The Phenolic Contents and Antimicrobial Activities of Some Marine Algae from the Mediterranean Sea (Algeria)

In this study, three marine algae collected from western coast of algerian mediteranean sea (Ulva lactuca, Dictyota dichotoma, and Corallina elongata) were tested using the agar-well diffusion method for their production of antibacterial and antifungal agents on various organisms that cause diseases of humans and plants (Eschirichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Salmonella sp, Candida albicans, and Penicillium sp.). The total phenol content and antimicrobial activity were determined using different crude seaweeds extracts (methanol, diethylether, and chloroform). The results show that the chloroform extracts of (Ulva lactuca and Corallina elongata) had the highest activity against E. coli and Salmonella sp. The methanol extract obtained from (Ulva lactuca, Dictyota dichotoma, and Corallina elongata) showed antifungal activity for Candida albicans. The results of the study revealed that the seaweeds from Algeria appear to have immense potential as a source of antibacterial and antifungal compounds; they can be used in treating diseases caused by these organisms.     

Effect of salt stress on the antimicrobial activity of <Emphasis Type="Italic">Ruta chalepensis</Emphasis> essential oils

In the current investigation, the biological activities of essential oils obtained from organs of Ruta chalepensis plants grown under salt stress (0, 50 and 100 mM NaCl) were analyzed. Their chemical composition was often investigated by GC/FID and GC–MS and the antimicrobial activities towards eight bacteria (Salmonella All, Salmonella K, Escherichia coli 45AG, Escherichia coli 45AI, Staphylococcus aureus 9402, Staphylococcus aureus 02B145, Listeria 477 and Pseudomonas aeruginosa ATCC 10145) and five fungi strains (Aspergillus, Saccharomycee crvisiale, Streptomyces griseus, Fusarium solani and Penicillium thomii) were studied. Results revealed that salt increased essential oil production in leaves at 50 and 100 mM NaCl. A total of 20 compounds were identified in leaves, undecan-2-one, nonan-2-one and geijerene being the dominant ones. In stems, 21 compounds were found; they were dominated by decan-2-one, geijerene, nonan-2-one and undecan-2-one. In contrast, roots exhibited a large variation with 25 volatile compounds and octyl acetate, methyl decanoate, phytyl acetate were the major ones. Salt stress induced significant antibacterial activity changes, mainly in leaves and stems. In leaves, the minimum inhibitory and bactericidal concentration decreased at 100 mM NaCl against Listeria 477, the two strains of E. coli (45AG and 45AI) and P. aeruginosa but it increased versus other bacteria. In stems, salt increased oil antibacterial activity against all strains except P. aeruginosa ATCC 10145. Root oil showed the least antibacterial activity under saline conditions versus Listeria 477 and P. aeruginosa ATCC 10145. As regards antifungal activity, NaCl reduced the antifungal activity of essential oils against the majority of fungi strains.     

A New Broad-Spectrum Peptide Antibiotic Produced by <Emphasis Type="Italic">Bacillus brevis</Emphasis> Strain MH9 Isolated from Margalla Hills of Islamabad,Pakistan

The antimicrobial peptide from a bacterial strain is isolated from soil sample of Margalla Hills of Islamabad, Pakistan. The peptide is found to significantly inhibit the growth of both Gram-positive (Staphylococcus aureus ATCC 6538 and Micrococcus luteus ATCC 10240) and Gram-negative (Escherichia coli ATCC 25922 and Salmonella typhi ATCC 14028) bacteria as compared to gramicidin as standard. The bacterium is identified as Bacillus brevis strain MH9 based on phenotype and phylogenetic analysis. The antibacterial polypeptide was produced optimally at 35 °C after 48 h of growth, precipitated by 50 % ammonium sulphate, and further purified using HPLC. The sequential steps of purification decrease the peptide contents with prominent antibacterial activity. The peptide composed of 11 amino acid was further characterized by FT-IR and NMR. Results suggested that the peptide molecule is a novel antibacterial agent that is effective against both Gram-positive and Gram-negative bacteria. This study may have important implications for new peptide antibiotic that could be a new addition to treat infections.     

