A thermostable type I-B CRISPR-Cas system for orthogonal and multiplexed genetic engineering

Enabling genetic manipulation and robustness of Bacillus methanolicus for methanol-based bio-manufacturing

Methanol-based biomanufacturing holds great promise for sustainability but is currently limited by the slow growth and low efficiency of natural or synthetic methylotrophic strains. In contrast, the thermophilic methylotroph Bacillus methanolicus exhibits rapid growth, high-temperatures tolerance, and efficient methanol utilization in defined mineral medium, making it a promising candidate for industrial applications. However, its potential is constrained by reluctant genetic modification and suboptimal robustness under fluctuating methanol concentrations. To address these limitations, we developed a comprehensive genetic manipulation system that includes an improved transformation approach, a homologous recombination-based knock-out/knock-in method, a constitutive promoter library spanning a 600-fold range of strengths, and an stringent xylose-inducible promoter with a wide dynamic range. Using these enabling tools, we enhanced the robustness of B. methanolicus under varying methanol concentrations by introducing a xylose pathway, which buffered intracellular formaldehyde accumulation. Co-utilization of methanol and xylose achieved a molar consumption ratio exceeding 4:1, indicating methanol served as the primary carbon source while xylose was auxiliary to enhance robustness. Subsequently, we developed a riboflavin cell factory by systemic engineering of B. methanolicus, achieving 2579 mg/L production in a 5-L bioreactor-the highest riboflavin titer reported for methanol-based production. This study establishes B. methanolicus as a versatile and accessible platform for sustainable methanol-based bio-manufacturing.

Developing a robust genome editing tool based on an endogenous type I-B CRISPR-Cas system in Saccharopolyspora spinosa

Saccharopolyspora spinosa is an industrial rare actinomycete capable of producing important environmental-friendly biopesticides, spinosyns. However, exploitation of S. spinosa has been limited due to its genetic inaccessibility and lack of effective genome engineering tools. In this work, we characterized the activity of an endogenous type I-B CRISPR-Cas system as well as its recognized protospacer adjacent motifs (PAMs) based on bioinformatics analysis combined with a plasmid interference assay in S. spinosa. By delivering editing plasmids containing a designed miniCRISPR array (repeat+self-targeting spacer+repeat) and repair templates, we achieved 100% editing efficiency for gene deletion. Using this tool, the genetic barrier composed of the restriction-modification (RM) systems was systematically disarmed. We showed that by disarming one type I RM system (encoded by A8926_1903/1904/1905) and two type II RM systems (encoded by A8926_1725/1726 and A8926_2652/2653) simultaneously, the transformation efficiency of the replicative and integrative plasmids (pSP01 and pSI01) was increased by approximately 3.9-fold and 4.2-fold, respectively. Using the engineered strain with simultaneous knock-out of these three RM genes as the starting strain, we achieved the deletion of 75-kb spinosyns biosynthetic gene cluster (BGC) as well as gene insertion at high efficiency. Collectively, we developed a reliable and highly efficient genome editing tool based on the endogenous type I CRISPR-Cas system combined with the disarmament of the RM systems in S. spinosa. This is the first time to establish an endogenous CRISPR-Cas-based genome editing tool in the non-model industrial actinomycetes.

Hi-TARGET: a fast, efficient and versatile CRISPR type I-B genome editing tool for the thermophilic acetogen Thermoanaerobacter kivui

BACKGROUND

Due to its ability to grow fast on CO2, CO and H2 at high temperatures and with high energy efficiency, the thermophilic acetogen Thermoanaerobacter kivui could become an attractive host for industrial biotechnology. In a circular carbon economy, diversification and upgrading of C1 platform feedstocks into value-added products (e. g., ethanol, acetone and isopropanol) could become crucial. To that end, genetic and bioprocess engineering tools are required to facilitate the development of bioproduction scenarios. Currently, the genome editing tools available for T. kivui present some limitations in speed and efficiency, thus restricting the development of a powerful strain chassis for industrial applications.

