The Resource Allocation Strategies of E.coli under Different Limitations of Ribosome Synthesis

Facing constant selection pressure, microorganisms have to wisely allocate their limited resources. Building ribosomes takes a significant amount of cellular resources and their abundance is found to be tightly linked to cell growth rate. However, contrary to the prevailing theory that ribosomes always work at maximal efficiency, we found that phosphorus-limited E. coli produce protein at the same rate but contain significantly fewer ribosomes than cells limited for carbon or nitrogen. Why and how do ribosomes perform differently under different nutrient limitations? By modeling ribosome dynamics on both the macroscopic and microscopic scales, with input from detailed experimental measurements, we discovered that C/N-limitation results in high rates of aborted translation. As predicted by the model and validated by experiment, this mechanism, while not optimized for steady-state translation efficiency, promotes rapid acceleration of growth rate upon nutrient repletion. This system provides a thought provoking example of an evolutionary trade-off between current growth and future expectation. Our findings also indicate a previously unappreciated role for premature termination, and add an unexpected nutrient-dependent sub-optimality to the bacterial growth laws.