Mycobacterium abscessus Mutants with a Compromised Functional Link between the Type VII ESX-3 System and an Iron Uptake Mechanism Reliant on an Unusual Mycobactin Siderophore

Abstract

The opportunistic pathogen Mycobacterium abscessus subsp. abscessus (Mab) has become an emerging public health threat due to the increasing number of Mab-associated chronic pulmonary disease cases. Treatment requires multiple drug courses and is often combined with surgical resection. Cure rates are only ~50% due to treatment failure and comorbidities. Deeper understanding of the biology of Mab is required to illuminate potential avenues for the development of better therapeutics against Mab infections. The ESX-3 type VII protein secretion system of Mab has an important role in host inflammatory and pathological responses during infection. In this work, we demonstrate a functional link between ESX-3 and an iron uptake system based on an unusual mycobactin-type siderophore (designated MBT Ab) and exploit this link to implement a large screen for transposon mutants with an impaired ESX-3. Most mutants we identified carry insertions in genes encoding predicted ESX-3 secretion machinery components or potential ESX-3 substrates. The mutants overproduce MBT Ab, a trait consistent with an iron uptake defect. Our characterization of MBT Ab revealed structural features reminiscent of nocardial mycobactin-like compounds with cytotoxicity. This finding raises the possibility that MBT Ab may play roles in pathogenesis unlinked to iron homeostasis. The mutants generated herein will facilitate research to better understand the role of ESX-3 and its interplay with the siderophore system.

Comprehensive essentiality analysis of the Mycobacterium kansasii genome by saturation transposon mutagenesis and deep sequencing

“…Interestingly, 14 of the CUTA segments identified were located adjacent to the 5′-end of genes encoding members of the PE/PPE protein families ( Data set S5 ), a group of mycobacterial secreted proteins involved in a wide range of processes, including iron uptake, adaptation to stress, and virulence ( 95 - 97 ). The Mk chromosome is predicted to encode 72 PE and 141 PPE proteins ( 24 ).…”

Targeting Siderophore-Mediated Iron Uptake in M. abscessus: A New Strategy to Limit the Virulence of Non-Tuberculous Mycobacteria

“…In light of these considerations, there is a great interest in deciphering the mechanisms of siderophore assembly in Mab , with the goal of targeting selected steps for the development of new drugs. Despite these mechanisms being still poorly characterized in NTM, many research works have been focused on gathering new data, especially in the last years [ 44 , 45 , 46 ]. These preliminary studies seem to support the role of siderophores during Mab infection and suggest a conservation of the enzymes involved in their production.…”

Impaired ESX‐3 Induces Bedaquiline Persistence in Mycobacterium abscessus Growing Under Iron‐Limited Conditions

“…Two siderophores, exochelin and mycobactin, are required for iron uptake in fast‐growing mycobacteria. [ 19,20 ] Indeed, ESX‐3 iron acquisition is mediated by iron‐bound mycobactin; supplementation with a 100‐fold excess of mycobactin restored the growth of mutant ESX‐3 strains of M. tuberculosis . [ 5,9 ] As such, mycobactin and exochelin may contribute to the change in M. abscessus growth observed after 100 h incubation in a low iron environment; though, a detailed exploration of the mechanism(s) remains to be conducted.…”