RESULTS

In this study, we developed the versatile genome editing tool Hi-TARGET, based on the endogenous CRISPR Type I-B system of T. kivui. Hi-TARGET demonstrated 100% efficiency for gene knock-out (from both purified plasmid and cloning mixture) and knock-in, and 49% efficiency for creating point mutations. Furthermore, we optimized the transformation and plating protocol and increased transformation efficiency by 245-fold to 1.96 × 104 ± 8.7 × 103 CFU μg-1. Subsequently, Hi-TARGET was used to demonstrate gene knock-outs (pyrE, rexA, hrcA), a knock-in (ldh::pFAST), a single nucleotide mutation corresponding to PolCC629Y, and knock-down of the fluorescent protein pFAST. Analysis of the ∆rexA deletion mutant created with Hi-TARGET revealed that the transcriptional repressor rexA is likely involved in the regulation of the expression of lactate dehydrogenase (ldh). Following genome engineering, an optimized curing procedure for edited strains was devised. In total, the time required from DNA to a clean, edited strain is 12 days, rendering Hi-TARGET a fast, robust and complete method for engineering T. kivui.

CONCLUSIONS

The CRISPR-based genome editing tool Hi-TARGET developed for T. kivui can be used for scarless deletion, insertion, point mutation and gene knock-down, thus fast-tracking the generation of industrially-relevant strains for the production of carbon-negative chemicals and fuels as well as facilitating studies of acetogen metabolism and physiology.

Awakening of the RuMP cycle for partial methylotrophy in the thermophile Parageobacillus thermoglucosidasius

Given sustainability and scalability concerns of using sugar feedstocks for microbial bioproduction of bulk chemicals, widening the feedstock range for microbial cell factories is of high interest. Methanol is a one-carbon alcohol that stands out as an alternative feedstock for the bioproduction of chemicals, as it is electron-rich, water-miscible and can be produced from several renewable resources. Bioconversion of methanol into products under thermophilic conditions (>50 °C) could be highly advantageous for industrial biotechnology. Although progress is being made with natural, thermophilic methylotrophic microorganisms, they are not yet optimal for bioproduction and establishing alternative thermophilic methylotrophic bioproduction platforms can widen possibilities. Hence, we set out to implement methanol assimilation in the emerging thermophilic model organism Parageobacillus thermoglucosidasius. We engineered P. thermoglucosidasius to be strictly dependent for its growth on methanol assimilation via the core of the highly efficient ribulose monophosphate (RuMP) cycle, while co-assimilating ribose. Surprisingly, this did not require heterologous expression of RuMP enzymes. Instead, by laboratory evolution we awakened latent, native enzyme activities to form the core of the RuMP cycle. We obtained fast methylotrophic growth in which ∼17 % of biomass was strictly obtained from methanol. This work lays the foundation for developing a versatile thermophilic bioproduction platform based on renewable methanol.

Bacillus methanolicus: an emerging chassis for low-carbon biomanufacturing

Bacillus methanolicus is a thermophilic methylotrophic bacterium that grows quickly on methanol in sea water-based media. It has been engineered for chemical bioproduction from methanol, but its efficiency needs improvement for industrialization. Synthetic biology approaches such as metabolic modeling and genome editing can reprogram B. methanolicus for low-carbon biomanufacturing.

Nanoencapsulation of Living Microbial Cells in Porous Covalent Organic Framework Shells

Encapsulating living cells within nanoshells offers an important approach to enhance their stability against environmental stressors and broaden their application scope. However, this often leads to impaired mass transfer at the cell biointerface. Strengthening the protective shell with well-defined, ordered transport channels is crucial to regulating molecular transport and maintaining cell viability and biofunctionality. Herein, we report the construction of covalent organic framework (COF) mesoporous shells for single-cell nanoencapsulation, providing selective permeability and comprehensive protection for living microbial cells. The COF shells ensure nutrient uptake while blocking large harmful molecules and UV-C radiation, thereby preserving cell viability and metabolic activity. Integration of such crystalline porous shells with genetically modified cell factories for metabolic production is further investigated, revealing no adverse effects, as demonstrated by riboflavin production. Moreover, the COF shell effectively shields cells, ensuring efficient bioproduction even after being treated under harsh conditions. This versatile encapsulation approach is applicable for different cell types, providing a robust platform for cell surface engineering.