Antibacterial compound produced by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> strain UICC B-40, an endophytic bacterium isolated from <Emphasis Type="Italic">Neesia altissima</Emphasis>

This study’s aim was to determine the identity of antibacterial compounds produced by Pseudomonas aeruginosa strain UICC B-40 and describe the antibacterial compounds’ mechanisms of action for damaging pathogenic bacteria cells. Isolation and identification of the compounds were carried out using thin layer chromatography (TLC), nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography mass spectrometry (LC-MS) analyses. Antibacterial activity was assayed via minimum inhibitory concentration (MIC) and the antibacterial compound mechanism was observed morphologically through scanning electron microscopy (SEM). This study successfully identified the (2E,5E)-phenyltetradeca-2,5-dienoate antibacterial compound (molecular weight 300 g/mol), composed of a phenolic ester, fatty acid and long chain of aliphatic group structures. MIC values for this compound were determined at 62.5 μg/ml against Staphylococcus aureus strain ATCC 25923. The mechanism of the compound involved breaking down the bacterial cell walls through the lysis process. The (2E,5E)-phenyltetradeca-2,5-dienoate compound exhibited inhibitory activity on the growth of Gram-positive bacteria.     

Isolation Purification and Characterization of Antimicrobial Peptides from <Emphasis Type="Italic">Cuminum cyminum</Emphasis> L. Seeds

In this work, antimicrobial peptides from Cuminum cyminum L. seeds were isolated and purified for the first time by 50% ethanol extraction, C18 reverse phase column chromatography and ion exchange chromatography for separation different peptides fraction. Then isolated fractions were characterized by Gel electrophoresis (SDS-PAGE), high-pressure liquid chromatography and the peptides components and molecular weights were determined by liquid chromatography and mass spectrometry. The extracts were tested against some strains of bacteria (E. coli and Staphylococcus aureus) and one strain of fungi (Candida albicans) using well diffusion and broth dilution assays. The extracts from C. cyminum L. seeds demonstrated a high degree of activity (some antibacterial effect) against the bacteria strains and аntifungal activity against the Candida albicans. However, the study indicates that the crude peptide extracts from C. cyminum L. seeds have promising antimicrobial and antioxidant activities that can be harnessed as leads for potential bioactive compounds.     

Molecular design and engineering of phosphopeptide ligands to target lung cancer polo-like kinase

Polo-like kinase (Plk) plays a central role in centrosome cycle and is closely associated with the oncogenesis of lung cancer. The protein consists of a catalytic kinase domain (KD) and a regulatory polo-box domain (PBD); either direct inhibition of the KD’s catalytic activity or indirect disruption of the PBD–substrate interaction can be used to potentially suppress the pathological activation of lung cancer Plk. Here, we reported a successful molecular design and engineering of phosphopeptide ligands to target Plk PBD domain by integrating in silico modeling and in vitro assay. In the procedure, a helical peptide segment hps was derived from dimerization interface of the complex crystal structure of domain dimer using bioinformatics approach, which was then used as sequence template to generate potent phosphopeptide binders of Plk PBD domain in terms of a systematic residue mutation profile. Fluorescence anisotropy assays were conducted to substantiate the findings and conclusions obtaining from the molecular engineering. Consequently, three helical phosphopeptides, including the native hps and its two mutants hps-m ₁ and hps-m ₂, were successfully designed that can independently rebind to Plk PBD domain with a moderate or high affinity (K _d = 127, 26, and 5 μM, respectively). These peptide ligands can be considered as potent self-competitors to disrupt PBD dimerization in lung cancer metastasis. Structural and energetic analysis revealed that hydrophobic forces and van der Waals contacts confer strong stability for domain–peptide complex system, while hydrogen bonds and electrostatic interactions contribute specificity and selectivity to the complex recognition.     

