Antibacterial Metabolites Research Articles

Antibacterial and Antifungal Activity of Metabolites from Basidiomycetes: A Review

Background/Objectives: The search for new antimicrobial molecules is important to expand the range of available drugs, as well as to overcome the drug resistance of pathogens. One of the promising sources of antibacterial and antifungal metabolites is basidial fungi, which have wide biosynthetic capabilities. Methods: The review summarized the results of studying the antimicrobial activity of extracts and metabolites from basidiomycetes published from 2018–2023. Results: In all studies, testing for antibacterial and antifungal activity was carried out in in vitro experiments. To obtain the extracts, mainly the fruiting bodies of basidiomycetes, as well as their mycelia and culture liquid were used. Antimicrobial activity was found in aqueous, methanol, and ethanol extracts. Antimicrobial metabolites of basidiomycetes were isolated mainly from the submerged culture of basidiomycetes. Metabolites active against Gram-positive and Gram-negative bacteria and mycelial and yeast-like fungi were identified. Conclusions: Basidiomycete extracts and metabolites have shown activity against collectible strains of bacteria and fungi and multi-resistant and clinical strains of pathogenic bacteria. The minimum inhibitory concentration (MIC) values of the most active metabolites ranged from 1 to 16.7 µg/mL.

Antimicrobial activity of blue mold (Penicillium italicum) Filtrates against some species of pathogenic bacteria

Background: Penicillium saprophytic species, which primarily consume organic biodegradable materials, is a common example of a fungal species. The preparation filtrates of Penicillium italicum, a saprophyte on citrus fruits frequently linked to post-harvest diseases in this crop, were included in the current investigation. Objective: This investigation aimed determine the most efficient culture medium for the production of antibacterial secondary metabolites. Patients and Methods: included identifying the growth medium for P. italicum and produce its metabolites through the use of gas chromatography-mass spectrometry (GC MS) for both solid-state fermentation filtrate (SSFF) and liquid fermentation filtrate (LFF). Additionally, the antimicrobial activity of the mold filtrate against certain pathogenic bacteria was assessed using the agar well diffusion method. Results: indicated that the biomass used for mold growth was heavier in SSFF than LFF, and according to the findings, the selective active isolate's crude filtrate from two duplicates of the P. italicum Yeast Extract Sucrose YES culture medium was 0.063 mg, while the crude extract from rotten orange (as a solid medium) containing P. italicum was 0.11 mg. Tetracosane and other substances with a track record of therapeutic activity were found in the two mold extracts, according to GC MS data. Overall, both SSFF and LFF demonstrated antibacterial activity against Klebsiella pneumonia, Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus, with the inhibition zones± standard deviation (IZ± SD) being 24.7± 0.57, 18.2± 0.28, 26.3± 0.59, 21.6± 0.51, and 32.8± 0.21 (for SSFF) mm and 0.0, 12.3±0.57, 28.16±0.20, 19.3±1.15, and 28±0.2 (for LFF) mm, respectively. Conclusion: the filtrate of P. italicum from a natural medium (rotted orange) as a solid state fermentation was more weighted and gave many effective metabolites compared to what was produced by liquid fermentation on a synthetic medium, and both liquid and solid fermentation filtrates demonstrated efficacy against harmful bacteria.

Isolation and Characterization of Some Potential Antibacterial Metabolites from Marine Microorganisms Collected in Egypt

Isolation and Characterization of Some Potential Antibacterial Metabolites from Marine Microorganisms Collected in Egypt

Secondary Metabolites Screening Using GC-MS and In-Vitro Biological Assessment Against Human Pathogenic Bacterial Strains of Viola Indica

