Advances of development and application amino acid biosensors / 生物工程学报

Amino acids are the basic building blocks of protein that are very important to the nutrition and health of humans and animals, and widely used in feed, food, medicine and daily chemicals. At present, amino acids are mainly produced from renewable raw materials by microbial fermentation, forming one of the important pillar industries of biomanufacturing in China. Amino acid-producing strains are mostly developed through random mutagenesis- and metabolic engineering-enabled strain breeding combined with strain screening. One of the key limitations to further improvement of production level is the lack of efficient, rapid, and accurate strain screening methods. Therefore, the development of high-throughput screening methods for amino acid strains is very important for the mining of key functional elements and the creation and screening of hyper-producing strains. This paper reviews the design of amino acid biosensors and their applications in the high-throughput evolution and screening of functional elements and hyper-producing strains, and the dynamic regulation of metabolic pathways. The challenges of existing amino acid biosensors and strategies for biosensor optimization are discussed. Finally, the importance of developing biosensors for amino acid derivatives is prospected.

Construction and application of a synthetic promoter library for Corynebacterium glutamicum / 生物工程学报

Promoter is an important genetic tool for fine-tuning of gene expression and has been widely used for metabolic engineering. Corynebacterium glutamicum is an important chassis for industrial biotechnology. However, promoter libraries that are applicable to C. glutamicum have been rarely reported, except for a few developed based on synthetic sequences containing random mutations. In this study, we constructed a promoter library based on the native promoter of odhA gene by mutating the -10 region and the bystanders. Using a red fluorescent protein (RFP) as the reporter, 57 promoter mutants were screened by fluorescence imaging technology in a high-throughput manner. These mutants spanned a strength range between 2.4-fold and 19.6-fold improvements of the wild-type promoter. The strongest mutant exhibited a 2.3-fold higher strength than the widely used strong inducible promoter Ptrc. Sequencing of all 57 mutants revealed that 55 mutants share a 1-4 bases shift (4 bases shift for 68% mutants) of the conserved -10 motif "TANNNT" to the 3' end of the promoter, compared to the wild-type promoter. Conserved T or G bases at different positions were observed for strong, moderate, and weak promoter mutants. Finally, five promoter mutants with different strength were employed to fine-tune the expression of γ-glutamyl kinase (ProB) for L-proline biosynthesis. Increased promoter strength led to enhanced L-proline production and the highest L-proline titer of 6.4 g/L was obtained when a promoter mutant with a 9.8-fold higher strength compared to the wild-type promoter was used for ProB expression. The use of stronger promoter variants did not further improve L-proline production. In conclusion, a promoter library was constructed based on a native C. glutamicum promoter PodhA. The new promoter library should be useful for systems metabolic engineering of C. glutamicum. The strategy of mutating native promoter may also guide the construction of promoter libraries for other microorganisms.

Recent advances in developing enabling technologies for Corynebacterium glutamicum metabolic engineering / 生物工程学报

Corynebacterium glutamicum is an important workhorse of industrial biotechnology, especially for amino acid bioindustry. This bacterium is being used to produce various amino acids at a level of over 6 million tons per year. In recent years, enabling technologies for C. glutamicum metabolic engineering have been developed and improved, which accelerated construction and optimization of microbial cell factoriers, expanding spectra of substrates and products, and facilitated basic researches on C. glutamicum. With these technologies, C. glutamicum has become one of the ideal microbial chasses. This review summarizes recent key technological developments of enabling technologies for C. glutamicum metabolic engineering and focuses on establishment and applications of CRISPR-based genome editing, gene expression regulation, adaptive laboratory evolution, and biosensor technologies.

CRISPR/Cas-based genome editing in Aspergillus niger / 生物工程学报

Aspergillus niger is a vital industrial workhouse widely used for the production of organic acids and industrial enzymes. This fungus is a crucial cell factory due to its innate tolerance to a diverse range of abiotic conditions, high production titres, robust growth during industrial scale fermentation, and status as a generally recognized as safe (GRAS) organism. Rapid development of synthetic biology and systems biology not only offer powerful approaches to unveil the molecular mechanisms of A. niger productivity, but also provide more new strategies to construct and optimize the A. niger cell factory. As a new generation of genome editing technology, the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR associated (Cas) system brings a revolutionary breakthrough in targeted genome modification for A. niger. In this review, we focus on current advances to the CRISPR/Cas genome editing toolbox, its application on gene modification and gene expression regulation in this fungal. Moreover, the future directions of CRISPR/Cas genome editing in A. niger are highlighted.

Methanol dehydrogenase, a key enzyme of one-carbon metabolism: a review / 生物工程学报

One-carbon compounds such as methanol and methane are cheap and readily available feedstocks for biomanufacturing. Oxidation of methanol to formaldehyde catalyzed by methanol dehydrogenase (MDH) is a key step of microbial one-carbon metabolism. A variety of MDHs that depend on different co-factors and possess different enzymatic properties have been discovered from native methylotrophs. Nicotinamide adenine dinucleotide (NAD)-dependent MDHs are widely used in constructing synthetic methylotrophs, whereas this type of MDH usually suffers from low methanol oxidation activity and low affinity to methanol. Consequently, methanol oxidation is considered as a rate-limiting step of methanol metabolism in synthetic methylotrophs. To accelerate methanol oxidation, thereby improving the methanol utilization efficiency of synthetic methylotrophs, massive researches have focused on discovery and engineering of MDHs. In this review, we summarize the ongoing efforts to discover, characterize, and engineer various types of MDHs as well as the applications of MDHs in synthetic methylotrophs. Directed evolution of MDH and construction of multi-enzyme complexes are described in detail. In the future prospective part, we discuss the potential strategies of growth-coupled protein evolution and rational protein design for acquisition of superior MDHs.