A highly efficient method for genomic deletion across diverse lengths in thermophilic Parageobacillus thermoglucosidasius

Parageobacillus thermoglucosidasius is emerging as a highly promising thermophilic organism for metabolic engineering. The utilization of CRISPR-Cas technologies has facilitated programmable genetic manipulation in P. thermoglucosidasius. However, the absence of thermostable NHEJ enzymes limited the capability of the endogenous type I CRISPR-Cas system to generate a variety of extensive genomic deletions. Here, two thermophilic NHEJ enzymes were identified and combined with the endogenous type I CRISPR-Cas system to develop a genetic manipulation tool that can achieve long-range genomic deletion across various lengths. By optimizing this tool-through adjusting the expression level of NHEJ enzymes and leveraging our discovery of a negative correlation between GC content of the guide RNA (gRNA) and deletion efficacy-we streamlined a comprehensive gRNA selection manual for whole-genome editing, achieving a 100 % success rate in randomly selecting gRNAs. Notably, using just one gRNA, we achieved genomic deletions spanning diverse length, exceeding 200 kilobases. This tool will facilitate the genomic manipulation of P. thermoglucosidasius for both fundamental research and applied engineering studies, further unlocking its potential as a thermophilic cell factory.

Biofuel production from lignocellulose via thermophile-based consolidated bioprocessing

The depletion of fossil fuels and their impact on the environment have led to efforts to develop alternative sustainable fuels. While biofuel derived from lignocellulose is considered a sustainable, renewable, and green energy source, enhancing biofuel production and achieving a cost-effective bioconversion of lignocellulose at existing bio-refineries remains a challenge. Consolidated bioprocessing (CBP) using thermophiles can simplify this operation by integrating multiple processes, such as hydrolytic enzyme production, lignocellulose degradation, biofuel fermentation, and product distillation. This paper reviews recent developments in the conversion of lignocellulose to biofuel using thermophile-based CBP. First, advances in thermostable enzyme and thermophilic lignocellulolytic microorganism discovery and development for lignocellulosic biorefinery use are outlined. Then, several thermophilic CBP candidates and thermophilic microbes engineered to drive CBP of lignocellulose are reviewed. CRISPR/Cas-based genome editing tools developed for thermophiles are also highlighted. The potential applications of the Design-Build-Test-Learn (DBTL) synthetic biology strategy for designing and constructing thermophilic CBP hosts are also discussed in detail. Overall, this review illustrates how to develop highly sophisticated thermophilic CBP hosts for use in lignocellulosic biorefinery applications.

Research Progress on the Mechanism and Application of the Type I CRISPR-Cas System

The CRISPR-Cas system functions as an adaptive immune mechanism in archaea and bacteria, providing defense against the invasion of foreign nucleic acids. Most CRISPR-Cas systems are classified into class 1 or class 2, with further subdivision into several subtypes. The primary distinction between class 1 and class 2 systems lies in the assembly of their effector modules. In class 1 systems, the effector complex consists of multiple proteins with distinct functions, whereas in class 2 systems, the effector is associated with a single protein. Class 1 systems account for approximately 90% of the CRISPR-Cas repertoire and are categorized into three types (type I, type IV, and type III) and 12 subtypes. To date, various CRISPR-Cas systems have been widely employed in the field of genetic engineering as essential tools and techniques for genome editing. Type I CRISPR-Cas systems remain a valuable resource for developing sophisticated application tools. This review provides a comprehensive review of the characteristics, mechanisms of action, and applications of class 1 type I CRISPR-Cas systems, as well as transposon-associated systems, offering effective approaches and insights for future research on the mechanisms of action, as well as the subsequent development and application of type I CRISPR-Cas systems.

