This study provides novel and unexpected insights into the involvement of a LuxR homolog in regulating a QS system in Gram-positive bacteria and demonstrates that functional GBL-based QS systems are conserved and active in R. erythropolis.
Abstract
Quorum sensing (QS) enables bacteria to coordinate collective behaviors, including the production of secondary metabolites with potential biotechnological applications, through the synthesis and detection of small signaling molecules. In Streptomyces, QS is well-described and mainly mediated by 2,3-disubstituted γ-butyrolactones (GBLs), which play key roles in the regulation of secondary metabolism and spore production. Despite their importance, GBL-based QS systems remain poorly characterized in other actinomycetal genera. Here, we investigated the distribution, structure, and function of GBL biosynthetic and regulatory systems within the genus Rhodococcus, focusing on the biocontrol strain Rhodococcus erythropolis R138. Comparative genomic analyses revealed that the scbA and scbR homologs, which are involved in GBL biosynthesis and detection, respectively, are widely conserved among Rhodococcus species and are organized within a conserved GBL gene cluster. Structural modeling using AlphaFold showed a high degree of conservation between ScbA and ScbR from Streptomyces coelicolor and their homologs in R. erythropolis R138. By combining liquid chromatography–mass spectrometry analyses with a GBL-specific reporter assay, we demonstrated that R. erythropolis R138 produces biologically active GBL(−like) molecules. Production of the investigated GBL molecules required the scbA gene, which restored spore production and promoted colony development in the scbA-deleted S. coelicolor strain during interaction with R. erythropolis R138. Transcriptional analyses further showed that both ScbR and a LuxR-like regulator may contribute to the fine-tuned regulation of scbA expression, revealing a complex regulatory network controlling GBL biosynthesis. This study provides novel and unexpected insights into the involvement of a LuxR homolog in regulating a QS system in Gram-positive bacteria. Together, these results demonstrate that functional GBL-based QS systems are conserved and active in R. erythropolis and likely widespread in the genus. This study expands current knowledge of QS in Actinomycetota and highlights the potential role of GBL signaling in regulating biotechnologically and ecologically relevant traits in Rhodococcus.
Quorum sensing (QS) is a cell-to-cell communication mechanism that enables bacteria to coordinate collective behaviors in response to population density. The BraI/R QS system is conserved among Burkholderia and Paraburkholderia species, and its regulatory role is still unknown. In this study, the BraI/R QS of P. kururiensis was investigated for biological control of another bacterial species. The results demonstrate that the functional BraI/R system influences interbacterial competition, as braI and braR mutant strains failed to inhibit the growth of Escherichia coli, in contrast to the wild-type strain. These findings suggest that the BraI/R QS system plays a regulatory role in modulating interspecies antagonism. Comparative exoproteome analyses were performed for the wild-type and the BraI/R QS-mutant P. kururiensis strains, revealing distinct protein populations, including structural and effector proteins of the Type VI secretion system (T6SS). Genomic mapping revealed that two of those T6SS-proteins were encoded within a specific T6SS gene cluster (T6SS-3), while others originate outside any major T6SS gene cluster. The identification of exoproteome targets regulated by the BraI/R QS system represents a significant advance toward the understanding of the molecular mechanisms underpinning P. kururiensis interactions with competing bacteria, further supporting its potential as a biological control agent against phytopathogenic and/or free-living species.
