Search Results (11)

The cell wall is an indispensable element of bacterial cells and a long-known target of many antibiotics. Penicillin, the first discovered beta-lactam antibiotic inhibiting the synthesis of cell walls, was successfully used to cure many bacterial infections. Unfortunately, pathogens eventually developed resistance to it. This started an arms race, and while novel beta-lactams, either natural or (semi)synthetic, were discovered, soon upon their application, bacteria were developing resistance. Currently, we are facing the threat of losing the race since more and more multidrug-resistant (MDR) pathogens are emerging. Therefore, there is an urgent need for developing novel approaches to combat MDR bacteria. The cell wall is a reasonable candidate for a target as it differentiates not only bacterial and human cells but also has a specific composition unique to various groups of bacteria. This ensures the safety and specificity of novel antibacterial agents that target this structure. Due to the shortage of low-molecular-weight candidates for novel antibiotics, attention was focused on peptides and proteins that possess antibacterial activity. Here, we describe proteinaceous agents of various origins that target bacterial cell wall, including bacteriocins and phage and bacterial lysins, as alternatives to classic antibiotic candidates for antimicrobial drugs. Moreover, advancements in protein chemistry and engineering currently allow for the production of stable, specific, and effective drugs. Finally, we introduce the concept of selective targeting of dangerous pathogens, exemplified by staphylococci, by agents specifically disrupting their cell walls. Full article

Bacteriocins are a class of proteins produced by bacteria that are toxic to other bacteria. These bacteriocins play a role in bacterial competition by helping to inhibit potential competitors. In this study, we isolated and purified a novel bacteriocin Pkmh, different from the previously reported bacteriocin PA166, from Pseudomonas sp. strain 166 by ammonium sulfate precipitation, dialysis membrane method, ion exchange chromatography, and gel filtration chromatography. SDS-PAGE (sodium dodecyl sulfate–polyacrylamide gel electrophoresis) revealed that the molecular weight of Pkmh is approximately 35 kDa. Pkmh exhibited potent antimicrobial activity against bovine Mannheimia haemolytica (M. haemolytica) with low cytotoxicity, and lower hemolytic activity was observed. In addition, Pkmh retained antimicrobial activity at different pH ranges (2–10) and temperature conditions (40, 60, 80, 100 °C). Our analysis of its antimicrobial mechanism showed that Pkmh acts on bacterial cell membranes, increasing their permeability and leading to cell membrane rupture and death. In conclusion, Pkmh exhibited low hemolytic activity, low toxicity, and potent antibacterial effects, suggesting its potential as a promising candidate for clinical therapeutic drugs. Full article

Pectobacterium carotovorum subsp. carotovorum (Pcc) is known to produce different types of bacteriocins, active protein substances that inhibit or kill related strains and are known to be induced by several factors. In this paper, we report the discovery, isolation, characterization, and functional analysis of Carocin S4, a novel low-molecular-weight bacteriocin (LMWB) from Pcc. A 2750 bp gene fragment was isolated from the chromosomal DNA of Pcc mutant strain rif-TO6, a rifampicin-resistant strain of TO6. The gene contains caroS4K and caroS4I within two open reading frames, which encode CaroS4K and CaroS4I, with molecular weights of about 90 kD and 10 kD, respectively. The unique characteristics of Carocin S4 were revealed after homology analysis with the previously discovered bacteriocins from Pcc. CaroS4K, which shares 23% and 85% homology with CaroS1K and CaroS3K, respectively, is also a deoxyribonuclease. However, unlike the two which can only hydrolyze genomic DNA, CaroS4K hydrolyzes both genomic and plasmid DNA. On the other hand, CaroS4K was found to be 90% homologous with CaroS2K but works differently in killing the target cell, as the latter is a ribonuclease. The optimal reaction temperature for CaroS4K to hydrolyze dsDNA is approximately 50 °C and requires the divalent metal ions Mg²⁺, Ca²⁺, and Zn²⁺ to catalyze its DNase activity. This study reveals another nuclease type of bacteriocin in Pcc, with CaroS4K and CaroS4I functioning as killer and immunity proteins, respectively. Full article

Pectobacterium carotovorum subsp. carotovorum (Pcc) is a Gram-negative phytopathogenic bacterium that produces carocin, a low-molecular-weight bacteriocin that can kill related strains in response to factors in the environment such as UV exposure or nutritional deficiency. The function of the catabolite activator protein (CAP), also known as the cyclic AMP receptor protein (CRP), as a regulator of carocin synthesis was examined. The crp gene was knocked out as part of the investigation, and the outcomes were assessed both in vivo and in vitro. Analysis of the DNA sequence upstream of the translation initiation site of carocin S3 revealed two putative binding sites for CRP that were confirmed using a biotinylated probe pull-down experiment. This study revealed that the deletion of crp inhibited genes involved in extracellular bacteriocin export via the flagellar type III secretion system and impacted the production of many low-molecular-weight bacteriocins. The biotinylated probe pull-down test demonstrated that when UV induction was missing, CRP preferentially attached to one of the two CAP sites while binding to both when UV induction was present. In conclusion, our research aimed to simulate the signal transduction system that controls the expression of the carocin gene in response to UV induction. Full article

