# Decoupling growth phase dependency and metal ion inhibition: A dual engineering strategy for the high-yield biosynthesis of microcin J25 in Escherichia coli

## TL;DR

This paper presents a new method to boost the production of a promising antimicrobial compound, microcin J25, by engineering bacteria to overcome growth and metal ion limitations.

## Contribution

A dual genetic engineering strategy that decouples production from growth phase and metal ion inhibition, achieving a 10-fold increase in microcin J25 yield.

## Key findings

- Fe²⁺ in tap water inhibits MccJ25 biosynthesis by repressing mcjA transcription, which can be reversed with bipyridine chelation.
- Genetic modifications using constitutive and medium-strength promoters, along with RBS optimization, increased MccJ25 yield to 430 mg/L.
- Optimal translation initiation efficiency maximized production without impairing bacterial growth.

## Abstract

Microcin J25 (MccJ25) has received substantial attention as a potential solution to the global threat of infection caused by antibiotic-resistant bacteria. However, the industrial fermentation of MccJ25 faces production bottlenecks. It is imperative to further explore the production optimization strategies for MccJ25 to formulate comprehensive approaches for its industrial-scale production and other downstream applications. Here, Fe²⁺ in tap water was identified as a critical inhibitor of MccJ25 biosynthesis, selectively repressing mcjA transcription, which was reversible via 2,2′-bipyridine-mediated chelation. To decouple production from growth phase dependency and Fe²⁺ interference, we engineered Escherichia coli BL21 cells by performing two genetic modifications. First, we replaced the native mcjA promoter with a constitutive promoter (PQ) to allow its mid-log phase expression. Second, we replaced the native mcjBCD promoter with a medium-strength variant (P2223) that delayed production kinetics without affecting final yields. However, the genomic integration of mcjD alleviated plasmid-borne toxicity, increasing the expression timing and doubling the yield to 240 mg/L. Finally, we computationally optimized the mcjA ribosome-binding site (RBS) to enhance translation efficiency. RBS optimization revealed that a moderate translation initiation efficiency (550,584 arbitrary units [au]) maximized production, whereas excessive efficiency (2,019,712 au) impaired growth and output. These interventions synergistically increased the MccJ25 titer 10-fold, reaching 430 mg/L in batch culture. Our findings establish a robust platform for MccJ25 overproduction, highlighting promoter engineering and translational tuning as pivotal strategies for antimicrobial peptide biosynthesis. This study provides insights for overcoming metabolic constraints in microbial fermentation, advancing the development of peptide-based therapeutics against multidrug-resistant pathogens.

Image, graphical abstract