Viola indica, a medicinal herb with a long history of traditional use in treating various diseases. In this study we analyzed methanolic extract of Viola indica for metabolite composition using GC-MS, and antibacterial activity through disc diffusion method. In GC-MS analysis, we found total of 25 metabolites in which the major metabolites were 9,12-Octadecadienoic acid (Z,Z)- (20%; 20.34 min), followed by Stigmasterol, 22,23-dihydro- (16%; 26 min) and α-Amyrin (12.38%; 26.65 min) . In antibacterial activity viola indica methanolic extract showed significant antibacterial effects against all bacterial strains. The highest antibacterial activity was recorded against Bacillus subtilis (8.50±0.20 mm), followed by Klebsiella pneumoniae (8.10±0.25 mm) zone of inhibition, while the lowest was recorded against Staphylococcus aureus (2.10±0.30 mm). The result of this study suggests that viola indica has potent antibacterial metabolites with good potential as a natural alternative to synthetic antibacterial agents. However, this study also suggest that more instrumental and biological research is required to explore it’s in-depth phytochemistry, pharmacological potential and toxicological properties.

Identification of antibacterial constituents from Rhododendron simsii Planch with an activity-guided method.

Bacterial infections and antibiotic resistance pose significant public health challenges globally. Natural products serve as valuable sources for discovering antimicrobial agents. Rhododendron simsii Planch, a folk medicine, is traditionally used to treat various inflammatory diseases. In this study, we investigated the antibacterial metabolites derived from R. simsii Planch. Rhodosimsiin A (1), bearing a 1,5-seco-1,6 and 3,6-epoxy grayanane diterpene skeleton, representing a novel 5/6/7/6/5 pentacyclic ring system, and 3β,16α-dihydroxy-6β-ethoxy-14β-acetoxy-grayan-1(5)-ene-10-one (4), which represents the first example of the degradation of C-20 and carbonylation in C-10 diterpenoid, together with two new grayanane diterpenes (2-3), three new triterpenes (13-15), and known analogs (5-12, 16-30), were isolated from the leaves of R. simsii Planch by using the bioassay-guided method. Their structures were elucidated by comprehensive spectroscopic analyses, and absolute configurations were established by single-crystal X-ray diffraction and calculated ECD spectra. Compounds 14, 15, 18, 20, 27, 28, and 30 exhibited potent antibacterial activity with an MIC50 of 1.4-24.3μg/mL against Staphylococcus aureus. The findings of this research indicate that secondary metabolites derived from R. simsii Planch are promising natural antimicrobial candidates.

Antibacterial and cytotoxic metabolites produced by Streptomyces tanashiensis BYF-112 isolated from Odontotermes formosanus

Chemical investigations of the termite-associated Streptomyces tanashiensis BYF-112 resulted in the discovery of four novel alkaloid derivatives: vegfrecines A and B (1 and 2), exfoliazone A (3), and venezueline H (7), in addition to nine known metabolites (4−6, 8−13). The structures of these compounds were elucidated through comprehensive spectroscopic analysis and comparison with existing literature data. Antibacterial assays revealed that viridomycin A (11) exhibited potent antibacterial activity against Staphylococcus aureus, with a zone of inhibition (ZOI) of 12.67 mm, in comparison to a ZOI of 17.67 mm for the positive control gentamicin sulfate. Viridomycin A (11) showed moderate activity against Micrococcus tetragenus and Pseudomonas syringae pv. actinidae, with ZOI values of 15.50 and 14.33 mm, respectively, which were inferior to those of gentamicin sulfate (34.67 and 24.00 mm). Viridomycin F (12) also exhibited moderate antibacterial effects against S. aureus, M. tetragenus, and P. syringae pv. actinidae, with ZOI values of 8.33, 16.50, and 10.83 mm, respectively. Cytotoxicity assays demonstrated that viridobruunine A (5), exfoliazone (6), viridomycin A (11), and X-14881E (13) exhibited significant cytotoxicity against human malignant melanoma (A375), ovarian cancer (SKOV-3), and gastric cancer (MGC-803) cell lines, with IC50 values ranging from 4.61 to 19.28 μmol·L−1. Furthermore, bioinformatic analysis of the complete genome of S. tanashiensis suggested a putative biosynthetic gene cluster (BGC) responsible for the production of compounds 1−12. These findings indicate that the secondary metabolites of insect-associated S. tanashiensis BYF-112 hold promise as potential sources of novel antibacterial and anticancer agents.

