Isogenic Bacteria Have Variable Lag Periods When Grown From a Single Cell Despite Having Identical Growth Conditions — 5a — Jacob Spreng, Manisha Guha, and Nicholas C. Butzin

Department of Biology and Microbiology; South Dakota State University; Brookings, SD, 57006; USA

Isogenic bacterial cultures are reported to exhibit uniform growth rates and lag periods at the population level, but this does not apply to individual cells. We diluted Bacillus megaterium (a gram-positive bacteria) to ~1 cell/well in a 96-well plate; the wells exhibited a wide range of lag periods, with no correlation between growth rate and the time to reach the log phase (lag period). While most wells reached the log phase simultaneously, there were always outlier cells with a longer or shorter lag period. We wanted to know if this variation is completely random or if bacteria employ a bet-hedging strategy, where the outlier cells offer a specific advantage. If the lag periods are random, we expect various short-lag and long-lag outlier numbers in each experiment, and, at times, there will be no outliers (the lag period is relatively the same between all wells). However, if this is not random, we expect these outliers to be at relatively consistent values. We observed a repeating pattern of short-lag and long-lag outlier clonal populations through multiple repetitions, suggesting that the formation of outliers is not completely random. Since cell growth depends on the type of carbon source, we aimed to determine if these outlier cells rely on specific carbon sources. We observed that these outliers form regardless of the carbon source. We also wondered if this phenomenon was unique to Gram-positive bacteria or prevails in all bacteria. To that end, we tested a Gram-negative bacterium, E. coli, with multiple carbon sources. Preliminary data shows that, like Bacillus sp., E. coli also has these outliers in a reproducible pattern. We wonder if cell shape or size is affecting the time cells lag. So, we will use microfluidic chambers and microscopy to observe the lag period of single cells.

South Dakota State University
Dr. Nicholas Butzin