Niilo Kaldalu - Academia.edu (original) (raw)

Papers by Niilo Kaldalu

YbeX of Escherichia coli, a member of the CorC protein family, is encoded in the same operon with... more YbeX of Escherichia coli, a member of the CorC protein family, is encoded in the same operon with ribosome-associated proteins YbeY and YbeZ. Here, we report the involvement of YbeX in ribosomal metabolism. The ΔybeX cells accumulate distinct 16S rRNA degradation intermediates in the 30S particles and the 70S ribosomes. E. coli lacking ybeX has a lengthened lag phase upon outgrowth from the stationary phase. This growth phenotype is heterogeneous at the individual cell level and especially prominent under low extracellular magnesium levels. The ΔybeX strain is sensitive to elevated growth temperatures and to several ribosome-targeting antibiotics that have in common the ability to induce the cold shock response in E. coli. Although generally milder, the phenotypes of the ΔybeX mutant overlap with those caused by ybeY deletion. A genetic screen revealed partial compensation of the ΔybeX growth phenotype by the overexpression of YbeY. These findings indicate an interconnectedness amon...

Springer eBooks, Oct 19, 2012

ABSTRACT The mqsRA locus of Escherichia coli K-12 codes for a translation-independent GCU site-sp... more ABSTRACT The mqsRA locus of Escherichia coli K-12 codes for a translation-independent GCU site-specific endoribonuclease MqsR and an antitoxin MqsA, which has an additional function as a transcriptional regulator of other genes. Besides binding to the regulatory region of its own promoter, the antitoxin MqsA binds to the promoter regions of cspD, rpoS, spy, and mcbR. By repressing these target genes, MqsRA participates in regulation of the general stress response and biofilm formation. Structural analyses have shown that MqsR belongs to the RelE superfamily and MqsR is thus the first known ribosome-independent mRNase belonging to this toxin family.

Methods in molecular biology, 2016

Genetically homogeneous bacterial cultures contain persisters, cells that are not killed by bacte... more Genetically homogeneous bacterial cultures contain persisters, cells that are not killed by bactericidal antibiotics. These cells are suggested to be involved in the establishment of chronic infections. Persister levels depend on growth conditions. Here, we discuss the parameters that have to be considered when measuring persister levels and provide a sample protocol to do it.

BMC Microbiology, Feb 21, 2013

Background: Bacterial toxin-antitoxin (TA) systems are formed by potent regulatory or suicide fac... more Background: Bacterial toxin-antitoxin (TA) systems are formed by potent regulatory or suicide factors (toxins) and their short-lived inhibitors (antitoxins). Antitoxins are DNA-binding proteins and auto-repress transcription of TA operons. Transcription of multiple TA operons is activated in temporarily non-growing persister cells that can resist killing by antibiotics. Consequently, the antitoxin levels of persisters must have been dropped and toxins are released of inhibition. Results: Here, we describe transcriptional cross-activation between different TA systems of Escherichia coli. We find that the chromosomal relBEF operon is activated in response to production of the toxins MazF, MqsR, HicA, and HipA. Expression of the RelE toxin in turn induces transcription of several TA operons. We show that induction of mazEF during amino acid starvation depends on relBE and does not occur in a relBEF deletion mutant. Induction of TA operons has been previously shown to depend on Lon protease which is activated by polyphospate accumulation. We show that transcriptional cross-activation occurs also in strains deficient for Lon, ClpP, and HslV proteases and polyphosphate kinase. Furthermore, we find that toxins cleave the TA mRNA in vivo, which is followed by degradation of the antitoxin-encoding fragments and selective accumulation of the toxin-encoding regions. We show that these accumulating fragments can be translated to produce more toxin. Conclusion: Transcriptional activation followed by cleavage of the mRNA and disproportionate production of the toxin constitutes a possible positive feedback loop, which can fire other TA systems and cause bistable growth heterogeneity. Cross-interacting TA systems have a potential to form a complex network of mutually activating regulators in bacteria.

