PhlG mediates the conversion of DAPG to MAPG in Pseudomonas fluorescens 2P24

New Insights into Pseudomonas spp.-Produced Antibiotics: Genetic Regulation of Biosynthesis and Implementation in Biotechnology

Pseudomonas bacteria are renowned for their remarkable capacity to synthesize antibiotics, namely mupirocin, gluconic acid, pyrrolnitrin, and 2,4-diacetylphloroglucinol (DAPG). While these substances are extensively employed in agricultural biotechnology to safeguard plants against harmful bacteria and fungi, their potential for human medicine and healthcare remains highly promising for common science. However, the challenge of obtaining stable producers that yield higher quantities of these antibiotics continues to be a pertinent concern in modern biotechnology. Although the interest in antibiotics of Pseudomonas bacteria has persisted over the past century, many uncertainties still surround the regulation of the biosynthetic pathways of these compounds. Thus, the present review comprehensively studies the genetic organization and regulation of the biosynthesis of these antibiotics and provides a comprehensive summary of the genetic organization of antibiotic biosynthesis pathways in pseudomonas strains, appealing to both molecular biologists and biotechnologists. In addition, attention is also paid to the application of antibiotics in plant protection.

Soil bacterium manipulates antifungal weapons by sensing intracellular type IVA secretion system effectors of a competitor

Soil beneficial bacteria can effectively inhibit bacterial pathogens by assembling contact-dependent killing weapons, such as the type IVA secretion system (T4ASS). It's not clear whether these antibacterial weapons are involved in biotrophic microbial interactions in soil. Here we showed that an antifungal antibiotic 2,4-DAPG production of the soil bacterium, Pseudomonas protegens can be triggered by another soil bacterium, Lysobacter enzymogenes, via T4ASS by co-culturing on agar plates to mimic cell-to-cell contact. We demonstrated that the induced 2,4-DAPG production of P. protegens is achieved by intracellular detection of the T4ASS effector protein Le1519 translocated from L. enzymogenes. We defined Le1519 as LtaE (Lysobacter T4E triggering antifungal effects), which specifically stimulates the expression of 2,4-DAPG biosynthesis genes in P. protegens, thereby protecting soybean seedlings from infection by the fungus Rhizoctonia solani. We further found that LtaE directly bound to PhlF, a pathway-specific transcriptional repressor of the 2,4-DAPG biosynthesis, then activated the 2,4-DAPG production. Our results highlight a novel pattern of microbial interspecies and interkingdom interactions, providing a unique case for expanding the diversity of soil microbial interactions.

Mechanistic insight into the free radical scavenging and xanthine oxidase (XO) inhibitor potent of monoacetylphloroglucinols (MAPGs)

Three novel antioxidant candidates based on phenolic polyketide, monoacetylphloroglucinol (MAPG), a natural antibiotic compound produced by plant growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens F113 have been proposed. Initially, a green and highly efficient route to the synthesis of MAPG and its two analogues from phloroglucinol (PG) has been developed. Afterward, their rational mechanism of antioxidant activity has been investigated based on thermodynamic descriptors involved in the double ( 2H+/2e-) radical trapping processes. These calculations have been performed using the systematic density functional theory (DFT) method at the B3LYP/Def2-SVP level of theory in the gas phase and aqueous solution. Our findings reveal that the double formal hydrogen atom transfer (df-HAT) mechanism is preferred in the gas phase, while the double sequential proton loss electron transfer (dSPLET) mechanism is preferred in aqueous solution for all MAPGs. The 6-OH group represents the most favourable site for trapping radical species for all MAPGs, which is supported by the pK_a values obtained from DFT calculations. The role of acyl substituents on the PG ring has been comprehensively discussed. The presence of acyl substituents has a strong influence on the thermodynamic parameters of the phenolic O-H bond in PG. These results are supported by frontier molecular orbitals (FMOs) analysis, where the addition of acyl substituents increases the chemical reactivity of MAPGs significantly. Based on molecular docking and molecular dynamics simulations (MDs), MAPGs are also predicted to be promising candidates for xanthine oxidase (XO) inhibition.HighlightsThe antioxidant activity of the three synthesised MAPGs has been investigated using the DFT method.Acyl substituents increase the chemical reactivity and antioxidant activity of MAPGs.df-HAT is the preferred mechanism in the gas phase.dSPLET seems to be more favoured in aqueous solution.MAPGs are expected to be promising xanthine oxidase (XO) inhibitors.

RpoZ regulates 2,4-DAPG production and quorum sensing system in Pseudomonas fluorescens 2P24

Introduction

Pseudomonas fluorescens 2P24 was isolated from soil of natural decay associated with wheat take-all and it can effectively control soil-borne diseases caused by a variety of plant pathogens. 2,4-diacetylphloroglucinol (2,4-DAPG), is produced by P. fluorescens 2P24 and plays an important role in the prevention and control of plant diseases. To understand the resistant mechanism, in this study, we conducted experiments to explore the regulation role of rpoZ in the synthesis of the antibiotic 2,4-DAPG and regulation of QS system.

Methods

A random mini-Tn5 mutagenesis procedure was used to screen regulators for phlA transcription in stain PM901, which containing a phlA∷lacZ transcriptional fusion reporter plasmid. We identified 12 insertion mutants could significantly change phlA gene expression. By analyzing the amino acid sequences of the interrupted gene, we obtained a mutant strain Aa4-29 destroyed the rpoZ gene, which encodes the omiga subunit. We constructed the plasmid of rpoZ mutant (pBBR-△rpoZ) transformed into competent cells of P. fluorescens 2P24 by electro-transformation assay. The strains of P. fluorescens 2P24/pBBR, 2P24-△rpoZ/pBBR, 2P24-△rpoZ/pBBR-rpoZ were used to evaluate the regulation role of rpoZ in 2,4-DAPG production and quorum sensing system.