Leucocin C-607, a Novel Bacteriocin from the Multiple-Bacteriocin-Producing <Emphasis Type="Italic">Leuconostoc pseudomesenteroides</Emphasis> 607 Isolated from Persimmon

Leuconostoc pseudomesenteroides 607, isolated from persimmon fruit, was found to have high inhibitory activity against Listeria monocytogenes and several other Gram-positive bacteria. Inhibitory substances were purified from culture supernatant by ion-exchange chromatography, Sep-Pak C₁₈ cartridge, and reverse-phase high-performance liquid chromatography (RP-HPLC). Two antibacterial peptides were observed during the purification procedures. One of these peptides had a molecular size of 4623.05 Da and a partial N-terminal amino acid sequence of NH₂-KNYGNGVHxTKKGxS, in which the YGNGV motif is specific for class IIa bacteriocins. A BLAST search revealed that this bacteriocin was similar to leucocin C from Leuconostoc mesenteroides. Leucocin C-specific primers were designed and a single PCR product was amplified. Analysis of the nucleotide sequence has revealed a putative peptide differing by only one amino acid residue from the sequence of leucocin C. No identical peptide or protein has been reported in the literature, and this peptide, termed leucocin C-607, was therefore considered to be a new variant of leucocin C produced by Leuc. pseudomesenteroides 607. Another antibacterial peptide purified from the same culture supernatant had a molecular size of 3007.7 or 3121.97 Da. However, detailed information regarding this second peptide remains to be determined. Distinct characteristics, such as heat stability and inhibitory spectrum, were observed for the two bacteriocins produced by Leuc. pseudomesenteroides 607. These results suggested that Leuc. pseudomesenteroides 607 produces leucocin C-607 along with another unknown bacteriocin.     

Antifungal activity of 3-acetylbenzamide produced by actinomycete WA23-4-4 from the intestinal tract of <Emphasis Type="Italic">Periplaneta americana</Emphasis>

Actinomycetes are well-known for producing numerous bioactive secondary metabolites. In this study, primary screening by antifungal activity assay found one actinomycete strain WA23-4-4 isolated from the intestinal tract of Periplaneta americana that exhibited broad spectrum antifungal activity. 16S rDNA gene analysis of strain WA23-4-4 revealed close similarity to Streptomyces nogalater (AB045886) with 86.6% sequence similarity. Strain WA23-4-4 was considered as a novel Streptomyces and the 16s rDNA sequence has been submitted to GenBank (accession no. KX291006). The maximum antifungal activity of WA23-4-4 was achieved when culture conditions were optimized to pH 8.0, with 12% inoculum concentration and 210 ml ISP2 medium, which remained stable between the 5^th and the 9^th day. 3-Acetyl benzoyl amide was isolated by ethyl acetate extraction of WA23-4-4 fermentation broth, and its molecular formula was determined as C₉H₉NO₂ based on MS, IR, ¹H, and ¹³C NMR analyses. The compound showed significant antifungal activity against Candida albicans ATCC 10231 (MIC: 31.25 μg/ml) and Aspergillus niger ATCC 16404 (MIC: 31.25 μg/ml). However, the compound had higher MIC values against Trichophyton rubrum ATCC 60836 (MIC: 500 μg/ml) and Aspergillus fumigatus ATCC 96918 (MIC: 1,000 μg/ml). SEM analysis showed damage to the cell membrane of Candida albicans ATCC 10231 and to the mycelium of Aspergillus niger ATCC 16404 after being treatment with 3-acetyl benzoyl amide. In conclusion, this is the first time that 3-acetyl benzoyl amide has been identified from an actinomycete and this compound exhibited antifungal activity against Candida albicans ATCC 10231 and Aspergillus niger ATCC 16404.     

