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.
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, suggesting that the BraI/R QS system plays a regulatory role in modulating interspecies antagonism.
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
While strain XJ-10 showed no detectable acylase activity, it exhibited significant degradation activity against AHL, suggesting a distinct QQ mechanism, and 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
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.
D. Nwobodo, M. Egbujor, Samuel S. Kiprotich et al.· FEMS Microbiology Reviews· 0 citations
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 and 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