Results

According to β-galactosidase activity, we found that rpoZ positively regulated the expression of phlA (a synthesis gene of 2,4-DAPG) and PcoI (a synthesis gene of PcoI/PcoR QS signal system) at the transcriptional level. The production of 2,4-DAPG antibiotic and signal molecule AHL was influenced by rpoZ. Further, rpoZ was involved in regulating rsmA expression. RpoZ also has a certain regulatory effect on rpoS transcription, but no effect on the transcription of phlF, emhABC and emhR. According to the biocontrol assay, P. fluorescens 2P24 strains with rpoZ showed obvious antagonism ability against the Rhizoctonia solani in cotton, while the mutant strain of rpoZ lost the biocontrol effect. RpoZ had a significant effect on the swimming and biofilm formation in P. fluorescens 2P24.

Conclusion

Our data showed that rpoZ was an important regulator of QS system, 2,4-DAPG in P. fluorescens 2P24. This may imply that P. fluorescens 2P24 has evolved different regulatory features to adapt to different environmental threats.

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

Bacterial secondary metabolites represent an invaluable source of bioactive molecules for the pharmaceutical and agrochemical industries. Although screening campaigns for the discovery of new compounds have traditionally been strongly biased towards the study of soil-dwelling Actinobacteria, the current antibiotic resistance and discovery crisis has brought a considerable amount of attention to the study of previously neglected bacterial sources of secondary metabolites. The development and application of new screening, sequencing, genetic manipulation, cultivation and bioinformatic techniques have revealed several other groups of bacteria as producers of striking chemical novelty. Biosynthetic machineries evolved from independent taxonomic origins and under completely different ecological requirements and selective pressures are responsible for these structural innovations. In this review, we summarize the most important discoveries related to secondary metabolites from alternative bacterial sources, trying to provide the reader with a broad perspective on how technical novelties have facilitated the access to the bacterial metabolic dark matter.

Partial purification and characterization of 2, 4-diacetylphloroglucinol producing Pseudomonas fluorescens VSMKU3054 against bacterial wilt disease of tomato

We find out the antimicrobial potential of partially purified 2,4-diacetylphloroglucinol (DAPG) against Ralstonia solanacearum and fungal plant pathogens isolated from tomato rhizobacterium Pseudomonas fluorescens VSMKU3054. The present study is mainly focused on the control of wilt disease of tomato by our isolate VSMKU3054 and DAPG. The cell free culture filtrate of P. fluorescens VSMKU3054 was significantly arrested the growth of R. solanacearum and fungal pathogens such as Rhizoctonia solani, Sclerotium rolfsii, Macrophomina phaseolina and Fusarium oxysporum compared to control. The existence of DAPG from the crude metabolites of P. fluorescens VSMKU3054 was confirmed on TLC with Rf value 0.34, which is coincide with that of authentic phloroglucinol. The partially purified DAPG exhibited much higher activity against R. solanacearum at 30 µg/ml than the fungal plant pathogens compared to control. The antimicrobial partially purified compound was identified as DAPG by UV, FT-IR and GC-MS analysis. The percentage of live cells of R. solanacearum when supplemented with DAPG at 30 µg/ml, significantly controlled the living nature of R. solanacearum up to 68% compared to tetracycline and universal control observed under high content screening analysis. The selected isolate P. fluorescens VSMKU3054 and DAPG significantly controlled wilt disease of tomato up to 59.5% and 42.12% on 3rd and 7th days compared to positive and negative control by detached leaf assay. Further, in silico analysis revealed that high interaction of DAPG encoding protease with lectin which is associated with R. solanacearum. Based on our findings, we confirmed that P. fluorescens VSMKU3054 and DAPG could be used a potential bio inoculants for the management of bacterial wilt disease of tomato.

A greatly improved procedure for the synthesis of an antibiotic-drug candidate 2,4-diacetylphloroglucinol over silica sulphuric acid catalyst: multivariate optimisation and environmental assessment protocol comparison by metrics

Efforts toward the development of a straightforward greener Gram-scale synthesis of the antibiotic compound 2,4-diacetylphloroglucinol (DAPG) have been developed. This beneficial procedure was accomplished through the Friedel–Crafts acylation of phloroglucinol over inexpensive heterogeneous silica sulphuric acid (SSA) catalyst via ultrasound-assisted (US) synthesis under solvent-free condition. The influences of various parameters such as temperature, catalyst loading, and reaction time on the reaction performance were analysed using a multivariate statistical modelling response surface methodology (RSM). A high yield of DAPG (95%) was achieved at 60 °C after 15–20 min reaction with the presence of 10% (w/w) SSA as the catalyst. Column chromatography-free and a Gram scale-up reaction also exhibited the practical applicability of this newly developed protocol. The SSA catalyst was recovered and recycled up to 10 consecutive runs with no appreciable loss of activity. A plausible mechanism for the Friedel–Crafts acylation of phloroglucinol is proposed. Moreover, an environmental assessment has been carried out over this present method and compared with several established literature using the EATOS software and the Andraos algorithm to assess the consumption of the substrates, solvents, catalysts, and the production of coupled products or by-products. In addition, their energy consumptions were also determined. The data collected showed that the present method is the most promising one, characterised by the highest environmental impact profile against all the other reported methods. The physicochemical properties of the synthesised DAPG were assessed and exhibited reasonable oral bioavailability drug property as determined by Lipinski's rules.

A greatly improved procedure for the synthesis of antibiotic 2,4-diacetylphloroglucinol has been developed via a newly advanced synthetic method.