Loss of topoisomerase I function affects the RpoS-dependent and GAD systems of acid resistance in Escherichia coli

Abstract

Acid resistance (AR) in Escherichia coli is important for its survival in the human gastrointestinal tract and involves three systems. The first AR system is dependent on the sigma factor RpoS. The second system (the GAD system) requires the glutamate decarboxylase isoforms encoded by the gadA and gadB genes. The third system (the ARG system) requires the arginine decarboxylase encoded by adiA. Loss of topoisomerase I function from topA deletion or Tn10 insertion mutations lowered the resistance to killing by pH 2 or 2?5 treatment by 10-fold to >100-fold. The RpoS and GAD systems were both affected by the topA mutation, but the ARG system of AR was not affected. Northern blot analysis showed that induction of gadA and gadB transcription in stationary phase and at pH 5?5 was decreased in the topA mutant. Western blot analysis showed that the topA mutation did not affect accumulation of RpoS, GadX or GadW proteins. Topoisomerase I might have a direct influence on the transcription of AR genes. This influence does not involve R-loop formation as the overexpression of RNase H did not alleviate the decrease of AR caused by the topA mutation. The effect of the topA mutation could be suppressed by an hns mutation, so topoisomerase I might be required to counteract the effect of H-NS protein on gene expression, in addition to its influence on RpoS-dependent transcription.

EVOLUTIONARY ADAPTATION TO ENVIRONMENTAL pH IN EXPERIMENTAL LINEAGES OF ESCHERICHIA COLI

“…Alkaline stress resistance may involve different mechanisms, with some evidence suggesting that a protein repair mechanism of L‐isoaspartyl protein carboxyl methyltransferase (PCM) becomes important only in high pH conditions (Hicks et al 2005). Further genetic analysis of our 5.3 and 7.8 pH‐evolved lines would be of particular interest to investigators considering the observations in 5.5 pH and 8.0 pH of topoisomerase I influence on RpoS‐dependent and GadA and GadB systems (Stewart et al 2005), and the decarboxylase activity noted at pH 5.6 linked to chloride ion exchange activities of ClC‐ec1 (Gut et al 2006), or the identification of alkaline resistance activity through ATP synthase and NhaA/MdfA antiporters (Padan et al 2005). The need for a molecular‐to‐ecological integration (Portner et al 2006) in addressing the issue of pathogenic bacteria in the environment may have benefited from this study of experimental evolutionary adaptation to environmental pH.…”

Bacterial Cell Killing Mediated by Topoisomerase I DNA Cleavage Activity

“…During infection, these challenge conditions are part of the host defense, so potential resistance against topoisomerase I-targeting drugs through loss of topA gene expression would at the same time reduce the ability of the drugresistant bacteria to survive the host challenge. Loss of the topA gene has also been shown more recently to decrease acid resistance of E. coli significantly (37). The recent emergence of multidrug-resistant bacterial pathogens in both community and hospital settings (38 -40) represents an urgent public health problem.…”

Targeting Bacterial Topoisomerases: How to Counter Mechanisms of Resistance

“…Loss of topoisomerase I function from topA gene mutations in E. coli has been shown to reduce survival following challenges of high temperature [97,98], acid [99], and oxidative stress challenge [100,101]. Perturbation of E. coli topoisomerase I interactions with RNA polymerase has been shown to increase susceptibility to antibacterial compounds and suppress the SOS-dependent elevation of mutation frequency associated with antibiotic resistance development [102].…”