Stochastic transcriptional pulses orchestrate flagellar biosynthesis in Escherichia coli

Abstract

The classic picture of flagellum biosynthesis in Escherichia coli, inferred from population measurements, depicts a deterministic program where promoters are sequentially up-regulated and are maintained steadily active throughout exponential growth. However, complex regulatory dynamics at the single-cell level can be masked by bulk measurements. Here, we discover that in individual E. coli cells, flagellar promoters are stochastically activated in pulses. These pulses are coordinated within specific classes of promoters and comprise “on” and “off” states, each of which can span multiple generations. We demonstrate that in this pulsing program, the regulatory logic of flagellar assembly dictates which promoters skip pulses. Surprisingly, pulses do not require specific transcriptional or translational regulation of the flagellar master regulator, FlhDC, but instead appears to be essentially governed by an autonomous posttranslational circuit. Our results suggest that even topologically simple transcriptional networks can generate unexpectedly rich temporal dynamics and phenotypic heterogeneities.

Nongenetic individuality, changeability, and inheritance in bacterial behavior

“…This type of asymmetry could lead to differences in the total number of such structures, as well as in their positioning on the cell envelope ( 31 ), both of which could affect the behavior. Changeability could then reflect processes occurring at shorter timescales, such as pulses of expression from promoters regulating flagellar synthesis ( 32 ), as well as more deterministic processes related to cell-cycle progression, such as the increased drag caused by cell growth. The main appeal of the statistical method for decomposing the total diversity described here is that it provides a higher-level overview of behavioral diversity in a population without the necessity to keep track of the large number of physiological and molecular factors known to influence the swimming behavior.…”

Non-Genetic Diversity in Chemosensing and Chemotactic Behavior

“…Recently, a study by the Cluzel lab revealed how regulated stochasticity in gene expression plays an important role in the transcription network governing E. coli chemotaxis [35]. In E. coli, there are 14 operons collectively encoding the flagellar components and the chemotaxis machinery.…”

“…Using a microfluidic device called the "mother machine" where a single cell's lineage can be monitored over multiple division events, the Cluzel lab quantified the expression of class I, II, and III genes over multiple generations using fluorescent reporters [35]. While the class I genes were expressed constitutively, class II and III gene expression occurred in pulses lasting multiple generations interspersed with long periods of inactivity (Figure 1e).…”

Quorum sensing sets the stage for the establishment and vertical transmission of Sodalis praecaptivus in tsetse flies

“…The strain expressing mCherry was constructed using the Lambda red recombineering methods reported previously [27] using a construct comprising a Zeocin resistance cassette linked to an mCherry allele that was codon-optimized for expression in gamma-Proteobacteria [58,59].…”