Abstract
Nutrient shifts from glycolytic-to-gluconeogenic carbon sources can create large sub-populations of extremely antibiotic tolerant bacteria, called persisters. Positive feedback in Escherichia coli central metabolism was believed to play a key role in the formation of persister cells. To examine whether positive feedback in nutrient transport can also support high persistence to β-lactams, we performed nutrient shifts for E. coli from gluconeogenic carbon sources to fatty acid (FA). We observed tri-phasic antibiotic killing kinetics characterized by a transient period of high antibiotic tolerance, followed by rapid killing then a slower persister-killing phase. The duration of transient tolerance (3–44 h) varies with pre-shift carbon source and correlates strongly with the time needed to accumulate the FA degradation enzyme FadD after the shift. Additionally, FadD accumulation time and thus transient tolerance time can be reduced by induction of the glyoxylate bypass prior to switching, highlighting that two interacting feedback loops simultaneously control the length of transient tolerance. Our results demonstrate that nutrient switches along with positive feedback are not sufficient to trigger persistence in a majority of the population but instead triggers only a temporary tolerance. Additionally, our results demonstrate that the pre-shift metabolic state determines the duration of transient tolerance and that supplying glyoxylate can facilitate antibiotic killing of bacteria.
Highlights
Antibiotic tolerance describes the ability of bacteria to survive longer periods of antibiotic treatment while remaining genetically susceptible to antibiotic killing (Meylan et al, 2018)
We demonstrate that the activity of the positive feedback loop in the glyoxylate bypass modulates the timing of both transient tolerance and FadD production on shifts to fatty acid (FA)
The fatty acyl-CoA ligase FadD controls the uptake and activation of extracellular free FAs to acyl-CoAs, which are catabolized by a series of FA degradation (Fad) enzymes to acetyl-CoA for use in central metabolism
Summary
Antibiotic tolerance describes the ability of bacteria to survive longer periods of antibiotic treatment while remaining genetically susceptible to antibiotic killing (Meylan et al, 2018). Tolerance can promote the ability of bacteria to acquire antibiotic resistance (Levin-Reisman et al, 2017; Windels et al, 2019; Liu et al, 2020), which reduces antibiotic efficacy in clinical settings and is contributing to an impending global public health crisis (Aslam et al, 2018; Talebi Bezmin Abadi et al, 2019) These public health problems have led to increased interest in understanding antibiotic tolerance mechanisms in microbes. Antibiotic tolerant cells were shown to have lower levels of ATP (Shan et al, 2017; Manuse et al, 2021), increased levels of alarmones (Hauryliuk et al, 2015; Svenningsen et al, 2019), and reduced translation (Gefen et al, 2008) These metabolic mechanisms alter the efficacy of antibiotics, leading to the prolonged survival of antibiotic tolerant cells (Stokes et al, 2019). Several stochastic mechanisms for generating and maintaining low metabolic activity, stochastic induction of toxin-antitoxin pairs and stochastic accumulation of (p)ppGpp, have been explored in connection with persistence (Balaban, 2004; Germain et al, 2015; Schmitz et al, 2017; Svenningsen et al, 2019; Evans and Zhang, 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
