Abstract
Under certain kinds of cytoplasmic stress, Escherichia coli selectively reproduce by distributing the newer cytoplasmic components to new-pole cells while sequestering older, damaged components in cells inheriting the old pole. This phenomenon is termed polar aging or cell division asymmetry. It is unknown whether cell division asymmetry can arise from a periplasmic stress, such as the stress of extracellular acid, which is mediated by the periplasm. We tested the effect of periplasmic acid stress on growth and division of adherent single cells. We tracked individual cell lineages over five or more generations, using fluorescence microscopy with ratiometric pHluorin to measure cytoplasmic pH. Adherent colonies were perfused continually with LBK medium buffered at pH 6.00 or at pH 7.50; the external pH determines periplasmic pH. In each experiment, cell lineages were mapped to correlate division time, pole age and cell generation number. In colonies perfused at pH 6.0, the cells inheriting the oldest pole divided significantly more slowly than the cells inheriting the newest pole. In colonies perfused at pH 7.50 (near or above cytoplasmic pH), no significant cell division asymmetry was observed. Under both conditions (periplasmic pH 6.0 or pH 7.5) the cells maintained cytoplasmic pH values at 7.2–7.3. No evidence of cytoplasmic protein aggregation was seen. Thus, periplasmic acid stress leads to cell division asymmetry with minimal cytoplasmic stress.
Highlights
Asymmetry is a much debated property of the bacterial cell [1,2,3,4,5,6,7,8]; see Table 1
We show that extracellular and periplasmic acid increases cell division asymmetry within an E. coli colony, compared to colonies cultured at pH 7.5
Cell division asymmetry occurs at external pH 6.0 but not at external pH 7.5
Summary
Asymmetry is a much debated property of the bacterial cell [1,2,3,4,5,6,7,8]; see Table 1. Some bacteria show morphological and functional asymmetry, such as Caulobacter crescentus whose cell division yields a stalked cell and a flagellated cell. Others such as Escherichia coli show bilateral symmetry and generate daughter cells that appear functionally equivalent. The old-pole and new-pole cells may show differential division times and reproductive potential, a property termed cell division asymmetry [4, 7, 9]. Old-pole cells undergo polar aging, defined as an increase in division time and higher rates of cell death over several generations
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