Phytochemical profiling and antibacterial activities of Ziziphora tenuior root extracts: a molecular docking against VanA of vancomycin-resistant enterococci.

Medicinal plants, renowned for their antibacterial phytocompounds and secondary metabolites, hold significant promise in addressing antibiotic-resistant bacterial strains. This study aimed to conduct phytochemical profiling of the methanolic and dichloromethane extracts of Ziziphora tenuior root using the GC-MS technique. These extracts' antioxidant potential was assessed via DPPH assay and their antibacterial activity was evaluated against S. aureus, E. coli, and VRE bacterial strains. Furthermore, the drug-ligand interactions between the extracts' biocompounds and d-alanyl-d-lactate ligase (VanA) protein of vancomycin-resistant enterococci strains (VRE) were analyzed using molecular docking. Based on the results, 74% of methanolic extract consisted of (3methyl, 24S)-stigmast-5-en-3-ol (which is a β-sitosterol), followed by Tetrasiloxane, decamethyl (15.5%), and 1-methyl-4-phenyl-5-thioxo-1,2,4-triazolidin-3-one (10.5%). Also, the only predominant compound identified in the dichloromethane extract was Benzo[h]quinoline, 2,4-dimethyl-. Both extracts showed antioxidant activity, while the antioxidant activity of the methanolic extract (IC50 = 95.33μg/ml) was significantly higher than that of the dichloromethane extract (IC50 = 934.23μg/ml). Also, both extracts displayed substantial antibacterial efficacy against the tested pathogens, particularly against VRE. Moreover, the in silico analysis revealed that (3methyl, 24S)-stigmast-5-en-3-ol and Benzo[h]quinoline,2,4-dimethyl- exhibited notable interactions with VanA through docking energy values of -9.0 and -9.1kcal/mol, respectively. Furthermore, these compounds formed 2 and 1 hydrogen bonds with VanA, respectively, highlighting their potential as effective interactants. These findings provide valuable visions into the therapeutic potentials of these plant-derived biocompounds in combating antibiotic-resistant bacterial infections.

Anti-bacterial effects, and metabolites derived from bifidobacterial fermentation of an exopolysaccharide of Cs-HK1 medicinal fungus

This study was to investigate the antibacterial effects and metabolites derived from bifidobacterial fermentation of an exopolysaccharide EPS-LM produced by a medicinal fungus Cordyceps sinensis, Cs-HK1. EPS-LM was a partially purified polysaccharide fraction which was mainly composed of Man, Glc and Gal at 7.31:12.95:1.00 mol ratio with a maximum molecular weight of 360 kDa. After fermentation of EPS-LM in two bifidobacterial cultures, B. breve and B. longum, the culture digesta showed significant antibacterial activities, inhibiting the proliferation and biofilm formation of Escherichia coli. Based on untargeted metabolomic profiling of the digesta, the levels of short chain fatty acids, carboxylic acids, benzenoids and their derivatives were all increased significantly (p < 0.01), which probably contributed to the enhanced antibacterial activity by EPS-LM. Since EPS-LM was only slightly consumed for the bifidobacterial growth, it mainly stimulated the biosynthesis of bioactive metabolites in the bifidobacterial cells. The results also suggested that EPS-LM polysaccharide may have a regulatory function on the bifidobacterial metabolism leading to production of antibacterial metabolites, which may be of significance for further exploration.

