Bacterial-Derived Plant Protection Metabolite 2,4-Diacetylphloroglucinol: Effects on Bacterial Cells at Inhibitory and Subinhibitory Concentrations

Abstract

2,4-Diacetylphloroglucinol (2,4-DAPG) is a well-known bacterial secondary metabolite, however, its mechanism of inhibitory and subinhibitory action on bacterial cells is still poorly understood. The mechanism of 2,4-DAPG action on model bacterial strains was investigated using fluorescent spectroscopy and the action of the antibiotic was found to involve a rapid increase in membrane permeability that was accompanied by a reduction in its viability in nutrient-poor medium. At the same time, antibacterial action in nutrient-rich medium developed for several hours. Atomic force microscopy demonstrated time-dependent disturbances in the outer membrane of Escherichia coli when exposed to 2,4-DAPG, while Staphylococcusaureus cells have been visualized with signs of intracellular leakage. In addition, 2,4-DAPG inhibited the metabolic activity of S. aureus and E. coli bacterial cells in mature biofilms. Observed differences in the antibiofilm activity were dependent upon antibiotic concentration. The intracellular targets of the action of 2,4-DAPG were assessed using bacterial biosensors with inducible bioluminescence corresponding to DNA and protein damage. It was unable to register any positive response from either sensor. As a result, the bactericidal action of 2,4-DAPG is believed to be associated with the destruction of the bacterial barrier structures. The subinhibitory effect of 2,4-diacetylphloroglucinol was tested on quorum-sensing mediated processes in Pectobacterium carotovorum. Subinhibitory concentrations of 2,4-DAPG were found to lower the biosynthesis of acyl-homoserine lactones in P. carotovorum in a dose-dependent manner. Further investigation elucidated that 2,4-DAPG inhibits the metabolic activity of bacteria without affecting their viability.

Pseudomonas bijieensis Strain XL17 within the P. corrugata Subgroup Producing 2,4-Diacetylphloroglucinol and Lipopeptides Controls Bacterial Canker and Gray Mold Pathogens of Kiwifruit

“…Our genomic analyses and metabolic analyses on strain XL17 and previous studies on potent biocontrol pseudomonads [69,73,74], including strains Pf275 and 2P24 [65,68], strongly suggest that DAPG and lipopeptides are the key antimicrobial metabolites from strain XL17 to breach the cell envelopes of Psa and B. cinerea. On the other hand, DAPG and cyclic lipopeptides produced by plant-associated pseudomonads [73][74][75][76][77] may be toxic to plants [74,78]. Thus, we did a phytotoxic test and demonstrated that strain XL17 and its CF were not toxic to rice seeds and seedlings but increased rice shoot height and dry weight.…”

The Mode of Action of Cyclic Monoterpenes (−)-Limonene and (+)-α-Pinene on Bacterial Cells

“…As reported in [46], intracellular targets of 2,4-diacetylphloroglucinol action were assessed using bacterial biosensors with inducible bioluminescence corresponding to DNA and protein damage. However, unlike our study, it was not possible to register a positive response from any biosensor.…”

“…However, unlike our study, it was not possible to register a positive response from any biosensor. As a result, the bactericidal effect of 2,4-DAPG is believed to be related to the destruction of bacterial barrier structures [46].…”

Phloroglucinol Derivatives in Plant-Beneficial Pseudomonas spp.: Biosynthesis, Regulation, and Functions

“…DAPG exhibits high antimicrobial activity against several bacteria, including the Gram-positive model Bacillus subtilis and the Gram-negative plant pathogen Pseudomonas syringae [13]. Conversely, it is quite inefficient against Pseudomonas aeruginosa and Pseudomonas fluorescens strains [13,111]. This discrepancy could originate from differential membrane permeability and/or the presence of detoxifying efflux pumps.…”

“…This discrepancy could originate from differential membrane permeability and/or the presence of detoxifying efflux pumps. It has been proposed that DAPG targets the bacterial envelop [111], but little is known about the mode of action of DAPG towards bacteria. At subinhibitory concentrations, DAPG has been shown to reduce biofilm and spore formation in B. subtilis [112].…”