Cysteine desulfurase (IscS)-mediated fine-tuning of bioenergetics and SUF expression prevents <i>Mycobacterium tuberculosis</i> hypervirulence.

Abstract

Iron-sulfur (Fe-S) biogenesis requires multiprotein assembly systems, SUF and ISC, in most prokaryotes. <i>M. tuberculosis</i> (<i>Mtb</i>) encodes a complete SUF system, the depletion of which was bactericidal. The ISC operon is truncated to a single gene <i>iscS</i> (cysteine desulfurase), whose function remains uncertain. Here, we show that <i>Mtb</i>Δ<i>iscS</i> is bioenergetically deficient and hypersensitive to oxidative stress, antibiotics, and hypoxia. <i>Mtb</i>Δ<i>iscS</i> resisted killing by nitric oxide (NO). RNA sequencing indicates that IscS is important for expressing regulons of DosR and Fe-S-containing transcription factors, WhiB3 and SufR. Unlike wild-type <i>Mtb</i>, <i>Mtb</i>Δ<i>iscS</i> could not enter a stable persistent state, continued replicating in mice, and showed hypervirulence. The <i>suf</i> operon was overexpressed in <i>Mtb</i>Δ<i>iscS</i> during infection in a NO-dependent manner. Suppressing <i>suf</i> expression in <i>Mtb</i>Δ<i>iscS</i> either by CRISPR interference or upon infection in inducible NO-deficient mice arrests hypervirulence. Together, <i>Mtb</i> redesigned the ISC system to "fine-tune" the expression of SUF machinery for establishing persistence without causing detrimental disease in the host.