Absolute measurements of mRNA translation in C. crescentus reveal important fitness costs of vitamin B12 scavenging

Caulobacter crescentus is a model for the bacterial cell cycle which culminates in asymmetric cell division, yet little is known about the absolute levels of protein synthesis of the cellular parts needed to complete the cell cycle. Here we utilize ribosome profiling to provide absolute measurements of mRNA translation of the C. crescentus genome, providing an important resource for the complete elucidation of the cell cycle gene-regulatory program. Analysis of protein synthesis rates revealed [~]4.5% of cellular protein synthesis are for genes related to vitamin B12 import (btuB) and B12 independent methionine biosynthesis (metE) when grown in common growth media lacking B12. While its facultative B12 lifestyle provides a fitness advantage in the absence of B12, we find that it provides lower fitness of the cells in the presence of B12, potentially explaining why many Caulobacter species have lost the metE gene and become obligates for B12.