Abstract
The production efficiency of microbial cell factories is sometimes limited by the lack of effective methods to regulate multiple targets in a coordinated manner. Here taking the biosynthesis of glucosamine-6-phosphate (GlcN6P) in Bacillus subtilis as an example, a ‘design–build–test–learn’ framework was proposed to achieve efficient multiplexed optimization of metabolic pathways. A platform strain was built to carry biosensor signal-amplifying circuits and two genetic regulation circuits. Then, a synthetic CRISPR RNA array blend for boosting and leading (ScrABBLE) device was integrated into the platform strain, which generated 5,184 combinatorial assemblies targeting three genes. The best GlcN6P producer was screened and engineered for the synthesis of valuable pharmaceuticals N-acetylglucosamine and N-acetylmannosamine. The N-acetylglucosamine titer reached 183.9 g liter–1 in a 15-liter bioreactor. In addition, the potential generic application of the ScrABBLE device was also verified using three fluorescent proteins as a case study.

This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 per month
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Rent or buy this article
Get just this article for as long as you need it
$39.95
Prices may be subject to local taxes which are calculated during checkout






Data availability
All data supporting the findings of this study are available in the article and its supplementary files. Reads from NGS of the ScrABBLE device for GlcN6P production are available at Sequence Read Archive (PRJNA818127). Sanger sequencing source data can be found on GitHub (https://github.com/KevinW03/Dynamic-model-of-metabolic-pathways-related-to-GlcN6P-and-GlcNAc). Sequences with the necessary annotations of the plasmids used in this study are uploaded to Benchling, and the corresponding URLs are shown in Supplementary Note 3. Flow cytometry data are deposited at Flow Repository (FR-FCM-Z55M, FR-FCM-Z56B and FR-FCM-Z5F6). Source data are provided with this paper.
Code availability
The MATLAB code used in this study can be found on GitHub (https://github.com/KevinW03/Dynamic-model-of-metabolic-pathways-related-to-GlcN6P-and-GlcNAc).
References
Meng, F. & Ellis, T. The second decade of synthetic biology: 2010–2020. Nat. Commun. 11, 5174 (2020).
Voigt, C. A. Synthetic biology 2020–2030: six commercially-available products that are changing our world. Nat. Commun. 11, 6379 (2020).
Naseri, G. & Koffas, M. A. G. Application of combinatorial optimization strategies in synthetic biology. Nat. Commun. 11, 2446 (2020).
Brooks, S. M. & Alper, H. S. Applications, challenges, and needs for employing synthetic biology beyond the lab. Nat. Commun. 12, 1390 (2021).
Xu, P. Production of chemicals using dynamic control of metabolic fluxes. Curr. Opin. Biotechnol. 53, 12–19 (2018).
Keasling, J. et al. Microbial production of advanced biofuels. Nat. Rev. Microbiol. 19, 701–715 (2021).
Lee, S. Y. et al. A comprehensive metabolic map for production of bio-based chemicals. Nat. Catal. 2, 18–33 (2019).
Nielsen, J. & Keasling, J. D. Engineering cellular metabolism. Cell 164, 1185–1197 (2016).
Hossain, G. S., Saini, M., Miyake, R., Ling, H. & Chang, M. W. Genetic biosensor design for natural product biosynthesis in microorganisms. Trends Biotechnol. 38, 797–810 (2020).
Peralta-Yahya, P. P., Zhang, F., Del Cardayre, S. B. & Keasling, J. D. Microbial engineering for the production of advanced biofuels. Nature 488, 320–328 (2012).
You, J. et al. Microbial production of riboflavin: biotechnological advances and perspectives. Metab. Eng. 68, 46–58 (2021).
Luo, X. et al. Complete biosynthesis of cannabinoids and their unnatural analogues in yeast. Nature 567, 123–126 (2019).
Leyn, S. A. et al. Genomic reconstruction of the transcriptional regulatory network in Bacillus subtilis. J. Bacteriol. 195, 2463–2473 (2013).
Kalamorz, F., Reichenbach, B., März, W., Rak, B. & Görke, B. Feedback control of glucosamine-6-phosphate synthase GlmS expression depends on the small RNA GlmZ and involves the novel protein YhbJ in Escherichia coli. Mol. Microbiol. 65, 1518–1533 (2007).
