A reliable clock for your microbiome: Genetic oscillator records changes in microbiome growth patterns in vivo -- ScienceDailyThe system uses an oscillating gene circuit, called a repressilator, as a kind of genetic clock to measure bacterial growth. The repressilator consists of three bacterial genes that code for three proteins (tetR, cl, and lacI), each of which blocks the expression of one of the other proteins. The genes are linked into a negative feedback loop, so that when the concentration of one of the repressor proteins falls below a certain level, the protein it had been repressing is expressed, which blocks the expression of the third protein, and the process repeats in a cyclical fashion. When all three genes are inserted into a plasmid and introduced into bacteria, the number of negative feedback loop cycles completed can serve as a record of how many cell divisions the bacteria have undergone. Every time the bacteria divide, any repressor proteins present in their cytoplasm are diluted, so their concentration gradually falls and triggers the expression of the next protein in the repressilator cycle. Crucially, the repressilator cycle repeats after 15.5 bacterial generations regardless of how quickly or slowly the bacteria are growing. This allows it to act as an objective measurement of time, much like a clock or a watch.