Structural insights into the inhibition of bacterial RecA by naphthalene polysulfonated compounds

Silver single atoms and nanoparticles on floatable monolithic photocatalysts for synergistic solar water disinfection

Photocatalytic water disinfection technology is highly promising in off-grid areas due to abundant year-round solar irradiance. However, the practical use of powdered photocatalysts is impeded by limited recovery and inefficient inactivation of stress-resistant bacteria in oligotrophic surface water. Here we prepare a floatable monolithic photocatalyst with ZIF-8-NH2 loaded Ag single atoms and nanoparticles (AgSA+NP/ZIF). Atomically dispersed Ag sites form an Ag-N charge bridge, extending the lifetime of charge carriers and thereby promoting reactive oxygen species (ROS) generation. The photothermal effect of the plasmonic Ag nanoparticles reduces the bacterial resistance to ROS and impairs DNA repair capabilities. Under sunlight irradiation, the synergistic effect of Ag single atoms and nanoparticles enables 4.0 cm2 AgSA+NP/ZIF to achieve over 6.0 log inactivation (99.9999%) for the stress-resistant Escherichia coli (E. coli) in oligotrophic surface water within 30 min. Furthermore, 36 cm2 AgSA+NP/ZIF is capable of disinfecting at least 10.0 L of surface water, which meets the World Health Organization (WHO) recommended daily per capita drinking water allocation (8.0 L). This study presents a decentralized and sustainable approach for water disinfection in off-grid areas.

Cyclic di-AMP regulates genome stability and drug resistance in Mycobacterium through RecA-dependent and RecA-independent recombination

In Escherichia coli, RecA plays a central role in the rescue of stalled replication forks, double-strand break (DSB) repair, homologous recombination (HR), and induction of the SOS response. While the RecA-dependent pathway is dominant, alternative HR pathways that function independently of RecA do exist, but relatively little is known about the underlying mechanism. Several studies have documented that a variety of proteins act as either positive or negative regulators of RecA to ensure high-fidelity HR and genomic stability. Along these lines, we previously demonstrated that the second messenger cyclic di-AMP (c-di-AMP) binds to mycobacterial RecA proteins, but not to E. coli RecA, and inhibits its DNA strand exchange activity in vitro via the disassembly of RecA nucleoprotein filaments. Herein, we demonstrate that Mycobacterium smegmatis ΔdisA cells, which lack c-di-AMP, exhibit increased DNA recombination, higher frequency of mutation, and gene duplications during RecA-dependent and RecA-independent DSB repair. We also found that c-di-AMP regulates SOS response by inhibiting RecA-mediated self-cleavage of LexA repressor and its absence enhances drug resistance in M. smegmatis ΔdisA cells. Together, our results uncover a role of c-di-AMP in the maintenance of genomic stability through modulation of DSB repair in M. smegmatis.

Differential requirement for RecFOR pathway components in Thermus thermophilus

Recombinational repair is an important mechanism that allows DNA replication to overcome damaged templates, so the DNA is duplicated timely and correctly. The RecFOR pathway is one of the common ways to load RecA, while the RuvABC complex operates in the resolution of DNA intermediates. We have generated deletions of recO, recR and ruvB genes in Thermus thermophilus, while a recF null mutant could not be obtained. The recO deletion was in all cases accompanied by spontaneous loss of function mutations in addA or addB genes, which encode a helicase-exonuclease also key for recombination. The mutants were moderately affected in viability and chromosome segregation. When we generated these mutations in a Δppol/addAB strain, we observed that the transformation efficiency was maintained at the typical level of Δppol/addAB, which is 100-fold higher than that of the wild type. Most mutants showed increased filamentation phenotypes, especially ruvB, which also had DNA repair defects. These results suggest that in T. thermophilus (i) the components of the RecFOR pathway have differential roles, (ii) there is an epistatic relationship of the AddAB complex over the RecFOR pathway and (iii) that neither of the two pathways or their combination is strictly required for viability although they are necessary for normal DNA repair and chromosome segregation.