Journal of Bacteriology, Jul 1, 2010

RNA Biology, Nov 18, 2017

The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and pr... more The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and protein synthesis by targeting cellular mRNAs. As an exception, E. coli MazF was reported to cleave also 16S rRNA at a single site and separate an anti-Shine-Dalgarno sequence-containing RNA fragment from the ribosome. We noticed extensive rRNA fragmentation in response to induction of the toxins MazF and MqsR, which suggested that these toxins can cleave rRNA at multiple sites. We adapted differential RNA-sequencing to map the toxin-cleaved 5′- and 3′-ends. Our results show that the MazF and MqsR cleavage sites are located within structured rRNA regions and, therefore, are not accessible in assembled ribosomes. Most of the rRNA fragments are located in the aberrant ribosomal subunits that accumulate in response to toxin induction and contain unprocessed rRNA precursors. We did not detect MazF- or MqsR-cleaved rRNA in stationary phase bacteria and in a...

BMC Microbiology, 2008

Background A fundamental characteristic of cells is the ability to divide. To date, most paramete... more Background A fundamental characteristic of cells is the ability to divide. To date, most parameters of bacterial cultures, including cell division, have been measured as cell population averages, assuming that all bacteria divide at a uniform rate. Results We monitored the division of individual cells in Escherichia coli cultures during different growth phases. Our experiments are based on the dilution of green fluorescent protein (GFP) upon cell division, monitored by flow cytometry. The results show that the vast majority of E. coli cells in exponentially growing cultures divided uniformly. In cultures that had been in stationary phase up to four days, no cell division was observed. However, upon dilution of stationary phase culture into fresh medium, two subpopulations of cells emerged: one that started dividing and another that did not. These populations were detectable by GFP dilution and displayed different side scatter parameters in flow cytometry. Further analysis showed tha...

mBio, Jan 12, 2018

Persistence is a reversible and low-frequency phenomenon allowing a subpopulation of a clonal bac... more Persistence is a reversible and low-frequency phenomenon allowing a subpopulation of a clonal bacterial population to survive antibiotic treatments. Upon removal of the antibiotic, persister cells resume growth and give rise to viable progeny. Type II toxin-antitoxin (TA) systems were assumed to play a key role in the formation of persister cells in based on the observation that successive deletions of TA systems decreased persistence frequency. In addition, the model proposed that stochastic fluctuations of (p)ppGpp levels are the basis for triggering activation of TA systems. Cells in which TA systems are activated are thought to enter a dormancy state and therefore survive the antibiotic treatment. Using independently constructed strains and newly designed fluorescent reporters, we reassessed the roles of TA modules in persistence both at the population and single-cell levels. Our data confirm that the deletion of 10 TA systems does not affect persistence to ofloxacin or ampicill...

Microbiology and Molecular Biology Reviews, 2020

Many bacterial pathogens can permanently colonize their host and establish either chronic or recu... more Many bacterial pathogens can permanently colonize their host and establish either chronic or recurrent infections that the immune system and antimicrobial therapies fail to eradicate. Antibiotic persisters (persister cells) are believed to be among the factors that make these infections challenging. Persisters are subpopulations of bacteria which survive treatment with bactericidal antibiotics in otherwise antibiotic-sensitive cultures and were extensively studied in a hope to discover the mechanisms that cause treatment failures in chronically infected patients; however, most of these studies were conducted in the test tube.

