Nitrogen Starvation Induces Persister Cell Formation in Escherichia coli

Abstract

To cope with fluctuations in their environment, bacteria have evolved multiple adaptive stress responses. One such response is the nitrogen regulation stress response, which allows bacteria, such as Escherichia coli, to cope with and overcome conditions of nitrogen limitation. This response is directed by the two-component system NtrBC, where NtrC acts as the major transcriptional regulator to activate the expression of genes to mount the response. Recently, my colleagues and I showed that NtrC directly regulates the expression of the relA gene, the major (p)ppGpp synthetase in E. coli, coupling the nitrogen regulation stress and stringent responses. As elevated levels of (p)ppGpp have been implicated in the formation of persister cells, here, I investigated whether nitrogen starvation promotes their formation and whether the NtrC-RelA regulatory cascade plays a role. The results reveal that nitrogen-starved E. coli synthesizes (p)ppGpp and forms a higher percentage of persister cells than nonstarved cells and that both NtrC and RelA are important for these processes. This study provides novel insights into how the formation of persisters can be promoted in response to a nutritional stress. IMPORTANCE Bacteria often reside in environments where nutrient availability is scarce; therefore, they have evolved adaptive responses to rapidly cope with conditions of feast and famine. Understanding the mechanisms that underpin the regulation of how bacteria cope with this stress is a fundamentally important question in the wider context of understanding the biology of the bacterial cell and bacterial pathogenesis. Two major adaptive mechanisms to cope with starvation are the nitrogen regulation (ntr) stress and stringent responses. Here, I describe how these bacterial stress responses are coordinated under conditions of nitrogen starvation to promote the formation of antibiotic-tolerant persister cells by elevating levels of the secondary messenger (p)ppGpp.

Fatty acid starvation activates RelA by depleting lysine precursor pyruvate

“…5A-C). Recently, RelA-dependent antibiotic tolerance was also observed during nitrogen starvation (Brown, 2019). Interestingly, the observation that the antibiotic tolerance induced by FA inhibitors can be completely reversed by supplementing lysine shows therapeutic potential of our study ( Fig.…”

Existence of log-phase Escherichia coli persisters and lasting memory of a starvation pulse

“…We have shown that a one-hour starvation pulse prior to the addition of the antibiotic affects long-term survival. This finding is consistent with a previous study of a temporal nitrogen downshift prior to antibiotics treatment, which was shown to elevate the persister level at 24 hours in a relA dependent manner [29]. Our study demonstrated that the memory can be remarkably long-lasting, as one-hour carbon starvation gave an increase in survival for at least 4 days in the wildtype strain grown in glucose medium.…”

Role of DNA Methylation in Persister Formation in UropathogenicE. coli

“…Our transcriptome analysis identified that crucial transcriptional regulators were massively downregulated in Δdam (Supplementary Table 2), these regulators are known to be involved in persister formation with the actication of stress response, including LexA 44 NtrB 45 , Fis 46 , Fnr, Lrp 47 , SoxS 48 , ArcA 47 49 , which may be responsible for the defect in persister formation in the Δdam mutant or survival in various stresses as shown in this study. It also revealed that demethylation in the Δdam mutant impaired persister formation by affecting extensive gene expression, such as upregulating genes involved in flagellar synthesis and assembly and galactose metabolism, propanoate metabolism and downregulating genes involved in different types of fimbrial biosynthesis, pilus synthesis, metabolism (carbon and nitrogen source), sugar phosphotransferase systems (PTS) and secretion-related pathways.…”