Engineering Synthetic Multistress Tolerance in Escherichia coli by Using a Deinococcal Response Regulator, DR1558

Comparative genomics of Deinococcus radiodurans: unveiling genetic discrepancies between ATCC 13939K and BAA-816 strains

The Deinococcus genus is renowned for its remarkable resilience against environmental stresses, including ionizing radiation, desiccation, and oxidative damage. This resilience is attributed to its sophisticated DNA repair mechanisms and robust defense systems, enabling it to recover from extensive damage and thrive under extreme conditions. Central to Deinococcus research, the D. radiodurans strains ATCC BAA-816 and ATCC 13939 facilitate extensive studies into this remarkably resilient genus. This study focused on delineating genetic discrepancies between these strains by sequencing our laboratory's ATCC 13939 specimen (ATCC 13939K) and juxtaposing it with ATCC BAA-816. We uncovered 436 DNA sequence differences within ATCC 13939K, including 100 single nucleotide variations, 278 insertions, and 58 deletions, which could induce frameshifts altering protein-coding genes. Gene annotation revisions accounting for gene fusions and the reconciliation of gene lengths uncovered novel protein-coding genes and refined the functional categorizations of established ones. Additionally, the analysis pointed out genome structural variations due to insertion sequence (IS) elements, underscoring the D. radiodurans genome's plasticity. Notably, ATCC 13939K exhibited a loss of six ISDra2 elements relative to BAA-816, restoring genes fragmented by ISDra2, such as those encoding for α/β hydrolase and serine protease, and revealing new open reading frames, including genes imperative for acetoin decomposition. This comparative genomic study offers vital insights into the metabolic capabilities and resilience strategies of D. radiodurans.

Systemic metabolic engineering of Enterobacter aerogenes for efficient 2,3-butanediol production

2,3-Butanediol (2,3-BDO) is an important gateway molecule for many chemical derivatives. Currently, microbial production is gradually being recognized as a green and sustainable alternative to petrochemical synthesis, but the titer, yield, and productivity of microbial 2,3-BDO remain suboptimal. Here, we used systemic metabolic engineering strategies to debottleneck the 2,3-BDO production in Enterobacter aerogenes. Firstly, the pyruvate metabolic network was reconstructed by deleting genes for by-product synthesis to improve the flux toward 2,3-BDO synthesis, which resulted in a 90% increase of the product titer. Secondly, the 2,3-BDO productivity of the IAM1183-LPCT/D was increased by 55% due to the heterologous expression of DR1558 which boosted cell resistance to abiotic stress. Thirdly, carbon sources were optimized to further improve the yield of target products. The IAM1183-LPCT/D showed the highest titer of 2,3-BDO from sucrose, 20% higher than that from glucose, and the yield of 2,3-BDO reached 0.49 g/g. Finally, the titer of 2,3-BDO of IAM1183-LPCT/D in a 5-L fermenter reached 22.93 g/L, 85% higher than the wild-type strain, and the titer of by-products except ethanol was very low. KEY POINTS: Deletion of five key genes in E. aerogenes improved 2,3-BDO production The titer of 2,3-BDO was increased by 90% by regulating metabolic flux Response regulator DR1558 was expressed to increase 2,3-BDO productivity.

Deionococcus proteotlycius Genomic Library Exploration Enhances Oxidative Stress Resistance and Poly-3-hydroxybutyrate Production in Recombinant Escherichia coli

Cell growth is inhibited by abiotic stresses during industrial processes, which is a limitation of microbial cell factories. Microbes with robust phenotypes are critical for its maximizing the yield of the target products in industrial biotechnology. Currently, there are several reports on the enhanced production of industrial metabolite through the introduction of Deinococcal genes into host cells, which confers cellular robustness. Deinococcus is known for its unique genetic function thriving in extreme environments such as radiation, UV, and oxidants. In this study, we established that Deinococcus proteolyticus showed greater resistance to oxidation and UV-C than commonly used D. radiodurans. By screening the genomic library of D. proteolyticus, we isolated a gene (deipr_0871) encoding a response regulator, which not only enhanced oxidative stress, but also promoted the growth of the recombinant E. coli strain. The transcription analysis indicated that the heterologous expression of deipr_0871 upregulated oxidative-stress-related genes such as ahpC and sodA, and acetyl-CoA-accumulation-associated genes via soxS regulon. Deipr_0871 was applied to improve the production of the valuable metabolite, poly-3-hydroxybutyrate (PHB), in the synthetic E. coli strain, which lead to the remarkably higher PHB than the control strain. Therefore, the stress tolerance gene from D. proteolyticus should be used in the modification of E. coli for the production of PHB and other biomaterials.