G. T. Cordeiro, Yara Martins da Silva, Giovanna Fernandes Lessa et al.· Proteomics· 0 citations
The bacterial Quorum Sensing system refers to the recognition of signaling molecules called autoinducers produced by bacteria when a certain cell density is reached in the environment. Those cell-density-dependent autoinducers regulate and coordinate diverse functional processes, such as bioluminescence, biofilm production, sporulation, and even the expression of some virulence factors, among others. There is a wide variety of autoinducers, and for Gram-negative bacteria, the canonical autoinducers are the N-acyl-homoserine lactones (AI-1). Presently, the production of autoinducers in Leptospira has not been described; therefore, the objective of this study was to detect and identify autoinducers in this bacterial genus. We report here the expression of AI-1 in cultures ≥2.4 × 108 of Leptospira meyeri. Ethyl acetate extracts of Leptospira culture supernatants were capable of activating the β-galactosidase system in the biosensor Agrobacterium tumefaciens strain NTL4. Partial identification of the leptospiral supernatant extracts was done by thin-layer chromatography (TLC), showing a similar retention factor to the synthetic standard N-Octanoyl-DL-homoserine lactone (C8-AHL) in the Leptospira supernatant extracts. In addition, infrared spectroscopy (IR) analysis showed peaks corresponding to the lactone and amide groups in both the C8-AHL standard and the Leptospira meyeri culture extracts. Moreover, High-Performance Liquid Chromatography–Mass Spectrometry (HPLC-MS/MS) confirmed the same retention time (10.7 ± 0.1 min) in both the Leptospira meyeri supernatant extracts and the C8-AHL standard. These results show that Leptospira meyeri synthesizes N-acyl homoserine lactone family autoinducers, particularly the N-Octanoyl-DL-homoserine lactone, and lay the groundwork for future research on Quorum Sensing systems in Leptospira.
Luz Olivia Castillo-Sánchez, A. de la Peña-Moctezuma, G. Bautista-Trujillo et al.· Microorganisms· 0 citations
Quorum sensing (QS) is critically involved in mediating microbial interactions and serves as a central regulatory mechanism in bacterial pathogenesis. As an emerging countermeasure, quorum quenching (QQ) suppresses QS-regulated virulence through enzymatic or chemical disruption of signal systems. N-acyl homoserine lactone (AHL), an evolutionarily conserved QS signal, coordinates the pathogenicity of multiple plant pathogens, particularly Dickeya zeae, which causes soft rot disease in various crops and leads to substantial agricultural losses. In this study, the QQ strain Acinetobacter schindleri XJ-10 was evaluated for its capacity to degrade AHL and attenuate the pathogenicity of D. zeae EC1 in host plants. Notably, strain XJ-10 exhibited efficient AHL degradation at 0.2 mmol/L within 24 h, achieving a degradation efficiency of 98.80%. Subsequently, gas chromatography–mass spectrometry (GC-MS) analysis identified N-hexanoyl-L-homoserine lactone and propanamide as key intermediates during AHL degradation, confirming complete mineralization to CO2 and H2O. Based on the structural characterization of AHL and its intermediates, the metabolic pathway within strain XJ-10 was proposed. The degradation pathway initiates with the hydrolysis of the ester ring of N-hexanoyl-L-homoserine lactone, generating N-hexanoyl-L-homoserine. Subsequent carbon–nitrogen bond scission is predicted to yield N-cyclohexyl-propanamide, which is further catabolized to produce hexanamide and propanamide. Furthermore, strain XJ-10 exhibited biocontrol activity against soft rot disease affecting potato (Solanum tuberosum), radish (Raphanus sativus), and Chinese cabbage (Brassica rapa subsp. pekinensis), as its crude enzyme extract effectively reduced disease incidence and severity in planta. While strain XJ-10 showed no detectable acylase activity, it exhibited significant degradation activity against AHL, suggesting a distinct QQ mechanism. Collectively, these findings broaden the scope of QQ-based biocontrol strategies and enhance mechanistic insights into managing bacterial diseases through QS modulation.
