Experimental mito-nuclear introgression lines (MNILs) were established by backcrossing isofemale lines of D. subobscura originating from the same populations. MNILs were subjected to a series of life-history experiments designed to test the fitness of the bearers of different combinations of two main mtDNA haplotypes on their own nuclear background, as well as on the background of the opposite haplotype. By having 11 replicas of the four mito-nuclear combinations, we could test not only the adaptive significance of the differences between the two main haplotypes but also the influence of additional variation present within each of the 11 combinations on fitness. Testing the fitness of individuals of both sexes enabled us to examine if sex-specific selection has a role in maintaining the frequencies of the two mtDNA haplotypes in nature. Conducting the fitness assays on two different temperatures enabled us to test whether different temperatures favor specific mtDNA haplotypes or mito-nuclear genotypes and consequently promote stable sympatric mtDNA variation. The results show weak signature of genotype-by-environment interactions, and no sex-specific selection regarding differences between the two main haplotypes. However, individual models across different life-history components showed these two mechanisms at play in promoting mtDNA variability present in specific mito-nuclear crosses. Our models show that mito-nuclear interactions are, in fact, more important as units of selection.

This work builds upon our previous “repopulation upon shattering” (RUS) studies in the yeast-like microbe Ustilago maydis, focusing mainly on a deeper understanding of the suicidal type of death caused by self-generated hypoxia (SGH). The key findings are: (1) the massive loss of viability induced by SGH occurs via programmed cell death (PCD), (2) the PCD-released materials are more beneficial for the surviving cells than the nutrients liberated from cells that die through necrotic processes, (3) products of PCD can stimulate growth even in the presence of growth-suppressive necromass, (4) the beneficial effects of substances released through PCD extend to two other species within the family Ustilaginaceae, and (5) U. maydis exhibited a remarkable ability to withstand the negative effects of non-PCD necromass. The third and fifth points are of special note. The third indicates that PCD-derived materials are essential for critical initial regrowth in post-stress environments where there is a high presence of non-PCD necromass. As the revitalized population strengthens, it would correspondingly enhance the communal ability to exploit more challenging nutrients. The robust resilience of U. maydis survivors against non-PCD necromass could represent an important fitness determinant, mediating competitive success in mixed microbial communities where non-PCD necromass imposes selective pressure. Thus, while providing valuable insights, the study also underscores the need for further research, especially in understanding the molecular underpinnings of the RUS phenomenon.

The atmosphere is a dynamic reservoir for microorganisms and antimicrobial resistance genes (ARGs), yet the seasonal interplay of microbial communities, resistance and virulence determinants with environmental conditions remains poorly characterized, particularly in polluted urban areas. This study presents year-round (summer 2024-spring 2025) shotgun metagenomic monitoring of airborne microbiomes across the Belgrade metropolitan area, a European air pollution hotspot. While community composition shifted seasonally, with an enrichment of Bacillota in autumn and stress-tolerant genera in winter, opportunistic pathogens including Pseudomonas and Acinetobacter were detected year-round. The airborne resistome and mobilome exhibited pronounced seasonal restructuring, with winter showing the highest diversity of resistance genes and plasmid-associated sequences. Mobility-associated genes, including unique toxins and plasmid maintenance systems, were also most prominent in winter. Pathogen-host interaction profiling revealed a functional shift from respiratory and colonization-associated Gram-positive taxa such as Streptococcus pneumoniae and Staphylococcus aureus in autumn to enteric pathogens like Escherichia coli and Salmonella enterica in winter. Network analysis showed that winter formed the densest co-occurrence network, suggesting enhanced potential for co-selection of resistance and virulence traits. Specific plasmid-associated ARGs displayed seasonal patterns, with bla_CTX-M linked to multiple plasmids in summer, while bla_TEM and aph genes were more prominent in winter. Our findings illustrate that seasonal variations in the airborne genetic landscape are linked to environmental factors and fluctuating reservoirs of clinically relevant resistance and virulence determinants. This highlights the need for integrated longitudinal aerobiome surveillance to understand its implications for public health within the One Health framework.

This work builds upon our previous “repopulation upon shattering” (RUS) studies in the yeast-like microbe Ustilago maydis, focusing mainly on a deeper understanding of the suicidal type of death caused by self-generated hypoxia (SGH). The key findings are: 1) the massive loss of viability induced by SGH occurs via programmed cell death (PCD), 2) the PCD-released materials are more beneficial for the surviving cells than the nutrients liberated from cells that die through necrotic processes, 3) products of PCD can stimulate growth even in the presence of growth-suppressive necromass, and 4) the beneficial effects of substances released through PCD extend to two other species within the family Ustilaginaceae. Additionally, U. maydis exhibited a remarkable ability to withstand the negative effects of non-PCD necromass. These results suggest PCD-released materials are essential for critical initial regrowth in post-stress environments where there is a high presence of non-PCD necromass. As the revitalized population strengthens, it would correspondingly enhance the communal ability to exploit more challenging nutrients. Alongside with the robust resilience of U. maydis survivors against non-PCD necromass, the PCD mode of dying may improve the fitness of this microorganism in harsh and fluctuating environments, warranting further investigation.