# Mycobacterium Transcriptional Factor BlaI Regulates Cell Division and Growth and Potentiates β-Lactam Antibiotic Efficacy Against Mycobacteria

## TL;DR

This study shows that overexpressing the BlaI protein in mycobacteria disrupts cell division, slows growth, and increases sensitivity to beta-lactam antibiotics.

## Contribution

The study reveals a novel regulatory role of BlaI in mycobacterial cell division and antibiotic susceptibility.

## Key findings

- BlaI overexpression causes cell elongation, multi-septa formation, and growth delay in Mycobacterium smegmatis.
- BlaI enhances beta-lactam antibiotic sensitivity by altering cell wall permeability and gene expression.
- BlaI downregulates ftsQ and Rv1303, impairing ATP synthesis and cell division processes.

## Abstract

Cell division is critical for the survival, growth, pathogenesis, and antibiotic susceptibility of Mycobacterium tuberculosis (Mtb). However, the regulatory networks governing the transcription of genes involved in cell growth and division in Mtb remain poorly understood. This study aimed to investigate the impact of BlaI overexpression on cell division and growth in Mtb and elucidate the underlying mechanisms. Mycobacterium smegmatis mc2155 was used as the model organism. Recombinant strains overexpressing BlaI were constructed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), ethidium bromide and Nile red uptake assays, minimum inhibitory concentration (MIC) determination, drug resistance analysis, quantitative real-time PCR (qRT-PCR) assays, and electrophoretic mobility shift assay (EMSA) were employed to assess changes in bacterial morphology, cell wall permeability, antibiotic susceptibility, gene transcription levels, and the interaction between BlaI and its target genes. Overexpression of BlaI disrupted bacterial division in M. smegmatis, leading to growth delay, cell elongation, and formation of multi-septa. It also altered the lipid permeability of the cell wall and enhanced the sensitivity of M. smegmatis to β-lactam antibiotics. BlaI overexpression affected the transcription of cell division-related genes, particularly downregulating ftsQ. Additionally, BlaI negatively regulated the transcription of Rv1303—a gene co-transcribed with ATP synthase-encoding genes—inhibiting ATP synthesis. This impaired the phosphorylation of division complex proteins, ultimately affecting cell division and cell wall synthesis. Overexpression of BlaI in Mtb interferes with bacterial division, slows growth, and alters gene expression. Our findings identify a novel role for BlaI in regulating mycobacterial cell division and β-lactam susceptibility, providing a foundation for future mechanistic studies in M. tuberculosis, with validation required to assess relevance to clinical tuberculosis—though validation in M. tuberculosis and preclinical models is required.