Condition-dependent amorphous protein agglomerates control cytoplasmic rheology.

Area of Science:

• Microbiology and Biophysics
• Investigating molecular dynamics within bacterial cells.

Background:

• Bacterial cytoplasm exhibits molecular crowding, hindering large molecule diffusion and affecting cellular functions.
• Existing models do not fully explain the observed variations in cytoplasmic diffusion and rheology.

Purpose of the Study:

• To investigate the factors influencing cytoplasmic diffusion and rheology in Escherichia coli.
• To identify the molecular mechanisms behind variations in diffusion under different growth conditions.

Main Methods:

• Utilized single-particle tracking to monitor the diffusion of a 40-nm particle in Escherichia coli.
• Employed photoactivated light microscopy and electron microscopy to analyze protein behavior.
• Assessed the correlation between diffusion coefficients and protein abundance, specifically amino acid metabolism proteins (COG category 'E').

Main Results:

• Observed a three-fold variation in particle diffusion across exponential growth conditions.
• Found a significant anticorrelation between diffusion coefficient and the abundance of amino acid metabolism proteins.
• Demonstrated that lower diffusion correlates with increased cytoplasmic elasticity and identified protein agglomerate formation as a key factor.

Conclusions:

• Cytoplasmic diffusion and rheology are significantly influenced by the formation of protein agglomerates, particularly from amino acid metabolism proteins.
• Condition-induced changes in proteome composition directly impact cytoplasmic rheology through protein aggregation.
• This study reveals a novel mechanism controlling molecular transport and cellular mechanics in bacteria.