In nature, living organisms produce a wide variety of specialized metabolites to perform many biological functions. Among these specialized metabolites, some carry halogen atoms on their structure, which can modify their chemical characteristics. Research into this type of molecule has focused on how organisms incorporate these atoms into specialized metabolites. Several families of enzymes have been described gathering metalloenzymes, flavoproteins, or S-adenosyl-L-methionine (SAM) enzymes that can incorporate these atoms into different types of chemical structures. However, even though the first halogenation enzyme was discovered in a fungus, this clade is still lagging behind other clades such as bacteria, where many enzymes have been discovered. This review will therefore focus on all halogenation enzymes that have been described in fungi and their associated metabolites by searching for proteins available in databases, but also by using all the available fungal genomes. In the second part of the review, the chemical diversity of halogenated molecules found in fungi will be discussed. This will allow the highlighting of halogenation mechanisms that are still unknown today, therefore, highlighting potentially new unknown halogenation enzymes.

A putative Type III Polyketide synthase (PKSIII) encoding gene was identified from a marine yeast, Naganishia uzbekistanensis strain Mo29 (UBOCC-A-208024) (formerly named as Cryptococcus sp.) isolated from deep-sea hydrothermal vents. This gene is part of a distinct phylogenetic branch compared to all known terrestrial fungal sequences. This new gene encodes a C-terminus extension of 74 amino acids compared to other known PKSIII proteins like Neurospora crassa. Full-length and reduced versions of this PKSIII were successfully cloned and overexpressed in a bacterial host, Escherichia coli BL21 (DE3). Both proteins showed the same activity, suggesting that additional amino acid residues at the C-terminus are probably not required for biochemical functions. We demonstrated by LC-ESI-MS/MS that these two recombinant PKSIII proteins could only produce tri- and tetraketide pyrones and alkylresorcinols using only long fatty acid chain from C8 to C16 acyl-CoAs as starter units, in presence of malonyl-CoA. In addition, we showed that some of these molecules exhibit cytotoxic activities against several cancer cell lines.

Terephthalic acid (TPA), one of the two monomeric building blocks of polyethylene terephthalate (PET), is a recalcitrant aromatic compound commonly present in industrial waste streams. Understanding its biodegradation pathways in fungi is essential for developing effective bioremediation strategies. In this study, we report for the first time the capacity of Rhizopusarrhizus to metabolise TPA and utilise TPA as a carbon source. A reverse isotope-labelling approach combined with gas chromatography-mass spectrometry was employed to trace the metabolic fate of TPA through central carbon metabolism. Our results demonstrate rapid and complete consumption of TPA by R. arrhizus PR1 within 24-48 h. TPA-derived carbon atoms were efficiently incorporated into the tricarboxylic acid (TCA) cycle and subsequently distributed into various biosynthetic pathways, including amino acid and lipid biosynthesis. Furthermore, exposure to TPA induced a metabolic shift from fermentation to a respiro-fermentative state, as evidenced by increased TCA cycle activity and upregulation of mitochondrial pyruvate transport systems. The concomitant production of industrially relevant organic acids, such as lactic acid and fumaric acid from TPA highlights this fungi's potential for innovative biotechnological applications aimed at plastic waste valorisation and the advancement of a circular bioeconomy.

Marine-derived fungi represent a valuable and under-investigated source of bioactive compounds. Growing in an environment characterized by specific conditions such as high salinity, these organisms produce distinctive chemical entities, including halogenated metabolites that hold great promise for drug discovery. Our previous metabolomics studies showed the presence of halogenated and potentially previously undescribed compounds in a seawater-derived fungal strain Penicillium canescens MMS194. A comprehensive chemical study conducted on this strain led to the isolation of 15 compounds belonging to three chemical families, indole diterpenoids (1-7), polyketides (8-9) and oxalicine-related meroterpenoids (10-15). Nine compounds (1, 2, 4-6, 8, 10, 12 and 13) were described for the first time, including two halogenated products (1 and 8), and their structures were determined based on NMR, HRMS, and TDDFT-ECD data. The isolates were evaluated for their cytotoxic, antimicrobial, and antiviral activities. The known chlorinated indole diterpenoid 3 (pennigritrem) showed the best cytotoxic and antimicrobial activities with IC₅₀ values ranging between 5.0 μM to 34.8 μM. This study suggests the potential of chlorinated fungal metabolites for therapeutic applications, and shows the value of the species P. canescens for the discovery of chemically diverse natural products, including halogenated compounds.