Promoter activity dynamics in the lag phase of Escherichia coli

Abstract

BackgroundLag phase is a period of time with no growth that occurs when stationary phase bacteria are transferred to a fresh medium. Bacteria in lag phase seem inert: their biomass does not increase. The low number of cells and low metabolic activity make it difficult to study this phase. As a consequence, it has not been studied as thoroughly as other bacterial growth phases. However, lag phase has important implications for bacterial infections and food safety. We asked which, if any, genes are expressed in the lag phase of Escherichia coli, and what is their dynamic expression pattern.ResultsWe developed an assay based on imaging flow cytometry of fluorescent reporter cells that overcomes the challenges inherent in studying lag phase. We distinguish between lag1 phase- in which there is no biomass growth, and lag2 phase- in which there is biomass growth but no cell division. We find that in lag1 phase, most promoters are not active, except for the enzymes that utilize the specific carbon source in the medium. These genes show promoter activities that increase exponentially with time, despite the fact that the cells do not measurably increase in size. An oxidative stress promoter, katG, is also active. When cells enter lag2 and begin to grow in size, they switch to a full growth program of promoter activity including ribosomal and metabolic genes.ConclusionsThe observed exponential increase in enzymes for the specific carbon source followed by an abrupt switch to production of general growth genes is a solution of an optimal control model, known as bang-bang control. The present approach contributes to the understanding of lag phase, the least studied of bacterial growth phases.

Synthesis and degradation of FtsZ quantitatively predict the first cell division in starved bacteria

“…This occurs even in the absence of cell division. Biosynthesis without division echoed earlier work about net protein synthesis in lag phase before division (Madar et al , ). Mechanistically, the glucose‐induced activity may be explained by a combination of phenomena: (i) The glucose pulse is directly conveyed into metabolism and sweeps through the network.…”

Resuscitation of Pseudomonas aeruginosa from dormancy requires hibernation promoting factor (PA4463) for ribosome preservation

“…When the cells switch to slow-growth conditions, the number of ribosomes per cell diminishes through degradation or by partitioning to daughter cells. However, slowly growing and dormant cells must have mechanisms to maintain sufficient quantities of premade macromolecules, including ribosomes, to allow de novo protein synthesis and cell regrowth when conditions become favorable (37). Mechanisms have evolved to avoid complete loss of these essential macromolecules when cells are dormant.…”

Global Inhibition with Specific Activation: How p53 and MYC Redistribute the Transcriptome in the DNA Double-Strand Break Response

“…For example, alternative sigma factors in bacteria activate particular sets of genes during stress conditions; these compete with the housekeeping sigma factor, which is involved in general transcription (Browning and Busby, 2016). In bacteria transferred from nutrient-depleted to nutrient-rich medium, enzymes that metabolize the carbon source present in the medium are selectively transcribed, while most promoters are not active; normal promoter activity is restored upon transition to normal growth (Madar et al, 2013). …”