Gram-negative bacilli-derived peptide antibiotics developed since 2000

Gram-negative bacilli such as Pseudomonas spp., Pseudoalteromonas sp., Angiococcus sp., Archangium sp., Burkholderia spp., Chromobacterium sp., Chondromyces sp., Cystobacter sp., Jahnella sp., Janthinobacterium sp., Lysobacter spp., Paraliomyxa sp., Photobacterium spp., Photorhabdus sp., Pontibacter sp., Ruegeria sp., Serratia sp., Sorangium sp., Sphingomonas sp., and Xenorhabdus spp. produce an enormous array of short peptides of 30 residues or fewer that are potential pharmaceutical drugs and/or biocontrol agents. The need for novel lead antibiotic compounds is urgent due to increasing drug resistance, and this review summarises 150 Gram-negative bacilli-derived compounds reported since 2000, including 40 cyclic lipopeptides from Pseudomonas spp.; nine aromatic peptides; eight glycopeptides; 45 different cyclic lipopeptides; 24 linear lipopeptides; eight thiopeptides; one lasso peptide; ten typical cyclic peptides; and five standard linear peptides. The current and potential therapeutic applications of these peptides, including structures and antituberculotic, anti-cyanobacterial, antifungal, antibacterial, antiviral, insecticidal, and antiprotozoal activities are discussed.     

A physiological comparative study of acid tolerance of <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> ZDY 2013 and <Emphasis Type="Italic">L. plantarum</Emphasis> ATCC 8014 at membrane and cytoplasm levels

This study aimed to disclose the acid tolerance mechanism of Lactobacillus plantarum by comparing L. plantarum ZDY 2013 with the type strain L. plantarum ATCC 8014 in terms of cell membrane, energy metabolism, and amino acid metabolism. L. plantarum ZDY 2013 had a superior growth performance under acidic condition with 100-fold higher survival rate than that of L. plantarum ATCC 8014 at pH 2.5. To determine the acid tolerance physiological mechanism, cell integrity was investigated through scanning electron microscopy. The study revealed that L. plantarum ZDY 2013 maintained cell morphology and integrity, which is much better than L. plantarum ATCC 8014 under acid stress. Analysis of energy metabolism showed that, at pH 5.0, L. plantarum ZDY 2013 enhanced the activity of Na⁺/K⁺-ATPase and decreased the ratio of NAD⁺/NADH in comparison with L. plantarum ATCC 8014. Similarly, amino acid metabolism of intracellular arginine, glutamate, and alanine was improved in L. plantarum ZDY 2013. Correspondingly, the activity of arginine deiminase and glutamate decarboxylase of L. plantarum ZDY 2013 increased by 1.2-fold and 1.3-fold compared with L. plantarum ATCC 8014 in acid stress. In summary, it is demonstrated that the special physiological behaviors (integrity of cell membrane, enhanced energy metabolism, increased amino acid and enzyme level) of L. plantarum ZDY 2013 can protect the cells from acid stress.     

The influence of polyhexamethylene guanidine derivatives introduced into polyhydroxybutyrate on biofilm formation and the activity of bacterial enzymes

Escherichia coli and Staphylococcus aureus were able to produce biofilm on the surface of polyhydroxybutyrate (PHB), but their abundance depended on type and the concentrations of the polyhexamethylene guanidine (PHMG) derivatives introduced in PHB. Different types of PHMG derivatives inhibited S. aureus ATCC 6538P biofilm formation, but PHB with PHMG salt of sulfanilic acid stimulated E. coli ATCC 8739 biofilm formation. The presence of all PHMG derivatives decreased significantly the number of viable cells of the test bacteria directly proportional to the concentration of the biocidal agent. PHMG derivatives affected the activity of microbiological hydrolases with different degrees. Some of them (PHB with PHMG stearate) stimulated activity of E. coli ATCC 8739 hydrolases, other (PHB with the PHMG salt of sulfanilic acid) inhibited activity of the S. aureus ATCC 6538P hydrolases. The PHMG derivatives introduced in PHB also inhibited the activity of bacterial dehydrogenases.     