Smart Materials and Structures

Smart and soft electroactive polymer actuators have many beneficial properties, making them attra... more Smart and soft electroactive polymer actuators have many beneficial properties, making them attractive for biomimetic and biomedical applications. However, the selection of components to fabricate biofriendly composites has been limited. Although biofriendly options for electrodes and membranes are available, the conventional ionic liquids (ILs) often used as the electrolytes in the actuators have been considered toxic in varying degrees. Here we present a smart electroactive composite with carefully designed and selected components that have shown low toxicity and a biofriendly nature. In the present study, polypyrrole-PVdF trilayer actuators using six different choline ILs were prepared and characterized. Choline ILs have shown promise in applications where low environmental and biological impact is critical. Despite this, the anions in ILs have a strong impact on toxicity. To evaluate how the anions effect the bioactivity of the ILs used to prepare the actuators, the ILs were tested on different microbial cultures (Escherichia coli, Staphylococcus aureus, Shewanella oneidensis MR-1) and HeLa cells. All of the selected choline ILs showed minimal toxic effects even at high concentrations. Electro-chemomechanical characterization of the actuators indicated that polypyrrole-PVdF actuators with choline ILs are viable candidates for soft robotic applications. From the tested ILs, choline acetate showed the highest strain difference and outperformed the reference system containing an imidazolium-based IL.

Science Signaling

Bacterial persisters survive antibiotic treatment and can cause chronic infections. In this issue... more Bacterial persisters survive antibiotic treatment and can cause chronic infections. In this issue of Science Signaling, Pontes and Groisman suggest that there is no specific molecular pathway responsible for persister formation in Salmonella and that slow growth is the decisive factor.

mBio

I n a recent paper, Nigam and colleagues analyzed the stress-related effects of the endoribonucle... more I n a recent paper, Nigam and colleagues analyzed the stress-related effects of the endoribonuclease toxin MazF on the Escherichia coli proteome (1). The authors from the lab of Hanna Engelberg-Kulka-the discoverer of the mazEF toxin-antitoxin system (2)-claim that MazF creates a unique stress-induced translation machinery (STM). The STM hypothesis states that the toxin cleaves selected mRNAs within 5=-leader sequences to produce a pool of leaderless transcripts that are, in turn, translated by special stress ribosomes (3, 4). The latter are formed when the toxin cleaves off an anti-Shine-Dalgarno sequence-containing fragment from the 3= end of 16S rRNA in mature ribosomes (3). Thus, MazF is postulated to reshape translation in stressed E. coli similarly to how the S factor reshapes transcription.

mBio

W e thank David W. Holden and Jeff Errington for their comments (1). We agree that scientific res... more W e thank David W. Holden and Jeff Errington for their comments (1). We agree that scientific research is inherently error-prone. Therefore, validation, reassessment, and reinterpretation of one's own and others' results is part of the scientific approach, regardless of whether the conclusions are affirming or critical. We also agree that further work is needed to establish whether, and in which settings, each individual toxin-antitoxin (TA) system contributes to persister formation in Escherichia coli K-12 and/or in other bacterial species. In the following paragraphs, we express our opinion on the topics on which Holden and Errington saw some overstatements and factual inaccuracies in our paper (2).

RNA Biology, 2016

The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and pr... more The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and protein synthesis by targeting cellular mRNAs. As an exception, E. coli MazF was reported to cleave also 16S rRNA at a single site and separate an anti-Shine-Dalgarno sequence-containing RNA fragment from the ribosome. We noticed extensive rRNA fragmentation in response to induction of the toxins MazF and MqsR, which suggested that these toxins can cleave rRNA at multiple sites. We adapted differential RNAsequencing to map the toxin-cleaved 5 0 -and 3 0 -ends. Our results show that the MazF and MqsR cleavage sites are located within structured rRNA regions and, therefore, are not accessible in assembled ribosomes. Most of the rRNA fragments are located in the aberrant ribosomal subunits that accumulate in response to toxin induction and contain unprocessed rRNA precursors. We did not detect MazF-or MqsR-cleaved rRNA in stationary phase bacteria and in assembled ribosomes. Thus, we conclude that MazF and MqsR cleave rRNA precursors before the ribosomes are assembled and potentially facilitate the decay of surplus rRNA transcripts during stress.

