Mechanistic insights into E. coli recovery from growth arrest.

Bacteria survive hostile conditions by shutting down protein synthesis, but how they restart growth remains poorly understood. Here, we use an E. coli ΔrimM strain, which exhibits a prolonged growth arrest, as a model to investigate how bacteria recover from this state and restore protein synthesis. RimM is a conserved ribosome maturation factor for the 3'-major (head) domain of the 16S rRNA within the bacterial 30S subunit. The loss of RimM causes a longer delay in recovery than other 30S maturation factors, including RbfA. Cryo-EM analysis of ΔrimM ribosomes suggests a delayed recruitment of ribosomal proteins to the 30S head domain and increased occupancy of the initiation factors IF1 and IF3, as well as recruitment of the silencing factor RsfS to the 50S subunit. These coordinated changes provide a safeguarding mechanism to block the assembly of premature 70S ribosomes. Notably, while the delayed 30S assembly in ΔrimM reduces the activity of global protein synthesis during the recovery phase, bacteria attempt to compensate for this deficiency by producing higher levels of the ribosomal machinery, indicating a programmatic change in energy allocation. These findings highlight the importance of the RimM-assisted assembly of the ribosomal head domain for bacterial recovery from growth arrest.