Bacteria adapt nutrient deprivation by reducing vacant 70S ribosomes via the silencing factor RsfS

Abstract Bacteria downregulate protein synthesis to conserve energy during nutrient deprivation stress. The stringent response is a widely recognized strategy employed by bacteria to counter this stress by suppressing de novo ribosome synthesis, while leaving the pre-existing ribosomes unaffected. The conserved bacterial ribosome silencing factor (RsfS) has been identified as the sole factor affecting the equilibrium between pre-existing 70S ribosomes and their subunits; however, the detailed mechanism remains elusive. Here we demonstrate how bacteria adapt to nutrient deprivation through RsfS-mediated processes. During nutrient downshift, vacant 70S ribosomes (without translating mRNAs and tRNAs) tend to accumulate in the cells, causing a devastating energy drain by stimulating the activity of GTPase proteins such as EF-G. RsfS exclusively dissociates the vacant 70S ribosomes, leaving those involved in translation with tRNAs intact, thus conserving cellular energy and resources. This process facilitates the expression of enzymes essential for biosynthetic pathways and energy production. These observations reveal the translational regulatory role of RsfS in efficiently utilizing cellular resources during starvation conditions.