Scientific Reports, 2016

is an antimicrobial with a direct reactivity against thiol groups. It is active against Gram-posi... more is an antimicrobial with a direct reactivity against thiol groups. It is active against Gram-positive and Gram-negative bacteria, yeasts and filamentous fungi. By reacting with thiol groups it causes direct damage to proteins but, as a result, is very short-living and interconverts into an array of reaction products. Our aim was to characterize thiol reactivity of G1 and its conversion products and establish how much of antimicrobial and cytotoxic effects are due to the primary activity of G1 and how much can be attributed to its reaction products. Stability of G1 in growth media as well as its conversion in the presence of thiols was characterized. The structures of G1 decomposition products were determined using NMR and mass-spectroscopy. Concentration-and time-dependent killing curves showed that G1 is bacteriostatic for Escherichia coli at the concentration of 16 μg/ml and bactericidal at 32 μg/ml. However, G1 is inefficient against nongrowing E. coli. Addition of cysteine to medium reduces the antimicrobial potency of G1. Nevertheless, the reaction products of G1 and cysteine enabled prolonged antimicrobial action of the drug. Therefore, the activity of 2-bromo-5-(2-bromo-2-nitrovinyl)furan is a sum of its immediate reactivity and the antibacterial effects of the conversion products.

Applied microbiology and biotechnology, Jan 4, 2016

Persisters-a drug-tolerant sub-population in an isogenic bacterial culture-have been featured thr... more Persisters-a drug-tolerant sub-population in an isogenic bacterial culture-have been featured throughout the last decade due to their important role in recurrent bacterial infections. Numerous investigations detail the mechanisms responsible for the formation of persisters and suggest exciting strategies for their eradication. In this review, we argue that the very term "persistence" is currently used to describe a large and heterogeneous set of physiological phenomena that are functions of bacterial species, strains, growth conditions, and antibiotics used in the experiments. We caution against the oversimplification of the mechanisms of persistence and urge for a more rigorous validation of the applicability of these mechanisms in each case.

YbeX of Escherichia coli, a member of the CorC protein family, is encoded in the same operon with... more YbeX of Escherichia coli, a member of the CorC protein family, is encoded in the same operon with ribosome-associated proteins YbeY and YbeZ. Here, we report the involvement of YbeX in ribosomal metabolism. The ΔybeX cells accumulate distinct 16S rRNA degradation intermediates in the 30S particles and the 70S ribosomes. E. coli lacking ybeX has a lengthened lag phase upon outgrowth from the stationary phase. This growth phenotype is heterogeneous at the individual cell level and especially prominent under low extracellular magnesium levels. The ΔybeX strain is sensitive to elevated growth temperatures and to several ribosome-targeting antibiotics that have in common the ability to induce the cold shock response in E. coli. Although generally milder, the phenotypes of the ΔybeX mutant overlap with those caused by ybeY deletion. A genetic screen revealed partial compensation of the ΔybeX growth phenotype by the overexpression of YbeY. These findings indicate an interconnectedness amon...

Springer eBooks, Oct 19, 2012

ABSTRACT The mqsRA locus of Escherichia coli K-12 codes for a translation-independent GCU site-sp... more ABSTRACT The mqsRA locus of Escherichia coli K-12 codes for a translation-independent GCU site-specific endoribonuclease MqsR and an antitoxin MqsA, which has an additional function as a transcriptional regulator of other genes. Besides binding to the regulatory region of its own promoter, the antitoxin MqsA binds to the promoter regions of cspD, rpoS, spy, and mcbR. By repressing these target genes, MqsRA participates in regulation of the general stress response and biofilm formation. Structural analyses have shown that MqsR belongs to the RelE superfamily and MqsR is thus the first known ribosome-independent mRNase belonging to this toxin family.