Phytochemical characterisation of dichloromethane and methanolic extracts of the Ziziphora tenuior leaves and evaluation of their antioxidant and antibacterial activities

Medicinal plants, known for their antibacterial phytocompounds and secondary metabolites, offer promising potential in combating antibiotic-resistant bacteria. This study aimed to perform a phytochemical analysis of the methanol and dichloromethane extracts obtained from Ziziphora tenuior leaves using GC-MS. Furthermore, the antioxidant activity of the extracts was evaluated through the DPPH assay. And, their antibacterial activity was assessed against S. aureus, E. coli, methicillin-resistant S. aureus, and vancomycin-resistant enterococcus (VRE) bacterial strains. Based on the results 90-92% of these extracts consisted of phytocompounds with pharmaceutical properties. Of these, 5-methyl- 2-(1-methylethylidele), Cyclohexanone (Pulegone; C10H16O) comprised the highest percentage of the extracts, constituting 62% of methanolic extract and 81% of dichloromethane extract. Also, both methanolic and dichloromethane extracts showed potent antioxidant activity with IC50 of 277.6 µg/ml and 49.6 µg/ml, respectively. Moreover, these extracts demonstrated considerable antibacterial activity against the tested pathogens, especially against S. aureus and VRE.

Phage-resistant Streptomyces abietis and its telomycin bioactive metabolite as a possible alternative to antibiotics

Multidrug-resistant pathogens are now thought to be the primary global causes of disease and death. Therefore, it is imperative to develop new effective bioactive compounds from microbial sources, such as Streptomyces species. Nevertheless, the pharmaceutical industry suffered financial losses and low-quality end products as a result of Streptomyces bacteriophage contamination. To reduce the likelihood of phage-induced issues in the medical industry, it is crucial to develop a method for finding phage-resistant strains. Hence, we aimed to isolate and characterize Streptomyces spp. and Streptomyces phages from various rhizospheric soil samples in Egypt and to investigate their antibacterial activities. Moreover, we targeted development of a Streptomyces phage-resistant strain to extract its active metabolites and further testing its antibacterial activity. Herein, the antibacterial activities of the isolated 58 Streptomyces isolates showed that 10 (17.2 %) Streptomyces isolates had antibacterial activities against the tested bacteria including Listeria monocytogenes, E. coli O157, Acinetobacter baumannii, methicillin resistant-vancomycin-intermediate Staphylococcus aureus (MRSA-VISA) and Micrococcus luteus. Three lytic bacteriophages (ϕPRSC1, ϕPRSC2, and ϕPRSC4) belonging to the families Siphoviridae and Podoviridae were obtained from the rhizospheric soil samples using the most potent S. abietis isolate as the host strain. The three isolated Streptomyces phages were thermostable, ultraviolet stable, infectious, and had a wide range of hosts against the 10 tested Streptomyces isolates with antibacterial activities. The DNA of the ϕPRSC1 and ϕPRSC4 phages were resistant to digestion by EcoRI and HindIII, but the DNA of ϕPRSC2 was resistant to digestion by EcoRI and sensitive to digestion by HindIII. Of note, we developed a S. abietis strain resistant to the three isolated phages and its antibacterial activities were twice that of the wild strain. Finally, telomycin was recognized as an antibacterial metabolite extracted from phage-resistant S. abietis strain, which was potent against the tested Gram-positive bacteria including L. monocytogenes, MRSA-VISA, and M. luteus. Thus, our findings open new horizons for researching substitute antimicrobial medications for both existing and reemerging illnesses.

Mass spectrometry-based metabolomics for the investigation of antibiotic-bacterial interactions.

With the development of analytical technologies especially mass spectrometry, metabolomics is becoming increasingly hot in the field of studying antibiotic-bacterial interactions. On the one hand, metabolomics can reveal metabolic perturbations in bacteria in the presence of antibiotics and expose metabolic mechanisms. On the other hand, through in-depth analysis of bacterial metabolic profiles, biomarkers and bioactive secondary metabolites with great potential as drug precursors can be discovered. This review focuses on the experimental workflow of bacterial metabolomics and its application to study the interaction between bacteria and antibiotics. Metabolomics improves the understanding of antibiotic lethality, reveals metabolic perturbations in antibiotic-resistant bacteria, guides the diagnosis and antibiotic treatment of infectious diseases, and aids in the exploration of antibacterial metabolites in nature. Furthermore, current limitations and directions for future developments in this area are discussed.

