A Comparison of Isolation Methods for Black Fungi Degrading Aromatic Toxins

The origin of human pathogenicity and biological interactions in Chaetothyriales

Fungi in the order Chaetothyriales are renowned for their ability to cause human infections. Nevertheless, they are not regarded as primary pathogens, but rather as opportunists with a natural habitat in the environment. Extremotolerance is a major trend in the order, but quite different from black yeasts in Capnodiales which focus on endurance, an important additional parameter is advancing toxin management. In the ancestral ecology of rock colonization, the association with metabolite-producing lichens is significant. Ant-association, dealing with pheromones and repellents, is another mainstay in the order. The phylogenetically derived family, Herpotrichiellaceae, shows dual ecology in monoaromatic hydrocarbon assimilation and the ability to cause disease in humans and cold-blooded vertebrates. In this study, data on ecology, phylogeny, and genomics were collected and analyzed in order to support this hypothesis on the evolutionary route of the species of Chaetothyriales. Comparing the ribosomal tree with that of enzymes involved in toluene degradation, a significant expansion of cytochromes is observed and the toluene catabolism is found to be complete in some of the Herpotrichiellaceae. This might enhance human systemic infection. However, since most species have to be traumatically inoculated in order to cause disease, their invasive potential is categorized as opportunism. Only in chromoblastomycosis, true pathogenicity might be surmised. The criterion would be the possible escape of agents of vertebrate disease from the host, enabling dispersal of adapted genotypes to subsequent generations.

Black Fungi on Stone-Built Heritage: Current Knowledge and Future Outlook

Black fungi are considered as one of the main group of microorganisms responsible for the biodeterioration of stone cultural heritage artifacts. In this paper, we provide a critical analysis and review of more than 30 years of studies on black fungi isolated from stone-built heritage from 1990 to date. More than 109 papers concerning the fungal biodeterioration activity of stone were analysed. The main findings were a check list of the black fungal taxa involved in the biodeterioration of stone-built heritage, with a particular reference to meristematic black fungi, the main biodeterioration pattern attributed to them, and the methods of study including the new molecular advances. A particular focus was to discuss the current approaches to control black fungi from stone-built heritage and future perspectives. Black fungi are notoriously hard to remove or mitigate, so new methods of study and of control are needed, but it is also important to combine classical methods with new approaches to improve current knowledge to implement future conservation strategies.

Black Fungi and Stone Heritage Conservation: Ecological and Metabolic Assays for Evaluating Colonization Potential and Responses to Traditional Biocides

Identifying species involved in biodeterioration processes is helpful, however further effort is needed to assess their ecological requirements and actual activity. Black fungi (BF) represent one of the most underestimated threats to stone cultural heritage in the Mediterranean basin; they are difficult to kill or remove due to their ability to grow inside the rock and cope with several stresses. Despite this, little is known about BF and factors favoring their growth on stone surfaces. Eighteen BF species were here investigated for temperature and salt tolerance, and metabolic traits by plate assays. The relation between some highly damaged monuments and their BF settlers was assessed using X-ray diffraction analysis, mercury intrusion porosimetry, and SEM. The sensitiveness to four commonly used traditional biocides was also tested. All strains were able to grow within the range of 5–25 °C and in the presence of 3.5% NaCl. Instrumental analyses were fundamental in discovering the relation between halophilic strains and weathered marble sculptures. The acid, cellulase, esterase, and protease production recorded proved BF’s potential to produce a chemical action on carbonate stones and likely affect other materials/historical artefacts. Besides, the use of carboxymethylcellulose and Tween 20 should be evaluated in restoration practice to prevent tertiary bioreceptivity. Agar diffusion tests helped identify the most resistant species to biocides, opening the perspective of its use as reference organisms in material testing procedures.