The proteinaceous compounds produced by lactic acid bacteria are called bacteriocins and have a wide variety of bioactive properties. However, bacteriocin’s commercial availability is limited due to short stability periods and low yields. Therefore, the objective of this study was to synthesize bacteriocin-derived silver nanoparticles (Bac10307-AgNPs) extracted from Lactobacillus acidophilus (L. acidophilus), which may have the potential to increase the bioactivity of bacteriocins and overcome the hurdles. It was found that extracted and purified Bac10307 had a broad range of stability for both temperature (20–100 °C) and pH (3–12). Further, based on Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS–PAGE) analysis, its molecular weight was estimated to be 4.2 kDa. The synthesized Bac10307-AgNPs showed a peak of surface plasmon resonance at 430 nm λmax. Fourier transform infrared (FTIR) confirmed the presence of biological moieties, and transmission electron microscopy (TEM) coupled with Energy dispersive X-Ray (EDX) confirmed that AgNPs were spherical and irregularly shaped, with a size range of 9–20 nm. As a result, the Bac10307-AgNPs displayed very strong antibacterial activity with MIC values as low as 8 μg/mL for Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), when compared to Bac10307 alone. In addition, Bac10307-AgNPs demonstrated promising in vitro antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) (IC₅₀ = 116.04 μg/mL) and in vitro cytotoxicity against human liver cancer cells (HepG2) (IC₅₀ = 135.63 μg/mL), more than Bac10307 alone (IC₅₀ = 139.82 μg/mL against DPPH and 158.20 μg/mL against HepG2). Furthermore, a protein–protein molecular docking simulation study of bacteriocins with target proteins of different biological functions was also carried out in order to ascertain the interactions between bacteriocins and target proteins. Full article

The plant pathogen Pectobacterium carotovorum subsp. carotovorum (previously Erwinia carotovora subsp. carotovora) causes soft rot and stem rot diseases in a variety of crops, including Chinese cabbage, potato, and tomato. The flagellar-type III secretion systems were used by Pcc’s virulence mechanism to export proteins or bacteriocins to the outside of the cell. DGC, a virulence factor that cyclizes c-di-GMP, a common secondary signal in physiological processes and toxin control systems of many bacteria, was discovered in Pcc’s genomic DNA. The dgc gene in Pcc was blocked using the method of homologous recombination in our study. In the in vivo setting, the results demonstrated that the dgc knockout strain does not release low molecular weight bacteriocins. The bacteriocin gene (carocin S2, carocin S3, carocin S4) and the flagellar-type III secretion system genes were also unable to be transcribed by the dgc knockout strain in the transcription experiment. We also observed that the amount of bacteriocin expressed changed when the amount of L-glutamine in the environment exceeded a particular level. These data suggested that L-glutamine influenced physiological processes in Pcc strains in some way. We hypothesized a relationship between dgc and the genes involved in Pcc LMWB external export via the flagellar-type secretion system based on these findings. In this study, the current findings led us to propose a mechanism in which DGC’s cyclic di-GMP might bind to receptor proteins and positively regulate bacteriocin transcription as well as the synthesis, mobility, and transport of toxins. Full article

Zymomonas mobilis is an ethanologenic, facultatively anaerobic alpha-proteobacterium, known for its inhibitory effect on the growth of a wide variety of microorganisms. This property might be interesting for the design of novel antimicrobials, yet it has negative implications for biotechnology, as it hinders the use of Z. mobilis as a producer microorganism in cocultivation. So far, the chemical nature of its inhibitory compound(s) has not been established. In the present study, we demonstrate that the putative inhibitor is a low-molecular-weight (below 3 kDa), thermostable compound, resistant to protease treatment, which is synthesized under aerobic conditions in Z. mobilis strains via the active respiratory chain. It is also synthesized by aerated nongrowing, glucose-consuming cells in the presence of chloramphenicol, thus ruling out its bacteriocin-like peptide nature. The inhibitory activity is pH-dependent and strongly correlated with the accumulation of propionate and acetate in the culture medium. Although, in Z. mobilis, the synthesis pathways of these acids still need to be identified, the acid production depends on respiration, and is much less pronounced in the non-respiring mutant strain, which shows low inhibitory activity. We conclude that propionate and acetate play a central role in the antimicrobial effects of Z. mobilis, which itself is known to bear high resistance to organic acids. Full article

