Besides genome editing, CRISPR-Cas12a has recently been used for DNA detection applications with attomolar sensitivity but, to our knowledge, it has not been used for the detection of small molecules. Bacterial allosteric transcription factors (aTFs) have evolved to sense and respond sensitively to a variety of small molecules to benefit bacterial survival. By combining the single-stranded DNA cleavage ability of CRISPR-Cas12a and the competitive binding activities of aTFs for small molecules and double-stranded DNA, here we develop a simple, supersensitive, fast and high-throughput platform for the detection of small molecules, designated CaT-SMelor ( C RISPR-Cas12a- and aT F-mediated s mall m ol e cu l e detect or ). CaT-SMelor is successfully evaluated by detecting nanomolar levels of various small molecules, including uric acid and p -hydroxybenzoic acid among their structurally similar analogues. We also demonstrate that our CaT-SMelor directly measured the uric acid concentration in clinical human blood samples, indicating a great potential of CaT-SMelor in the detection of small molecules.

Coenzyme Q10 (CoQ10) is an important component of the respiratory chain in humans and some bacteria. As a high-value-added nutraceutical antioxidant, CoQ10 has excellent capacity to prevent cardiovascular disease. The content of CoQ10 in the industrial Rhodobacter sphaeroides HY01 is hundreds of folds higher than normal physiological levels. In this study, we found that overexpression or optimization of the synthetic pathway failed CoQ10 overproduction in the HY01 strain. Moreover, under phosphate- limited conditions (decreased phosphate or in the absence of inorganic phosphate addition), CoQ10 production increased significantly by 12% to220 mg/L, biomass decreased by 12%, and the CoQ10 productivity of unit cells increased by 27%. In subsequent fed-batch fermentation, CoQ10 production reached 272 mg/L in the shake-flask fermentation and 1.95 g/L in a 100-L bioreactor under phosphate limitation. Furthermore, to understand the mechanism associated with CoQ10 overproduction under phosphate- limited conditions, the comparatve transcriptome analysis was performed. These results indicated that phosphate limitation combined with glucose fed-batch fermentation represented an effective strategy for CoQ10 production in the HY01. Phosphate limitation induced a pleiotropic effect on cell metabolism, and that improved CoQ10 biosynthesis efficiency was possibly related to the disturbance of energy metabolism and redox potential.

Direct cloning of biosynthetic gene clusters (BGCs) from microbial genomes facilitates natural product-based drug discovery. Here, by combining Cas12a and the advanced features of bacterial artificial chromosome library construction, we developed a fast yet efficient in vitro platform for directly capturing large BGCs, named CAT-FISHING (CRISPR/Cas12a-mediated fast direct biosynthetic gene cluster cloning). As demonstrations, several large BGCs from different actinomycetal genomic DNA samples were efficiently captured by CAT-FISHING, the largest of which was 145 kb with 75% GC content. Furthermore, the directly cloned, 110 kb long, cryptic polyketide encoding BGC from Micromonospora sp. 181 was then heterologously expressed in a Streptomyces chassis. It turned out to be a new macrolactam compound, marinolactam A, which showed promising anticancer activity. Our results indicate that CAT-FISHING is a powerful method for complicated BGC cloning, and we believe that it would be an important asset to the entire community of natural product-based drug discovery.

Directly cloning of biosynthetic gene clusters (BGCs) from even unculturable microbial genomes revolutionized nature products-based drug discovery. However, it is still very challenging to efficiently cloning, for example, the large (e.g. > 80kb) BGCs, especially for samples with high GC content in Streptomyces. In this study, by combining the advantages of CRISPR/Cas12a cleavage and bacterial artificial chromosome (BAC) library construction, we developed a simple, fast yet efficient in vitro platform for direct cloning of large BGCs based on CRISPR/Cas12a, named CAT-FISHING (CRISPR/Cas12a-mediated fast direct biosynthetic gene cluster cloning). It was demonstrated by the efficient direct cloning of large DNA fragments from bacterial artificial chromosomes or high GC (>70%) Streptomyces genomic DNA. Moreover, surugamides, encoded by a captured 87-kb gene cluster, was expressed and identified in a cluster-free Streptomyces chassis. These results indicate that CAT-FISHING is now poised to revolutionize bioactive small molecules (BSMs) drug discovery and lead a renaissance of interest in microorganisms as a source of BSMs for drug development. SIGNIFICANCE STATEMENTNatural products (NPs) are one of the most important resources for drug leads. One bottleneck of NPs-based drug discovery is the inefficient cloning approach for BGCs. To address it, we established a simple, fast and efficient BGC directed cloning method CAT-FISHING by combining the advantages of CRISPR/Cas12a (e.g. high specificity) and bacterial artificial chromosome (BAC) library (e.g. large DNA fragment and high GC content). As demonstrations, a series of DNA fragments ranging from 49 kb to 139 kb were successfully cloned. After further optimization, our method was able to efficiently clone and express an 87-kb long, GC-rich (76%) surugamides BGC in a Streptomyces chassis with reduced time-cost. CAT-FISHING presented in this study would much facilitate the process of NPs discovery.cosmid, fosmid and BAC) construction, recombination-based or RecET/Redαβ-based cloning, and Gibson assembly etc (Table 1). Additionally, the emergence of the CRISPR/Cas9 technique has enabled several new DNA cloning methods such as ExoCET, and CATCH etc (3-5). However, it is relatively cumbersome and time-consuming of using the aforementioned methods. Simple, fast and efficient strategy for large BGCs, especially with high GC content, is in urgent need to make natural BSMs accessible and affordable.

No abstract