Cysteine desulfurase (IscS)–mediated fine-tuning of bioenergetics and SUF expression prevents Mycobacterium tuberculosis hypervirulence

Abstract

Iron-sulfur (Fe-S) biogenesis requires multiprotein assembly systems, SUF and ISC, in most prokaryotes. M. tuberculosis ( Mtb ) encodes a complete SUF system, the depletion of which was bactericidal. The ISC operon is truncated to a single gene iscS (cysteine desulfurase), whose function remains uncertain. Here, we show that Mtb Δ iscS is bioenergetically deficient and hypersensitive to oxidative stress, antibiotics, and hypoxia. Mtb Δ iscS 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 Mtb , Mtb Δ iscS could not enter a stable persistent state, continued replicating in mice, and showed hypervirulence. The suf operon was overexpressed in Mtb Δ iscS during infection in a NO-dependent manner. Suppressing suf expression in Mtb Δ iscS either by CRISPR interference or upon infection in inducible NO-deficient mice arrests hypervirulence. Together, Mtb redesigned the ISC system to “fine-tune” the expression of SUF machinery for establishing persistence without causing detrimental disease in the host.