Antioxidant defense of Deinococcus radiodurans: how does it contribute to extreme radiation resistance?

PURPOSE

Deinococcus radiodurans is an extremely radioresistant bacterium characterized by D10 of 10 kGy, and able to grow luxuriantly under chronic ionizing radiation of 60 Gy/h. The aim of this article is to review the antioxidant system of D. radiodurans and its possible role in the unusual resistance of this bacterium to ionizing radiation.

CONCLUSIONS

The unusual radiation resistance of D. radiodurans has apparently evolved as a side effect of the adaptation of this extremophile to other damaging environmental factors, especially desiccation. The antioxidant proteins and low-molecular antioxidants (especially low-molecular weight Mn2+ complexes and carotenoids, in particular, deinoxanthin), as well as protein and non-protein regulators, are important for the antioxidant defense of this species. Antioxidant protection of proteins from radiation inactivation enables the repair of DNA damage caused by ionizing radiation.

Production of Cadaverine in Recombinant Corynebacterium glutamicum Overexpressing Lysine Decarboxylase (ldcC) and Response Regulator dr1558

In this study, the response regulator DR1558 from Deinococcus radiodurans was overexpressed in recombinant Corynebacterium glutamicum with lysine decarboxylase (ldcC). The recombinant C. glutamicum strain overexpressing dr1558 and ldcC produced 5.9 g/L of cadaverine by flask cultivation, whereas the control strain overexpressing only ldcC produced 4.5 g/L of cadaverine. To investigate the mechanism underlying the effect of DR1558, the expression levels of genes related to central metabolism and lysine-biosynthesis were analyzed by quantitative-real time polymerase chain reaction. The results showed that phosphoenolpyruvate carboxykinase (pck) was downregulated, and pyruvate kinase (pyk) and other lysine biosynthesis genes were upregulated. Furthermore, in fed-batch fermentation, C. glutamicum coexpressing dr1558 produced 25.14 g/L of cadaverine, a 1.25-fold increase in concentration relative to the control. These results suggested that the heterologous expression of dr1558 may improve the production of biorefinery products by recombinant C. glutamicum.

Biosynthesis pathways and strategies for improving 3-hydroxypropionic acid production in bacteria

3-Hydroxypropionic acid (3-HP) represents an economically important platform compound from which a panel of bulk chemicals can be derived. Compared with petroleum-dependent chemical synthesis, bioproduction of 3-HP has attracted more attention due to utilization of renewable biomass. This review outlines bacterial production of 3-HP, covering aspects of host strains (e.g., Escherichia coli and Klebsiella pneumoniae), metabolic pathways, key enzymes, and hurdles hindering high-level production. Inspired by the state-of-the-art advances in metabolic engineering and synthetic biology, we come up with protocols to overcome the hurdles constraining 3-HP production. The protocols range from rewiring of metabolic networks, alleviation of metabolite toxicity, to dynamic control of cell size and density. Especially, this review highlights the substantial contribution of microbial growth to 3-HP production, as we recognize the synchronization between cell growth and 3-HP formation. Accordingly, we summarize the following growth-promoting strategies: (i) optimization of fermentation conditions; (ii) construction of gene circuits to alleviate feedback inhibition; (iii) recruitment of RNA polymerases to overexpress key enzymes which in turn boost cell growth and 3-HP production. Lastly, we propose metabolic engineering approaches to simplify downstream separation and purification. Overall, this review aims to portray a picture of bacterial production of 3-HP.

Synthetic reconstruction of extreme high hydrostatic pressure resistance in Escherichia coli

Although high hydrostatic pressure (HHP) is an interesting parameter to be applied in bioprocessing, its potential is currently limited by the lack of bacterial chassis capable of surviving and maintaining homeostasis under pressure. While several efforts have been made to genetically engineer microorganisms able to grow at sublethal pressures, there is little information for designing backgrounds that survive more extreme pressures. In this investigation, we analyzed the genome of an extreme HHP-resistant mutant of E. coli MG1655 (designated as DVL1), from which we identified four mutations (in the cra, cyaA, aceA and rpoD loci) causally linked to increased HHP resistance. Analysing the functional effect of these mutations we found that the coupled effect of downregulation of cAMP/CRP, Cra and the glyoxylate shunt activity, together with the upregulation of RpoH and RpoS activity, could mechanistically explain the increased HHP resistance of the mutant. Using combinations of three mutations, we could synthetically engineer E. coli strains able to comfortably survive pressures of 600-800 MPa, which could serve as genetic backgrounds for HHP-based biotechnological applications.

