Black Fungi and Hydrocarbons: An Environmental Survey for Alkylbenzene Assimilation

Abstract

Environmental pollution with alkylbenzene hydrocarbons such as toluene is a recurring phenomenon. Their toxicity and harmful effect on people and the environment drive the search for sustainable removal techniques such as bioremediation, which is based on the microbial metabolism of xenobiotic compounds. Melanized fungi present extremophilic characteristics, which allow their survival in inhospitable habitats such as those contaminated with hydrocarbons. Screening methodologies for testing the microbial assimilation of volatile organic compounds (VOC) are scarce despite their importance for the bioremediation of hydrocarbon associated areas. In this study, 200 strains of melanized fungi were isolated from four different hydrocarbon-related environments by using selective methods, and their biodiversity was assessed by molecular and ecological analyses. Seventeen genera and 27 species from three main orders, namely Chaetothyriales, Cladosporiales, and Pleosporales, were identified. The ecological analysis showed a particular species distribution according to their original substrate. The isolated strains were also screened for their toluene assimilation potential using a simple and inexpensive methodology based on miniaturized incubations under controlled atmospheres. The biomass produced by the 200 strains with toluene as the sole carbon source was compared against positive and negative controls, with glucose and with only mineral medium, respectively. Nineteen strains were selected as the most promising for further investigation on the biodegradation of alkylbenzenes.

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

“…In this study, E. xenobiotica was recorded in 73% (22/30) of the sampled cars, and so it is not a surprise if it has been reported recently (maybe by chance) as responsible for cutaneous infections in a car mechanics [88]. The profuse isolation of Exophiala dermatitidis (a species associated with deep mycoses in immunocompromised and healthy individuals) [89,90] in a car garage [32] highlights the potential risks for automotive engine and fuel manipulation. Further studies focused on the biodiversity of fungi that colonize devices subjected to both car fuel exposure and human manipulation are essential for a better understanding of pathogenicity and biohazard assessment, and also for their potential use as bioremediation agents.…”

“…The diversity of black fungi at higher taxonomic ranks is dominated by members of the Eurotiomycetes (class), Chaetothyriales (order), and Herpotrichielaceae (family), similar to other hydrocarbon-contaminated sites [32,61,62]. Concerning the species found (32), the majority were recorded in DCT (21), followed by GPD (14) and DPD (13).…”

“…The diversity of black fungi at higher taxonomic ranks is dominated by members of the Eurotiomycetes (class), Chaetothyriales (order), and Herpotrichielaceae (family), similar to other hydrocarbon-contaminated sites [32,61,62]. Concerning the species found (32), the majority were recorded in DCT (21), followed by GPD (14) and DPD (13). Half of the taxa found (50%, 16/32) could not be assigned to known species, resulting occasionally in low identity scores even when a more conserved target is used.…”

“…The first category includes wet oligotrophic environments subjected to extreme temperatures and biocidal products (e.g., detergents) such as dishwashers, kitchen sinks [11][12][13][14][15][16], moist surfaces and wet cells in bathrooms [17][18][19][20][21], laundry machines [22][23][24], hospital environments [25], and public bathing facilities [26,27]. The second consists of niches related to petroleum and coal products, including gasoline car tanks, creosote-treated wood (e.g., railway sleepers), surfaces containing machinery oil, dirt, and hydrocarbon-polluted soils [14,24,[28][29][30][31][32]. Due to their oligotrophic nature and low competitiveness under standard laboratory conditions, these fungi typically require specific isolation methods that control fast-growing microorganisms.…”

“…Due to their oligotrophic nature and low competitiveness under standard laboratory conditions, these fungi typically require specific isolation methods that control fast-growing microorganisms. Several protocols have been developed to isolate black fungi in relation to the type of sample and/or the desired fungal traits: (1) pre-incubation in acidic medium at high temperature to favor thermophilic species [33]; (2) extraction via mineral oil to select hydrophobic black fungal propagules [30,31]; and (3) enrichment on volatile aromatic hydrocarbons including toluene, styrene, or a mixture of phenolic compounds to isolate fungi with aromatic-degrading abilities [24,32,[34][35][36].…”