Structural investigation of Fe(III)-salen complexes as “turn-on” fluorogenic probes for selective detection of pyrophosphate ions

In this work, we revisited the disassembly approach (also known as the Zelder's approach) recently proposed for sensing pyrophosphate (PPi) in water and based on the decomposition of metal-salen complexes. A systematic study devoted to the structural optimization of this novel class of PPi-responsive fluorogenic probes was conducted. Screening of eight different vicinal diamines (i.e., bridge of the salen ligand) combined with the use of 8-formyl-7hydroxycoumarin (i.e., salicylaldehyde derivative) as the fluorescent reporter, has led to a set of novel and fully characterized coumarin-salen Fe(III) complexes. A series of analytical validations helped us to identify that coumarin-salen Fe(III) complexes derived from ethylenediamine and racemic 1,2-propylenediamine backbones exhibit the best and selective PPi-sensing performances (the limits of detection were estimated as 3.15 × 10-6 M and 2.81 × 10-6 M respectively). The implementation of both fluorescence time-course measurements and RP-HPLC-fluorescence analyses has enabled us to gain further insights into the disassembly-based probes' activation mechanism. This study therefore contributes to demonstrate that the disassembly approach is a valuable strategy to achieve fluorogenic activity-based sensing of anions

Cost-effective hybrid long-short read assembly delineates alternative GC-rich Streptomyces hosts for natural product discovery

With the advent of rapid automated in silico identification of biosynthetic gene clusters (BGCs), genomics presents vast opportunities to accelerate natural product (NP) discovery. However, prolific NP producers, Streptomyces, are exceptionally GC-rich (>80%) and highly repetitive within BGCs. These pose challenges in sequencing and high-quality genome assembly which are currently circumvented via intensive sequencing. Here, we outline a more cost-effective workflow using multiplex Illumina and Oxford Nanopore sequencing with hybrid long-short read assembly algorithms to generate high quality genomes. Our protocol involves subjecting long read-derived assemblies to up to 4 rounds of polishing with short reads to yield accurate BGC predictions. We successfully sequenced and assembled 8 GC-rich Streptomyces genomes whose lengths range from 7.1 to 12.1 Mb with a median N50 of 8.2 Mb. Taxonomic analysis revealed previous misrepresentation among these strains and allowed us to propose a potentially new species, Streptomyces sydneybrenneri. Further comprehensive characterization of their biosynthetic, pan-genomic and antibiotic resistance features especially for molecules derived from type I polyketide synthase (PKS) BGCs reflected their potential as alternative NP hosts. Thus, the genome assemblies and insights presented here are envisioned to serve as gateway for the scientific community to expand their avenues in NP discovery