Abstract
Mycobacterium abscessus complex has been characterized in the last decade as part of a cluster of mycobacteria that evolved from an opportunistic to true human pathogen; however, the factors responsible for pathogenicity are still undefined. It appears that the success of mycobacterial infection is intrinsically related with the capacity of the bacteria to regulate intracellular iron levels, mostly using iron storage proteins. This study evaluated two potential M. abscessus subsp. massiliense genes involved in iron storage. Unlike other opportunist or pathogenic mycobacteria studied, M. abscessus complex has two genes similar to ferritins from M. tuberculosis (Rv3841), and in M. abscessus subsp. massiliense, those genes are annotated as mycma_0076 and mycma_0077. Molecular dynamic analysis of the predicted expressed proteins showed that they have a ferroxidase center. The expressions of mycma_0076 and mycma_0077 genes were modulated by the iron levels in both in vitro cultures as well as infected macrophages. Structural studies using size-exclusion chromatography, circular dichroism spectroscopy and dynamic light scattering showed that r0076 protein has a structure similar to those observed in the ferritin family. The r0076 forms oligomers in solution most likely composed of 24 subunits. Functional studies with recombinant proteins, obtained from heterologous expression of mycma_0076 and mycma_0077 genes in Escherichia coli, showed that both proteins were capable of oxidizing Fe2+ into Fe3+, demonstrating that these proteins have a functional ferroxidase center. In conclusion, two ferritins proteins were shown, for the first time, to be involved in iron storage in M. abscessus subsp. massiliense and their expressions were modulated by the iron levels.
Highlights
The Mycobacterium abscessus complex, composed of M. abscessus subsp. abscessus, M. abscessus subsp. massiliense, and M. abscessus subsp. bolletii has emerged as human pathogens in the last few years (Petrini, 2006; Medjahed et al, 2010; Lee et al, 2015; Tortoli et al, 2016)
The present study demonstrates for the first time that M. abscessus subsp. massiliense has two ferritin proteins involved in iron storage and related in the iron homeostasis both in vitro and in infected macrophages
To identify possible genes coding for bacterioferritin and ferritin in the M. abscessus subsp. massiliense genome, a Basic Local Alignment Search Tool (BLAST) using the genes bfrA (Rv1876) and bfrB (Rv3841) from M. tuberculosis H37Rv performed against M. abscessus genomes and M. abscessus subsp. massiliense did not present any gene with significant similarity to the Rv1876 gene (Supplementary Table S1)
Summary
The Mycobacterium abscessus complex, composed of M. abscessus subsp. abscessus, M. abscessus subsp. massiliense, and M. abscessus subsp. bolletii has emerged as human pathogens in the last few years (Petrini, 2006; Medjahed et al, 2010; Lee et al, 2015; Tortoli et al, 2016). Bolletii has emerged as human pathogens in the last few years (Petrini, 2006; Medjahed et al, 2010; Lee et al, 2015; Tortoli et al, 2016). Mycobacteria belonging to this complex cause several diseases in humans. These include severe lung, skin, post-traumatic, and post-surgical infections, especially in patients that have cystic fibrosis as well as in immunocompetent individuals (Medjahed et al, 2010). Infections in humans can occur by both direct and indirect transmission (Bryant et al, 2013; Lee et al, 2015; Bryant et al, 2016)
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