensing Systems on Azorhizobium caulinodans Biofilm Formation and Host Colonization.

Xiaolin Liu,Zhihong Xie,Kaiye Zhang,Dandan Wang,Yanan Liu,Desheng Zou

doi:10.3389/fmicb.2020.563367

Abstract

Biofilm formation is important for establishing plants-microbe associations. The role of calcium on biofilm formation has been studied in many bacteria except rhizobia. In this study, we investigated the role of calcium for biofilm formation in Azorhizobium caulindans, which forms nodules in the stem and root of its host plant Sesbania rostrata. We found that calcium is essential for A. caulindans biofilm formation, in addition to the presence of extracellular matrix components, eDNA and proteins. Also, calcium-mediated biofilm formation was tested with chemotaxis, motility, cyclic di-GMP synthesis, and quorum sensing mutants. Finally, calcium was found to promote S. rostrata root colonization of A. caulinodans. In total, these results show that calcium is essential for A. caulindans biofilm formation, and it affects the interaction between A. caulinodans and host plant.

Highlights

Environmental bacteria often form communities on biotic or abiotic surfaces called biofilms
We found that A. caulinodans forms a thicker and broader biofilm in tryptone and yeast extract (TY) medium compared to L3 medium after 3–5 days (Figure 1A)
The present work revealed that calcium plays a significant role in A. caulindans biofilm formation and A. caulindans colonization of S. rostrata

Summary

Introduction

Environmental bacteria often form communities on biotic or abiotic surfaces called biofilms. Biofilm formation enables bacteria to survive in harsh environments or build an association with hosts (Tallawi et al, 2017). The extracellular matrix provides a three-dimensional frame to stabilize the structure of biofilm, regulates the adhesion of bacteria to biotic or abiotic surface, and accommodates extracellular enzymes to digest biopolymers (Flemming and Wingender, 2010). Bacteria generate the Calcium-Mediated Biofilm of A. caulinodans extracellular matrix, and the components of the matrix changes depending on the bacterial species and growth conditions (Flemming and Wingender, 2010; Tallawi et al, 2017). In addition to polysaccharides and proteins, many bacteria contain additional components, such as extracellular DNA (eDNA) and fimbriae in biofilm (Tallawi et al, 2017)

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Results

Conclusion