Carocin S2 is a bacteriocin with a low molecular weight generated by Pectobacterium carotovorum subsp. carotovorum 3F3 strain. The caroS2K gene, which is found in the genomic DNA alongside the caroS2I gene, which codes for an immunity protein, encodes this bacteriocin. We explored the residues responsible for Carocin S2’s cytotoxic or RNA-se activity using a structure-based mutagenesis approach. The minimal antibiotic functional region starts at Lys691 and ends at Arg783, according to mutational research. Two residues in the identified region, Phe760 and Ser762, however, are unable to demonstrate this activity, suggesting that these sites may interact with another domain. Small modifications in the secondary structure of mutant caroS2K were revealed by circular dichroism (CD) spectroscopy and intrinsic tryptophan fluorescence (ITF), showing ribosomal RNA cleavage in the active site. A co-immunoprecipitation test indicated that the immunity protein CaroS2I binds to CaroS2K’s C-terminus, while a region under the uncharacterized Domain III inhibits association of N-terminally truncated CaroS2K from interacting with CaroS2I. Carocin S2, a ribosomal ribonuclease bacteriocin, is the first to be identified with a domain III that encodes the cytotoxic residues as well as the binding sites between its immunity and killer proteins. Full article

With the aim of developing a new food starter culture, twenty-three psychrotrophic lactic acid bacteria (LAB) were isolated from 16 kimchi samples. One strain, Leuconostoc gelidum subsp. aenigmaticum LS4, which had typical psychrotrophic characteristics, was selected, and its phenotypic and genomic properties as a starter culture were investigated. The complete genome of L. aenigmaticum LS4 consisted of one circular chromosome (1,988,425 bp) and two plasmids (19,308 bp and 11,283 bp), with a guanine–cytosine content of 36.8%. L. aenigmaticum LS4 could grow at 5 °C but not at 37 °C, and maximum cell growth was obtained at 15~25 °C. L. aenigmaticum LS4 did not show any harmful characteristics such as hemolysis, undesirable enzyme activities, biogenic amine production, or antibiotic resistance. L. aenigmaticum LS4 was investigated for its suitability for technological processes (pH, temperature and NaCl treatment). L. aenigmaticum LS4 exhibited strong antimicrobial activity caused by the production of organic acids and bacteriocin, and it produced an exopolysaccharide composed of glucose with a molecular weight of 3.7 × 10⁶ Da. Furthermore, L. aenigmaticum LS4 improved the organoleptic qualities of kimchi juice. Our results indicate that L. aenigmaticum LS4 could be used as a functional starter culture for food (vegetable or fruit) fermentation at low temperatures. Full article

Extremophilic microorganisms attract researchers by their unique characteristics, primarily antagonistic ones, acquired in the process of survival in extreme natural conditions. The antimicrobial potential of the metabolites of these microorganisms is quite broad, from the food industry to therapeutic drugs. Microbial mats of Lake Baikal are a source of unique and diverse microorganisms. The study aimed to evaluate the antimicrobial activity of bacterial strains isolated from the bottom sediments of the lake. Using heterotrophic growth conditions, seven bacterial strains were isolated from samples collected in several coastal zones of Lake Baikal. Thisstudy identified both widespread strains of the genera Pseudomonas and Bacillus and rare genera Micrococcus and Acinetobacterrepresentatives. Metabolites of five strains were found to have a broad spectrum of antimicrobial activity. Four large fractions of metabolites of the isolated strains wereidentified. Two peptides of the isolated fractions of metabolites (one is produced by microorganisms of all five isolated strains, another—only by Pseudomonas putida) are low molecular weight oligopeptides. These peptides were proved to be bacteriocins. Full article

Decades of antibiotic misuse in clinical settings, animal feed, and within the food industry have led to a concerning rise in antibiotic-resistant bacteria. Every year, antimicrobial-resistant infections cause 700,000 deaths, with 10 million casualties expected by 2050, if this trend continues. Hence, innovative solutions are imperative to curb antibiotic resistance. Bacteria produce a potent arsenal of drugs with remarkable diversity that are all distinct from those of current antibiotics. Bacteriocins are potent small antimicrobial peptides synthetized by certain bacteria that may be appointed as alternatives to traditional antibiotics. These molecules are strategically employed by commensals, mostly Firmicutes, to colonize and persist in the human gut. Bacteriocins form channels in the target cell membrane, leading to leakage of low-molecular-weight, causing the disruption of the proton motive force. The objective of this review was to list and discuss the potential of bacteriocins as antimicrobial therapeutics for infections produced mainly by resistant pathogens. Full article