Activated DBP degradation and relevant signal transduction path via quorum sensing autoinducers in Streptomyces sp. SH5.

Microbe-mediated DBP (dibutyl phthalate) mineralization is acknowledged to be affected by diverse extracellular factors. However, little is known about the regulatory effects from quorum sensing (QS) signals. In this study, extracellularly applied QS signals A-like (hydroxymethyl dihydrofuran) was discovered to significantly enhance DBP degradation efficiency in Streptomyces sp. SH5. Monobutyl phthalate, protocatechuic acid and beta-ketoadipate were discovered as degradation intermediates by HPLC-TOF-MS/MS. Multi-omics analysis revealed the up-regulation of multiple hydrolases, transferases and decarboxylases that potentially contributed to A-like accelerated DBP degradation. Transcription of Orf2708, an orthologue of global transcriptional activator, was significantly induced by A-like. Orf2708 was demonstrated to interact specifically with the promoter of hydrolase orf2879 gene by EMSA, and the overexpression of orf2879 led to an enhanced DBP degradation in SH5. Taken together with the molecular docking studies showing the stability of ligand-receptor complex of A-like and its potential receptor Orf3712, a hierarchical regulatory cascade underlying the QS signal mediated DBP degradation was proposed as A-like/Orf3712 duplex formation, enhanced orf2708 expression and the downstream specific activation of hydrolase Orf2879. Our study presents the first evidence of GBLs-type promoted DBP degradation among bacteria, and the elucidated signal transduction path indicates a universal application potential of this activation strategy.

Application of potential probiotic strain Streptomyces sp. SH5 on anti-Aeromonas infection in zebrafish larvae.

Pre-treatment of Streptomyces sp. SH5 on zebrafish lead to a significant enhancement of larvae survival upon Aeromonas hydrophila challenging. SH5 was able to colonize in zebrafish approximately at 1 × 102.6 cells per fish for at least seven days. The presence of SH5 strongly repelled the A. hydrophila colonization in zebrafish, and maximally, a 67.53% reduction rate was achieved. A more diversified flora was discovered in the SH5-treated zebrafish larvae at both phylum and genus levels. The expression of immune response genes of SH5-treated zebrafish, including TLR3, lysozyme and NOS2α, were enhanced at initial stage, while, that of various inflammatory stimuli genes including 1L-1ß, 1L-6 and MyD88 were decreased at all tested timepoints. SH5 was shown to inhibit virulence factors production and the expression of corresponding virulence genes in A. hydrophila, suggesting its quorum sensing inhibitory potential. These results indicated favorable application perspectives of SH5 in resisting pathogenic infection in aquaculture.

Anti-Vibrio dibutyl phthalate from marine-derived Streptomyces sp. S073.

Marine Streptomyces S073 was previously shown to have strong anti-Vibrio activity, and its antibacterial mechanism was proposed to be associated with siderophore-mediated iron competition and other antagonistic agents. In this study, anti-Vibrio compounds produced by S073 were isolated by bioassay-guided fractionation using column chromatography and HPLC, and the target compound in the most active fraction was identified as dibutyl phthalate (DBP) by various spectroscopic analyses, including EI-MS, 1H NMR and 13C NMR. The DBP-producing capacity of S073 was 2.39 mg/L in ISP1 culture media. Pure DBP was demonstrated to have strong inhibitory activity on Vibiro parahaemolyticus growth with an MIC of 31.25 mg/L. When standard DBP was supplemented into the S073 fermentation broth in a gradient method, an additive inhibitory effect on V. parahaemolyticus was observed, indicating the important role of DBP in driving anti-Vibrio activity in S073 metabolites pool. A synergistic additive effect between DBP and florfenicol was observed in the Vibrio inhibition. These results indicate that, to achieve Vibrio-inhibition, S073 exerted multifaceted strategies, which included DBP-mediated antagonism and siderophore-governed iron competition. The application potential of S073 as an aquaculture probiotic was evaluated, and the safety risks associated with the endocrine disruptor attributes of DBP were discussed.