Winkler, W. C., Nahvi, A., Roth, A., Collins, J. A. & Breaker, R. R. Control of gene expression by a natural metabolite-responsive ribozyme. Nature 428, 281–286 (2004).
Park, S. A. et al. Bacillus subtilis as a robust host for biochemical production utilizing biomass. Crit. Rev. Biotechnol. 41, 827–848 (2021).
Wu, Y. et al. Design of a programmable biosensor–CRISPRi genetic circuits for dynamic and autonomous dual-control of metabolic flux in Bacillus subtilis. Nucleic Acids Res. 48, 996–1009 (2020).
Chen, J. K., Shen, C. R. & Liu, C. L. N-Acetylglucosamine: production and applications. Mar. Drugs 8, 2493–2516 (2010).
Carrillo, N. et al. Safety and efficacy of N-acetylmannosamine (ManNAc) in patients with GNE myopathy: an open-label phase 2 study. Genet. Med. 23, 2067–2075 (2021).
Teng, Y. et al. Biosensor-enabled pathway optimization in metabolic engineering. Curr. Opin. Biotechnol. 75, 102696 (2022).
Tian, R. et al. Synthetic N-terminal coding sequences for fine-tuning gene expression and metabolic engineering in Bacillus subtilis. Metab. Eng. 55, 131–141 (2019).
Tan, S. -I. & Ng, I. -S. New insight into plasmid-driven T7 RNA polymerase in Escherichia coli and use as a genetic amplifier for a biosensor. ACS Synth. Biol. 9, 613–622 (2020).
Espah Borujeni, A., Channarasappa, A. S. & Salis, H. M. Translation rate is controlled by coupled trade-offs between site accessibility, selective RNA unfolding and sliding at upstream standby sites. Nucleic Acids Res. 42, 2646–2659 (2014).
Liu, Y. et al. A dynamic pathway analysis approach reveals a limiting futile cycle in N-acetylglucosamine overproducing Bacillus subtilis. Nat. Commun. 7, 11933 (2016).
Klein, D. J. Structural basis of glmS ribozyme activation by glucosamine-6-phosphate. Science 313, 1752–1756 (2006).
Blencke, H. -M. et al. Transcriptional profiling of gene expression in response to glucose in Bacillus subtilis: regulation of the central metabolic pathways. Metab. Eng. 5, 133–149 (2003).
Yang, S., Du, G., Chen, J. & Kang, Z. Characterization and application of endogenous phase-dependent promoters in Bacillus subtilis. Appl. Microbiol. Biotechnol. 101, 4151–4161 (2017).
Wu, Y. et al. CAMERS-B: CRISPR/Cpf1 assisted multiple-genes editing and regulation system for Bacillus subtilis. Biotechnol. Bioeng. 117, 1817–1825 (2020).
Lee, S. W. & Oh, M. K. A synthetic suicide riboswitch for the high-throughput screening of metabolite production in Saccharomyces cerevisiae. Metab. Eng. 28, 143–150 (2015).
Na, D. et al. Metabolic engineering of Escherichia coli using synthetic small regulatory RNAs. Nat. Biotechnol. 31, 170–174 (2013).
McCarty, N. S., Graham, A. E., Studená, L. & Ledesma-Amaro, R. Multiplexed CRISPR technologies for gene editing and transcriptional regulation. Nat. Commun. 11, 1281 (2020).
Qi, L. S. et al. Repurposing CRISPR as an RNA-guided platform for sequence-specific control of gene expression. Cell 152, 1173–1183 (2013).
Li, H. et al. Combinatorial CRISPR interference library for enhancing 2,3-BDO production and elucidating key genes in cyanobacteria. Front. Bioeng. Biotechnol. 10, 913820 (2022).
Shaw, W. M. et al. Inducible expression of large gRNA arrays for multiplexed CRISPRai applications. Nat. Commun. 13, 4984 (2022).
Larson, M. H. et al. CRISPR interference (CRISPRi) for sequence-specific control of gene expression. Nat. Protoc. 8, 2180–2196 (2013).
Magnusson, J. P., Rios, A. R., Wu, L. & Qi, L. S. Enhanced Cas12a multi-gene regulation using a CRISPR array separator. eLife 10, e66406 (2021).
Liao, C. et al. Modular one-pot assembly of CRISPR arrays enables library generation and reveals factors influencing crRNA biogenesis. Nat. Commun. 10, 2948 (2019).