New algorithm for the analysis of nucleotide and amino acid evolutionary relationships based on Klein four-group

Phylogenetics is the study of ancestral relationships among biological species. Such sequence analyses are often represented as phylogenetic trees. The branching pattern of each tree and its topology reflect the evolutionary relatedness between analyzed sequences. We present a Klein four-group algorithm (K4A) for the evolutionary analysis of nucleotide and amino acid sequences. Klein four-group set of operators consists of: identity e (U), and three elements-a = transition (C), b = transversion (G) and c = transition-transversion or complementarity (A). We generated Klein four-group based distance matrices of: 1. Cayley table (CK4), 2. Table rows (K4R), 3. Table columns (K4C), and 4. Euclidean 2D distance (K4E). The performance of the matrices was tested on a dataset of RecA proteins in bacteria, eukaryotes (Rad51 homolog) and archaea (RadA homolog). RecA and its functional homologs are found in all species, and are essential for the repair and maintenance of DNA. Consequently, they represent a good model for the study of evolutionary relationship of protein and nucleotide sequences. The ancestral relationship between the sequences was correctly classified by all K4A matrices concerning general topology. All distance matrices exhibited small variations among species, and overall results of tree classification were in agreement with the general patterns obtained by standard BLOSUM and PAM substitution matrices. During the evolution of a code there is a phase of optimization of system rules, the ambiguity of a code is eliminated, and the system starts producing specific components. Klein four-group algorithm is consistent with the concept of ambiguity reduction. It also enables the use of different genetic code table variants optimized for particular transitions in evolution based on biological specificity.

Malonylome analysis uncovers the association of lysine malonylation with metabolism and acidic stress in pathogenic Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb), the pathogenic agent of tuberculosis, remains a primary inducement of morbidity and mortality globally. Mtb have evolved mechanisms to recognize diverse signals, such as acidic pH within phagolysosomes and therefore to reprogram multiple physiological and metabolic processes to adapt to intracellular survival. Moreover, lysine malonylation has been suggested to participate in regulation of enzymes in carbon metabolism. However, lysine malonylation in Mtb and its association with acidic pH associated metabolism adaptation remain unknown. Here, we systematically characterized the comparative malonylome of Mtb H37Rv grown in normal (7H9-Tyloxapol (Ty)-7.4) and acidic (7H9-Ty-4.5) medium mimicking lysosome pH. In total, 2467 lysine malonylation sites within 1026 proteins were identified, which related to diverse biological processes, particularly accumulated in metabolic process. 1090 lysine malonylation sites from 562 proteins were quantified, among which 391 lysine malonylation sites in 273 protein were down-regulated while 40 lysine malonylation sites from 36 proteins were up-regulated in acidic medium, indicating that malonylation may participate in acidic pH associated metabolism. Accordingly, the enzyme activity of GlcB was reduced under acidic stress corresponding to decreased malonylation of GlcB compared with that of normal condition and this was further demonstrated by site-specific mutations. We further found that Mtb-CobB, a sirtuin-like deacetylase and desuccinylase, involved in demalonylase activity. Together, the Mtb malonylome not only indicates the critical role of malonylation in metabolism regulation, but may provide new insights of malonylation on metabolism adaptation to acidic micro-environment in vivo.

Antibiotic resistance: The challenges and some emerging strategies for tackling a global menace

Background

Antibiotic resistance is currently the most serious global threat to the effective treatment of bacterial infections. Antibiotic resistance has been established to adversely affect both clinical and therapeutic outcomes, with consequences ranging from treatment failures and the need for expensive and safer alternative drugs to the cost of higher rates of morbidity and mortality, longer hospitalization, and high‐healthcare costs. The search for new antibiotics and other antimicrobials continues to be a pressing need in humanity's battle against bacterial infections. Antibiotic resistance appears inevitable, and there is a continuous lack of interest in investing in new antibiotic research by pharmaceutical industries. This review summarized some new strategies for tackling antibiotic resistance in bacteria.