Repurposing endogenous type I-E CRISPR-Cas systems for natural product discovery in Streptomyces

The multifunctional proteins of class 2 CRISPR systems such as Cas9, have been employed to activate cryptic biosynthetic gene clusters (BGCs) in Streptomyces, which represent a large and hidden reservoir of natural products. However, such approaches are not applicable to most Streptomyces strains with reasons to be comprehended. Inspired by the prevalence of the class 1 subtype especially the type I-E CRISPR system in Streptomyces, here we report the development of the type I-E CRISPR system into a series of transcriptional regulation tools. We further demonstrate the effectiveness of such activators in nine phylogenetically distant Streptomyces strains. Using these tools, we successfully activate 13 out of 21 BGCs and lead to the identification and characterization of one polyketide, one Ripp and three alkaloid products. Our work is expected to have a profound impact and to facilitate the discovery of numerous structurally diverse compounds from Streptomyces.

AI-based automated construction of high-precision Geobacillus thermoglucosidasius enzyme constraint model

Geobacillus thermoglucosidasius NCIMB 11955 possesses advantages, such as high-temperature tolerance, rapid growth rate, and low contamination risk. Additionally, it features efficient gene editing tools, making it one of the most promising next-generation cell factories. However, as a non-model microorganism, a lack of metabolic information significantly hampers the construction of high-precision metabolic flux models. Here, we propose a BioIntelliModel (BIM) strategy based on artificial intelligence technology for the automated construction of enzyme-constrained models. 1). BIM utilises the Contrastive Learning Enabled Enzyme Annotation (CLEAN) prediction tool to analyse the entire genome sequence of G. thermoglucosidasius NCIMB 11955, uncovering potential functional proteins in non-model strains. 2). The MetaPatchM module of BIM automates the repair of the metabolic network model. 3). The Tianjin University of Science and Technology-kcat (TUST-kcat) module predicts the kcat values of enzymes within the model. 4). The Enzyme-insert procedure constructs an enzyme-constrained model and performs a global scan to address overconstraint issues. Enzymatic data were automatically integrated into the metabolic flux model, creating an enzyme-constrained model, ec_G-ther11955. To validate model accuracy, we used both the p-thermo and ec_G-ther11955 models to predict riboflavin production strategies. The ec_G-ther11955 model demonstrated significantly higher accuracy. To further verify its efficacy, we employed ec_G-ther11955 to guide the rational design of L-valine-producing strains. Using the Optimisation Procedure for Identifying All Genetic Manipulations Leading to Targeted Overproductions (OptForce), Predictive Knockout Targeting (PKT), and Flux Scanning based on Enforced Objective Flux (FSEOF) algorithms, we identified 24 knockout and overexpression targets, achieving an accuracy rate of 87.5%. Ultimately, this led to an increase of 664.04% in L-valine titre. This study provides a novel strategy for rapidly constructing non-model strain models and demonstrates the tremendous potential of artificial intelligence in metabolic engineering.

Unleashing the potential: type I CRISPR-Cas systems in actinomycetes for genome editing

Covering: up to the end of 2023Type I CRISPR-Cas systems are widely distributed, found in over 40% of bacteria and 80% of archaea. Among genome-sequenced actinomycetes (particularly Streptomyces spp.), 45.54% possess type I CRISPR-Cas systems. In comparison to widely used CRISPR systems like Cas9 or Cas12a, these endogenous CRISPR-Cas systems have significant advantages, including better compatibility, wide distribution, and ease of operation (since no exogenous Cas gene delivery is needed). Furthermore, type I CRISPR-Cas systems can simultaneously edit and regulate genes by adjusting the crRNA spacer length. Meanwhile, most actinomycetes are recalcitrant to genetic manipulation, hindering the discovery and engineering of natural products (NPs). The endogenous type I CRISPR-Cas systems in actinomycetes may offer a promising alternative to overcome these barriers. This review summarizes the challenges and recent advances in CRISPR-based genome engineering technologies for actinomycetes. It also presents and discusses how to establish and develop genome editing tools based on type I CRISPR-Cas systems in actinomycetes, with the aim of their future application in gene editing and the discovery of NPs in actinomycetes.