Lipophilic gold(I) complexes with 1,3,4-oxadiazol-2-thione or 1,3-thiazolidine-2-thione moieties: synthesis and their cytotoxic and antimicrobial activities

Novel lipophilic gold(I) complexes containing 1,3,4-oxadiazol-2-thione or 1,3-thiazolidine-2-thione derivatives were synthesized and characterized by IR, high resolution mass spectrometry, and ¹H, ¹³C ³¹P NMR. The cytotoxicity of the compounds was evaluated considering cisplatin and/or auranofin as reference in different tumor cell lines: colon cancer (CT26WT), metastatic skin melanoma (B16F10), breast adenocarcinoma (MCF-7), cervical carcinoma (HeLa), glioblastoma (M059 J). Normal human lung fibroblasts (GM07492-A) and kidney normal cell (BHK-21) were also evaluated. The gold(I) complexes were more active than their respective free ligands and cisplatin. Furthermore, antibacterial activity was evaluated against Gram-positive bacteria Staphylococcus aureus ATCC 25213, Staphylococcus epidermidis ATCC 12228 and Gram-negative bacteria Escherichia coli ATCC 11229 and Pseudomonas aeruginosa ATCC 27853 and expressed as the minimum inhibitory concentration (MIC). The complexes exhibited lower MIC values when compared to the ligands and chloramphenicol against Gram-positive bacteria and Gram-negative bacteria. Escherichia coli was sensitive one to the action of gold(I) complexes.     

Probiotic Characteristics of <Emphasis Type="Italic">Lactobacillus curvatus</Emphasis> DN317, a Strain Isolated from Chicken Ceca

The probiotic characteristics of Lactobacillus curvatus DN317, a strain isolated from chicken ceca, were evaluated. This strain was selected for study from the isolated Lactobacillus strains because it has specific anti-microbial activity against Campylobacter jejuni ATCC 33560, Camp. jejuni NCTC 11168, Listeria monocytogenes ATCC 7644, and Bacillus subtilis ATCC 8633. Lact. curvatus DN317 showed an auto-aggregation percentage of 72% and presented the highest co-aggregation with Lact. monocytogenes ATCC 7644 (68%) compared to B. subtilis ATCC 8633 (45%), Camp. jejuni ATCC 33560 (36%), and Camp. jejuni NCTC 11168 (35%). The data revealed that Lact. curvatus DN317 could survive at 0.25% bile, maintain viability at pH 2.5 for 30 min, produce biosurfactants, and adhere to Caco-2 cells. Quantification of IL-6, IL-8, IL-10, and β-defensin 2 levels shows that Lact. curvatus DN317 induces an increase in IL-8 and β-defensin 2 secretion, while the levels of IL-6 and IL-10 do not change. Lact. curvatus DN317 showed high levels of esterase and cysteine arylamidase activities (5); moderate levels of esterase lipase, β-galactosidase, and α-galactosidase activities (4, 3); and weak levels of leucine arylamidase, valine arylamidase, and acid phosphatase activity (1). Various activities were obtained of α-chymotrypsin, β-glucuronidase, β-glucosidase, and N-acetyl-β-glucosaminidase, which have been associated with intestinal diseases. Lact. curvatus DN317 lowered the cholesterol level in MRS with and without bile. Antibiotic susceptibility tests indicated that DN317 was sensitive to ampicillin, gentamicin, kanamycin, streptomycin, tetracycline, clindamycin, erythromycin, and vancomycin but was resistant to chloramphenicol and ciprofloxacin. These results suggest that Lact. curvatus DN317 could potentially function as a probiotic.     

Characterization of Antimicrobial and Antioxidative Peptides Synthesized by <Emphasis Type="Italic">L. rhamnosus</Emphasis> C6 Fermentation of Milk

Lactobacillus rhamnosus C6 was used for milk fermentation with the aim of synthesizing antimicrobial and antioxidant peptides rich preparations. The proteolysis was checked for an incubation period of 72 h to check the extent of both bioactivities in fermentate. The 36 h incubated fermentate showed higher inhibition zone diameter against E. coli ATCC 25922 as well as antioxidant activity. Ultrafiltrate was further purified by solid phase extraction and then subjected to reverse phase chromatography. Among 12 fractions collected, higher activity containing fractions were sequenced through LC–MS and characterized. Total 49 peptide sequences identified including 13 novel sequences rich in proline with helix forming ability. Higher antimicrobial activity containing fractions have potent previously reported Casicidin-17 peptides along with a series of proline rich peptides. Antioxidant rich peptides profile contains 21 peptide of smaller sequence of mainly 9–12 amino acids with lower molecular weight. This study demonstrates the capacity of L. rhamnosus C6 to release antioxidative and antimicrobial peptide by proteolysis of milk proteins through peptide profiling and characterization.     

