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Leaderless bacteriocins are a unique class of bacteriocins that possess antimicrobial activity after translation and have few cases of documented resistance. Aureocin A53 and lacticin Q are considered two of the most well-studied leaderless bacteriocins. Here, we used in silico genome mining to search for novel aureocin A53-like leaderless bacteriocins in GenBank and MGnify. We identified 757 core peptides across 430 genomes with 75 species found currently without characterized leaderless bacteriocin production. These include putative novel species containing bacteriocin gene clusters (BGCs) from the genera Streptomyces (sp. NBC_00237) and Agrococcus (sp. SL85). To date, all characterized leaderless bacteriocins have been found within the phylum Bacillota, but this study identified 97 core peptides within the phylum Actinomycetota. Members of this phylum are traditionally associated with the production of antibiotics, such is the case with the genus Streptomyces . Actinomycetota is an underexplored phylum in terms of bacteriocin production with no characterized leaderless bacteriocin production to date. The two novel leaderless bacteriocins arcanocin and arachnicin from Actinomycetota members Arcanobacterium sp. and Arachnia sp., respectively, were chemically synthesized and antimicrobial activity was verified. These peptides were encoded in human gut (PRJNA485056) and oral (PRJEB43277) microbiomes, respectively. This research highlights the biosynthetic potential of Actinomycetota in terms of leaderless bacteriocin production and describes the first antimicrobial peptides encoded in the genera Arcanobacterium and Arachnia .IMPORTANCEBacteriocins are gathering attention as alternatives to current antibiotics given the increasing incidence of antimicrobial resistance. Leaderless bacteriocins are considered a commercially attractive subclass of bacteriocins due to the ability to synthesize active peptide and low levels of documented resistance. Therefore, in this work, we mined publicly available data to determine how widespread and diverse leaderless bacteriocins are within the domain of bacteria. Actinomycetota, known for its antibiotic producers but lacking described and characterized bacteriocins, proved to be a rich source of leaderless bacteriocins-97 in total. Two such peptides, arcanocin and arachnicin, were chemically synthesized and have antimicrobial activity. These bacteriocins may provide a novel source of novel antimicrobials that could aid in the development of future alternative antimicrobials and highlight that the Actinomycetota are an underexplored resource of bacteriocin peptides., Competing Interests: The authors declare no conflict of interest.

Introduction: Antimicrobial-resistant pathogens present an ongoing threat to human and animal health, with deaths linked to antimicrobial resistance (AMR) predicted to increase annually. While the misuse and overuse of antibiotics in humans undoubtedly contribute to this escalation, antibiotic use in the veterinary field, including companion animals, also plays a contributing role. Pet owners' desire to improve the quality of life of their pets is likely to support antibiotic use in this field. Consequently, there is a need for antibiotic alternatives to treat bacterial infections. This study set out to screen for antimicrobial peptides known as bacteriocins from bacterial isolates of aerobic/microaerophilic environments of canine sources and determine their potential as antibiotic alternatives against clinically relevant pathogens., Methods: Following a laboratory-based protocol, 22 bacterial isolates were subjected to whole-genome sequencing (WGS), and a total of 14 putative novel bacteriocins were identified from both class I and II bacteriocin classes. One particular bacteriocin, herein named caledonicin, was identified via in silico analysis from a Staphylococcus caledonicus strain and partially purified for further in vitro evaluation., Results: Caledonicin is a 64-amino acid (IAANLGVSSGTAYS MANALNNISNVATA LTIIGTFTGVGTIGSGIA ATILAILKKKGVAAAAAF) novel circular bacteriocin most closely related to enterocin_NKR-5-3B based on core peptide alignment (39.1%), with a molecular weight of 6077.1 Da. Caledonicin exhibits a broad-spectrum of activity against a range of pathogenic bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus pseudintermedius (MRSP), and Listeria monocytogenes ; and the gut-related bacterium associated with Crohn's disease, Mediterraneibacter gnavus ATCC 29149 (previously Ruminococcus gnavus ATCC 29149)., Discussion: This represents the first bacteriocin screening study involving bacteria from canine sources and confirms this is a rich environment for bacteriocin-producing strains. This study also identifies and characterises the first novel bacteriocin from the staphylococcal species, Staphylococcus caledonicus., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 O’Connor, O’Connor, Hourigan, Murray, de Farias, Field, Hill and Ross.)

Vancomycin-resistant enterococci (VRE) are major opportunistic pathogens and the causative agents of serious diseases, such as urinary tract infections and endocarditis. VRE strains mainly include species of Enterococcus faecium and E. faecalis which can colonise the gastrointestinal tract (GIT) of patients and, following growth and persistence in the gut, can transfer to blood resulting in systemic dissemination in the body. Advancements in genomics have revealed that hospital-associated VRE strains are characterised by increased numbers of mobile genetic elements, higher numbers of antibiotic resistance genes and often lack active CRISPR-Cas systems. Additionally, comparative genomics have increased our understanding of dissemination routes among patients and healthcare workers. Since the efficiency of currently available antibiotics is rapidly declining, new measures to control infection and dissemination of these persistent pathogens are urgently needed. These approaches include combinatory administration of antibiotics, strengthening colonisation resistance of the gut microbiota to reduce VRE proliferation through commensals or probiotic bacteria, or switching to non-antibiotic bacterial killers, such as bacteriophages or bacteriocins. In this review, we discuss the current knowledge of the genomics of VRE isolates and state-of-the-art therapeutic advances against VRE infections., (© 2024. The Author(s).)

The development of HER2-targeted therapies has led to a dramatic improvement in outcomes for breast cancer patients. However, nearly all patients with metastatic HER2-positive breast cancer will eventually progress on these therapies due to innate or acquired resistance. Recent evidence suggests that the endosomal recycling of HER2 plays an important role in regulating its oncogenic signalling. Here we report that the expression of Rab coupling protein (RCP), a key regulator of endosomal recycling, positively correlates with that of HER2 and HER3 in breast tumours, and high RCP expression is predictive of poor relapse-free and overall survival in patients with HER2-amplified breast cancer. Chemical and genetic inhibition of endosomal recycling leads to a reduction in the total cellular levels of HER2 and HER3 and inhibits the activation of their downstream signalling pathways. We find that HER2 and HER3 that have been internalised from the plasma membrane are diverted to lysosomes for degradation when endosomal recycling is blocked. Primaquine (PQ), a small molecule inhibitor of the endosomal recycling pathway, synergises with HER2-targeting tyrosine kinase inhibitors and overcomes innate and acquired resistance to these TKIs. Moreover, TKI-induced drug tolerant persister cells are vulnerable to endosomal recycling inhibitors. These findings suggest that inhibition of endosomal recycling represents a promising therapeutic strategy for treating drug resistant HER2-positive breast cancer., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)