Industrial biotechnology goes thermophilic: Thermoanaerobes as promising hosts in the circular carbon economy

Transitioning away from fossil feedstocks is imperative to mitigate climate change, and necessitates the utilization of renewable, alternative carbon and energy sources to foster a circular carbon economy. In this context, lignocellulosic biomass and one-carbon compounds emerge as promising feedstocks that could be renewably upgraded by thermophilic anaerobes (thermoanaerobes) via gas fermentation or consolidated bioprocessing to value-added products. In this review, the potential of thermoanaerobes for cost-efficient, effective and sustainable bioproduction is discussed. Metabolic and bioprocess engineering approaches are reviewed to draw a comprehensive picture of current developments and future perspectives for the conversion of renewable feedstocks to chemicals and fuels of interest. Selected bioprocessing scenarios are outlined, offering practical insights into the applicability of thermoanaerobes at a large scale. Collectively, the potential advantages of thermoanaerobes regarding process economics could facilitate an easier transition towards sustainable bioprocesses with renewable feedstocks.

Multiplex CRISPR-Cas Genome Editing: Next-Generation Microbial Strain Engineering

Genome editing is a crucial technology for obtaining desired phenotypes in a variety of species, ranging from microbes to plants, animals, and humans. With the advent of CRISPR-Cas technology, it has become possible to edit the intended sequence by modifying the target recognition sequence in guide RNA (gRNA). By expressing multiple gRNAs simultaneously, it is possible to edit multiple targets at the same time, allowing for the simultaneous introduction of various functions into the cell. This can significantly reduce the time and cost of obtaining engineered microbial strains for specific traits. In this review, we investigate the resolution of multiplex genome editing and its application in engineering microorganisms, including bacteria and yeast. Furthermore, we examine how recent advancements in artificial intelligence technology could assist in microbial genome editing and engineering. Based on these insights, we present our perspectives on the future evolution and potential impact of multiplex genome editing technologies in the agriculture and food industry.

Parageobacillus thermoglucosidasius as an emerging thermophilic cell factory

Parageobacillus thermoglucosidasius is a thermophilic and facultatively anaerobic microbe, which is emerging as one of the most promising thermophilic model organisms for metabolic engineering. The use of thermophilic microorganisms for industrial bioprocesses provides the advantages of increased reaction rates and reduced cooling costs for bioreactors compared to their mesophilic counterparts. Moreover, it enables starch or lignocellulose degradation and fermentation to occur at the same temperature in a Simultaneous Saccharification and Fermentation (SSF) or Consolidated Bioprocessing (CBP) approach. Its natural hemicellulolytic capabilities and its ability to convert CO to metabolic energy make P. thermoglucosidasius a potentially attractive host for bio-based processes. It can effectively degrade hemicellulose due to a number of hydrolytic enzymes, carbohydrate transporters, and regulatory elements coded from a genomic cluster named Hemicellulose Utilization (HUS) locus. The growing availability of effective genetic engineering tools in P. thermoglucosidasius further starts to open up its potential as a versatile thermophilic cell factory. A number of strain engineering examples showcasing the potential of P. thermoglucosidasius as a microbial chassis for the production of bulk and fine chemicals are presented along with current research bottlenecks. Ultimately, this review provides a holistic overview of the distinct metabolic characteristics of P. thermoglucosidasius and discusses research focused on expanding the native metabolic boundaries for the development of industrially relevant strains.

Application of functional genomics for domestication of novel non-model microbes

With the expansion of domesticated microbes producing biomaterials and chemicals to support a growing circular bioeconomy, the variety of waste and sustainable substrates that can support microbial growth and production will also continue to expand. The diversity of these microbes also requires a range of compatible genetic tools to engineer improved robustness and economic viability. As we still do not fully understand the function of many genes in even highly studied model microbes, engineering improved microbial performance requires introducing genome-scale genetic modifications followed by screening or selecting mutants that enhance growth under prohibitive conditions encountered during production. These approaches include adaptive laboratory evolution, random or directed mutagenesis, transposon-mediated gene disruption, or CRISPR interference (CRISPRi). Although any of these approaches may be applicable for identifying engineering targets, here we focus on using CRISPRi to reduce the time required to engineer more robust microbes for industrial applications.

ONE-SENTENCE SUMMARY

The development of genome scale CRISPR-based libraries in new microbes enables discovery of genetic factors linked to desired traits for engineering more robust microbial systems.