Calcium-dependent antibacterial activity of donkey’s milk against <Emphasis Type="Italic">Salmonella</Emphasis>

The aim of this study was to examine the antibacterial activity of raw donkey’s milk (DM) against Salmonella Enteritidis and Salmonella Typhimurium as well as to determine the dependence of this antibacterial activity on calcium, lysozyme and lactoferrin content. Antibacterial assays were conducted in DM artificially contaminated with these Salmonella serotypes and then incubated at 38 °C for 8 hours. Calcium concentration was found to have a strong influence on the antibacterial activity of the contaminated DM samples supplemented with CaCl₂ and EDTA. The antibacterial activity of DM against the tested Salmonella strains was observed to be strongly calcium dependent, with the addition of CaCl₂ to DM samples improving its antibacterial potential against both pathogens. Salmonella Enteritidis appeared to be less sensitive to the antimicrobial agents in DM than S. Typhimurium. One explanation is the calcium-dependant antibacterial activity of DM is attributable to the calcium-binding ability of its lysozyme. Lysozyme may be the main antibacterial agent, most probably via a nonenzymatic mode of action against tested Salmonella strains.     

Antimicrobial Activities of Novel Peptides Derived from Defensin Genes of <Emphasis Type="Italic">Brassica hybrid</Emphasis> cv Pule

Plant defensins are small and basic antimicrobial peptides characterized by conserved cysteine stabilizing structure with α-helix and triple strand antiparallel β-sheet. In the present study, two novel defensin genes, designated as BhDef1 and BhDef2, was isolated from Brassica hybrid cv Pule, a native unexplored Brassicaceae species found in Thailand. The full-length cDNA of BhDef1 and BhDef2 were 240 and 258 bp encoding a 79 and 85 amino acid residues with 29 and 25 amino acid signal peptide at N-terminal, respectively. The putative BhDef1 and BhDef2 mature proteins showed significant similarity to other Brassicaceae defensins. Their secondary structure comprises of one α-helix and a triple stranded β-sheet stabilized by four disulphide bridges of eight cysteines. BhDef1 and BhDef2 also contain a highly conserved γ-core and α-core motif exhibiting antifungal activity against Colletotrichum gloeosporioides causing anthracnose disease. Six out of eight synthetic BhDef peptide derivatives showed antibacterial activity against both gram-positive bacteria and gram-negative bacteria used in this study. BhDef14, the derivative of BhDef1, showed the highest activity against two test pathogenic bacteria. This activity could probably due to a net positively charge and alpha-helical conformation which are known as the key determinant for the bacterial membrane disruption. To our knowledge, this is the first report on defensin genes isolated from B. hybrid cv Pule. The synthetic peptides designed from their sequences showed antifungal and antibacterial activity.     

Evaluation of lytic bacteriophages for control of multidrug-resistant <Emphasis Type="Italic">Salmonella</Emphasis> Typhimurium

Background

The emergence of antibiotic-resistant bacteria can cause serious clinical and public health problems. This study describes the possibility of using bacteriophages as an alternative agent to control multidrug-resistant Salmonella Typhimurium.

Methods

The potential lytic bacteriophages (P22-B1, P22, PBST10, PBST13, PBST32, and PBST 35) were characterized by morphological property, heat and pH stability, optimum multiplicity of infection (MOI), and lytic activity against S. Typhimurium KCCM 40253, S. Typhimurium ATCC 19585, ciprofloxacin-induced antibiotic-resistant S. Typhimurium ATCC 19585, and S. Typhimurium CCARM 8009.

