Putrescine controls the formation ofEscherichia colipersister cells tolerant to aminoglycoside netilmicin

Abstract

Persisters are suggested to be the products of a phenotypic variability that are quasi-dormant forms of regular bacterial cells highly tolerant to antibiotics. Our previous investigations revealed that a decrease in antibiotic tolerance of Escherichia coli cells could be reached through the inhibition of key enzymes of polyamine synthesis (putrescine, spermidine). We therefore assumed that polyamines could be involved in persister cell formation. Data obtained in our experiments with the polyamine-deficient E. coli strain demonstrate that the formation of persisters tolerant to netilmicin is highly upregulated by putrescine in a concentration-dependent manner when cells enter the stationary phase. This period is also accompanied by dissociation of initially homogenous subpopulation of persister cells to some fractions differing in their levels of tolerance to netilmicin. With three independent experimental approaches, we demonstrate that putrescine-dependent upregulation of persister cell formation is mediated by stimulation of rpoS expression. Complementary activity of putrescine and RpoS results in ~ 1000-fold positive effect on persister cell formation.

Reduction in adaptor amounts establishes degradation hierarchy among protease substrates

“…Control experiments showed no differences among the three strains when exposed to ciprofloxacin (Fig. 5C), in agreement with previous findings (34,35).…”

“…Oat and the ClpXP Substrate RpoS. Putrescine is required for persistence toward aminoglycoside antibiotics in E. coli (34,35). In Pseudomonas aeruginosa, inactivation of the putrescine aminotransferase gene spuC (a homolog of the Salmonella oat gene) reduces persister formation (36).…”

“…The alternative sigma factor RpoS promotes persister formation toward aminoglycoside antibiotics in E. coli (34,35). In Salmonella, PhoP increases RpoS stability by activating transcription of the iraP gene (37), which specifies an antiadaptor for RssB, the adaptor that delivers RpoS to the protease ClpXP (30).…”

Polyamines Stimulate the Level of the σ38 Subunit (RpoS) of Escherichia coli RNA Polymerase, Resulting in the Induction of the Glutamate Decarboxylase-dependent Acid Response System via the gadE Regulon

“…Because some of the strains used in the literature, including those used to develop the concept of a polyamine modulon (MA261) (59) contain an amber mutation in codon 33, further work is needed to determine which strains have this amber mutation and to evaluate whether the effect of added polyamines is solely the result of read-through of such an amber mutation. Thus, Tkachenko et al (60) in their studies on bacterial persister cells specifically showed that putrescine increased RpoS levels both in rpoS amber and non-amber cells.…”

Novel RpoS-Dependent Mechanisms Strengthen the Envelope Permeability Barrier during Stationary Phase

“…Clinically, persisters have been found to be important to the pathogenesis of infections, including persistent tuberculosis, reoccurring uropathogenic E. coli infections, and Pseudomonas aeruginosa infections in cystic fibrosis patients (10)(11)(12)(13)(14). The rate of persister formation is much higher in stationary-phase cells than in actively growing cells (10,(15)(16)(17)(18)(19). In addition to increasing rates of persister formation, stationary phase can also increase rates of resistance and tolerance to antibiotics (18,(20)(21)(22)(23).…”