The role of nitrogen-responsive regulators in controlling inorganic polyphosphate synthesis in Escherichia coli

Abstract

Inorganic polyphosphate (polyP) is synthesized by bacteria under stressful environmental conditions and acts by a variety of mechanisms to promote cell survival. While the kinase that synthesizes polyP (PPK, encoded by the ppk gene) is well known, ppk transcription is not activated by environmental stress and little is understood about how environmental stress signals lead to polyP accumulation. Previous work has shown that the transcriptional regulators DksA, RpoN (σ54) and RpoE (σ24) positively regulate polyP production, but not ppk transcription, in Escherichia coli . In this work, we examine the role of the alternative sigma factor RpoN and nitrogen starvation stress response pathways in controlling polyP synthesis. We show that the RpoN enhancer binding proteins GlnG and GlrR impact polyP production, and uncover a new role for the nitrogen phosphotransferase regulator PtsN (EIIANtr) as a positive regulator of polyP production, acting upstream of DksA, downstream of RpoN and apparently independently of RpoE. However, neither these regulatory proteins nor common nitrogen metabolites appear to act directly on PPK, and the precise mechanism(s) by which polyP production is modulated after stress remain(s) unclear. Unexpectedly, we also found that the genes that impact polyP production vary depending on the composition of the rich media in which the cells were grown before exposure to polyP-inducing stress. These results constitute progress towards deciphering the regulatory networks driving polyP production under stress, and highlight the remarkable complexity of this regulation and its connections to a broad range of stress-sensing pathways.

Proteomics analysis reveals a role forE. colipolyphosphate kinase in membrane structure and polymyxin resistance during starvation

“…We theorize that PPK may play an important role in this context. Notably, transcription of the ppk-ppx regulon does not change significantly during MOPS treatment [29] and the immediate molecular events that activate PPK during stresses of any kind remain unclear [29,[65][66][67]. Our work predicts that genes encoding PPK activators are also likely to play a role in polymyxin resistance.…”

Polyphosphate kinase regulates LPS structure and polymyxin resistance during starvation in E. coli

“…We theorize that PPK may play an important role in this context. Notably, the immediate molecular events that activate PPK during stresses of any kind remain unclear [ 26 , 67 – 69 ]. Our work predicts that genes encoding PPK activators are also likely to play a role in polymyxin resistance.…”

Microbial musings – Summer 2022

“…However, they show that none of the small molecules that reflect the nitrogen status of the cell can allosterically regulate Ppk activity. They conclude that, similar to other known regulators of polyP production, their new factors all appear to be regulating indirectly and finally present a new refined model of the cascade of regulator factors that appear to be involved in this complex process [25].…”

“…While the enzyme mechanism itself is well understood, with E. coli again providing a model system [24], the regulation of Ppk activity and the transcription of ppk is less well studied and here the authors Marvin C. Bowlin and Abagail Long from the group of Michael J. Gray at the University of Alabama at Birmingham, USA, look further into this question [25]. Gray's group has done much to place polyP within the larger picture of cellular physiology and regulation, specifically the stringent response, which was nicely summarized recently by Michael Downey (@DowneyUOttawa) at the University of Ottawa, Canada [26].…”