Low microbial diversity, yeast prevalence, and nematode-trapping fungal presence in fungal colonization and leaf microbiome of Serjania erecta

Medicinal plant microbiomes undergo selection due to secondary metabolite presence. Resident endophytic/epiphytic microorganisms directly influence plant’s bioactive compound synthesis. Hypothesizing low microbial diversity in Serjania erecta leaves, we assessed leaf colonization by epiphytic and endophytic fungi. Given its traditional medicinal importance, we estimated diversity in the endophytic fungal microbiome. Analyses included scanning electron microscopy (SEM), isolation of cultivable species, and metagenomics. Epiphytic fungi interacted with S. erecta leaf tissues, horizontally transmitted via stomata/trichome bases, expressing traits for nematode trapping. Cultivable endophytic fungi, known for phytopathogenic habits, didn’t induce dysbiosis symptoms. This study confirms low leaf microbiome diversity in S. erecta, with a tendency towards more fungal species, likely due to antibacterial secondary metabolite selection. The classification of Halicephalobus sp. sequence corroborated the presence of nematode eggs on the epidermal surface of S. erecta by SEM. In addition, we confirmed the presence of methanogenic archaea and a considerable number of methanotrophs of the genus Methylobacterium. The metagenomic study of endophytic fungi highlighted plant growth-promoting yeasts, mainly Malassezia, Leucosporidium, Meyerozyma, and Hannaella. Studying endophytic fungi and S. erecta microbiomes can elucidate their impact on beneficial bioactive compound production, on the other hand, it is possible that the bioactive compounds produced by this plant can recruit specific microorganisms, impacting the biological system.

Antibacterial Activity and Metabolite Content of Water and Methanolic Extracts of Purple and White Bougainvillea sp.

Bougainvillea sp. is a common ornamental plant grown all over Malaysia with several medicinal claims including the treatment for bacterial infection. This study investigated the extraction of the bracts and leaves of purple and white Bougainvillea sp. using methanol and water, tested the extracts' antibacterial activity against Escherichia coli and Bacillus cereus, and identified the metabolites using gas chromatography and mass spectrometry (GC/MS). The extraction yields of the extracts ranged from 9.6% to 31.3% with the highest yield observed in purple Bougainvillea sp. methanolic leaf extract. No significant differences were observed between water and methanol extraction of the bract samples, while in leaf samples, significantly higher extraction yield can be achieved using 80% aqueous methanol. All the extracts exhibited mild antibacterial activities against E. coli and B. cereus and especially higher in the methanolic extracts of bracts of white and leaves of purple Bougainvillea sp. A total of 71 volatile compounds were identified using GC/MS, in which 55 and 60 compounds were identified in bract and leaf extracts, respectively. The two extracts with the highest antibacterial activities shared six similar metabolites which are pyridine, benzoic acid, 2-methoxy-4-vinylphenol, methyl hexadecanoic acid, n-hexadecanoic acid and phytol. These compounds are known to possess antibacterial as well as other bioactivities. In conclusion, the metabolite identification and profile provide more insight into the antibacterial activity of the leaf and bract extracts of Bougainvillea sp., which might be further explored as a potential natural antibacterial agent source.

Preliminary Screening on Antibacterial Crude Secondary Metabolites Extracted from Bacterial Symbionts and Identification of Functional Bioactive Compounds by FTIR, HPLC and Gas Chromatography-Mass Spectrometry.

