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

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 <i>Azorhizobium caulindans</i>, which forms nodules in the stem and root of its host plant <i>Sesbania rostrata</i>. We found that calcium is essential for <i>A. caulindans</i> 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 <i>S. rostrata</i> root colonization of <i>A. caulinodans</i>. In total, these results show that calcium is essential for <i>A. caulindans</i> biofilm formation, and it affects the interaction between <i>A. caulinodans</i> and host plant.