Checking fidelity in cell division: Everything has to go right during cell division, so a checkpoint mechanism known as the spindle-assembly checkpoint prevents mitosis from proceeding unless the kinetochores that attach chromosomes to the spindle microtubules are properly engaged. Two papers now reveal the detailed molecular choreography that allows a single, unattached kinetochore to arrest cell division: Lara-Gonzalez et al. used a visual probe that tracks a specific form of one of the checkpoint complex proteins, and Piano et al. used a biochemical reconstitution of the checkpoint. Together, these studies reveal how protein interaction, spatial constraints, phosphorylation, and catalytic conversion of the protein Mad2 to its active form allow this all-important sensor to function. Science , this issue p. 64 , p. 67

In the harshest environmental conditions of the Antarctic desert, normally incompatible with active life, microbes are adapted to exploit the cryptoendolithic habitat (i.e., pore spaces of rocks) and represent the predominant life-forms. In the rocky niche, microbes take advantage of the thermal buffering, physical stability, protection against UV radiation, excessive solar radiation, and water retention—of paramount importance in one of the driest environments on Earth. In this work, high-throughput sequencing and culture-dependent approaches have been combined, for the first time, to untangle the diversity and distribution of black fungi in the Antarctic cryptoendolithic microbial communities, hosting some of the most extreme-tolerant microorganisms. Rock samples were collected in a vast area, along an altitudinal gradient and opposite sun exposure—known to influence microbial diversity—with the aim to compare and integrate results gained with the two approaches. Among black fungi, Friedmanniomyces endolithicus was confirmed as the most abundant taxon. Despite the much stronger power of the high-throughput sequencing, several species were not retrieved with DNA sequencing and were detectable by cultivation only. We conclude that both culture-dependent and -independent analyses are needed for a complete overview of black fungi diversity. The reason why some species remain undetectable with molecular methods are speculated upon. The effect of environmental parameters such as sun exposure on relative abundance was clearer if based on the wider biodiversity detected with the molecular approach.

The French–Italian Concordia Research Station, situated on the Antarctic Polar Plateau at an elevation of 3233 m above sea level, offers a unique opportunity to study the presence and variation of microbes introduced by abiotic or biotic vectors and, consequently, appraise the amplitude of human impact in such a pristine environment. This research built upon a previous work, which explored microbial diversity in the surface snow surrounding the Concordia Research Station. While that study successfully characterized the bacterial assemblage, detecting fungal diversity was hampered by the low DNA content. To address this knowledge gap, in the present study, we optimized the sampling by increasing ice/snow collected to leverage the final DNA yield. The V4 variable region of the 16S rDNA and Internal Transcribed Spacer (ITS1) rDNA was used to evaluate bacterial and fungal diversity. From the sequencing, we obtained 3,352,661 and 4,433,595 reads clustered in 930 and 3182 amplicon sequence variants (ASVs) for fungi and bacteria, respectively. Amplicon sequencing revealed a predominance of Basidiomycota (49%) and Ascomycota (42%) in the fungal component; Bacteroidota (65.8%) is the main representative among the bacterial phyla. Basidiomycetes are almost exclusively represented by yeast-like fungi. Our findings provide the first comprehensive overview of both fungal and bacterial diversity in the Antarctic Polar Plateau’s surface snow/ice near Concordia Station and to identify seasonality as the main driver of microbial diversity; we also detected the most sensitive microorganisms to these factors, which could serve as indicators of human impact in this pristine environment and aid in planetary protection for future exploration missions.

The Antarctic continent hosts highly specialized microbial ecosystems, particularly within endolithic habitats, where microorganisms colonize the interior of rocks in order to withstand conditions that otherwise cannot support life. Previous studies have characterized the composition and abundance of these communities, as well as their different degrees of stress power; furthermore, the effect of different lithic substrates in shaping their associated bacterial assemblages has been extensively investigated. By contrast, how rock typology exerts fungal endolithic colonization still remains unexplored. In this study, we have considered and compared fungal communities inhabiting granite and sandstone rocks collected across Victoria Land, Antarctica, using high-throughput sequencing of the Internal Transcribed Spacer (ITS) region. Our analyses revealed that both rock types were dominated by Ascomycota, with a marked prevalence of lichen-forming fungi, particularly within the class Lecanoromycetes. However, granite-supported communities exhibited significantly higher species richness, likely driven by the structural heterogeneity of the substrate and the presence of fissures enabling chasmoendolithic colonization. In contrast, sandstone communities were more specialized and dominated by strict cryptoendolithic taxa capable of surviving within the rock’s pore spaces. Differential abundance analysis identified key species associated with each substrate, including the lichen Buellia frigida in granite and the black fungus Friedmanniomyces endolithicus in sandstone, two endemic species in Antarctica. Moreover, the use of presence/absence- versus abundance-based diversity metrics revealed contrasting ecological patterns; substrate type had a stronger influence on species presence, whereas geographic location more significantly shaped abundance profiles, highlighting the complex interplay between both factors in determining fungal community composition. Additionally, alpha diversity analyses showed significantly higher species richness in granite compared to sandstone, suggesting that structural heterogeneity and chasmoendolithism may promote a more diverse fungal assemblage.

In this study, we compared the bacterial diversity of two independent snow and ice sampling campaigns conducted in 2015–2016 and 2018–2019 at Dome C, Concordia Station, Antarctica. Using 16S rRNA gene amplicon sequencing, we analysed 81 samples and, after quality filtering and rarefaction, obtained approximately 3.8 million high-quality reads. Alpha diversity analyses revealed comparable richness between the two sampling periods, while community evenness was higher in 2018–2019. In contrast, all beta diversity metrics consistently showed significant differences in community composition between years, while beta dispersion analyses indicated distinct levels of heterogeneity within the year. The results of the Raup-Crick null model (R0) analyses showed that the observed differences did not deviate from random expectations under the applied null hypothesis. Overall, these results indicate pronounced interannual variability in bacterial assemblages at Concordia Station and suggest that temporal changes in community composition are consistent with assembly processes dominated by episodic inputs and limited persistence under extreme environmental conditions. This study implements previous investigations by providing a comparative temporal perspective and contributes to a better understanding of microbial dynamics in one of the most isolated and low-biomass environments on Earth.