Deciphering the potential niche of novel black yeast fungal isolates in a biological soil crust based on genomes, phenotyping, and melanin regulation

Black yeasts are polyextremotolerant fungi that contain high amounts of melanin in their cell wall and maintain a primarily yeast form. These fungi grow in xeric, nutrient deplete environments which implies that they require highly flexible metabolisms and the ability to form lichen-like mutualisms with nearby algae and bacteria. However, the exact ecological niche and interactions between these fungi and their surrounding community is not well understood. We have isolated two novel black yeast fungi of the genus Exophiala: JF 03-3F “Goopy” E. viscosium and JF 03-4F “Slimy” E. limosus, which are from dryland biological soil crusts. A combination of whole genome sequencing and various phenotyping experiments have been performed on these isolates to determine their fundamental niches within the biological soil crust consortium. Our results reveal that these Exophiala spp. are capable of utilizing a wide variety of carbon and nitrogen sources potentially from symbiotic microbes, they can withstand many abiotic stresses, and can potentially provide UV resistance to the crust community in the form of secreted melanin. Besides the identification of two novel species within the genus Exophiala, our study also provides new insight into the production and regulation of melanin in extremotolerant fungi.

The response of desert biocrust bacterial communities to hydration-desiccation cycles

Rain events in arid environments are highly unpredictable, interspersing extended periods of drought. Therefore, tracking changes in desert soil bacterial communities during hydration-desiccation cycles in the field, was seldom attempted. Here, we assessed rain-mediated dynamics of active community in the Negev Desert biological soil crust (biocrust), and evaluated the changes in bacterial composition, potential function, photosynthetic activity, and extracellular polysaccharide (EPS) production. We predicted that increased biocrust moisture would resuscitate the phototrophs, while desiccation would inhibit their activity. Our results show that hydration increased chlorophyll content, resuscitated the biocrust Cyanobacteria, enhanced EPS production, and induced potential phototrophic functions. However, decrease in the soil water content did not immediately decrease the phototrophs activity, though chlorophyll levels decreased. Moreover, while the Cyanobacteria relative abundance significantly increased, Actinobacteria, the former dominant taxa, significantly decreased in abundance. We propose that, following a rain event, the response of the active bacterial community lagged the soil moisture content due to the production of EPS which delayed the desiccation of the biocrust community.

Novel lichen-dominated hypolithic communities in the Namib Desert

The ventral surfaces of translucent rocks from hot desert pavements often harbor hypolithic microbial communities, which are mostly dominated by cyanobacteria. The Namib Desert fog belt supports extensive hypolithic colonization of quartz rocks, which are also colonized by lichens on their dorsal surfaces. Here, we aim to evaluate whether lichens colonize the ventral surface of the rocks (i.e., show hypolithic lifestyle) and compare the bacterial composition of these coastal hypolithic communities with those found inland. Fungal DNA barcoding and fungal and bacterial Illumina metabarcoding were combined with electron microscopy to characterize the composition and spatial structure of hypolithic communities from two (coastal and inland) areas in the Namib Desert. We report, for the first time, the structure and composition of lichen-dominated hypolithic communities found in the coastal zone of the Namib Desert with extensive epilithic lichen cover. Lichen modified areoles with inverted morphology of the genus Stellarangia (three lineages) and Buellia (two lineages) were the main components of these hypolithic communities. Some of these lineages were also found in epilithic habitats. These lichen-dominated hypolithic communities differed in structural organization and bacterial community composition from those found in inland areas. The hypolithic lichen colonization characterized here seems not to be an extension of epilithic or biological soil crust lichen growths but the result of specific sublithic microenvironmental conditions. Moisture derived from fog and dew could be the main driver of this unique colonization.

Belnapia mucosa sp. nov. and Belnapia arida sp. nov., isolated from desert biocrust

Two novel Gram-staining-negative, aerobic, cocci-shaped, non-motile, non-spore forming, pink-pigmented bacteria designated strains T6T and T18T, were isolated from a biocrust (biological soil crust) sample from the vicinity of the Tabernas Desert (Spain). Both strains were catalase-positive and oxidase-negative, and grew under mesophilic, neutrophilic and non-halophilic conditions. According to the 16S rRNA gene sequences, strains T6T and T18T showed similarities with Belnapia rosea CGMCC 1.10758T and Belnapia moabensis CP2CT (98.11 and 98.55% gene sequence similarity, respectively). The DNA G+C content was 69.80 and 68.96% for strains T6T and T18T, respectively; the average nucleotide identity by blast (ANIb) and digital DNA–DNA hybridization (dDDH) values confirmed their adscription to two novel species within the genus Belnapia . The predominant fatty acids were summed feature 8 (C18 : 1ω7c/C18 : 1ω6c), C16 : 0, C18 : 1 2-OH and summed feature 3 (C16 : 1ω7c/C16 : 1ω6c). According to he results of the polyphasic study, strains T6T and T18T represent two novel species in the genus Belnapia (which currently includes only three species), for which names Belnapia mucosa sp. nov. (type strain T6T = CECT 30228T=DSM 112073T) and Belnapia arida sp. nov. (type strain T18T=CECT 30229T=DSM 112074T) are proposed, respectively.