Results

P22-B1 and P22 belong to Podoviridae family and PBST10, PBST13, PBST32, and PBST 35 show a typical structure with polyhedral head and long tail, belonging to Siphoviridae family. Salmonella bacteriophages were highly stable at the temperatures (< 60 °C) and pHs (5.0–11.0). The reduction rates of host cells were increased at the MOI-dependent manner, showing the highest reduction rate at MOI of 10. The host cells were most effectively reduced by P22, while P22-B1 showed the least lytic activity. The ciprofloxacin-induced antibiotic-resistant S. Typhimurium ATCC 19585, and clinically isolated antibiotic-resistant S. Typhimurium CCARM 8009 were resistant to ciprofloxacin, levofloxacin, norfloxacin, and tetracycline. P22 showed the highest lytic activity against S. Typhimurium KCCM 40253 (> 5 log reduction), followed by S. Typhimurium ATCC 19585 (4 log reduction) and ciprofloxacin-induced antibiotic-resistant S. Typhimurium ATCC 19585 (4 log reduction).

Conclusion

The results would provide vital insights into the application of lytic bacteriophages as an alternative therapeutics for the control of multidrug-resistant pathogens.

     

Antimicrobial activity of endogenous peptides of the moss <Emphasis Type="Italic">Physcomitrella patens</Emphasis>

Plant and animal cells contain pools of endogenous peptides, which are the degradation products of functionally active proteins. It is known that these peptides can possess biological activity; however, the functions of most of them are unknown. The goal of the present study was to estimate the antimicrobial potential of endogenous peptides resulting from the degradation of functional proteins in cells of the moss Physcomitrella patens. Earlier, 117 peptides possessing an antimicrobial potential predicted in silico have been identified in the peptidomes of three types of P. patens cells by mass spectrometry. In the present work, the antimicrobial activity of six of these peptides toward the gram-positive bacteria Bacillus subtilis SHgw and Clavibacter michiganensis pv. michiganensis and gram-negative bacteria Escherichia coli K12 and Xanthomonas arboricola 3004 has been revealed. The results have shown that three of six peptides inhibit the growth of the phytopathogenic bacteria X. arboricola and C. m. pv. michiganensis; four peptides inhibit the growth of the gram-negative bacterium E. coli K12, and one peptide inhibits the growth of the gram-positive bacterium B. subtilis. It has been found that the peptides inhibiting the bacterial growth are predominantly the fragments of ribosomal proteins. The work confirms the potential of the biological activity of peptides that are the degradation products of functional proteins.     

Comparison of Antimicrobial Properties of Silver Nanoparticles Synthesized from Selected Bacteria

Green silver nanoparticle (AgNP) biosynthesis is facilitated by the enzyme mediated reduction of Ag ions by plants, fungi and bacteria. The antimicrobial activity of green AgNPs is useful to overcome the challenge of antimicrobial resistance. Antimicrobial properties of biosynthesized AgNPs depend on multiple factors including culture conditions and the microbial source. The antimicrobial activity of AgNPs biosynthesized by Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and Acinetobacter baumannii (confirmed clinical isolate) were investigated in this study. Biosynthesis conditions (AgNO₃ concentration, pH, incubation temperature and incubation time) were optimized to obtain the maximum AgNP yield. Presence of AgNPs was confirmed by observing a characteristic UV–Visible absorbance peak in 420–435 nm range. AgNP biosynthesis was optimal at 0.4 g/L AgNO₃ concentration under alkaline conditions at 60–70 °C. The biosynthesized AgNPs showed higher stability compared to chemogenized AgNPs in the presence of electrolytes. AgNPs synthesized by P. aeruginosa were the most stable while NPs of S. aureus were the least stable. AgNPs synthesized by P. aeruginosa and S. aureus showed good antimicrobial potential against E. coli, P. aeruginosa, S. aureus, MRSA and Candida albicans. AgNPs synthesized by S. aureus had greater antimicrobial activity. The antimicrobial activity of NPs may vary depending on the size and the morphology of NPs.