Asymmetric division and polar growth define a non-canonical cell cycle in Bradyrhizobium.

Abstract

Bradyrhizobia are widely used as plant growth promoters in agriculture, yet their cell biology remains poorly understood. Here, we described for the first time, nucleoid segregation dynamics and the cell cycle of Bradyrhizobium at the cellular level. We show that highly asymmetric polar growth generates a short daughter cell and a longer mother cell at each division. Nucleoid compaction and positioning change across growth phases, culminating in a highly compacted, asymmetrically positioned nucleoid in stationary phase. ParB presents a subpolar localization, at the nucleoid periphery. Despite this pronounced cellular asymmetry and the presence of a single large chromosome, chromosome conformation capture reveals a global chromosome organization similar to that of bacteria undergoing conventional binary fission Together, these findings uncover a distinctive cell cycle program in Bradyrhizobium. showing that such extreme asymmetry in growth and division, significantly different from closely related characterized -Proteobacteriota, is compatible with conserved principles of chromosome organization.