Colony dimorphism in bradyrhizobium strains

Area of Science:

• Microbiology
• Bacteriology

Background:

• Bradyrhizobium spp. are crucial nitrogen-fixing bacteria associated with legumes.
• Bacterial colony morphology can indicate physiological differences within a strain.
• Understanding colony type dynamics is important for microbial ecology and symbiosis.

Purpose of the Study:

• To investigate the phenomenon of colony dimorphism in Bradyrhizobium spp.
• To quantify the switching rates and equilibrium proportions between two colony types.
• To determine the growth characteristics of different colony types within strains.

Main Methods:

• Studied ten Bradyrhizobium spp. isolates from various legumes, forming two colony types.
• Subcultured 7-day-old colonies to assess cell type switching.
• Employed a computerized iterative procedure to calculate switching rates and predict equilibrium proportions.

Main Results:

• Significant variation in equilibrium proportions between colony types across strains (0.0216 to 0.9999).
• Switching rates differed, with some strains favoring wet-to-dry and others dry-to-wet transitions.
• Wetter colony types generally exhibited growth rates similar to or greater than drier types, with mean generation time differences of 0.37 h.

Conclusions:

• Colony dimorphism, characterized by two persistent colony types, is likely a common trait in Bradyrhizobium strains.
• The observed differences in switching rates and growth impact the population dynamics of Bradyrhizobium.
• This study provides quantitative insights into the stability and characteristics of distinct colony morphotypes.