The diversity and composition of Antarctic cryptoendolithic microbial communities in the Marsanalogue site of Helliwell Hills (Northern Victoria Land, Continental Antarctica) are investigated, for the first time, applying both culture-dependent and highthroughput sequencing approaches. The study includes all the domains of the tree of life: Eukaryotes, Bacteria and Archaea to give a complete overview of biodiversity and community structure. Furthermore, to explore the geographic distribution of endoliths throughout the Victoria Land (Continental Antarctica), we compared the fungal and bacterial community composition and structure of endolithically colonized rocks, collected in >30 sites in 10 years of Italian Antarctic Expeditions. Compared with the fungi and other eukaryotes, the prokaryotic communities were richer in species, more diverse and highly heterogeneous. Despite the diverse community compositions, shared populations were found and were dominant in all sites. Local diversification was observed and included prokaryotes as members of Alphaproteobacteria and Crenarchaeota (Archaea), the last detected for the first time in these cryptoendolithic communities. Few eukaryotes, namely lichen-forming fungal species as Lecidella grenii, were detected in Helliwell Hills only. These findings suggest that geographic distance and isolation in these remote areas may promote the establishment of peculiar locally diversified microorganisms.

To date, the highly adapted cave microbial communities are challenged by the expanding anthropization of these subterranean habitats. Although recent advances in characterizing show-caves microbiome composition and functionality, the anthropic effect on promoting the establishment, or reducing the presence of specific microbial guilds has never been studied in detail. This work aims to investigate the whole microbiome (Fungi, Algae, Bacteria and Archaea) of four Italian show-caves, displaying different environmental and geo-morphological conditions and one recently discovered natural cave to highlight potential human-induced microbial traits alterations. Results indicate how show-caves share common microbial traits in contrast to the natural one; the first are characterized by microorganisms related to outdoor environment and/or capable of exploiting extra inputs of organic matter eventually supplied by tourist flows (i.e. Chaetomium and Phoma for fungi and Pseudomonas for bacteria). Yet, variation in microalgae assemblage composition was reported in show-caves, probably related to the effect of the artificial lighting. This study provides insights into the potential microbiome cave contamination by human-related bacteria (e.g. Lactobacillus and Staphylococcus) and commensal/opportunistic human associated fungi (e.g. Candida) and dermatophytes. This work is critical to untangle caves microbiome towards management and conservation of these fragile ecosystems.

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The metacommunity framework has been rarely adopted to investigate the underlying ecological mechanisms shaping microbial communities. With the aid of advanced molecular techniques, we investigated sediment communities of Fungi, Bacteria and Archaea in four Italian show caves aiming to disentangle the effects induced by tourists on species richness and composition from environmental filtering and dispersal driven mechanisms. We modelled community changes against human disturbance —measured as the distance from the tourist path—demonstrating that the presence of visitors in caves decreases fungal species richness and causes species replacement in Bacteria and Archaea. Environmental filtering affects species richness and composition of Fungi and species richness of Archaea, while a minor role was played by dispersal, influencing only species richness in Fungi. We provide new perspectives on the dynamics of microbial communities under human disturbance suggesting that a proper understanding of the underlying selective mechanisms requires a comprehensive and multi-taxonomic approach.

In the ice-free areas of Victoria Land in continental Antarctica, where the conditions reach the limits for life sustainability, highly adapted and extreme-tolerant microbial communities exploit the last habitable niches inside porous rocks (i.e. cryptoendolithic communities). These guilds host the main standing biomass and principal, if not sole, contributors to environmental/biogeochemical cycles, driving ecosystem processes and functionality in these otherwise dead lands. Although knowledge advances on their composition, ecology, genomic and metabolic features, a large-scale perspective of occurring interactions and interconnections within and between endolithic fungal assemblages is still lacking to date. Unravelling the tight relational network among functional guilds in the Antarctic cryptoendolithic communities may represent a main task. Aiming to fill this knowledge gap, we performed a correlation-network analysis based on amplicon-sequencing data of 74 endolithic microbiomes collected throughout Victoria Land. Endolithic communities' compositional pattern was largely dominated by Lichenized fungi group (83.5%), mainly represented by Lecanorales and Lecideales, followed by Saprotrophs (14.2%) and RIF+BY (2.4%) guilds led by Tremellales and Capnodiales respectively. Our findings highlighted that fungal functional guilds' relational spectrum was dominated by cooperative interactions led by lichenised and black fungi, deeply engaged in community trophic sustain and protection, respectively. On the other hand, a few negative correlations found may help in preserving niche boundaries between microbes living in such strict spatial association.