Secondary metabolites, bioactive compounds produced by living organisms, can unveil symbiotic relationships in nature. In this study, soilborne entomopathogenic nematodes associated with symbiotic bacteria (Xenorhabdus stockiae and Photorhabdus luminescens) were extracted from solvent supernatant containing secondary metabolites, demonstrating significant inhibitory effects against E. coli, S. aureus, B. subtilus, P. mirabilis, E. faecalis, and P. stutzeri. The characterization of these secondary metabolites by Fourier transforms infrared spectroscopy revealed amine groups of proteins, hydroxyl and carboxyl groups of polyphenols, hydroxyl groups of polysaccharides, and carboxyl groups of organic acids. Furthermore, the obtained crude extracts were analyzed by high-performance liquid chromatography for the basic identification of potential bioactive peptides. Gas chromatography-mass spectrometry analysis of ethyl acetate extracts from Xenorhabdus stockiae identified major compounds including nonanoic acid derivatives, proline, paromycin, octodecanal derivatives, trioxa-5-aza-1-silabicyclo, 4-octadecenal, methyl ester, oleic acid, and 1,2-benzenedicarboxylicacid. Additional extraction from Photorhabdus luminescens yielded functional compounds such as indole-3-acetic acid, phthalic acid, 1-tetradecanol, nemorosonol, 1-eicosanol, and unsaturated fatty acids. These findings support the potential development of novel natural antimicrobial agents for future pathogen suppression.

In vitro Antibacterial Activity and Secondary Metabolite Profiling of Endolichenic Fungi Isolated from Genus Parmotrema.

The endolichenic fungi are an unexplored group of organisms for the production of bioactive secondary metabolites. The aim of the present study is to determine the antibacterial potential of endolichenic fungi isolated from genus Parmotrema. The study is continuation of our previous work, wherein a total of 73 endolichenic fungi were isolated from the lichenized fungi, which resulted in 47 species under 23 genera. All the isolated endolichenic fungi were screened for preliminary antibacterial activity. Five endolichenic fungi-Daldinia eschscholtzii, Nemania diffusa, Preussia sp., Trichoderma sp. and Xylaria feejeensis, were selected for further antibacterial activity by disc diffusion method. The zone of inhibition ranged from 14.3 ± 0.1 to 23.2 ± 0.1. The chemical composition of the selected endolichenic fungi was analysed through GC-MS, which yielded a total of 108 compounds from all the selected five endolichenic fungi. Diethyl phthalate, 1-hexadecanol, dibutyl phthalate, n-tetracosanol-1, 1-nonadecene, pyrrol[1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methyl) and tetratetracontane were found to be common compounds among one or the other endolichenic fungi, which possibly were responsible for antibacterial activity. GC-MS data were further analysed through Principal Component Analysis which showed D. eschscholtzii to be with unique pattern of expression of metabolites. Compound confirmation test revealed coumaric acid to be responsible for antibacterial activity in D. eschscholtzii. So, the study proves that endolichenic fungi that inhabit lichenized fungal thalli could be a source of potential antibacterial compounds.

Investigating lactic acid bacteria genus Lactococcus lactis properties: Antioxidant activity, antibiotic resistance, and antibacterial activity against multidrug-resistant bacteria Staphylococcus aureus