Effect of DR1558, a Deinococcus radiodurans response regulator, on the production of GABA in the recombinant Escherichia coli under low pH conditions

BACKGROUND

Gamma aminobutyric acid (GABA) is an important platform chemical, which has been used as a food additive and drug. Additionally, GABA is a precursor of 2-pyrrolidone, which is used in nylon synthesis. GABA is usually synthesized from glutamate in a reaction catalyzed by glutamate decarboxylase (GAD). Currently, there are several reports on GABA production from monosodium glutamate (MSG) or glucose using engineered microbes. However, the optimal pH for GAD activity is 4, which is the limiting factor for the efficient microbial fermentative production of GABA as fermentations are performed at pH 7. Recently, DR1558, a response regulator in the two-component signal transduction system was identified in Deinococcus radiodurans. DR1558 is reported to confer cellular robustness to cells by binding the promoter regions of genes via DNA-binding domains or by binding to the effector molecules, which enable the microorganisms to survive in various environmental stress conditions, such as oxidative stress, high osmotic shock, and low pH.

RESULTS

In this study, the effect of DR1558 in enhancing GABA production was examined using two different strategies: whole-cell bioconversion of GABA from MSG and direct fermentative production of GABA from glucose under acidic culture conditions. In the whole-cell bioconversion, GABA produced by E. coli expressing GadBC and DR1558 (6.52 g/L GABA from 13 g/L MSG·H₂O) in shake flask culture at pH 4.5 was 2.2-fold higher than that by E. coli expressing only GadBC (2.97 g/L of GABA from 13 g/L MSG·H₂O). In direct fermentative production of GABA from glucose, E. coli ∆gabT expressing isocitrate dehydrogenase (IcdA), glutamate dehydrogenase (GdhA), GadBC, and DR1558 produced 1.7-fold higher GABA (2.8 g/L of GABA from 30 g/L glucose) than E. coli ∆gabT expressing IcdA, GdhA, and GadBC (1.6 g/L of GABA from 30 g/L glucose) in shake flask culture at an initial pH 7.0. The transcriptional analysis of E. coli revealed that DR1558 conferred acid resistance to E. coli during GABA production. The fed-batch fermentation of E. coli expressing IcdA, GdhA, GadBC, and DR1558 performed at pH 5.0 resulted in the final GABA titer of 6.16 g/L by consuming 116.82 g/L of glucose in 38 h.

CONCLUSION

This is the first report to demonstrate GABA production by acidic fermentation and to provide an engineering strategy for conferring acid resistance to the recombinant E. coli for GABA production.

Improved tolerance of Escherichia coli to oxidative stress by expressing putative response regulator homologs from Antarctic bacteria

Response regulator (RR) is known a protein that mediates cell's response to environmental changes. The effect of RR from extremophiles was still under investigation. In this study, response regulator homologs were mined from NGS data of Antarctic bacteria and overexpressed in Escherichia coli. Sixteen amino acid sequences were annotated corresponding to response regulators related to the two-component regulatory systems; of these, 3 amino acid sequences (DRH632, DRH1601 and DRH577) with high homology were selected. These genes were cloned in pRadGro and expressed in E. coli. The transformant strains were subjected to various abiotic stresses including oxidative, osmotic, thermal stress, and acidic stress. There was found that the robustness of E. coli to abiotic stress was increased in the presence of these response regulator homologs. Especially, recombinant E. coli overexpressing drh632 had the highest survival rate in oxidative, hypothermic, osmotic, and acidic conditions. Recombinant E. coli overexpressing drh1601 showed the highest tolerance level to osmotic stress. These results will be applicable for development of recombinant strains with high tolerance to abiotic stress.

Techniques for enhancing the tolerance of industrial microbes to abiotic stresses: A review

The diversity of stress responses and survival strategies evolved by microorganism enables them to survive and reproduce in a multitude of harsh environments, whereas the discovery of the underlying resistance genes or mechanisms laid the foundation for the directional enhancement of microbial tolerance to abiotic stresses encountered in industrial applications. Many biological techniques have been developed for improving the stress resistance of industrial microorganisms, which greatly benefited the bacteria on which industrial production is based. This review introduces the main techniques for enhancing the resistance of microorganisms to abiotic stresses, including evolutionary engineering, metabolic engineering, and process engineering, developed in recent years. In addition, we also discuss problems that are still present in this area and offer directions for future research.