Novel Lichen-Dominated Hypolithic Communities In the Namib Desert

The ventral surfaces of translucent pebbles from hot desert pavements often harbor hypolithic microbial communities, which are mostly dominated by cyanobacteria. The Namib Desert fog belt supports extensive hypolithic colonization of quartz pebbles but they are also colonized by lichens on their dorsal surfaces. Hence, our aim is to evaluate whether lichens colonize the ventral surface of the rocks (i.e., show hypolithic lifestyle) and compare the bacterial composition of these coastal hypolithic communities with those found inland. Fungal DNA barcoding and fungal and bacterial Illumina metabarcoding were combined with electron microscopy to characterize the composition and spatial structure of hypolithic communities from two (coastal and inland) areas in the Namib Desert. We report, for the first time, the structure and composition of lichen-dominated hypolithic communities found in the coastal zone of the Namib Desert with extensive epilithic lichen cover. Lichen modified areoles with inverted morphology of the genus Stellarangia (three lineages) and Buellia (two lineages) were the main components of these hypolithic communities. Some of these lineages were also found in epilithic habitats. These lichen-dominated hypolithic communities differed in structural organization and bacterial community composition from those found in inland areas. The hypolithic lichen colonization characterized here seems not to be an extension of epilithic or biological soil crust lichen growths, but the result of specific sublithic microenvironmental conditions. Moisture derived from fog and dew could be the main driver of this unique colonization.

The response of desert biocrust bacterial communities to hydration-desiccation cycles

Rain events in arid environments are highly unpredictable, interspersing extended periods of drought. Therefore, following changes in desert soil bacterial communities during hydration-desiccation cycles in the field, was seldom attempted. Here, we assessed rain-mediated dynamics of active community in the Negev Desert biological soil crust (biocrust), and evaluated the changes in bacterial composition, potential function, and photosynthetic activity. We predicted that increased biocrust moisture would resuscitate the phototrophs, while desiccation would inhibit their activity. Our results show that hydration increased chlorophyll content, resuscitated the biocrust Cyanobacteria, and induced potential phototrophic functions. However, decrease in the soil water content did not immediately decrease the phototrophs activity, though chlorophyll levels decreased. Moreover, while the Cyanobacteria relative abundance significantly increased, Actinobacteria, the former dominant taxa, significantly decreased in abundance. We propose that, following a rain event biocrust moisture significantly decreased, almost to drought levels, yet the response of the active bacterial community lagged, in contrast to topsoil. Possible explanations to the described rain-mediated bacteria dynamics are discussed.

Spider Community Variability and Response to Restoration in Arid Grasslands of the Pacific Northwest, USA

Grassland restoration in North America has intensified but its impact on major invertebrate groups, including spiders, is unclear. We studied three grassland locations in the Pacific Northwest, USA, to (1) describe variability in spider communities, (2) identify environmental variables that may underlie patterns in spider communities, and (3) determine whether spiders and environmental variables differ between actively (removal of disturbances, then plant with natives) vs. passively restored sites (removal of disturbance only). We found spider richness, diversity, and composition differed among the three locations but abundance did not. Sites with more litter and invasive grass cover had more spiders while sites at higher elevation and with more forb and biological soil crust cover had increased spider richness and diversity. Spider community composition was associated with elevation and litter cover. Surprisingly, no spider community or environmental variables differed between actively and passively restored sites, except that litter cover was higher in passively restored sites. This study demonstrates that even in superficially similar locations, invertebrate communities may differ greatly and these differences may prevent consistent responses to active vs. passive restoration. If increasing biodiversity or the abundance of invertebrate prey are goals, then environmental factors influencing spider communities should be taken into account in restoration planning.

On the effect of different moss species on soil erosion, percolation and carbon relocation

<p>For decades, soil erosion has been a major environmental problem as it degrades the most productive soil layers, which threatens, among other things, food production worldwide. Although these effects have been known for a long time, there are still a variety of challenges to mitigating soil erosion in different ecosystems. As climate change progresses, the risk of soil loss increases, making the preparation of effective solutions very urgent. A current research focus is on the restoration of a protective soil cover following disturbances in the vegetation layer, e.g., through the reestablishment of biological soil crust communities. These are often dominated by bryophytes in humid climates. So far, several studies examined the general protective influence of bryophytes against soil erosion, however only few of them addressed how individual species affect specific erosion processes in detail.</p><p>To fill this research gap we investigated the impact of six moss species on soil erosion, percolation and carbon relocation by means of rainfall simulations. Therefore, we used topsoil substrate from four sites in the Schönbuch Nature Park in South Germany which covers different kinds of bedrock and varying soil texture and pH. Subsequently, they were sieved by 6.3 mm and filled into metal infiltration boxes (40 x 30 cm) up to a height of 6.5 cm. The moss species differ in origin (either collected in the field or cultivated in the lab) as well as growth form (pleurocarpous or acrocarpous). Rainfall simulations were performed for bare soil substrates, as well as for moss-covered soil substrates six months later and both in dry and wet conditions. Additionally, we conducted rainfall simulations with leaf and coniferous litter on bare soil substrates. During the simulations we monitored soil moisture in two position - 3 cm depth plus soil surface - with biocrust wetness probes (BWP) and quantified surface runoff, percolation and sediment discharge. Afterwards we determined carbon contents of the sediment and dissolved organic carbon in the liquid phase of runoff and percolated water.</p><p>While surface runoff was increased by 5% due to the litter cover compared to the bare soil substrate, sediment discharge decreased to 97%. Runoff rates could also be mitigated by 90 % as a result of the moss cover. Furthermore, due to the dense moss cover sediment rates were almost reduced to zero. Preliminary results show that there are differences between the moss species in terms of sediment discharge, but not in context with runoff. The analyses of carbon contents in surface runoff and the percolated water are still in progress, as is the evaluation of the BWP measurements. These outcomes will be presented at vEGU21.</p>