UC San Diego

Variations in growth rate for Escherichia coli were partly explained by the mother’s asymmetrical partitioning of damage and expressed gene products to its daughters. Between a daughter pair, the old daughter receives more damage and fewer expressed gene products, resulting in slower growth and thus said to be aging. Because ribosomes serve as cellular protein factories and are positively correlated with growth rate, it was hypothesized that ribosomes could also be allocated asymmetrically. By following cells with yfp-labeled ribosomes under time-lapse microscopy, we found that new daughters overall had a higher level of ribosomes than did old daughters, and the stronger asymmetry was associated with daughter pairs from old mothers. Moreover, we found the ribosome concentration to be higher at the old pole at birth and thereafter successively decreasing at the old pole and partly becoming redistributed to the mid-section as the cell elongates. At the time of division, ribosomes, at pinching site where the two new poles are being produced, were unevenly distributed, which was then associated with a higher ribosomal content in the new daughter and positively correlated with higher growth rate.