The distinct cell physiology of Bradyrhizobium at the population and cellular level

Abstract

The alfa-Proteobacteria belonging to Bradyrhizobium genus are microorganisms of extreme slow growth. Despite their extended use as inoculants in soybean production, their physiology remains poorly characterized. In this work, we produced quantitative data on four different isolates: B. diazoefficens USDA110, B. diazoefficiens USDA122 , B. japonicum E109 and B. japonicum USDA6 which are representative of specific genomic profiles. Notably, we found conserved physiological traits spanning Bradyrhizobium: i) the lag and initial exponential growth phases display cell aggregation; ii) the increase in nutrient concentration hinders growth; iii) cell size does not correlate with cell age; and vi) cell cycle presents an extreme polar growth. Meanwhile, fitness, cell size and in vitro growth widely vary across isolates correlating to ribosomal RNA operon number. In summary, this study provides novel empirical data that enriches the comprehension of the Bradyrhizobium (slow) growth dynamics and cell cycle.