Qin, L., Liu, X., Xu, K. & Li, C. Mining and design of biosensors for engineering microbial cell factory. Curr. Opin. Biotechnol. 75, 102694 (2022).
Lu, Z. et al. CRISPR-assisted multi-dimensional regulation for fine-tuning gene expression in Bacillus subtilis. Nucleic Acids Res. 47, e40 (2019).
Schilling, C., Koffas, M. A. G., Sieber, V. & Schmid, J. Novel prokaryotic CRISPR–Cas12a-based tool for programmable transcriptional activation and repression. ACS Synth. Biol. 9, 3353–3363 (2020).
Liu, Y., Wan, X. & Wang, B. Engineered CRISPRa enables programmable eukaryote-like gene activation in bacteria. Nat. Commun. 10, 3693 (2019).
Dong, C., Fontana, J., Patel, A., Carothers, J. M. & Zalatan, J. G. Synthetic CRISPR–Cas gene activators for transcriptional reprogramming in bacteria. Nat. Commun. 9, 2489 (2018).
Ho, H.-I., Fang, J. R., Cheung, J. & Wang, H. H. Programmable CRISPR–Cas transcriptional activation in bacteria. Mol. Syst. Biol. 16, e9427 (2020).
Zalatan, J. G. et al. Engineering complex synthetic transcriptional programs with CRISPR RNA scaffolds. Cell 160, 339–350 (2015).
Deaner, M., Mejia, J. & Alper, H. S. Enabling graded and large-scale multiplex of desired genes using a dual-mode dCas9 activator in Saccharomyces cerevisiae. ACS Synth. Biol. 6, 1931–1943 (2017).
Gaugué, I., Oberto, J. & Plumbridge, J. Regulation of amino sugar utilization in Bacillus subtilis by the GntR family regulators, NagR and GamR. Mol. Microbiol. 92, 100–115 (2014).
Bowman, E. K. & Alper, H. S. Microdroplet-assisted screening of biomolecule production for metabolic engineering applications. Trends Biotechnol. 38, 701–714 (2020).
Gibson, D. G. et al. Enzymatic assembly of DNA molecules up to several hundred kilobases. Nat. Methods 6, 343–345 (2009).
Rahmer, R., Heravi, K. M. & Altenbuchner, J. Construction of a super-competent Bacillus subtilis 168 using the PmtlA-comKS inducible cassette. Front. Microbiol. 6, 1431 (2015).
Niu, T. et al. Engineering a glucosamine-6-phosphate responsive glmS ribozyme switch enables dynamic control of metabolic flux in Bacillus subtilis for overproduction of N-acetylglucosamine. ACS Synth. Biol. 7, 2423–2435 (2018).
Liu, H. & Naismith, J. H. An efficient one-step site-directed deletion, insertion, single and multiple-site plasmid mutagenesis protocol. BMC Biotechnol. 8, 91 (2008).
Altenbuchner, J. Editing of the Bacillus subtilis genome by the CRISPR–Cas9 system. Appl. Environ. Microbiol. 82, 5421–5427 (2016).
Sato, K., Akiyama, M. & Sakakibara, Y. RNA secondary structure prediction using deep learning with thermodynamic integration. Nat. Commun. 12, 941 (2021).
Meyer, A. J., Segall-Shapiro, T. H., Glassey, E., Zhang, J. & Voigt, C. A. Escherichia coli ‘Marionette’ strains with 12 highly optimized small-molecule sensors. Nat. Chem. Biol. 15, 196–204 (2019).
Acknowledgements
This work was supported by the National Key R&D Program of China (2020YFA0908300 to L.L. and 2018YFA0900300 to G.D.), the National Natural Science Foundation of China (32021005 and 32070085 to L.L. and 31930085 to G.D.), the China National Postdoctoral Program for Innovative Talents (BX2021113 to Y.W.), the China Postdoctoral Science Foundation (2021M701458 to Y.W.), the Natural Science Foundation of Jiangsu Province (BK20221083 to Y.W.) and the Fundamental Research Funds for the Central Universities (USRP52019A and JUSRP221013 to L.L. and JUSRP121010 to X.L.).
