⚡ Core Concept: Recombinant Microbial Systems & Metabolic Engineering
Microbial biotechnology harnesses engineered bacteria (e.g., Escherichia coli) and yeast (Saccharomyces cerevisiae) as living bio-factories. Expression vectors optimize promoter strength, ribosome binding site (RBS) spacing, codon usage, and metabolic flux to synthesize recombinant biopharmaceuticals and industrial chemicals.
1. High-Level Protein Expression Vectors
Recombinant expression vectors feature tightly regulated promoter systems such as the T7 RNA polymerase / pET system. Host strains (e.g., BL21(DE3)) harbor a chromosomal copy of T7 RNA polymerase under the control of the IPTG-inducible lacUV5 promoter. Addition of IPTG induces T7 polymerase expression, which selectively transcribes the target gene driven by the T7 promoter at extraordinary speed.
2. Metabolic Pathway Engineering
Metabolic engineering involves the rational rewiring of enzymatic cascades to maximize carbon flux toward target metabolites while minimizing by-product accumulation. Techniques include CRISPR-Cas9 genome editing for gene knockouts, synthetic ribosome binding sites (RBS calculators) to balance multi-enzyme stoichiometry, and directed evolution to enhance substrate specificity and catalytic efficiency ($k_{cat}/K_m$).