Methods in molecular biology, 2016

Genetically homogeneous bacterial cultures contain persisters, cells that are not killed by bacte... more Genetically homogeneous bacterial cultures contain persisters, cells that are not killed by bactericidal antibiotics. These cells are suggested to be involved in the establishment of chronic infections. Persister levels depend on growth conditions. Here, we discuss the parameters that have to be considered when measuring persister levels and provide a sample protocol to do it.

BMC Microbiology, Feb 21, 2013

Background: Bacterial toxin-antitoxin (TA) systems are formed by potent regulatory or suicide fac... more Background: Bacterial toxin-antitoxin (TA) systems are formed by potent regulatory or suicide factors (toxins) and their short-lived inhibitors (antitoxins). Antitoxins are DNA-binding proteins and auto-repress transcription of TA operons. Transcription of multiple TA operons is activated in temporarily non-growing persister cells that can resist killing by antibiotics. Consequently, the antitoxin levels of persisters must have been dropped and toxins are released of inhibition. Results: Here, we describe transcriptional cross-activation between different TA systems of Escherichia coli. We find that the chromosomal relBEF operon is activated in response to production of the toxins MazF, MqsR, HicA, and HipA. Expression of the RelE toxin in turn induces transcription of several TA operons. We show that induction of mazEF during amino acid starvation depends on relBE and does not occur in a relBEF deletion mutant. Induction of TA operons has been previously shown to depend on Lon protease which is activated by polyphospate accumulation. We show that transcriptional cross-activation occurs also in strains deficient for Lon, ClpP, and HslV proteases and polyphosphate kinase. Furthermore, we find that toxins cleave the TA mRNA in vivo, which is followed by degradation of the antitoxin-encoding fragments and selective accumulation of the toxin-encoding regions. We show that these accumulating fragments can be translated to produce more toxin. Conclusion: Transcriptional activation followed by cleavage of the mRNA and disproportionate production of the toxin constitutes a possible positive feedback loop, which can fire other TA systems and cause bistable growth heterogeneity. Cross-interacting TA systems have a potential to form a complex network of mutually activating regulators in bacteria.

Journal of Bacteriology, Jul 1, 2010

RNA Biology, Nov 18, 2017

The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and pr... more The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and protein synthesis by targeting cellular mRNAs. As an exception, E. coli MazF was reported to cleave also 16S rRNA at a single site and separate an anti-Shine-Dalgarno sequence-containing RNA fragment from the ribosome. We noticed extensive rRNA fragmentation in response to induction of the toxins MazF and MqsR, which suggested that these toxins can cleave rRNA at multiple sites. We adapted differential RNA-sequencing to map the toxin-cleaved 5′- and 3′-ends. Our results show that the MazF and MqsR cleavage sites are located within structured rRNA regions and, therefore, are not accessible in assembled ribosomes. Most of the rRNA fragments are located in the aberrant ribosomal subunits that accumulate in response to toxin induction and contain unprocessed rRNA precursors. We did not detect MazF- or MqsR-cleaved rRNA in stationary phase bacteria and in a...

BMC Microbiology, 2008

Background A fundamental characteristic of cells is the ability to divide. To date, most paramete... more Background A fundamental characteristic of cells is the ability to divide. To date, most parameters of bacterial cultures, including cell division, have been measured as cell population averages, assuming that all bacteria divide at a uniform rate. Results We monitored the division of individual cells in Escherichia coli cultures during different growth phases. Our experiments are based on the dilution of green fluorescent protein (GFP) upon cell division, monitored by flow cytometry. The results show that the vast majority of E. coli cells in exponentially growing cultures divided uniformly. In cultures that had been in stationary phase up to four days, no cell division was observed. However, upon dilution of stationary phase culture into fresh medium, two subpopulations of cells emerged: one that started dividing and another that did not. These populations were detectable by GFP dilution and displayed different side scatter parameters in flow cytometry. Further analysis showed tha...