BackgroundLactic acid bacteria (LAB) are utilized as a starter culture in the manufacturing of fermented dairy items, as a preservative for various food products, and as a probiotic. In our country, some research has been carried out, even if LAB plays a principal role in food preservation and improves the texture and taste of fermented foods, that is why we tried to evaluate their probiotic effect. The objective of this research was to determine the antibacterial activity of Lactococcus lactis (L. lactis) against Staphylococcus aureus (S. aureus) ATCC 29213, investigate their antioxidant activity, and characterize their sensitivity against 18 antibiotics. MethodsA total of 23 LAB (L. lactis subsp. cremoris, L. lactis subsp. Lactis diacetylactis, L. lactis subsp. lactis) were isolated from cow's raw milk. The antibacterial activity was performed using two techniques, competition for nutrients and a technique utilizing components nature, using the disk diffusion method. The sensitivity of the studied LAB to different antibiotics was tested on Man rogosa sharp (MRS) agar using commercial antibiotic disks. All strains of LAB were examined for their antioxidant activity. The antioxidant activity of L. lactis was tested by 2,2-diphenyl-1 picrylhydrazyl (DPPH). ResultsThe results showed that the MRS medium was more adapted than Muller Hinton Agar (MHA) to investigate the antibacterial activity of L. lactis against S. aureus ATCC 29213. Also, L. lactis exhibited a notable degree of antibacterial activity against S. aureus ATCC 29213. L. Lactis subsp. Lactis displayed higher antibacterial activities, followed by L. lactis ssp. lactis biovar. diacetylactis, and lastly, L. lactis ssp. cremoris against S. aureus ATCC 29213. Lc 26 among all strains of L. lactis showed a high potential antibacterial activity reaching 40 ± 3 mm against S. aureus ATCC 29213. All strains of L. lactis showed a slightly moderate antioxidant activity (10.56 ± 1.28%-26.29 ± 0.05 %). The results of the antibiotic resistance test indicate that all strains of L. lactis were resistant to cefotaxime, sulfamethoxazole-trimethoprim, and streptomycin and were sensitive to Ampicillin, Amoxicillin, Penicillin G, Teicoplanin, Vancomycin, Gentamicin 500, Tetracycline, and Chloramphenicol. These test results indicate that this strain falls within the criteria of not posing any harmful effects on human health. The important antibacterial properties recorded for all L. Lactis strains were derived from the production of antibacterial active metabolites, such as protein, diacetyl, hydrogen peroxide, and lactic acid, together with the fight for nutrients. ConclusionThis study suggests that the strains of L. lactis could be added as an antibacterial agent against S. aureus ATCC 29213 and can provide an important nutritional property for their antioxidant potential.

Isolation and identification of NEAU-CP5: A seed-endophytic strain of B. velezensis that controls tomato bacterial wilt

Bacterial wilt of tomato caused by Ralstonia solanacearum is a critical soilborne disease that drastically reduces yield. In the current study, an endophytic strain NEAU-CP5 with strong antagonistic activity against R. solanacearum was isolated from tomato seeds and characterized. The strain was identified as Bacillus velezensis based on 16S rRNA gene and whole genome sequence analysis. NEAU-CP5 can secrete amylase, protease, and cellulase, and also produce known antibacterial metabolites, including cyclo (leucylprolyl), cyclo (phenylalanyl-prolyl), cyclo (Pro-Gly), 3-benzyl-2,5-piperazinedione, pentadecanoic acid, eicosane, 2-methyoic acid, isovaleric acid, dibuty phthalate, and esters of fatty acids (HFDU), which may be responsible for its strong antibacterial activity. Fourteen gene clusters associated with antibacterial properties were also identified in the whole genome sequence of NEAU-CP5. Pot experiment demonstrated that the application of 108 CFU/mL NEAU-CP5 on tomato plants significantly reduced the incidence of tomato bacterial wilt by 68.36 ± 1.67 %. NEAU-CP5 also increased the activity of defense-related enzymes (CAT, POD, PPO, SOD, and PAL) in tomato plants. This is the first report of an effective control of bacterial wilt on tomato plants by B. velezensis and highlights the potential of NEAU-CP5 as a potential biocontrol agent for the management of tomato bacterial wilt.

Preliminary Purification and Partial Characterization of a Functional Bacteriocin of Lacticaseibacillus paracasei Zhang and Mining for its Gene Cluster.

Bacteriocins produced by lactic acid bacteria (LAB) have good potential for use as food biopreservatives. Lacticaseibacillus paracasei Zhang (L. paracasei Zhang) is both a food use and a probiotic bacterium. This study aimed to purify and preliminary characterize the active antibacterial metabolite of L. paracasei Zhang. The cell-free supernatant of L. paracasei Zhang was collected and purified by ultrafiltration and gel filtration chromatography. The 1-3kDa active fraction could inhibit the growth of Staphylococcus aureus but not Escherichia coli. Further antibacterial activity assays revealed its capacity to suppress various foodborne and human opportunistic pathogens (including Staphylococcus aureus, Pseudomonas fluorescens, Pseudomonas aeruginosa, Listeria monocytogenes, and Bacillus cereus), but not fungi. The antibacterial activity showed good tolerance to heat (40 to 100°C), acid-base (pH 2-3 and pH 6-10), and digestions by a number of industrial and animal/human enzymes (such as trypsin, pepsin, α-amylase, and protease K, except papain); these desired properties make it a suitable biopreservative to be used in harsh and complex industrial production processes. The high papain sensitivity suggested a proteinaceous/peptide nature of the bioactivity. Moreover, our genomic data mining for bacteriocin through BAGEL4 revealed an area of interest encoding a complete set of putative genes required for bacteriocin production. In conclusion, our study showed that L. paracasei Zhang can produce extracellular functional antibacterial metabolite, likely a class II bacteriocin. Our preliminary extraction and characterization of the active metabolite demonstrated that it has good potential to be used as a biopreservative or an agent for suppressing gastrointestinal infections.

