No abstract

Here, we describe two N -acetyl-cysteinylated streptophenazines ( 1 and 2 ) produced by the soil-derived Streptomyces sp. ID63040 and identified through a metabolomic approach. These metabolites attracted our interest due to their low occurrence frequency in a large library of fermentation broth extracts and their consistent presence in biological replicates of the producer strain. The compounds were found to possess broad-spectrum antibacterial activity while exhibiting low cytotoxicity. The biosynthetic gene cluster from Streptomyces sp. ID63040 was found to be highly similar to the streptophenazine reference cluster in the MIBiG database, which originates from the marine Streptomyces sp. CNB-091. Compounds 1 and 2 were the main streptophenazine products from Streptomyces sp. ID63040 at all cultivation times but were not detected in Streptomyces sp. CNB-091. The lack of obvious candidates for cysteinylation in the Streptomyces sp. ID63040 biosynthetic gene cluster suggests that the N -acetyl-cysteine moiety derives from cellular functions, most likely from mycothiol. Overall, our data represent an interesting example of how to leverage metabolomics for the discovery of new natural products and point out the often-neglected contribution of house-keeping cellular functions to natural product diversification.

The quorum sensing two-component system (TCS) QseBC has been linked to virulence, motility and metabolism regulation in multiple Gram-negative pathogens, including EnterohaemorrhagicEscherichia coli(EHEC), UropathogenicE. coli(UPEC) andSalmonella enterica. In EHEC, the sensor histidine kinase (HK) QseC detects the quorum sensing signalling molecule AI-3 and also acts as an adrenergic sensor binding host epinephrine and norepinephrine. Downstream changes in gene expression are mediated by phosphorylation of its cognate response regulator (RR) QseB, and cross-talk with non-cognate regulators KdpE and QseF to activate motility and virulence. In UPEC, cross-talk between QseBC and TCS PmrAB is crucial in the regulation and phosphorylation of QseB RR that acts as a repressor of multiple pathways, including motility. Here, we investigated QseBC regulation of motility in the atypical EnteropathogenicE. coli(EPEC) strain O125ac:H6, causative agent of persistent diarrhoea in children, and its possible cross-talk with the KdpDE and PmrAB TCS. We showed that in EPEC QseB acts as a repressor of genes involved in motility, virulence and stress response, and in absence of QseC HK, QseB is activated by the non-cognate PmrB HK, similarly to UPEC. We show that in absence of QseC, phosphorylated QseB activates its own expression, and is responsible for the low motility phenotypes seen in a QseC deletion mutant. Furthermore, we showed that KdpD HK regulates motility in an independent manner to QseBC and through a third unidentified party different to its own response regulator KdpE. We showed that PmrAB has a role in iron adaptation independent to QseBC. Finally, we showed that QseB is the responsible for activation of colistin and polymyxin B resistance genes while PmrA RR acts by preventing QseB binding to the promoter of polymyxin resistance genes.

No abstract

Here, we describe two N-acetyl-cysteinylated streptophenazines (1 and 2) produced by soil-derived Streptomyces sp. ID63040 and identified through a metabolomic approach. These metabolites attracted our interest due to their low occurrence frequency in a large library of fermentation broth extracts and their consistent presence in biological replicates of the producer strain. The compounds were found to possess broad-spectrum antibacterial activity while exhibiting low cytotoxicity. The biosynthetic gene cluster from Streptomyces sp. ID63040 was found to be highly similar to the streptophenazine reference cluster in the MIBiG database, which originates from the marine Streptomyces sp. CNB-091. Compounds 1 and 2 were the main streptophenazine products from Streptomyces sp. ID63040 at all cultivation times, but were not detected in Streptomyces sp. CNB-091. The lack of obvious candidates for cysteinylation in the Streptomyces sp. ID63040 biosynthetic gene cluster suggests that the N-acetyl-cysteine moiety derives from cellular functions, most likely from mycothiol. Overall, our data represent an interesting example on how to leverage metabolomics for the discovery of new natural products and point out to the often-neglected contribution of house-keeping cellular functions to natural product diversification.