Volatile Organic Compounds in the Azteca/Cecropia Ant-Plant Symbiosis and the Role of Black Fungi

Black fungi of the order Chaetothyriales are grown by many tropical plant-mutualistic ants as small so-called “patches” in their nests, which are located inside hollow structures provided by the host plant (“domatia”). These fungi are introduced and fostered by the ants, indicating that they are important for the colony. As several species of Chaetothyriales tolerate, adsorb, and metabolize toxic volatiles, we investigated the composition of volatile organic compounds (VOCs) of selected domatia in the Azteca/Cecropia ant-plant mutualism. Concentrations of VOCs in ant-inhabited domatia, empty domatia, and background air were compared. In total, 211 compounds belonging to 19 chemical families were identified. Ant-inhabited domatia were dominated by ketones with 2-heptanone, a well-known ant alarm semiochemical, as the most abundant volatile. Empty domatia were characterized by relatively high concentrations of the monoterpenes d-limonene, p-cymene and β-phellandrene, as well as the heterocyclic sulphur-containing compound, benzothiazole. These compounds have biocidal properties and are primarily biosynthesized by plants as a defense mechanism. Interestingly, most of the latter compounds were present at lower concentrations in ant inhabited domatia than in non-colonized ones. We suggest that Chaetothyriales may play a role in reducing the VOCs, underlining that the mutualistic nature of these fungi as VOCs accumulation might be detrimental for the ants, especially the larvae.

Hydrocarbon-Contaminated Sites: Is There Something More Than Exophiala xenobiotica? New Insights into Black Fungal Diversity Using the Long Cold Incubation Method

Human-made hydrocarbon-rich environments are important reservoirs of microorganisms with specific degrading abilities and pathogenic potential. In particular, black fungi are of great interest, but their presence in the environment is frequently underestimated because they are difficult to isolate. In the frame of a biodiversity study from fuel-contaminated sites involving 30 diesel car tanks and 112 fuel pump dispensers (52 diesel and 60 gasoline, respectively), a total of 181 black fungal strains were isolated. The long cold incubation (LCI) of water-suspended samples, followed by plating on Dichloran Rose Bengal Chloramphenicol Agar (DRBC), gave isolation yields up to six times (6.6) higher than those of direct plating on DRBC, and those of enrichment with a phenolic mix. The sequencing of ITS and LSU-rDNA confirmed the dominance of potentially pathogenic fungi from the family Herpotrichiellaceae and Exophiala xenobiotica. Moreover, other opportunistic species were found, including E. opportunistica, E. oligosperma, E. phaeomuriformis, and Rhinocladiella similis. The recurrent presence of E. crusticola, Knufia epidermidis, Aureobasidium melanogenum, Cladosporium spp., and Scolecobasidium spp. was also recorded. Interestingly, 12% of total isolates, corresponding to 50% of taxa found (16/32), represent new species. All the novel taxa in this study were isolated by LCI. These findings suggest that black fungal diversity in hydrocarbon-rich niches remains largely unexplored and that LCI can be an efficient tool for further investigations.

Fungal Melanins and Applications in Healthcare, Bioremediation and Industry

Melanin is a complex multifunctional pigment found in all kingdoms of life, including fungi. The complex chemical structure of fungal melanins, yet to be fully elucidated, lends them multiple unique functions ranging from radioprotection and antioxidant activity to heavy metal chelation and organic compound absorption. Given their many biological functions, fungal melanins present many possibilities as natural compounds that could be exploited for human use. This review summarizes the current discourse and attempts to apply fungal melanin to enhance human health, remove pollutants from ecosystems, and streamline industrial processes. While the potential applications of fungal melanins are often discussed in the scientific community, they are successfully executed less often. Some of the challenges in the applications of fungal melanin to technology include the knowledge gap about their detailed structure, difficulties in isolating melanotic fungi, challenges in extracting melanin from isolated species, and the pathogenicity concerns that accompany working with live melanotic fungi. With proper acknowledgment of these challenges, fungal melanin holds great potential for societal benefit in the coming years.

