Insights into the Mode of Action of the Sactibiotic Thuricin CD

Abstract

Thuricin CD is a two-component bacteriocin, consisting of the peptides Trnα and Trnβ, and belongs to the newly designated sactibiotic subclass of bacteriocins. While it is clear from studies conducted thus far that it is a narrow-spectrum bacteriocin, requiring the synergistic activity of the two peptides, the precise mechanism of action of thuricin CD has not been elucidated. This study used a combination of flow cytometry and traditional culture-dependent assays to ascertain the effects of the thuricin CD peptides on the morphology, physiology and viability of sensitive Bacillus firmus DPC6349 cells. We show that both Trnα and Trnβ are membrane-acting and cause a collapse of the membrane potential, which could not be reversed even under membrane-repolarizing conditions. Furthermore, the depolarizing action of thuricin CD is accompanied by reductions in cell size and granularity, producing a pattern of physiological alterations in DPC6349 cells similar to those triggered by the pore-forming single-component bacteriocin Nisin A, and two-component lacticin 3147. Taken together, these results lead us to postulate that the lytic activity of thuricin CD involves the insertion of thuricin CD peptides into the membrane of target cells leading to permeabilization due to pore formation and consequent flux of ions across the membrane, resulting in membrane depolarization and eventual cell death.

Thuricin Z: A Narrow‐Spectrum Sactibiotic that Targets the Cell Membrane

“…It has been shown that subtilosin A binds to the cell membrane and creates transient pores, thereby leading to an efflux of intracellular ions and ATP and eventually to cell death . Similar observations have also been made for the two‐component sactibiotic thuricin CD . However, thuricin H shows a distinct mode of action and does not bind cell membranes or result in any detectable changes in membrane permeability .…”

Radical S-Adenosylmethionine Enzymes Involved in RiPP Biosynthesis

“…A recent mode of action study has shown that thuricin CD inserts into the membrane of the target cell, forms pores, and causes ion leakage, membrane depolarization, and finally, cell lysis. 54 Structural elucidation studies of thuricin CD have shown that each of the two components contains three sactionines. The linkages in Trnα are from Cys5, Cys9, and Cys13 to Thr28, Thr25, and Ser21, respectively.…”

Metabolic functions of the human gut microbiota: the role of metalloenzymes

“…These peptides are thought to act by creating pores in the bacterial membrane, causing an inux of ions that leads to membrane depolarization and cell death. 153,154 Subtilosin A, produced by strains of Bacillus subtilis, was the rst sactipeptide to be identied and characterized ( Fig. 3a).…”

“…151,152 Subtilosin A demonstrates relatively broad bacteriocidal activity against Gram-positive pathogenic bacteria implicated in bacterial vaginosis, food poisoning, and hospital infections, including Gardnerella vaginalis, Listeria monocytogenes, Enterococcus faecium, and Staphylococcus aureus. 153,158,159 Other sactipeptides have been isolated exclusively from gut microbes, such as thuricin CD 154,[160][161][162] (Fig. 3a) and thurincin H 163,164 (Fig.…”