Pseudomonas sp. MUP55, isolated from rainfall water in Western Australia, was characterized by polyphasic taxonomy and functional assays. Whole-genome and 16S rRNA phylogeny placed Pseudomonas sp. MUP55 in the Pseudomonas fluorescens species group. Massetolide A/D was identified as the leading candidate bioactive compound(s), consistent with its biosynthetic gene cluster, GNPS library matching, and loss of activity in regulatory mutants. The strain showed broad-spectrum antimicrobial activity against bacterial (Escherichia coli and Xanthomonas campestris) and fungal (Fusarium oxysporum and Rhizoctonia solani) plant pathogens. GacA regulates Massetolide production: a P58L mutation abolished synthesis and reduced biocontrol efficacy. Metabolomic and transcriptomic analysis of a ΔpvfC mutant revealed that the pvf cluster regulates specialized metabolism while also contributing to secreted growth-inhibitory activity. The pvf cluster differentially regulates dual siderophore systems and uncouples the co-regulated small RNAs rsmY and rsmZ in the Gac/Rsm cascade. Deletion of pvfC partially reduced the growth-inhibitory activity of Pseudomonas sp. MUP55 supernatants against bacterial pathogens, indicating that pvfC also influences secreted antimicrobial activity beyond its global regulatory role. These findings establish Pseudomonas sp. MUP55 as a taxonomically novel, mechanistically characterized biocontrol agent with potential for sustainable agriculture.
Hussain Alattas, Samuele Sala, Joseph Boctor et al.· International Journal of Mol...· 0 citations
Abstract Quorum sensing (QS) is a cell-density-dependent communication system that coordinates bacterial virulence, biofilm formation, motility, and stress adaptation, making it a compelling target for antivirulence intervention. Due to the possibility of sulfonyl (-SO₂-) and sulfinyl (-S = O-) functional groups to impart specific electronic and steric properties that can modulate bacterial signaling and receptor interactions, organosulfur compounds are increasingly gaining attention. This review highlights recent advances in the development of sulfonyl- and sulfinyl-containing organosulfur compounds as modulators of QS and biofilm formation in clinically relevant Gram-negative pathogens. Both natural and synthetic quorum-sensing inhibitors are considered, with activity directed toward LuxR-type regulators, diffusible signal factor (DSF)-mediated systems, and the Las/Rhl networks of Gram-negative bacteria, including Pseudomonas aeruginosa, Vibrio spp., Chromobacterium violaceum, and Xylella fastidiosa. Emphasis is placed on emerging structure-activity relationships and mechanistic insights derived from biochemical and computational studies. Key challenges, including resistance potential, pharmacological constraints, and delivery considerations, are also discussed. Together, we provide an integrated microbiological and medicinal chemistry perspective for the rational development of organosulfur-based strategies to attenuate QS-regulated pathogenicity.
D. Nwobodo, M. Egbujor, Samuel S. Kiprotich et al.· FEMS Microbiology Reviews· 0 citations
ABSTRACT Quorum sensing (QS) is widely involved in the regulation of the biological functions and pathogenic processes of bacteria in a cell density-dependent manner. The anthranilic acid signal is directly sensed by the receptor RaaR, a transcription regulator, to control the expression level of downstream target genes in Ralstonia solanacearum, thus affecting the QS signals generation and the bacterial virulence. Here, we reported that 4-Aminobenzoic acid (PABA), a structural analogue of anthranilic acid, not only significantly inhibited the production of extracellular polysaccharides (EPS), biofilm formation, and motility of R. solanacearum, but also reduced the expression level of QS signaling molecules. We also found that PABA can directly bind to RaaR and prevented it from interacting with the promoters of target genes associated with the QS system and virulence of R. solanacearum. Point mutations in RaaR at residues F137 and I270 abolished the binding between RaaR and PABA, indicating that these two amino acid residues are likely critical for the interaction between RaaR and PABA. These findings indicated that PABA could be a candidate inhibitor of anthranilic acid signaling to interfere with the QS systems of R. solanacearum to attenuate the virulence. Together, our work presented a non-antibiotic-based treatment strategy and provided a theoretical basis for the development of novel antibacterial treatment.
Chuanwang Yao, Wanlian Zhang, Zizi Lin et al.· Virulence· 0 citations