The biocontrol potentiality of Bacillus amyloliquefaciens against postharvest soft rot of tomatoes and insights into the underlying mechanisms

Tomatoes can easily be affected by soft rot, one of the main postharvest infections caused by a bacterium called Pectobacterium carotovorum. This study examined the soft rot control effectiveness by Bacillus amyloliquefaciens in tomatoes, and identify the underlying action mechanisms from the perspective of the inhibition effects of antibacterial metabolites derived from B. amyloliquefaciens on pathogen and the influences of this antagonist on reactive oxygen species (ROS) scavenging capability of the fruit. The results demonstrated that B. amyloliquefaciens effectively lessened postharvest soft rot occurrence in tomatoes. The non-volatile metabolites synthesized by B. amyloliquefaciens suppressed P. carotovorum subsp. brasiliense (Pcb) growth in vitro and in vivo. The antibacterial ingredients presented in methanol-soluble sediments obtained from non-volatile metabolites. UHPLC-ESI-MS spectra revealed that the primary antibacterial ingredients were C12-C15 surfactin analogues, along with C14-C16 iturins and C16-C17 fengycins. Moreover, B. amyloliquefaciens could raise the activity of enzymatic ROS scavenging system in tomatoes, including several antioxidases and the enzymes related to glutathione peroxidase (GPX) and ascorbate-glutathione (AsA-GSH) cycles. In addition, B. amyloliquefaciens increased the levels of non-enzymatic system for ROS scavenging, including AsA and GSH. Together, O2-·production rate, H2O2 and malondialdehyde (MDA) levels were reduced. It suggested that B. amyloliquefaciens enhanced the ROS scavenging ability of tomatoes, thereby improving their resistance to the pathogen.

Serine deamination by human serine racemase synergizes with antibiotics to curtail the replication of Chlamydia trachomatis

The obligate intracellular bacterium, Chlamydia trachomatis, has evolved to depend on its human host for many metabolites, including most amino acids and three of the four nucleotides. Given this, it is not surprising that depletion of a single amino acid in the host cell growth medium blocks chlamydial replication. Paradoxically, supra-normal levels of some amino acids also block productive replication of Chlamydia. Here, we have determined how elevated serine levels, generated by exogenous supplementation, impede chlamydial inclusion development and reduce the generation of infectious progeny. Our findings reveal that human serine racemase, which is broadly expressed in multiple tissues, potentiates the anti-chlamydial effect of elevated serine concentrations. In addition to reversibly converting l-serine to d-serine, serine racemase also deaminates serine via β-elimination. We have determined that d-serine does not directly impact Chlamydia; rather, ammonia generated by serine deamination limits the productive chlamydial replication. Our findings imply that ammonia produced within host cells can traverse the chlamydial inclusion membrane. Further, this property of serine deaminase can be exploited to sensitize Chlamydia to concentrations of doxycycline that are otherwise not bactericidal. Because exogenously elevated levels of serine can be tolerated over extended periods, the broad expression pattern of serine racemase indicates it to be a host enzyme whose activity can be directed against multiple intracellular bacterial pathogens. From a therapeutic perspective, demonstrating host metabolism can be skewed to generate an anti-bacterial metabolite that synergizes with antibiotics, we believe our results provide a new approach to target intracellular pathogens.