In the current work, in continuation of our recent research, we synthesized and studied new chimeric compounds, including the ribosome-targeting antibiotic chloramphenicol (CHL) and the membrane-penetrating cation triphenylphosphonium (TPP), which are linked by alkyl groups of different lengths. Using various biochemical assays, we showed that these CAM-Cn-TPP compounds bind to the bacterial ribosome, inhibit protein synthesis in vitro and in vivo in a way similar to that of the parent CHL, and significantly reduce membrane potential. Similar to CAM-C4-TPP, the mode of action of CAM-C10-TPP and CAM-C14-TPP in bacterial ribosomes differs from that of CHL. By simulating the dynamics of CAM-Cn-TPP complexes with bacterial ribosomes, we proposed a possible explanation for the specificity of the action of these analogs in the translation process. CAM-C10-TPP and CAM-C14-TPP more strongly inhibit the growth of the Gram-positive bacteria, as compared to CHL, and suppress some CHL-resistant bacterial strains. Thus, we have shown that TPP derivatives of CHL are dual-acting compounds targeting both the ribosomes and cellular membranes of bacteria. The TPP fragment of CAM-Cn-TPP compounds has an inhibitory effect on bacteria. Moreover, since the mitochondria of eukaryotic cells possess qualities similar to those of their prokaryotic ancestors, we demonstrate the possibility of targeting chemoresistant cancer cells with these compounds.

Since the discovery of streptomycin, actinomycetes have been a useful source for new antibiotics, but there have been diminishing rates of new finds since the 1960s. The decreasing probability of identifying new active agents led to reduced interest in soil bacteria as a source for new antibiotics. At the same time, actinomycetes remain a promising reservoir for new active molecules. In this work, we present several reporter plasmids encoding visible fluorescent protein genes. These plasmids provide primary information about the action mechanism of antimicrobial agents at an early stage of screening. The reporters and the pipeline described have been optimized and designed to employ citizen scientists without specialized skills or equipment with the aim of essentially crowdsourcing the search for new antibiotic producers in the vast natural reservoir of soil bacteria. The combination of mechanism-based approaches and citizen science has proved its effectiveness in practice, revealing a significant increase in the screening rate. As a proof of concept, two new strains, Streptomyces sp. KB-1 and BV113, were found to produce the antibiotics pikromycin and chartreusin, respectively, demonstrating the efficiency of the pipeline.

The sustained rise of antimicrobial resistance (AMR) causes a strong need to develop new antibacterial agents. One of the methods for addressing the problem of antibiotic resistance is through the design of hybrid antibiotics. In this work, we proposed a synthetic route for the conjugation of an azithromycin derivative with chloramphenicol and metronidazole hemisuccinates and synthesized two series of new hybrid molecules 4a–g and 5a–g. While a conjugation did not result in tangible synergy for wild-type bacterial strains, new compounds were able to overcome AMR associated with the inducible expression of the ermC gene on a model E. coli strain resistant to macrolide antibiotics. The newly developed hybrids demonstrated a tendency to induce premature ribosome stalling, which might be crucial since they will not induce a macrolide-resistant phenotype in a number of pathogenic bacterial strains. In summary, the designed structures are considered as a promising direction for the further development of hybrid molecules that can effectively circumvent AMR mechanisms to macrolide antibiotics.

Since streptomycin discovery, actinomycetes were the main source for new antibiotics, but after the Golden age (1950-1960^th) the discovery rate significantly decreased. The high probability to rediscover well-known antibiotics led to a reduction in interest in soil bacteria as a source for new antibiotics. At the same time, actinomycetes remain a very promising reservoir for searching for new active molecules. In this work, we present several reporters containing eye-visible fluorescent protein genes, which can be used to increase the efficiency of determining the mechanism of antibiotics at the very initial stage of screening. Presented reporters and the following pipeline were optimized given the involvement of citizen scientists without specialized skills and equipment in order to utilize the reservoir of soil bacteria in the search for new antibiotic producers. The combination of mechanism-based approaches and civil science has proved its effectiveness in practice revealing a significant increase in the screening rate. Two new strains Streptomyces sp. KB-1 and BV113 were found to produce antibiotics pikromycin and chartreusin, respectively, demonstrating the efficiency of the pipeline.

Translation is a critical step in gene expression and a target for multiple antibiotics. Inhibition of protein synthesis by many antibiotics depends on mRNA context, making them selective towards particular mRNAs. Toe-printing is a standard low-throughput method to determine ribosome position along mRNA. Hereby we report the development and application of the Toe-seq method, combining toe-printing with next-generation sequencing. Toe-seq proved to be efficient to monitor translation and its inhibition by antibiotics for the library of over 37 000 mRNAs. Context-specificity of antibiotic action could be determined for different antibiotics via Toe-seq. Previously known sequence dependencies of translation inhibition were reproduced by Toe-seq. Data obtained by Toe-seq demonstrated context-specificity of etamycin A (EtaA) action whose binding site is located in the nascent peptide tunnel. Comparison of EtaA specificity with that of erythromycin (Ery) and tetracenomycin X (TcmX) revealed important differences and commonalities. Structural basis for the context-specificity of translation inhibition by EtaA has been deciphered by cryo-electron microscopy at 2.2 Å resolution. Toe-seq method allows one to monitor ribosome progression and stalling in vitro at a codon resolution, making it possible to assess antibiotics context specificity in a multiple parallel assay.

Antimicrobial peptides (AMPs) have recently attracted attention as promising antibacterial agents capable of acting against resistant bacterial strains. In this work, an approach was applied, consisting of the conjugation of a peptide related to the sequences of bactenecin 7 (Bac7) and oncocin (Onc112) with the alkyl(triphenyl)phosphonium (alkyl-TPP) fragment in order to improve the properties of the AMP and introduce new ones, expand the spectrum of antimicrobial activity, and reduce the inhibitory effect on the eukaryotic translation process. Triphenylphosphonium (TPP) derivatives of a decapeptide RRIRPRPPYL were synthesized. It was comprehensively studied how the modification of the AMP affected the properties of the new compounds. It was shown that while the reduction in the Bac7 length to 10 a.a. residues dramatically decreased the affinity to bacterial ribosomes, the modification of the peptide with alkyl-TPP moieties led to an increase in the affinity. New analogs with structures that combined a decapeptide related to Bac7 and Onc112—Bac(1–10, R/Y)—and TPP attached to the C-terminal amino acid residue via alkylamide linkers, inhibited translation in vitro and were found to be more selective inhibitors of bacterial translation compared with eukaryotic translation than Onc112 and Bac7. The TPP analogs of the decapeptide related to Bac7 and Onc112 suppressed the growth of both Gram-negative bacteria, similar to Onc112 and Bac7, and Gram-positive ones, similar to alkyl-TPP derivatives, and also acted against some resistant laboratory strains. Bac(1–10, R/Y)-C2-TPP, containing a short alkylamide linker between the decapeptide and TPP, was transferred into the E. coli cells via the SbmA transporter protein. TPP derivatives of the decapeptide Bac(1–10, R/Y) containing either a decylamide or ethylamide linker caused B. subtilis membrane depolarization, similar to alkyl-TPP. The Bac(1–10, R/Y)-C2-TPP analog was proven to be non-toxic for mammalian cells using the MTT test.