Mechanistic insights into <i>E. coli</i> recovery from growth arrest

Bacteria survive hostile conditions in clinically relevant conditions by shutting down protein synthesis, but how they restart growth remains poorly understood. Here, we use an <i>E. coli</i> Δ<i>rimM</i> strain, which exhibits a prolonged growth arrest, as a model to investigate how bacteria recover from this arrested 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 significantly longer delay in recovery than other 30S maturation factors, including RbfA - the presumed primary factor in 30S maturation. Cryo-EM analysis of Δ<i>rimM</i> ribosomes revealed 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 Δ<i>rimM</i> 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 to generate the ribosome machinery. These findings highlight the importance of the RimM-assisted assembly of the ribosomal head domain for bacterial recovery from growth arrest.