A widespread response of Gram-negative bacterial acyl-homoserine lactone receptors to Gram-positive Streptomyces γ-butyrolactone signaling molecules

Abstract

Cell-cell communication is critical for bacterial survival in natural habitats, in which miscellaneous regulatory networks are encompassed. However, elucidating the interaction networks of a microbial community has been hindered by the population complexity. This study reveals that γ-butyrolactone (GBL) molecules from Streptomyces species, the major antibiotic producers, can directly bind to the acyl-homoserine lactone (AHL) receptor of Chromobacterium violaceum and influence violacein production controlled by the quorum sensing (QS) system. Subsequently, the widespread responses of more Gram-negative bacterial AHL receptors to Gram-positive Streptomyces signaling molecules are unveiled. Based on the cross-talk between GBL and AHL signaling systems, combinatorial regulatory circuits (CRC) are designed and proved to be workable in Escherichia coli (E. coli). It is significant that the QS systems of Gram-positive and Gram-negative bacteria can be bridged via native Streptomyces signaling molecules. These findings pave a new path for unlocking the comprehensive cell-cell communications in microbial communities and facilitate the exploitation of innovative regulatory elements for synthetic biology.

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“…1b ). Furthermore, considering the diverse culturing conditions of Streptomyces , more AHL detection methods (agar plug method, co-cultivation method, Oxford cup method for liquid fermentation broth or extracts and another quick detection approach using E. coli reporter strain 35 ) were investigated. The results confirmed their efficiency in coupling with VRS-bAHL (Supplementary Figs.…”

“…In brief, cviI and cviI-12472 , AHL synthase genes from C. violaceum CV31532 and C. violaceum CV12472, respectively, were used as reporter genes 35 . Then we constructed another AHL indicator strain (CV609) through stepwise in-frame deletion of vioS and cviI of CV31532 (Supplementary Fig.…”

“…Although the underlying mechanism is not clear yet, CV609 can serve as an indicator strain with reduced sensitivity for short-chain AHLs. Besides, ΔcviI-12472 was also used as an AHL indicator strain 35 . Subsequently, a series of VRS-bAHLs were generated by combining the reporter genes cviI and cviI-12472 with three indicator strains (CV026, ΔcviI-12472 and CV609).…”

“…The most prominent feature of VRS-bAHL is high sensitivity and low background interference. Its hypersensitivity is attributed to the sensitive response of the receptors to AHLs in C. violaceum , and nanomolar concentrations of AHL would be able to activate violacein production or bioluminescence generation of indicator strains 35 . More strikingly, there was no obvious background interference observed for VRS-bAHL.…”

“…One of the potential interference could be from γ-butyrolactone signaling molecules of Streptomyces since they share some structural similarity with AHLs, and their influence on QS of C. violaceum was indicated previously. However, since the effective concentration of γ-butyrolactones inducing violacein generation is far beyond that of AHL 35 , they would have no or negligible interference on the performance of VRS-bAHL. In addition, the potential inhibitory activity of bioactive metabolites from Streptomyces against C. violaceum might be present, but it could be attenuated via dilution or reducing the loading amount of samples onto indicator strains.…”