Biology subjects

Kaeser, S.

Publications and source records attributed to Kaeser, S..

5 recordsLinked to original sources

bioRxiv2025

Beyond a Linear Structure: The Tubular Organization of the Tripartite Attachment Complex and the Functional Role of TAC53

The Tripartite Attachment Complex (TAC) is essential for mitochondrial DNA (kDNA) segregation in Trypanosoma brucei, providing a physical link between the flagellar basal body and the mitochondrial genome. Although the TACs hierarchical assembly and linear organization have been extensively studied, much remains to be discovered regarding its complete architecture and composition - for instance, our identification of a new TAC component underscores these knowledge gaps. Here, we use a combination of proteomics, RNA interference (RNAi), and Ultrastructure Expansion Microscopy (U-ExM) to characterize the TAC at high resolution and identify a novel component, TAC53 (Tb927.2.6100). Depletion of TAC53 in both procyclic and bloodstream forms results in kDNA missegregation and loss, a characteristic feature of TAC dysfunction. TAC53 localizes to the kDNA in a cell cycle-dependent manner and represents the most kDNA-proximal TAC component identified to date. U-ExM reveals a previously unrecognized tubular architecture of the TAC, with two distinct TAC structures per kDNA disc, suggesting a mechanism for precise kDNA alignment and segregation. Moreover, immunoprecipitation and imaging analyses indicate that TAC53 interacts with known TAC-associated proteins HMG44, KAP68, and KAP3, forming a network at TAC-kDNA the interface. These findings redefine our understanding of TAC architecture and function and identify TAC53 as a key structural component anchoring the mitochondrial genome in T. brucei. Significance StatementThis research identifies a new component (TAC53) of the tripartite attachment complex (TAC), a cellular machinery that anchors the mitochondrial DNA to a cytoskeletal structure, the basal body in Trypanosoma brucei. Using proteomics and high-resolution microscopy, we demonstrate that TAC53 is at the interface of the TAC and the mitochondrial DNA and likely the final piece in this structure. We also describe the overall tubular architecture of the TAC from the basal body to the mitochondrial matrix, and how the presence of two TAC structures per mitochondrial genome can explain the parasites ability to maintain its mitochondrial DNA accurately. In summary, we present a new component and the architecture of the currently best understood mitochondrial DNA segregation mechanism in biology.

cell biology↗

bioRxiv2025

Food-web coupling by mobile consumers has individual to ecosystem level effects

Mobile consumers serve as a ubiquitous link, coupling the dynamics and functions of different ecosystems, ranging from diel-vertical migration of zooplankton to seasonal movements of large ungulates. Despite mounting theoretical interest, experimental tests of the effects of consumer mobility in meta-ecosystems are virtually non-existent. Here, we used an experimental microcosm system to investigate how mobile consumers (Daphnia magna) mediate ecosystem biomass, community structure, and their own fitness by coupling spatially distinct aquatic ecosystems composed of two different protist communities. We found that consumer mobility significantly influenced the effect of consumption on ecosystem biomass and the growth and reproduction of the consumers, themselves. However, the direction and magnitude of these effects depended on community composition in the connected ecosystem. Further, we found consumer mobility consistently promoted the coexistence of a competing local species, regardless of community composition in the connected ecosystem. Our findings underscore the profound role of consumer mobility in shaping individual to ecosystem-level dynamics while emphasizing a strong mediating effect of community composition across the landscape.

ecology↗

bioRxiv2024

Terrestrial herbivory drives adaptive evolution in an aquatic community via indirect effects

Indirect ecological effects, which occur when the impact of one species on another is mediated by a third species or the shared environment, are ubiquitous in nature. Given the complexity of natural systems, indirect ecological effects were thought to be important in driving eco-evolutionary processes across community boundaries. However, we know remarkably little about such effects. Here we show that indirect effects of terrestrial insect (aphids) herbivory on macrophytes (duckweed) drives adaptive evolution of water fleas (Daphnia) in large outdoor aquatic mesocosms. Aphid herbivory reduced macrophyte growth and increased the abundance of phytoplankton, which in turn increased the abundance of Daphnia. Whole genome pool sequencing and phenotypic assays revealed an impact on the genetic compositions of the Daphnia populations and transplant experiments indicated that these evolutionary changes were adaptive. Furthermore, these changes in the aquatic community altered the interactions of the aphids and the macrophytes. These results demonstrate that indirect ecological effects can shape eco-evolutionary interactions between different communities.

evolutionary biology↗

bioRxiv2024

Zooplankton bacterial communities are influenced by infection status, environmental conditions and diet quantity across natural epidemics

Zooplankton-associated microbiomes play an important role for host health and contribute to ecosystem processes such as nutrient cycling. Yet, few studies have assessed how environmental gradients and biotic interactions, including parasitism and diet, may shape the microbiome composition of wild zooplankton. Here, we analysed the microbiomes of water fleas from the Daphnia longispina species complex using 16S rRNA gene sequencing and a long-term field dataset spanning six sampling events over 13 years. Sampling coincided with outbreaks of the virulent eukaryotic gut parasite Caullerya mesnili. Additionally, we explored how microbiome structure varied in relation to water parameters, phytoplankton density (i.e. Daphnia diet), and zooplankton density and community structure. Daphnia microbiomes displayed strong temporal variation, and comparatively small differences based on host infection status. Microbiome beta diversity correlated with phytoplankton density but not with its community composition, including green algae, protists and cyanobacteria. Environmental conditions, including temperature, dissolved oxygen and cyanobacterial abundance - previously found to drive Caullerya epidemics - were also associated with distinct microbiome structures. Importantly, microbiome beta diversity co-varied with infection prevalence, suggesting a link between microbiome shifts, epidemic size, and environmental conditions driving large epidemics. Dominant bacterial taxa correlated with Daphnia density, whereas the phylogenetic composition of rare taxa was associated with total zooplankton density. These findings demonstrate the dynamic nature of Daphnia microbiomes and suggest potential mechanisms by which they may mediate disease dynamics, particularly through associations with diet quantity, temperature, and host population density.

ecology↗

bioRxiv2021

Blue and green food webs respond differently to elevation and land use

While aquatic (blue) and terrestrial (green) food webs are parts of the same landscape, it remains unclear whether they respond similarly to shared environmental gradients. We use empirical community data from hundreds of sites across Switzerland, and show that blue and green food webs have different structural and ecological properties along elevation as a temperature proxy, and among various land-use types. Specifically, in green food webs, their modular structure increases with elevation and the overlap of consumers diet niche decreases, while the opposite pattern is observed in blue food webs. Such differences between blue and green food webs are particularly pronounced in farmland-dominated habitats, indicating that anthropogenic habitat modification moderates the climatic effects on food webs but differently in blue versus green systems. These findings indicate general structural differences between blue and green food webs and suggest their potential divergent future alterations through land use or climatic changes.

ecology↗