Structure and Mode-of-Action of the Two-Peptide (Class-IIb) Bacteriocins

This review focuses on the structure and mode-of-action of the two-peptide (class-IIb) bacteriocins that consist of two different peptides whose genes are next to each other in the same operon. Optimal antibacterial activity requires the presence of both peptides in about equal amounts. The two peptides are synthesized as preforms that contain a 15–30 residue double-glycine-type N-terminal leader sequence that is cleaved off at the C-terminal side of two glycine residues by a dedicated ABC-transporter that concomitantly transfers the bacteriocin peptides across cell membranes. Two-peptide bacteriocins render the membrane of sensitive bacteria permeable to a selected group of ions, indicating that the bacteriocins form or induce the formation of pores that display specificity with respect to the transport of molecules. Based on structure–function studies, it has been proposed that the two peptides of two-peptide bacteriocins form a membrane-penetrating helix–helix structure involving helix–helix-interacting GxxxG-motifs that are present in all characterized two-peptide bacteriocins. It has also been suggested that the membrane-penetrating helix–helix structure interacts with an integrated membrane protein, thereby triggering a conformational alteration in the protein, which in turn causes membrane-leakage. This proposed mode-of-action is similar to the mode-of-action of the pediocin-like (class-IIa) bacteriocins and lactococcin A (a class-IId bacteriocin), which bind to a membrane-embedded part of the mannose phosphotransferase permease in a manner that causes membrane-leakage and cell death

Antimicrobial interest of essential oils extracted from Tunisian plants

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Genetic determination and localization of multiple bacteriocins produced by Enterococcus faecium CWBI-B1430 and Enterococcus mundtii CWBI-B1431

peer reviewedEnterococcus faecium CWBI-B1430 and Enterococcus mundtii CWBI-B1431 from artisanalproduced Peruvian cheeses showed the presence of 4 putative bacteriocin genes: enterocin A, enterocin B, enterocin P, and mundticin KS. The multiple bacteriocin producer E. faecium CWBI-B1430 presented 1 plasmid of 34.6 kb, whereas E. mundtii CWBI-B1431 contained 1 plasmid of 11.0 kb. The structural gene responsible for mundticin KS production was located on 5.6 and 3.1 kb HindIII plasmid fragments. The reverse transcription-PCR analysis showed the expression of the bacteriocin genes enterocin A, enterocin B, and mundticin KS in E. faecium CWBI-B1430 and the bacteriocin genes enterocin P and mundticin KS in E. mundtii CWBI-B1431. To our knowledge, this is the first report of the expression of mundticin KS in E. faecium and enterocin P in E. mundtii

Legionella species diversity and dynamics from surface reservoir to tap water: from cold adaptation to thermophily

Water samples of the Drinking Water Supply System (DWSS) of the city of Braunschweig were analysed for its Legionella species composition using genus-specific PCR amplicons and single-strand conformation polymorphism (SSCP) fingerprint analyses based on 16S rRNA genes. These analyses comprised the whole supply chain including raw water, treatment process and large-scale storage, and a seasonal study of finished drinking water sampled monthly from cold and hot tap water. Treatment of raw water had a major impact on Legionella species by reducing their diversity and abundances. The Legionella species composition of the tap water was highly distinct from that of both source waters. In cold water, 8-14 different phylotypes of Legionella (PTLs) were observed per sample with relative abundances ranging from >1% to 53%. In hot water, L. pneumophila was present during all seasons at high relative abundances (8-40%) accompanied by 5-14 other PTLs of which 6 PTLs were in common with cold water. This thermophilic Legionella community, including L. pneumophila, was able to grow in the hot water above 50 °C. Such thermophilic Legionella populations are of general relevance for drinking water management and public health, but also for the ecology and evolution of the genus Legionella