# Bradyrhizobium diazoefficiens cultures display phenotypic heterogeneity

## TL;DR

This paper shows that Bradyrhizobium diazoefficiens, a nitrogen-fixing bacterium, has diverse cell types in culture, which may help it survive in different soil environments.

## Contribution

The study reveals phenotypic heterogeneity in B. diazoefficiens and its potential role in environmental adaptation.

## Key findings

- B. diazoefficiens cultures show distinct phenotypes based on surface properties and metabolic activity.
- Phenotypic differences include variations in cell size, ATP levels, chemotaxis, and respiration.
- Phenotypic heterogeneity is not heritable and equilibrates within 10 generations.

## Abstract

Bacteria growing in liquid culture are assumed to be homogenous in phenotype. Characterization of individual cells shows that some clonal cultures contain more than one phenotype. Bacteria appear to employ bet hedging where various phenotypes help the species survive in diverse niches in soil and rhizosphere environments. We asked whether the agriculturally significant bacterium Bradyrhizobium diazoefficiens USDA 110, which fixes nitrogen with soybean plants, displays phenotypic heterogeneity when grown under laboratory conditions. We observed differential binding of sugar-specific lectins in isogenic populations, revealing differential surface properties. We employed Percoll™ density gradient centrifugation to separate clonal populations of exponential and stationary phase B. diazoefficiens into four fractions and characterized their phenotype by proteomics. Specific phenotypes were then characterized in detail. Fractions varied by cell size, polyhydroxyalkanoate content, lectin binding profile, growth rate, cellular adenosine triphosphate, chemotaxis, and respiration activity. Phenotypes were not heritable because the specific buoyant densities of fractions equilibrated within 10 generations. We propose that heterogeneity helps slow growing B. diazoefficiens proliferate and maintain populations in the different environments in soil and the rhizosphere.