Haloalkalitolerant Fungi from Sediments of the Big Tambukan Saline Lake (Northern Caucasus): Diversity and Antimicrobial Potential

We have performed a characterization of cultivated haloalkalitolerant fungi from the sediments of Big Tambukan Lake in order to assess their biodiversity and antimicrobial activity. This saline, slightly alkaline lake is known as a source of therapeutic sulfide mud used in sanatoria of the Caucasian Mineral Waters, Russia. Though data on bacteria and algae observed in this lake are available in the literature, data on fungi adapted to the conditions of the lake are lacking. The diversity of haloalkalitolerant fungi was low and represented by ascomycetes of the genera Acremonium, Alternaria, Aspergillus, Chordomyces, Emericellopsis, Fusarium, Gibellulopsis, Myriodontium, Penicillium, and Pseudeurotium. Most of the fungi were characterized by moderate alkaline resistance, and they tolerated NaCl concentrations up to 10% w/v. The analysis of the antimicrobial activity of fungi showed that 87.5% of all strains were active against Bacillus subtilis, and 39.6% were also determined to be effective against Escherichia coli. The majority of the strains were also active against Aspergillus niger and Candida albicans, about 66.7% and 62.5%, respectively. These studies indicate, for the first time, the presence of polyextremotolerant fungi in the sediments of Big Tambukan Lake, which probably reflects their involvement in the formation of therapeutic muds.

Alkaliphilic/Alkali-Tolerant Fungi: Molecular, Biochemical, and Biotechnological Aspects

Biotechnologist interest in extremophile microorganisms has increased in recent years. Alkaliphilic and alkali-tolerant fungi that resist alkaline pH are among these. Alkaline environments, both terrestrial and aquatic, can be created by nature or by human activities. Aspergillus nidulans and Saccharomyces cerevisiae are the two eukaryotic organisms whose pH-dependent gene regulation has received the most study. In both biological models, the PacC transcription factor activates the Pal/Rim pathway through two successive proteolytic mechanisms. PacC is a repressor of acid-expressed genes and an activator of alkaline-expressed genes when it is in an active state. It appears, however, that these are not the only mechanisms associated with pH adaptations in alkali-tolerant fungi. These fungi produce enzymes that are resistant to harsh conditions, i.e., alkaline pH, and can be used in technological processes, such as in the textile, paper, detergent, food, pharmaceutical, and leather tanning industries, as well as in bioremediation of pollutants. Consequently, it is essential to understand how these fungi maintain intracellular homeostasis and the signaling pathways that activate the physiological mechanisms of alkali resistance in fungi.

Isolation and Characterization of a Novel Hydrophobin, Sa-HFB1, with Antifungal Activity from an Alkaliphilic Fungus, Sodiomyces alkalinus

The adaptations that alkaliphilic microorganisms have developed due to their extreme habitats promote the production of active natural compounds with the potential to control microorganisms, causing infections associated with healthcare. The primary purpose of this study was to isolate and identify a hydrophobin, Sa-HFB1, from an alkaliphilic fungus, Sodiomyces alkalinus. A potential antifungal effect against pathogenic and opportunistic fungi strains was determined. The MICs of Sa-HFB1 against opportunistic and clinical fungi ranged from 1 to 8 µg/mL and confirmed its higher activity against both non- and clinical isolates. The highest level of antifungal activity (MIC 1 µg/mL) was demonstrated for the clinical isolate Cryptococcus neoformans 297 m. The hydrophobin Sa-HFB1 may be partly responsible for the reported antifungal activity of S. alkalinus, and may serve as a potential source of lead compounds, meaning that it can be developed as an antifungal drug candidate.

Amplicon-Based Analysis of the Fungal Diversity across Four Kenyan Soda Lakes

Microorganisms have been able to colonize and thrive in extreme environments characterized by low/high pH, temperature, salt, or pressure. Examples of extreme environments are soda lakes and soda deserts. The objective of this study was to explore the fungal diversity across soda lakes Magadi, Elmenteita, Sonachi, and Bogoria in Kenya. A new set of PCR primers was designed to amplify a fragment long enough for the 454-pyrosequencing technology. Analysis of the amplicons generated showed that the new primers amplified for diverse fungal groups. A total of 153,634 quality-filtered, nonchimeric sequences derived from the 18S region of the rRNA region were used for community diversity analysis. The sequence reads were clustered into 502 OTUs at 97% similarity cut-off using BLASTn analysis of which 432 were affiliated to known fungal phylotypes and the rest to other eukaryotes. Fungal OTUs were distributed across 107 genera affiliated to the phyla Ascomycota, Basidiomycota, Glomeromycota, and and other unclassified groups refred to as Incertae sedis. The phylum Ascomycota was the most abundant in terms of OTUs. Overall, fifteen genera (Chaetomium, Monodictys, Arthrinium, Cladosporium, Fusarium, Myrothecium, Phyllosticta, Coniochaeta, Diatrype, Sarocladium, Sclerotinia, Aspergillus, Preussia, and Eutypa) accounted for 65.3% of all the reads. The genus Cladosporium was detected across all the samples at varying percentages with the highest being water from Lake Bogoria (51.4%). Good's coverage estimator values ranged between 97 and 100%, an indication that the dominant phylotypes were represented in the data. These results provide useful insights that can guide cultivation-dependent studies to understand the physiology and biochemistry of the as-yet uncultured taxa.

Fungal Endophytic Community and Diversity Associated with Desert Shrubs Driven by Plant Identity and Organ Differentiation in Extremely Arid Desert Ecosystem

Despite desert ecosystem being crucial to our understanding of natural geography, species evolution and global climate change, there is limited information on the dynamics of their composition and the diversity of endophytic fungi communities driven by plant identity and organ differentiation. Here, an extensive investigation of endophytic fungal microbiome in root, stem, and leaf organs associated with five xerophyte shrubs in an extremely arid desert, Northwest China, were examined. The fungal community dominated by Dothideomycetes and Pleosporales. Shrub species strongly drive the niche-based processes of endophytic fungi across the root, stem and leaf compartments. The diversity and composition of endophytic fungi in stem showed higher variability among plant species than leaf and root. The fungal communities in root libraries were more diverse and exhibited a remarkable differentiation of community composition. We further demonstrated the significant host preferences and tissue specificity of desert endophytic fungi, and unique specific taxa were also observed. The co-occurrence network revealed the coexistence of fungal endophytes in arid desert, and the root fungal network harbored the highest interspecies connectivity. Members of Pleosporales were the most common keystone species in the root fungal network. This is the first report of mycobiota in both plant species and organ differentiation in an extremely arid desert ecosystem.