Heterologous expression of biosynthetic gene clusters (BGCs) avails yield improvements and mining of natural products, but it is limited by lacking of more efficient Gram-negative chassis. The proteobacterium Schlegelella brevitalea DSM 7029 exhibits potential for heterologous BGC expression, but its cells undergo early autolysis, hindering further applications. Herein, we rationally construct DC and DT series genome-reduced S. brevitalea mutants by sequential deletions of endogenous BGCs and the nonessential genomic regions, respectively. The DC5 to DC7 mutants affect growth, while the DT series mutants show improved growth characteristics with alleviated cell autolysis. The yield improvements of six proteobacterial natural products and successful identification of chitinimides from Chitinimonas koreensis via heterologous expression in DT mutants demonstrate their superiority to wild-type DSM 7029 and two commonly used Gram-negative chassis Escherichia coli and Pseudomonas putida. Our study expands the panel of Gram-negative chassis and facilitates the discovery of natural products by heterologous expression.

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Metal-organic frameworks have been widely studied in the separation of C 2 hydrocarbons, which usually preferentially bind unsaturated hydrocarbons with the order of acetylene (C 2 H 2 ) > ethylene (C 2 H 4 ) > ethane (C 2 H 6 ). Herein, we report an ultramicroporous fluorinated metal-organic framework Zn-FBA (H 2 FBA = 4,4'-(hexafluoroisopropylidene)bis(benzoic acid)), shows a reversed adsorption order characteristic for C 2 hydrocarbons, that the uptake for C 2 hydrocarbons of the framework and the binding affinity between the guest molecule and the framework follows the order C 2 H 6 > C 2 H 4 > C 2 H 2 . Density-functional theory calculations confirm that the completely reversed adsorption order behavior is attributed to the close van der Waals interactions and multiple cooperative CÀ H•••F hydrogen bonds between the framework and C 2 H 6 . Moreover, Zn-FBA exhibits a high selectivity of about 2.9 for C 2 H 6 over C 2 H 4 at 298 K and 1 bar. The experimental breakthrough studies show that the high-purity C 2 H 4 can be obtained from C 2 H 6 and C 2 H 4 mixtures in one step.

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Lasso peptides are a subclass of ribosomally synthesized and post-translationally modified peptides (RiPPs) and feature the threaded, lariat knot-like topology. The basic post-translational modifications (PTMs) of lasso peptide contain two steps, including the leader peptide removal of the ribosome-derived linear precursor peptide by an ATP-dependent cysteine protease, and the macrolactam cyclization by an ATP-dependent macrolactam synthetase. Recently, advanced bioinformatic tools combined with genome mining have paved the way to uncover a rapidly growing number of lasso peptides as well as a series of PTMs other than the general class-defining processes. Despite abundant reviews focusing on lasso peptide discoveries, structures, properties, and physiological functionalities, few summaries concerned their unique PTMs. In this review, we summarized all the unique PTMs of lasso peptides uncovered to date, shedding light on the related investigations in the future.