Secretion of the siderophore rhizoferrin is regulated by the cAMP-PKA pathway and is involved in the virulence of Mucor lusitanicus

Abstract

Mucormycosis is a fungal infection caused by Mucorales, with a high mortality rate. However, only a few virulence factors have been described in these organisms. This study showed that deletion of rfs, which encodes the enzyme for the biosynthesis of rhizoferrin, a siderophore, in Mucor lusitanicus, led to a lower virulence in diabetic mice and nematodes. Upregulation of rfs correlated with the increased toxicity of the cell-free supernatants of the culture broth (SS) obtained under growing conditions that favor oxidative metabolism, such as low glucose levels or the presence of H2O2 in the culture, suggesting that oxidative metabolism enhances virulence through rhizoferrin production. Meanwhile, growing M. lusitanicus in the presence of potassium cyanide, N-acetylcysteine, a higher concentration of glucose, or exogenous cAMP, or the deletion of the gene encoding the regulatory subunit of PKA (pkaR1), correlated with a decrease in the toxicity of SS, downregulation of rfs, and reduction in rhizoferrin production. These observations indicate the involvement of the cAMP-PKA pathway in the regulation of rhizoferrin production and virulence in M. lusitanicus. Moreover, rfs upregulation was observed upon macrophage interaction or during infection with spores in mice, suggesting a pivotal role of rfs in M. lusitanicus infection.

Mucorales and Mucormycosis: Recent Insights and Future Prospects

“…In the case of Mucorales and mucormycosis, several studies established an apparent increase in virulence when the host iron-hiding systems fail, and an abnormally high free iron level is observed in blood [ 12 ]. Moreover, Mucorales have developed their own systems to acquire iron from their hosts, highlighting the vital role of iron for these pathogens during infection [ 13 , 14 , 15 ].…”

“…Another system developed by pathogens to acquire iron from the host is based on small compounds with high-affinity iron-chelating activity known as siderophores. In the case of Mucorales , the most specific siderophore is rhizoferrin, but this is also the least studied in mucormycosis [ 13 , 14 , 31 ]. Fungi synthesize their own siderophores but can also use the siderophores produced by other microorganisms [ 32 ].…”

Advances in understanding infections caused by the basal fungus Mucor

“…The deletion of this gene in M . lusitanicus leads to lower mortality in mice, while its overexpression increases virulence, suggesting a role of rhizoferrin in mucormycosis [ 36 ]. Interestingly, the expression of rfs is induced by the oxidative metabolism, which is also associated with the filamentous growth and virulence of Mucor [ 36 ].…”

Alternative in-vivo models of mucormycosis

“…Therefore, this review will focus on alternative model systems that have been exploited so far for mucormycosis studies, highlighting novel alternative model animals or adapted methods established in the last three to four years to avoid repetition of what has already been reviewed in detail by Jacobsen (2019) . The alternative animal models presented in the review have significantly contributed to fostering our understanding of previously undescribed virulence factors of Mucorales, some of which are unique to this group of fungi ( Patiño-Medina et al., 2018 ; Patiño-Medina et al., 2019a ; Wurster et al., 2020 ; Alejandre-Castañeda et al., 2022 ; Itabangi et al., 2022 ; Trieu et al., 2022 ; Szebenyi et al., 2023 ). Moreover, these models have unveiled pathogen recognition and immune evasion strategies of Mucoralean fungi that are relevant for interactions with the human host ( Chamilos et al., 2008a ; Hoffmann et al., 2013 ; Inglesfield et al., 2018 ; López-Muñoz et al., 2018 ; Hassan et al., 2021 ; Itabangi et al., 2022 ).…”