Author information
Authors and Affiliations
Contributions
Y.W. and L.L. conceived the study and wrote the manuscript with assistance from X.L., Y. Liu, J.L., G.D., R.L.-A. and J.C. Y.W. performed strain construction and screening, cell cultivation, fluorescence measurements, flow cytometry assays and FACS, fluorescence imaging and analysis, analytical experiments, sequencing analysis, kinetic model simulation and data visualization. Y. Li assisted in strain construction and screening, cell cultivation, fluorescence measurements, flow cytometry assays and FACS and analytical experiments. K.J. assisted in fluorescence imaging and analysis. L.Z. assisted in flow cytometry assays and FACS. All authors contributed ideas and reviewed the manuscript. L.L. supervised and held overall responsibility for the study.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature Chemical Biology thanks the anonymous reviewers for their contribution to the peer review of this work.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data
Extended Data Fig. 1 Knocking out of genes related to the catabolic pathway of aminosaccharide and the by-product (lactate and acetate) formation.
a Schematic representation of the metabolites (x1-x8) and reactions (v1-v11) used for reprogramming and kinetic model simulation. b Engineered strains, including BNZR0.00, BNZR0.10, BNZR0.40, and BNZR0.60, were constructed by knocking out the related genes. Seven colonies were picked to perform colony PCR for each strain, and the experiment was independently repeated three times with similar results. c The kinetic model simulations of metabolism in the engineered strains (BNZR0.00, BNZR0.10, BNZR0.40, and BNZR0.60) were performed in three situations, including untreated, supplying GlcN in the media, and introducing GNA1 to produce GlcNAc. Lines indicate mean and shaded areas are the SD, and the colors of the lines represent: black-Glc, red-GlcNAc, green-GlcN6P, yellow-HMP, blue-EMP, and magenta-PSP. Source data are provided as a Source Data file. The codes used in c can be found on GitHub.
Extended Data Fig. 2 Characterization of glucose-responsive promoters that were used for the construction of the feedforward GRC.
These promoters were investigated by expressing eGFP under different glucose concentrations. The expression of the commonly used constitutive promoter Pveg was also improved by adding glucose, but its dose-response pattern was far from the tested glucose-responsive promoters, suggesting that the improvement may result from the enhanced metabolism after supplying glucose. The numbered promoters with red shade were used for the construction of strains BNZR1.00, BNZR1.02, BNZR1.03, BNZR1.06, and BNZR1.12, respecitively. The values marked in bule represent the basal expression of these promoters without glucose. Data are presented as mean values ± SD from three independent biological replicates (n = 3). Source data are provided as a Source Data file.
Extended Data Fig. 3 Kinetic model simulations of cell metabolism after removing the feedback regulation in glmS.
a The definition of metabolites and reactions for kinetic model simulation. b The kinetic model simulations of metabolism in the engineered strains (BNZR1.00, BNZR1.06, and BNZR1.12) were performed in three situations: untreated, supplying GlcN in the media, and introducing GNA1 to produce GlcNAc. Lines indicate mean and shaded areas are the SD, and the colors of the lines represent: black-Glc, red-GlcNAc, green-GlcN6P, yellow-HMP, blue-EMP, and magenta-PSP. The codes used in b can be found on GitHub.
Extended Data Fig. 4 Evaluation of CRISPRi-based phase-dependent GRC.
Using P43-mCherry as the reporter, the performances of the phase-dependent GRC by replacing the promoter of dCas12a (a) or crRNA (b) were analyzed under glucose. By using PyteJ-mCherry as the reporter, the performances of the phase-dependent GRC by replacing the promoter of dCas12a (c) or crRNA (d) were analyzed, and these two designs were also tested under glucose (e,f). The red shade shows the time frame in which the phase-dependent GRC worked. a-f Lines indicate mean and shaded areas are the SD, and the data are presented as mean values ± SD from three independent biological replicates (n = 3). Source data are provided as a Source Data file.