Methods

To provide an overview of the recent research, we look at some new strategies for preventing resistance and/or reviving bacteria's susceptibility to already existing antibiotics.

Results

Substantial pieces of evidence suggest that antimicrobials interact with host immunity, leading to potent indirect effects that improve antibacterial activities and may result in more swift and complete bactericidal effects. A new class of antibiotics referred to as immuno‐antibiotics and the targeting of some biochemical resistance pathway components including inhibition of SOS response and hydrogen sulfide as biochemical underlying networks of bacteria can be considered as new emerging strategies to combat antibiotic resistance in bacteria.

Conclusion

This review highlighted and discussed immuno‐antibiotics and inhibition of SOS response and hydrogen sulfide as biochemical underlying networks of bacteria as new weapons against antibiotic resistance in bacteria.

Interaction of RecA mediated SOS response with bacterial persistence, biofilm formation, and host response

Antibiotics have a primary mode of actions, and most of them have a common secondary mode of action via reactive species (ROS and RNS) mediated DNA damage. Bacteria have been able to tolerate this DNA damage by SOS (Save-Our-Soul) response. RecA is the universal essential key protein of the DNA damage mediated SOS repair in various bacteria including ESKAPE pathogens. In addition, antibiotics also triggers activation of various other bacterial mechanisms such as biofilm formation, host dependent responses, persister subpopulation formation. These supporting the survival of bacteria in unfriendly natural conditions i.e. antibiotic presence. This review highlights the detailed mechanism of RecA mediated SOS response as well as role of RecA-LexA interaction in SOS response. The review also focuses on inter-connection between DNA damage repair pathway (like SOS response) with other survival mechanisms of bacteria such as host mediated RecA induction, persister-SOS interplay, and biofilm-SOS interplay. This understanding of inter-connection of SOS response with different other survival mechanisms will prove beneficial in targeting the SOS response for prevention and development of therapeutics against recalcitrant bacterial infections. The review also covers the significance of RecA as a promising potent therapeutic target for hindering bacterial SOS response in prevailing successful treatments of bacterial infections and enhancing the conventional antibiotic efficiency.

Pharmacophore screening, denovo designing, retrosynthetic analysis, and combinatorial synthesis of a novel lead VTRA1.1 against RecA protein of Acinetobacter baumannii

Antibiotics and disinfectants resistance is acquired by activating RecA-mediated DNA repair, which maintains ROS-dependent DNA damage caused by the antimicrobial molecules. To increase the efficacy of different antimicrobials, an inhibitor can be developed against RecA protein. The present study aims to design a denovo inhibitor against RecA protein of Acinetobacter baumannii. Pharmacophore-based screening, molecular mechanics, molecular dynamics simulation (MDS), retrosynthetic analysis, and combinatorial synthesis were used to design lead VTRA1.1 against RecA of A. baumannii. Pharmacophore models (structure-based and ligand-based) were created, and a phase library of FDA-approved drugs was prepared. Screening of the phase library against these pharmacophore models selected thirteen lead molecules. These filtered leads were used for the denovo fragment-based design, which produced 253 combinations. These designed molecules were further analyzed for its interaction with active site of RecA that selected a hybrid VTRA1. Further, retrosynthetic analysis and combinatorial synthesis produced 1000 analogs of VTRA1 by more than 100 modifications. These analogs were used for XP docking, binding free energy calculation, and MDS analysis which finally select lead VTRA1.1 against RecA protein. Further, mutations at the interacting residues of RecA with VTRA1.1, alter the unfolding rate of RecA, which suggests the binding of VTRA1.1 to these residues may alter the stability of RecA. It is also found that VTRA1.1 had reduced interaction of RecA with LexA and ssDNA polydT, showing the lead's efficacy in controlling the SOS response. Further, it was also observed that VTRA1.1 does not contain any predicted human off-targets and no cytotoxicity to cell lines. As functional RecA is involved in antimicrobial resistance, denovo designed lead VTRA1.1 against RecA may be further developed as a significant combination for therapeutic uses against A. baumannii.