# Identification of Mycobacterium tuberculosis intracellular survival-related virulence factors via CRISPR-based eukaryotic-like secretory protein mutant library screen

## TL;DR

This study identifies two proteins in tuberculosis bacteria that help it survive inside immune cells, offering new targets for drug development.

## Contribution

A CRISPR-based screen identified two novel M.tb effectors involved in intracellular survival.

## Key findings

- Rv0066c and Rv3139 are critical for M.tb intracellular survival, as their knockout strains showed reduced viability in macrophages.
- RNA-seq analysis revealed 138 differentially expressed genes in ΔRv0066c-infected macrophages, enriched in chemokine and signaling pathways.
- The study established a mutant library of eukaryotic-like secretory proteins for future functional studies.

## Abstract

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), remains a serious infectious disease posing significant global health challenges. A critical evolutionary feature of M.tb is its genome encoding a set of eukaryotic-like secretory proteins, which facilitate intracellular survival by manipulating host immune responses. However, the specific eukaryotic-like secretory proteins that facilitate M.tb intracellular survival and their regulatory mechanisms on host immunity remain uncharacterized. In this study, a mutant library comprising 137 potential eukaryotic-like secretory proteins was constructed using clustered regularly interspaced short palindromic repeats (CRISPR)-non-homologous end joining genome editing technology. Subsequently, macrophages were infected with the mutant library, and CRISPR sequencing enabled preliminary identification of virulence factors associated with bacterial intracellular persistence. To validate the screen, two genes (Rv0066c and Rv3139) exhibiting the most pronounced reduction in intracellular survival rates when mutated were selected for the construction of large-fragment knockout strains (ΔRv0066c and ΔRv3139). Subsequent macrophage infection assays reconfirmed the impaired intracellular survival of these two mutants. RNA-seq analysis was conducted to characterize host gene expression profiles during ΔRv0066c-infected macrophage interactions. RNA-seq analysis of macrophages infected with wild-type and ΔRv0066c strains identified 138 differentially expressed genes, with 75 upregulated and 63 downregulated in ΔRv0066c. Gene ontology clustering of these differentially expressed genes highlighted molecular functions related to chemokine binding, chemokine-mediated signaling pathways, Ras protein signal transduction, and calcineurin-mediated signaling. Collectively, this work established a potential eukaryotic-like secretory protein mutant library and identified two novel M.tb effectors governing intracellular survival, providing potential new targets for anti-TB drug development.

Eukaryotic-like secretory proteins that subvert host immunity to enable intracellular persistence are a key evolutionary adaptation of Mycobacterium tuberculosis (M.tb). In this study, we established a mutant library targeting 137 potential eukaryotic-like secretory proteins through clustered regularly interspaced short palindromic repeats (CRISPR)-non-homologous end joining genome editing technology. The library was subjected to macrophage infection assays, and CRISPR sequencing enabled identification of M.tb persistence-associated virulence determinants. Validation screens highlighted two genes (Rv0066c and Rv3139) that displayed the most significant intracellular survival defects to generate large-fragment knockout strains (ΔRv0066c and ΔRv3139). Macrophage infection experiments reconfirmed the compromised intracellular viability of both mutants. RNA-seq profiling of ΔRv0066c-infected macrophages identified 138 differentially expressed genes, with functional enrichment in chemokine signaling, Ras protein signal transduction, and calcineurin-mediated signaling. To conclude, this study identified two novel M.tb effectors contributing to intracellular survival as potential new targets for anti-TB drug development.