CRISPRi-mediated programming essential gene can as a Direct Enzymatic Performance Evaluation & Determination (DEPEND) system

A direct enzymatic evaluation platform (DEEP) to fine-tuning pyridoxal 5'-phosphate-dependent proteins for cadaverine production

Pyridoxal 5'-phosphate (pyridoxal phosphate, PLP) is an essential cofactor for multiple enzymatic reactions in industry. However, cofactor engineering based on PLP regeneration and related to the performance of enzymes in chemical production has rarely been discussed. First, we found that MG1655 strain was sensitive to nitrogen source and relied on different amino acids, thus the biomass was significantly reduced when PLP excess in the medium. Then, the six KEIO collection strains were applied to find out the prominent gene in deoxyxylulose-5-phosphate (DXP) pathway, where pdxB was superior in controlling cell growth. Therefore, the clustered regularly interspaced short palindromic repeats interference (CRISPRi) targeted on pdxB in MG1655 was employed to establish a novel direct enzymatic evaluation platform (DEEP) as a high-throughput tool and obtained the optimal modules for incorporating of PLP to enhance the biomass and activity of PLP-dependent enzymes simultaneously. As a result, the biomass has increased by 55% using P_lacI promoter driven pyridoxine 5'-phosphate oxidase (PdxH) with a trace amount of precursor. When the strains incorporated DEEP and lysine decarboxylase (CadA), the cadaverine productivity was increased 32% due to the higher expression of CadA. DEEP is not only feasible for high-throughput screening of the best chassis for PLP engineering but also practical in fine-tuning the quantity and quality of enzymes.

Challenges and opportunities of bioprocessing 5-aminolevulinic acid using genetic and metabolic engineering: a critical review

5-Aminolevulinic acid (5-ALA), a non-proteinogenic five-carbon amino acid, has received intensive attentions in medicine due to its approval by the US Food and Drug Administration (FDA) for cancer diagnosis and treatment as photodynamic therapy. As chemical synthesis of 5-ALA performed low yield, complicated processes, and high cost, biosynthesis of 5-ALA via C4 (also called Shemin pathway) and C5 pathway related to heme biosynthesis in microorganism equipped more advantages. In C4 pathway, 5-ALA is derived from condensation of succinyl-CoA and glycine by 5-aminolevulic acid synthase (ALAS) with pyridoxal phosphate (PLP) as co-factor in one-step biotransformation. The C5 pathway involves three enzymes comprising glutamyl-tRNA synthetase (GltX), glutamyl-tRNA reductase (HemA), and glutamate-1-semialdehyde aminotransferase (HemL) from α-ketoglutarate in TCA cycle to 5-ALA and heme. In this review, we describe the recent results of 5-ALA production from different genes and microorganisms via genetic and metabolic engineering approaches. The regulation of different chassis is fine-tuned by applying synthetic biology and boosts 5-ALA production eventually. The purification process, challenges, and opportunities of 5-ALA for industrial applications are also summarized.

CRISPRi-Mediated NIMPLY Logic Gate for Fine-Tuning the Whole-Cell Sensing toward Simple Urine Glucose Detection

Whole-cell biosensors have been regarded as a prominent alternative to chemical and physical biosensors due to their renewability, environmental friendliness, and biocompatibility. However, there is still a lack of noninvasive measurements of urine glucose, which plays a vital role in monitoring the risk of diabetes in the healthcare system, via whole-cell biosensors. In this study, we characterized a glucose-inducible promoter and further enhanced the sensing performance using three genetic effectors, which encompassed ribozyme regulator (RiboJ), clustered regularly interspaced short palindromic repeat interference (CRISPRi), and plasmid-based T7RNA polymerase (PDT7), to develop the noninvasive glucose biosensor by fluorescent signal. As a result, RiboJ increased dynamic range to 2989 au, but declined signal-to-noise (S/N) to 1.59, while CRISPRi-mediated NIMPLY gate intensified both dynamic range to 5720 au and S/N to 4.58. The use of single PDT7 orthogonal with T7 promoter in cells (i.e., P strain) achieved a 44 180 au of dynamic range with S/N at 3.08. By coupling the PDT7 and NIMPLY-mediated CRISPRi, we constructed an optimum PIGAS strain with the highest S/N value of 4.95. Finally, we adopted the synthetic bacteria into a microdevice to afford an integrative and portable system for daily urine glucose inspection, which would be an alternative approach for medical diagnosis in the future.