Synthetic biology for evolutionary engineering: from perturbation of genotype to acquisition of desired phenotype

With the increased attention on bio-based industry, demands for techniques that enable fast and effective strain improvement have been dramatically increased. Evolutionary engineering, which is less dependent on biological information, has been applied to strain improvement. Currently, synthetic biology has made great innovations in evolutionary engineering, particularly in the development of synthetic tools for phenotypic perturbation. Furthermore, discovering biological parts with regulatory roles and devising novel genetic circuits have promoted high-throughput screening and selection. In this review, we first briefly explain basics of synthetic biology tools for mutagenesis and screening of improved variants, and then describe how these strategies have been improved and applied to phenotypic engineering. Evolutionary engineering using advanced synthetic biology tools will enable further innovation in phenotypic engineering through the development of novel genetic parts and assembly into well-designed logic circuits that perform complex tasks.

Genome-scale biological models for industrial microbial systems

The primary aims and challenges associated with microbial fermentation include achieving faster cell growth, higher productivity, and more robust production processes. Genome-scale biological models, predicting the formation of an interaction among genetic materials, enzymes, and metabolites, constitute a systematic and comprehensive platform to analyze and optimize the microbial growth and production of biological products. Genome-scale biological models can help optimize microbial growth-associated traits by simulating biomass formation, predicting growth rates, and identifying the requirements for cell growth. With regard to microbial product biosynthesis, genome-scale biological models can be used to design product biosynthetic pathways, accelerate production efficiency, and reduce metabolic side effects, leading to improved production performance. The present review discusses the development of microbial genome-scale biological models since their emergence and emphasizes their pertinent application in improving industrial microbial fermentation of biological products.

In a quest for engineering acidophiles for biomining applications: challenges and opportunities

Biomining with acidophilic microorganisms has been used at commercial scale for the extraction of metals from various sulfide ores. With metal demand and energy prices on the rise and the concurrent decline in quality and availability of mineral resources, there is an increasing interest in applying biomining technology, in particular for leaching metals from low grade minerals and wastes. However, bioprocessing is often hampered by the presence of inhibitory compounds that originate from complex ores. Synthetic biology could provide tools to improve the tolerance of biomining microbes to various stress factors that are present in biomining environments, which would ultimately increase bioleaching efficiency. This paper reviews the state-of-the-art tools to genetically modify acidophilic biomining microorganisms and the limitations of these tools. The first part of this review discusses resilience pathways that can be engineered in acidophiles to enhance their robustness and tolerance in harsh environments that prevail in bioleaching. The second part of the paper reviews the efforts that have been carried out towards engineering robust microorganisms and developing metabolic modelling tools. Novel synthetic biology tools have the potential to transform the biomining industry and facilitate the extraction of value from ores and wastes that cannot be processed with existing biomining microorganisms.

Microbial radiation-resistance mechanisms

Organisms living in extreme environments have evolved a wide range of survival strategies by changing biochemical and physiological features depending on their biological niches. Interestingly, organisms exhibiting high radiation resistance have been discovered in the three domains of life (Bacteria, Archaea, and Eukarya), even though a naturally radiationintensive environment has not been found. To counteract the deleterious effects caused by radiation exposure, radiation- resistant organisms employ a series of defensive systems, such as changes in intracellular cation concentration, excellent DNA repair systems, and efficient enzymatic and non-enzymatic antioxidant systems. Here, we overview past and recent findings about radiation-resistance mechanisms in the three domains of life for potential usage of such radiationresistant microbes in the biotechnology industry.

PprM, a Cold Shock Domain-Containing Protein from Deinococcus radiodurans, Confers Oxidative Stress Tolerance to Escherichia coli

Escherichia coli is a representative microorganism that is frequently used for industrial biotechnology; thus its cellular robustness should be enhanced for the widespread application of E. coli in biotechnology. Stress response genes from the extremely radioresistant bacterium Deinococcus radiodurans have been used to enhance the stress tolerance of E. coli. In the present study, we introduced the cold shock domain-containing protein PprM from D. radiodurans into E. coli and observed that the tolerance to hydrogen peroxide (H₂O₂) was significantly increased in recombinant strains (Ec-PprM). The overexpression of PprM in E. coli elevated the expression of some OxyR-dependent genes, which play important roles in oxidative stress tolerance. Particularly, mntH (manganese transporter) was activated by 9-fold in Ec-PprM, even in the absence of H₂O₂ stress, which induced a more than 2-fold increase in the Mn/Fe ratio compared with wild type. The reduced production of highly reactive hydroxyl radicals (·OH) and low protein carbonylation levels (a marker of oxidative damage) in Ec-PprM indicate that the increase in the Mn/Fe ratio contributes to the protection of cells from H₂O₂ stress. PprM also conferred H₂O₂ tolerance to E. coli in the absence of OxyR. We confirmed that the H₂O₂ tolerance of oxyR mutants reflected the activation of the ycgZ-ymgABC operon, whose expression is activated by H₂O₂ in an OxyR-independent manner. Thus, the results of the present study showed that PprM could be exploited to improve the robustness of E. coli.