Dark-pigmented biodeteriogenic fungi in etruscan hypogeal tombs: New data on their culture-dependent diversity, favouring conditions, and resistance to biocidal treatments

Subterranean Cultural Heritage sites are frequently subject to biological colonization due to the high levels of humidity, even in conditions of low irradiance and oligotrophy. Here microorganisms form complex communities that may be dangerous through mineral precipitation, through the softening of materials or causing frequent surface discolorations. A reduction of contamination's sources along with the control of microclimatic conditions and biocide treatments (overall performed with benzalkonium chloride) are necessary to reduce microbial growths. Dark discolorations have been recorded in the painted Etruscan tombs of Tarquinia, two of which have been analyzed to collect taxonomical, physiological, and ecological information. Eighteen dark-pigmented fungi were isolated among a wider culturable fraction: nine from blackening areas and nine from door sealings, a possible route of contamination. Isolates belonged to three major groups: Chaetothyriales, Capnodiales (Family Cladosporiaceae), and Acremonium-like fungi. Exophiala angulospora and Cyphellophora olivacea, a novelty for hypogea, were identified, while others need further investigations as possible new taxa. The metabolic skills of the detected species showed their potential dangerousness for the materials. Their tolerance to benzalkonium chloride-based products suggested a certain favouring effect through the decreasing competitiveness of less resistant species. The type of covering of the dromos may influence the risk of outer contamination. Fungal occurrence can be favoured by root penetration.

Attempted Isolation of Cryptococcus Species and Incidental Isolation of Exophiala dermatitidis from Human Oral Cavities

Recent molecular studies suggest that Cryptococcus may inhabit the normal human mouth. We attempted to isolate Cryptococcus from 21 adult non-acutely ill patients and 40 volunteer medical and non-medical staff in Southeastern Wisconsin, USA. An upper lip sulcus culture and an oral rinse specimen were inoculated separately onto Staib (birdseed) agar containing chloramphenicol and incubated in gas impermeable zip lock bags at 35 °C. No cryptococci were grown from any of the 122 samples from the 61 subjects. Both specimens from a woman with no risk factors for fungal disease yielded a black yeast at 4 days on Staib agar. This isolate was shown to be Exophiala dermatitidis by colony and microscopic morphology, analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and sequencing through the internal transcribed spacer ribosomal RNA gene. This appears to be a novel isolation of E. dermatitidis from the oral cavity of a generally healthy human.

Fungal melanins that deteriorate paper cultural heritage: An overview

Paper-based works of art and documents of cultural importance kept in museums and libraries can show notorious signs of deterioration, including foxing stains, caused by fungal colonization. Some of the main chromophore agents of fungal origin that deteriorate paper and therefore affect paper cultural heritage both aesthetically and structurally are the group of pigments called melanins. Thus, knowledge of the diversity and features of fungal melanins and of the melanization pathways of fungi growing on paper is key to removing these pigments from paper-based works of cultural importance. This review provides an approach about the current knowledge of melanins synthesized by paper-colonizing fungi, their localization in the fungal structures, and their role in the deterioration of paper. This knowledge might contribute to developing new, effective, and sustainable strategies of restoration and conservation of historical documents and works of art based on paper.

A re-evaluation of the Chaetothyriales using criteria of comparative biology

Chaetothyriales is an ascomycetous order within Eurotiomycetes. The order is particularly known through the black yeasts and filamentous relatives that cause opportunistic infections in humans. All species in the order are consistently melanized. Ecology and habitats of species are highly diverse, and often rather extreme in terms of exposition and toxicity. Families are defined on the basis of evolutionary history, which is reconstructed by time of divergence and concepts of comparative biology using stochastical character mapping and a multi-rate Brownian motion model to reconstruct ecological ancestral character states. Ancestry is hypothesized to be with a rock-inhabiting life style. Ecological disparity increased significantly in late Jurassic, probably due to expansion of cytochromes followed by colonization of vacant ecospaces. Dramatic diversification took place subsequently, but at a low level of innovation resulting in strong niche conservatism for extant taxa. Families are ecologically different in degrees of specialization. One of the clades has adapted ant domatia, which are rich in hydrocarbons. In derived families, similar processes have enabled survival in domesticated environments rich in creosote and toxic hydrocarbons, and this ability might also explain the pronounced infectious ability of vertebrate hosts observed in these families. Conventional systems of morphological classification poorly correspond with recent phylogenetic data. Species are hypothesized to have low competitive ability against neighboring microbes, which interferes with their laboratory isolation on routine media. The dataset is unbalanced in that a large part of the extant biodiversity has not been analyzed by molecular methods, novel taxonomic entities being introduced at a regular pace. Our study comprises all available species sequenced to date for LSU and ITS, and a nomenclatural overview is provided. A limited number of species could not be assigned to any extant family.