Sec and Tat secretion protect Mycobacterium tuberculosis membranes

Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis, relies on proteins sent out of the cell to grow, survive and cause disease. Despite many individual studies, researchers lacked a unified view of the secretion machinery and how it helps the bacterium maintain its outer membrane. Led by Vinay Kumar Nandicoori, the team collected and organized published evidence into a systems-level map of Mtb secretion. That map spans three major pathways — Sec, Tat, and ESX — and includes 92 components with 198 mechanistic reactions. To understand how this machinery is controlled, the researchers combined the map with high-throughput ChIP-Seq and transcriptome datasets to look at regulatory patterns. Building from this integrated picture, they used genetic tools to test which parts of the secretion system are absolutely needed for normal growth and membrane stability. The work was designed to move beyond single proteins and offer a broad framework linking secretion pathways to the physical integrity of the bacterial membrane.

The study blended careful literature curation with experimental genetics and multiple molecular readouts. The authors assembled the secretion network and overlaid regulatory information from ChIP-Seq and transcriptome data. They then used CRISPRi to conditionally deplete two core components, SecA1 or TatA, and found that reducing either protein impaired growth in vitro and survival ex vivo. A quantitative secretome analysis showed decreased export of substrates that depend on SecA1 and TatA, while culture filtrates became enriched for cytosolic proteins — a sign that membranes were leaking. Membrane proteomics detected a shift in membrane-associated proteins, with increased metabolic and lipid-degrading proteins and fewer proteins involved in cell-wall and cell processes, consistent with loss of membrane stability. Ultrastructural examinations revealed physical defects and increased ethidium bromide uptake confirmed the membranes were more permeable. Together these methods demonstrated that SecA1 and TatA act as key guardians of membrane integrity.

These findings place secretion at the center of membrane homeostasis in Mtb and give researchers a new, integrated perspective on how the bacterium preserves its envelope while secreting the proteins it needs. By showing that SecA1 and TatA are critical for preventing membrane leakage, the work suggests that disrupting secretion can have widespread effects on membrane composition and bacterial survival. The comprehensive map, combined with ChIP-Seq, transcriptome, secretome and membrane proteomics datasets, creates a resource for further research into secretion-dependent pathogenesis. For the field, this means more targeted studies can probe how secretion contributes to virulence and how it might be exploited to weaken the bacterium. Ultimately, the study offers a practical framework for future experiments aimed at understanding and interfering with the secretion systems that help Mtb thrive.