Scientists have devised a method to measure the impact of age on the growth rates of cellular populations, a development that offers new ways to understand and model the growth of bacteria, and could provide new insights into how genetic factors affect their life cycle. The research, which appears in Evolution: International Journal of Organic Evolution, was conducted by scientists at New York University and the University of Tokyo.
When bacterial cells age, their capacity for reproduction is reduced. Individual cells within populations are subject to the force of selection, which results from differences in growth rates. Broadly speaking, growing populations are dominated by relatively young cells. A population's age structure, however, depends sensitively on the interplay between selection and the reproductive capacities of the cells.
The researchers sought to understand how changes in cells' reproductive capacity would affect the population's growth rate. This question dates back to seminal research in population genetics by Ronald Fisher in the 1930s and William Hamilton in the 1960s. Typically, the answer is indirect, and relies on a measured life table and reproductive capacity, which takes into account survival and birth rates.
The NYU and University of Tokyo researchers hypothesized that a more direct gauge would be to examine the bacteria's lineagestheir history over several generations. In other words, they proposed looking backward several generations into the population's tree of cell divisions. This allowed them to directly measure the response of the bacteria's growth rate to age-specific changes in mortality and reproductive capacity.
"The force of selection within populations leaves key signatures in the population's lineage tree," said Edo Kussell, a professor of biology at NYU's Center for Genomics and Systems Biology and the study's corresponding author. "Theory allows us to interpret these in po
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New York University