Multiple Classes of Antimicrobial Peptides in Amaranthus tricolor Revealed by Prediction, Proteomics, and Mass Spectrometric Characterization.

Traditional medicinal plants are rich reservoirs of antimicrobial agents, including antimicrobial peptides (AMPs). Advances in genomic sequencing, in silico AMP predictions, and mass spectrometry-based peptidomics facilitate increasingly high-throughput bioactive peptide discovery. Herein, Amaranthus tricolor aerial tissue was profiled via MS-based proteomics/peptidomics, identifying AMPs predicted in silico. Bottom-up proteomics identified seven novel peptides spanning three AMP classes including lipid transfer proteins, snakins, and a defensin. Characterization via top-down peptidomic analysis of Atr-SN1, Atr-DEF1, and Atr-LTP1 revealed unexpected proteolytic processing and enumerated disulfide bonds. Bioactivity screening of isolated Atr-LTP1 showed activity against the high-risk ESKAPE bacterial pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter cloacae). These results highlight the potential for integrating AMP prediction algorithms with complementary -omics approaches to accelerate characterization of biologically relevant AMP peptidoforms.

Antimicrobial peptides from Capsicum chinense fruits: agronomic alternatives against phytopathogenic fungi.

In recent years, the antimicrobial activity of peptides isolated from a wide variety of organs from plant species has been reported. However, a few studies have investigated the potential of antimicrobial peptides (AMPs) found in fruits, especially Capsicum chinense (pepper). The present study aimed to purify and characterize peptides from Capsicum chinense fruits and evaluate their inhibitory activities against different phytopathogenic fungi and also analyze the possible mechanisms of action involved in microbial inhibition. After fruit protein extraction and high-performance liquid chromatography (HPLC), different fractions were obtained, named F1 to F10. Peptides in the F4 and F5 fractions were sequenced and revealed similarity with the plant antimicrobial peptides like non-specific lipid transfer proteins and defensin-like peptide. The F4 and F5 fractions presented strong antimicrobial activity against the fungus Fusarium solani and Fusarium oxysporum, causing toxic effects on these fungi, leading to membrane permeabilization, endogenous reactive oxygen species increase, activation of metacaspase and loss of mitochondrial function.

Characterisation of antagonistic Bacillus paralicheniformis (strain EAL) by LC-MS, antimicrobial peptide genes, and ISR determinants.

Plants have their own defense mechanisms such as induced systemic resistance (ISR) and systemic-acquired resistance. Bacillus spp. are familiar biocontrol agents that trigger ISR against various phytopathogens by eliciting various metabolites and producing defense enzyme in the host plant. In this study, B. paralicheniformis (strain EAL) was isolated from the medicinal plant Enicostema axillare. Butanol extract of B. paralicheniformis showed potential antagonism against Fusarium oxysporum compared to control well (sterile distilled water) A liquid chromatography mass spectrometry analysis showed 80 different compounds. Among the 80 compounds, we selected citrulline, carnitine, and indole-3-ethanol based on mass-to-charge ratio, database difference, and resolution of mass spectrum. The synthetic form of the above compounds showed biocontrol activity against F. oxysporum under in vitro condition in combination, not as individual compounds. However, the PCR amplification of 11 antimicrobial peptide genes showed that none of the genes amplified in the strain. B. paralicheniformis inoculation challenged with F. oxysporum on tomato plants enhanced production of defense enzymes such as peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and proline compared to control plants (without inoculation of B. paralicheniformis) at significant level (p < 0.005). Stem of tomato plants expressed higher POD (2.2-fold), SOD (2.2-fold), PPO (1.9-fold), and PAL (1.3-fold) contents followed by the leaf and root. Elevated proline accumulation was observed in the leaf (1.8-fold) of tomato plants. Thus, results clearly showed potentiality of B. paralicheniformis (EAL) in activation of antioxidant defense enzyme against F. oxysporum-infected tomato plants and prevention of oxidative damage though hydroxyl radicals scavenging activities that suppress the occurrence of wilt diseases.

Identification of a Human Skin Commensal Bacterium that Selectively Kills Cutibacterium acnes.

The microbiome represents a vast resource for drug discovery, as its members engage in constant conflict to outcompete one another by deploying diverse strategies for survival. Cutibacterium acnes is one of the most common bacterial species on human skin and can promote the common disease acne vulgaris. By employing a combined strategy of functional screening, genetics, and proteomics we discovered a strain of Staphylococcus capitis (S. capitis E12) that selectively inhibited growth of C. acnes with potency greater than antibiotics commonly used in the treatment of acne. Antimicrobial peptides secreted from S. capitis E12 were identified as four distinct phenol-soluble modulins acting synergistically. These peptides were not toxic to human keratinocytes and the S. capitis extract did not kill other commensal skin bacteria but was effective against C. acnes on pig skin and on mice. Overall, these data show how a member of the human skin microbiome can be useful as a biotherapy for acne vulgaris.

Selection of antimicrobial frog peptides and temporin-1DRa analogues for treatment of bacterial infections based on their cytotoxicity and differential activity against pathogens.

Cationic, amphipathic, α-helical host-defense peptides (HDPs) that are naturally secreted by certain species of frogs (Anura) possess potent broad-spectrum antimicrobial activity and show therapeutic potential as alternatives to treat infections by multidrug-resistant pathogens. Fourteen amphibian skin peptides and twelve analogues of temporin-1DRa were studied for their antimicrobial activities against clinically relevant human or animal skin infection-associated pathogens. For comparison, antimicrobial potencies of frog skin peptides against a range of probiotic lactobacilli were determined. We used the VITEK 2 system to define a profile of antibiotic susceptibility for the bacterial panel. The minimal inhibitory concentration (MIC) values of the naturally occurring temporin-1DRa, CPF-AM1, alyteserin-1c, hymenochirin-2B, and hymenochirin-4B for pathogenic bacteria were threefold to ninefold lower than the values for the tested probiotic strains. Similarly, temporin-1DRa and its [Lys4 ], [Lys5 ], and [Aib8 ] analogues showed fivefold to 6.5-fold greater potency against the pathogens. In the case of PGLa-AM1, XT-7, temporin-1DRa and its [D-Lys8 ] and [Aib13 ] analogues, no apoptosis or necrosis was detected in human peripheral blood mononuclear cells at concentrations below or above the MIC. Given the differential activity against commensal bacteria and pathogens, some of these peptides are promising candidates for further development into therapeutics for topical treatment of skin infections.