Amino acid exporters and metabolic modification of Corynebacterium glutamicum - a review / 生物工程学报

Amino acids are important compounds with a wide range of applications in the food, medicine and chemical industries. Corynebacterium glutamicum is a powerful workhorse commonly used in industrial amino acid production, with the scale of more than one million tons. In addition to its efficient anabolism, the effective exporters also ensure the high amino acid production by C. glutamicum. In this review, the research progress of amino acid exporter of C. glutamicum is summarized, to provide the foundation for further improving amino acid production by C. glutamicum via metabolic engineering.

Systems biology for industrial biotechnology / 生物工程学报

In industrial biotechnology, microbial cell factories utilize renewable resources to produce energy, materials and chemicals. Industrial biotechnology plays an increasingly important role in solving the resource, energy and environmental problems. Systems biology has shed new light on industrial biotechnology, deepening our understanding of industrial microbial cell factories and their bioprocess from "Black-box" to "White-box". Systems-wide profiling of genome, transcriptome, proteome, metabolome, and fluxome has proven valuable to better unveil network operation and regulation on the genome scale. System biology has been successfully applied to create microbial cell factories for numerous products and derive attractive industrial processes, which has constantly expedited the development of industrial biotechnology. This review focused on the recent advance and applications of omics and trans-omics in industrial biotechnology, including genomics, transcriptomics, proteomics, metabolomics, fluxomics and genome scale modeling, and so on. Furthermore, this review also discussed the potential and promise of systems biology in industrial biotechnology.

Recent advances in directed evolution / 生物工程学报

Screening is the bottleneck of directed evolution. In order to address this problem, a series of novel semi-rational designed strategies have been developed based on combinatorial active-site saturation test and iterative saturation mutagenesis, including single code saturation mutagenesis, double code saturation mutagenesis and triple code saturation mutagenesis. By creation of "small and smart" high qualified mutant libraries and combinatorial mutagenesis of specific sites, these new strategies have been successfully applied in multiparameter optimization, e.g. stereo/regioselectivity and activity. This review summarized recent advances in directed evolution and its applications in biocatalysis field.

Deficiency of succinic dehydrogenase or succinyl-coA synthetase enhances the production of 5-aminolevulinic acid in recombinant Escherichia coli / 生物工程学报

5-aminolevulinic acid (ALA), a precursor for biosynthesis of pyrrole compounds in living organisms, has been widely used in agriculture and medical photodynamics therapy and is regarded as a promising value-added bio-based chemical. In the previous investigations on ALA production with recombinant Escherichia coli expressing heterogenous C4 pathway gene, LB media supplemented with glucose and ALA precursors succinate and glycine is widely used, leading to high production cost. Succinate participates in ALA biosynthesis in a form of succinyl-CoA. In this study, genes involved in succinyl-CoA consumption, sdhAB (encoding succinic dehydrogenase) or sucCD (encoding succinyl-CoA synthetase) of E. coli MG1655 was knocked out and tested for ALA accumulation. In comparison with the recombinant E. coli strain expressing heterogenous ALA synthetase, the sdhAB- or sucCD-deficient strain accumulate 25.59% and 12.40%, respectively, more ALA in a 5 L fermentor using a defined synthetic medium with glucose as main carbon source and without supplementation of succinate, providing a novel cost-effective approach for industrial production of ALA.

Construction and structural analysis of integrated cellular network of Corynebacterium glutamicum / 生物工程学报

Corynebacterium glutamicum is one of the most important traditional industrial microorganisms and receiving more and more attention towards a novel cellular factory due to the recently rapid development in genomics and genetic operation toolboxes for Corynebacterium. However, compared to other model organisms such as Escherichia coli, there were few studies on its metabolic regulation, especially a genome-scale integrated cellular network model currently missing for Corynebacterium, which hindered the systematic study of Corynebacterium glutamicum and large-scale rational design and optimization for strains. Here, by gathering relevant information from a number of public databases, we successfully constructed an integrated cellular network, which was composed of 1384 reactions, 1276 metabolites, 88 transcriptional factors and 999 pairs of transcriptional regulatory relationships. The transcriptional regulatory sub-network could be arranged into five layers and the metabolic sub-network presented a clear bow-tie structure. We proposed a new method to extract complex metabolic and regulatory sub-network for product-orientated study taking lysine biosynthesis as an example. The metabolic and regulatory sub-network extracted by our method was more close to the real functional network than the simplex biochemical pathways. The results would be greatly helpful for understanding the high-yielding biomechanism for amino acids and the re-design of the industrial strains.

Aspergillus niger as a potential cellular factory: prior knowledge and key technology / 生物工程学报

Aspergillus niger is an important industrial workhorse with extensive application in the sectors of industrial enzymes, heterogeneous proteins, organic acids and etc. The disclosure of its genomic sequence to the public brought the study of A. niger into the post-genomic era. Diverse omic data are being produced massively and rapidly, which largely upgrades our understanding to the hyperproduction mechanism of A. niger to a systems and molecular level. At meanwhile, its genetic operating system is becoming mature, which enables genome-scale genetic perturbation within A. niger. In conclusion, we are on the right way to redesign and engineer A. niger to an omnipotent cellular factory.