mBio, Jan 12, 2018

Persistence is a reversible and low-frequency phenomenon allowing a subpopulation of a clonal bac... more Persistence is a reversible and low-frequency phenomenon allowing a subpopulation of a clonal bacterial population to survive antibiotic treatments. Upon removal of the antibiotic, persister cells resume growth and give rise to viable progeny. Type II toxin-antitoxin (TA) systems were assumed to play a key role in the formation of persister cells in based on the observation that successive deletions of TA systems decreased persistence frequency. In addition, the model proposed that stochastic fluctuations of (p)ppGpp levels are the basis for triggering activation of TA systems. Cells in which TA systems are activated are thought to enter a dormancy state and therefore survive the antibiotic treatment. Using independently constructed strains and newly designed fluorescent reporters, we reassessed the roles of TA modules in persistence both at the population and single-cell levels. Our data confirm that the deletion of 10 TA systems does not affect persistence to ofloxacin or ampicill...

Microbiology and Molecular Biology Reviews, 2020

Many bacterial pathogens can permanently colonize their host and establish either chronic or recu... more Many bacterial pathogens can permanently colonize their host and establish either chronic or recurrent infections that the immune system and antimicrobial therapies fail to eradicate. Antibiotic persisters (persister cells) are believed to be among the factors that make these infections challenging. Persisters are subpopulations of bacteria which survive treatment with bactericidal antibiotics in otherwise antibiotic-sensitive cultures and were extensively studied in a hope to discover the mechanisms that cause treatment failures in chronically infected patients; however, most of these studies were conducted in the test tube.

Smart Materials and Structures

Smart and soft electroactive polymer actuators have many beneficial properties, making them attra... more Smart and soft electroactive polymer actuators have many beneficial properties, making them attractive for biomimetic and biomedical applications. However, the selection of components to fabricate biofriendly composites has been limited. Although biofriendly options for electrodes and membranes are available, the conventional ionic liquids (ILs) often used as the electrolytes in the actuators have been considered toxic in varying degrees. Here we present a smart electroactive composite with carefully designed and selected components that have shown low toxicity and a biofriendly nature. In the present study, polypyrrole-PVdF trilayer actuators using six different choline ILs were prepared and characterized. Choline ILs have shown promise in applications where low environmental and biological impact is critical. Despite this, the anions in ILs have a strong impact on toxicity. To evaluate how the anions effect the bioactivity of the ILs used to prepare the actuators, the ILs were tested on different microbial cultures (Escherichia coli, Staphylococcus aureus, Shewanella oneidensis MR-1) and HeLa cells. All of the selected choline ILs showed minimal toxic effects even at high concentrations. Electro-chemomechanical characterization of the actuators indicated that polypyrrole-PVdF actuators with choline ILs are viable candidates for soft robotic applications. From the tested ILs, choline acetate showed the highest strain difference and outperformed the reference system containing an imidazolium-based IL.

Science Signaling

Bacterial persisters survive antibiotic treatment and can cause chronic infections. In this issue... more Bacterial persisters survive antibiotic treatment and can cause chronic infections. In this issue of Science Signaling, Pontes and Groisman suggest that there is no specific molecular pathway responsible for persister formation in Salmonella and that slow growth is the decisive factor.

mBio

I n a recent paper, Nigam and colleagues analyzed the stress-related effects of the endoribonucle... more I n a recent paper, Nigam and colleagues analyzed the stress-related effects of the endoribonuclease toxin MazF on the Escherichia coli proteome (1). The authors from the lab of Hanna Engelberg-Kulka-the discoverer of the mazEF toxin-antitoxin system (2)-claim that MazF creates a unique stress-induced translation machinery (STM). The STM hypothesis states that the toxin cleaves selected mRNAs within 5=-leader sequences to produce a pool of leaderless transcripts that are, in turn, translated by special stress ribosomes (3, 4). The latter are formed when the toxin cleaves off an anti-Shine-Dalgarno sequence-containing fragment from the 3= end of 16S rRNA in mature ribosomes (3). Thus, MazF is postulated to reshape translation in stressed E. coli similarly to how the S factor reshapes transcription.

