A better understanding of the impact of antibiotics on bacteria is required to increase the efficiency of antibiotic treatments and to slow the emergence of resistance. Using Escherichia coli, we examined how bacteria exposed to sublethal concentrations of ampicillin adjust gene expression patterns and metabolism to simultaneously deal with the antibiotic-induced damage and maintain rapid growth. We found that the treated cells increased energy production, as well as translation and macromolecular repair and protection. These responses are adaptive, because they confer increased survival not only to lethal ampicillin treatment but also to non-antibiotic lethal stresses. This robustness is modulated by nutrient availability. Because different antibiotics and other stressors induce the same set of responses, we propose that it constitutes a general core hormetic stress response. It is plausible that this response plays an important role in the robustness of bacteria exposed to antibiotic treatments and constant environmental fluctuations in natural environments.
SignificanceAntibiotic resistance leads to substantial mortality and morbidity and significant economic cost because it seriously undermines our ability to treat bacterial infections. Therefore, a better understanding of the effect of antibiotics on bacteria is needed to increase the effectiveness of treatments and slow the emergence of resistance. The bactericidal effects of antibiotics are triggered by target-specific interactions, but there is growing evidence that an important part of their cytotoxicity results from metabolic disturbances induced by treatment. In this article, we report that the perturbation of DNA replication by a wide-spectrum antibiotic, trimethoprim, affects bacterial metabolism, which provokes the production of genotoxic agents and DNA damage, whose processing ultimately contributes to cell death under both aerobic and anaerobic conditions.
Mitomycin C (MMC) is a genotoxic agent that induces DNA cross-links, DNA alkylation, and the production of reactive oxygen species (ROS). MMC induces the SOS response and RpoS regulons in Escherichia coli. SOS-encoded functions are required for DNA repair, whereas the RpoS regulon is typically induced by metabolic stresses that slow growth. Thus, induction of the RpoS regulon by MMC may be coincidental, because DNA damage slows growth; alternatively, the RpoS regulon may be an adaptive response contributing to cell survival. In this study, we show that the RpoS regulon is primarily induced by MMC-induced ROS production. We also show that RpoS regulon induction is required for the survival of MMC-treated growing cells. The major contributor to RpoS-dependent resistance to MMC treatment is DNA polymerase Pol II, which is encoded by the polB gene belonging to the SOS regulon. The observation that polB gene expression is controlled by the two major stress response regulons that are required to maximize survival and fitness further emphasizes the key role of this DNA polymerase as an important factor in genome stability.
Replication arrests due to the lack or the inhibition of replicative helicases are processed by recombination proteins. Consequently, cells deficient in the Rep helicase, in which replication pauses are frequent, require the RecBCD recombination complex for growth. rep recA mutants are viable and display no growth defect at 37 or 42°C. The putative role of chaperone proteins in rep and rep recA mutants was investigated by testing the effects of dnaK mutations. dnaK756 and dnaK306 mutations, which allow growth of otherwise wild-type Escherichia coli cells at 40°C, are lethal in rep recA mutants at this temperature. Furthermore, they affect the growth of rep mutants, and to a lesser extent, that of recA mutants. We conclude that both rep and recA mutants require DnaK for optimal growth, leading to low viability of the triple (rep recA dnaK) mutant. rep recA mutant cells form colonies at low efficiency when grown to exponential phase at 30°C. Although the plating defect is not observed at a high temperature, it is not suppressed by overexpression of heat shock proteins at 30°C. The plating defect of rep recA mutant cells is suppressed by the presence of catalase in the plates. The cryosensitivity of rep recA mutants therefore results from an increased sensitivity to oxidative damage upon propagation at low temperatures.Interconnections between DNA replication and homologous recombination have been observed in a number of organisms and are likely to play an important role in the maintenance of genome integrity (reviewed in references 19, 21, and 29). An additional link was found with the observation that recombination enzymes act in Escherichia coli to rescue blocked replication forks (40). rep mutants were used to study the fate of replication forks upon blockage. The rep mutation causes a slow progression of chromosomal replication forks which suggests the occurrence of frequent pauses (6, 23). Because the Rep helicase is able to displace a DNA-bound protein in vitro, it was proposed that in vivo Rep could facilitate chromosomal replication by dislodging DNA-bound proteins from the path of the replication forks (28,46).rep mutants require the recombination complex RecBCD for viability (43), suggesting a link between replication fork arrest and homologous recombination. RecBCD initiates homologous recombination of linear DNA and is therefore essential for the repair of DNA double-strand breaks. It binds to DNA double-strand ends and opens while simultaneously degrading the DNA. Upon encounter with a specific sequence named CHI, RecBCD promotes the formation of single-stranded DNA recognized by RecA (reviewed in references 20, 25, and 33). rep recBC mutant lethality results from the occurrence of RuvABC-dependent DNA double-strand breaks (30, 40). The RuvAB proteins bind to Holliday junctions and catalyze branch migration. The RuvAB-bound DNA is cleaved by RuvC, which resolves the recombination intermediates by introducing nicks in strands of opposite polarity (reviewed in reference 44). To account for the action of...
Bacterial cells have characteristic spatial and temporal scales. For instance, Escherichia coli, the typical rod-shaped bacteria, always maintains a relatively constant cell width and cell division time. However, whether the external physical perturbation of cell width has an impact on cell division time remains largely unexplored. In this work, we developed two microchannel chips, namely straight channels and ‘necked’ channels, to precisely regulate the width of E. coli cells and to investigate the correlation between cell width and division time of the cells. Our results show that, in the straight channels, the wide cells divide much slower than narrow cells. In the ‘necked’ channels, the cell division is remarkably promoted compared to that in straight channels with the same width. Besides, fluorescence time-lapse microscopy imaging of FtsZ dynamics shows that the cell pre-constriction time is more sensitive to cell width perturbation than cell constriction time. Finally, we revealed a significant anticorrelation between the death rate and the division rate of cell populations with different widths. Our work provides new insights into the correlation between the geometrical property and division time of E. coli cells and sheds new light on the future study of spatial–temporal correlation in cell physiology.
The contribution of toxin-antitoxin systems to the persistence of bacteria to antibiotics has been intensively studied. This is also the case with the E. coli TisB/IstR toxin-antitoxin system, but the contribution of TisB to the persistence to antibiotics turned out to be not as straightforward as anticipated.
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