Extended Data Fig. 5 Kinetic model simulations of cell metabolism after repressing HMP, EMP, and PSP.
a Schematic diagram of the metabolites (x1-x8) and reactions (v1-v11) used for reprogramming and kinetic model simulation. b The kinetic model simulation of GlcN6P level without and with repressing the above three pathways. Random values between 0–97%, 0–95%, or 0–77% were generated to serve as repression intensities of genes zwf, pfkA, or glmM, and the levels of the intracellular GlcN6P in these three situations (weakening zwf, pfkA, or glmM) were studied by performing 1000 simulations (lines indicate mean and shaded areas the standard deviation). Lines indicate mean and shaded areas are the SD, and the colors of the lines represent: black-Glc, red-GlcNAc, green-GlcN6P, yellow-HMP, blue-EMP, and magenta-PSP. c The relationships between the predicted final concentration of GlcN6P and the generated repression intensities of these three target genes. Positive correlations can be found between the predicted GlcN6P concentrations and the repression intensities of the target genes. Source data are provided as a Source Data file. The codes used in b can be found on GitHub.
Extended Data Fig. 6 The first-round screening of the cells possesses higher fluorescence after installing the ScrABBLE device.
a FACS was performed to acquire the cells that possess higher fluorescence. After spreading them into the plates, the whole population in gate Q4 was sorted for further screening. b A total of 190 colonies were randomly selected and inoculated into two 96-well plates for fluorescence measurement. The colonies in green and yellow were picked, while the colonies in red and grey were discarded. c The crRNA arrays in 24 strains with the highest fluorescence were amplified for Sanger sequencing. Source data are provided in the Source Data file. Flow cytometry data is deposited at Flow Repository.
Extended Data Fig. 7 An erythromycin resistance gene was put into the BSAC of BNZR2.00 to couple the the cell growth with biosensor response.
a Schematic representation of the biosensor amplifier circuits integrated with an erythromycin resistance gene. b The effects on cell growth by changing the adding amount of erythromycin. The adding amount of erythromycin was optimized, and 50 μg/mL was the best. In this concentration of erythromycin, supplying IPTG (to achieve the BSAC activation mediated by the native intracellular GlcN6P) could increase cell growth, and supplying GlcN to further improve the GlcN6P level could get a better cell growth. b Data are presented as mean values ± SD from three independent biological replicates (n = 3), and the circles represent individual data points. Significance (p-value) was evaluated by two-sided t-test, n.s. presents p > 0.05. Source data are provided as a Source Data file.
Extended Data Fig. 8 Flow cytometry analysis of BSAC response in the engineered strains.
The fluorescence of eGFP in strains BNZR0.00, BNZR0.60, BNZR1.06 L, BNZR2.00, and BNZR2.01R-BNZR2.14R was determined by by flow cytometry at 12 h (green shade) and 24 h (blue shade). Flow cytometry data is deposited at Flow Repository.
Extended Data Fig. 9 Flow cytometry analysis of the repression intensities by the phase-dependent GRC on the target genes.
The fusion proteins composed of gene-sfGFP and mCherry expressed by a strong constitutive promoter P43 were introduced into strains BNZR2.00, BNZR2.03R, BNZR2.06R, BNZR2.12R, and BNZR2.09R, respectively. The samples at 36 h were analyzed by flow cytometry. Flow cytometry data is deposited at Flow Repository.
Extended Data Fig. 10 The analysis of the secondary structures of the RNAs in the crRNA arrays of BNZR2.03R, BNZR2.12R, and BNZR2.09R.
The results show that restricted access of dCas12a’s to some cleavage sites, and only the crRNA array of BNZR2.06R exposes the five cleavage sites of dCas12a.
Supplementary information
Supplementary Information
Supplementary Figs. 1–10, Tables 1–4, Notes 1–6 and References.
Supplementary Data
Statistical source data for Supplementary Figs. 2, 5 and 6.
Source data
Source Data Fig. 2
Statistical source data.
Source Data Fig. 3
Statistical source data.
Source Data Fig. 4
Statistical source data.
Source Data Fig. 5
Statistical source data.
Source Data Fig. 6
Statistical source data.
Source Data Extended Data Fig. 1
Unprocessed gel.
Source Data Extended Data Fig. 2
Statistical source data.
Source Data Extended Data Fig. 4
Statistical source data.
Source Data Extended Data Fig. 5
Statistical source data.
Source Data Extended Data Fig. 6
Statistical source data.
Source Data Extended Data Fig. 7
Statistical source data.
Rights and permissions
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
About this article
Cite this article
Wu, Y., Li, Y., Jin, K. et al. CRISPR–dCas12a-mediated genetic circuit cascades for multiplexed pathway optimization. Nat Chem Biol 19, 367–377 (2023). https://doi.org/10.1038/s41589-022-01230-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41589-022-01230-0