mBio

W e thank David W. Holden and Jeff Errington for their comments (1). We agree that scientific res... more W e thank David W. Holden and Jeff Errington for their comments (1). We agree that scientific research is inherently error-prone. Therefore, validation, reassessment, and reinterpretation of one's own and others' results is part of the scientific approach, regardless of whether the conclusions are affirming or critical. We also agree that further work is needed to establish whether, and in which settings, each individual toxin-antitoxin (TA) system contributes to persister formation in Escherichia coli K-12 and/or in other bacterial species. In the following paragraphs, we express our opinion on the topics on which Holden and Errington saw some overstatements and factual inaccuracies in our paper (2).

RNA Biology, 2016

The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and pr... more The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and protein synthesis by targeting cellular mRNAs. As an exception, E. coli MazF was reported to cleave also 16S rRNA at a single site and separate an anti-Shine-Dalgarno sequence-containing RNA fragment from the ribosome. We noticed extensive rRNA fragmentation in response to induction of the toxins MazF and MqsR, which suggested that these toxins can cleave rRNA at multiple sites. We adapted differential RNAsequencing to map the toxin-cleaved 5 0 -and 3 0 -ends. Our results show that the MazF and MqsR cleavage sites are located within structured rRNA regions and, therefore, are not accessible in assembled ribosomes. Most of the rRNA fragments are located in the aberrant ribosomal subunits that accumulate in response to toxin induction and contain unprocessed rRNA precursors. We did not detect MazF-or MqsR-cleaved rRNA in stationary phase bacteria and in assembled ribosomes. Thus, we conclude that MazF and MqsR cleave rRNA precursors before the ribosomes are assembled and potentially facilitate the decay of surplus rRNA transcripts during stress.

Scientific Reports, 2016

is an antimicrobial with a direct reactivity against thiol groups. It is active against Gram-posi... more is an antimicrobial with a direct reactivity against thiol groups. It is active against Gram-positive and Gram-negative bacteria, yeasts and filamentous fungi. By reacting with thiol groups it causes direct damage to proteins but, as a result, is very short-living and interconverts into an array of reaction products. Our aim was to characterize thiol reactivity of G1 and its conversion products and establish how much of antimicrobial and cytotoxic effects are due to the primary activity of G1 and how much can be attributed to its reaction products. Stability of G1 in growth media as well as its conversion in the presence of thiols was characterized. The structures of G1 decomposition products were determined using NMR and mass-spectroscopy. Concentration-and time-dependent killing curves showed that G1 is bacteriostatic for Escherichia coli at the concentration of 16 μg/ml and bactericidal at 32 μg/ml. However, G1 is inefficient against nongrowing E. coli. Addition of cysteine to medium reduces the antimicrobial potency of G1. Nevertheless, the reaction products of G1 and cysteine enabled prolonged antimicrobial action of the drug. Therefore, the activity of 2-bromo-5-(2-bromo-2-nitrovinyl)furan is a sum of its immediate reactivity and the antibacterial effects of the conversion products.

Applied microbiology and biotechnology, Jan 4, 2016

Persisters-a drug-tolerant sub-population in an isogenic bacterial culture-have been featured thr... more Persisters-a drug-tolerant sub-population in an isogenic bacterial culture-have been featured throughout the last decade due to their important role in recurrent bacterial infections. Numerous investigations detail the mechanisms responsible for the formation of persisters and suggest exciting strategies for their eradication. In this review, we argue that the very term "persistence" is currently used to describe a large and heterogeneous set of physiological phenomena that are functions of bacterial species, strains, growth conditions, and antibiotics used in the experiments. We caution against the oversimplification of the mechanisms of persistence and urge for a more rigorous validation of the applicability of these mechanisms in each case.