Gene expression cycles drive non-exponential bacterial growth.

Area of Science:

• Microbiology
• Systems Biology
• Cell Biology

Background:

• Bacterial populations typically grow exponentially, but individual cells exhibit diverse growth patterns.
• Observed single-cell growth includes super-exponential, convex, and linear trajectories in different species.
• Understanding the mechanisms behind these diverse growth patterns is crucial.

Purpose of the Study:

• To develop a single-cell model explaining diverse bacterial growth trajectories.
• To link gene expression, proteome allocation, and mass growth.
• To elucidate the regulatory mechanisms driving cell-cycle-specific elongation rates.

Main Methods:

• Developed a single-cell mathematical model.
• Linked gene expression dynamics to proteome allocation and cell mass growth.
• Calibrated model parameters using experimental data from various bacterial species.

Main Results:

• DNA-proportional mRNA transcription leads to near-exponential growth.
• Deviations from DNA-proportionality explain non-exponential growth patterns.
• Ribosome expression controls dry mass growth rate; cell envelope expression affects elongation rate.
• Cell-cycle-dependent transcription dynamics generate observed convex, super-exponential, and linear growth modes.

Conclusions:

• Cell-cycle-dependent gene expression timing dictates bacterial single-cell growth modes.
• The interplay between ribosomal and cell envelope protein expression regulates bacterial elongation.
• Provides a mechanistic basis for non-exponential single-cell growth in bacteria.