Biology subjects

Schmidt-Posthaus, H.

Publications and source records attributed to Schmidt-Posthaus, H..

6 recordsLinked to original sources

bioRxiv2026

Early-life conditions shape baseline immune gene expression, but not pathogen-induced immune activation, in brown trout

Early-life environment and parental background can shape immune phenotypes, but whether such differences persist during infection and influence the immune response remains unclear. We used single-cell RNA sequencing to characterize kidney immune responses in brown trout (Salmo trutta) from three origins differing in parental history and early rearing: wild parents with offspring reared in the wild; wild parents with offspring reared in a hatchery; and hatchery parents with offspring reared in a hatchery. All fish originated from the same river and showed no detectable genetic population structure. Fish were exposed to Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease, and analyzed 25 days later alongside unexposed controls. Across 18 scRNA-seq datasets, we identified 30 cell clusters and found a clear transcriptional imprint of developmental and parental history in the resting immune system. In unexposed fish, origin was associated with pronounced differences in gene expression, particularly in B cells. When fish were subsequently exposed to the pathogen and developed subclinical infections, both immune-cell composition and transcriptional state experienced pronounced changes: T cells increased in relative abundance, while B cells, neutrophils and proliferating progenitors showed the strongest transcriptional responses, consistent with an active but controlled subclinical response. Strikingly, the strong origin-dependent differences present before exposure largely disappeared after infection. Fish from all three backgrounds converged on a shared transcriptional response, and genes associated with origin showed little overlap with those responding to infection. Thus, at single-cell resolution in vivo, we identify infection-induced transcriptional convergence across distinct environmental and parental backgrounds. Our findings show that substantial baseline immune variation can persist under resting conditions yet be overridden by pathogen exposure, constraining distinct immune states towards a common response.

immunology↗

bioRxiv2026

Persistent maternal memory, transient offspring effects: the temporal and sex-specific architecture of heritable heat-stress responses in zebrafish

Environmental experiences can influence subsequent generations, yet little is known about the dynamics of such molecular memories across time, reproduction events, and offspring development. Here we provide a temporal map of the transmission of environmental information through egg provisioning and its phenotypic consequences in zebrafish. Specifically, we follow the effects of a 2-week heat wave across successive matings and two unexposed generations along a complete adult-to-egg-to-adult experimental trajectory, assessing gonad responses, maternal RNA, embryo survival, larval behaviour, adult stress resistance and liver transcriptomes. We find that oocyte maternal RNA retained a pronounced heat-shock signature across several weeks and multiple spawning events, with selected functional components persisting into oocytes of the next generation. Somatic responses followed a fundamentally different trajectory: effects on liver transcription were sex- and timepoint-specific, with minor intergenerational signatures of energy metabolism and metabolic stress in males. Parental heat exposure also altered offspring survival, larval behaviour and thermal tolerance, with progressively weakened effects across successive reproductive events and across generations. Our results reveal distinct temporal dynamics of environmental memory in the germline vs the developing and adult soma, with persistent molecular information in maternal provisioning coexisting with progressively fading offspring phenotypes. Such selective retention and loss of parental information align with theoretical predictions about the progressively declining value of inherited information and may determine the dynamics of cross-generational population-level responses to extreme events.

evolutionary biology↗

bioRxiv2026

Variation of anti-oomycete activity in Pseudomonas spp.: phenotypic characterization and comparative genomics

Pathogenic aquatic oomycetes Aphanomyces astaci and Saprolegnia parasitica represent a major threat to biodiversity and aquaculture production, but their interactions with host-associated microbes remain poorly understood. From a collection of bacterial isolates (n = 328) obtained from fish and crayfish hosts, we focused on Pseudomonas spp. (n = 66) and confirmed their previously reported strong inhibitory potential against A. astaci and S. parasitica. However, our results also revealed substantial inter- and intra-species variation in antagonism. To capture this variation, we selected eight isolates belonging to different P. fluorescens, P. putida, and P. syringae species groups and displaying contrasting levels of anti-oomycete activity for further phenotypic assays and comparative genomic analysis. Across these isolates, mycelial inhibition was markedly stronger against A. astaci than against S. parasitica, indicating species-specific differences in susceptibility. Comparative genomic analysis revealed substantial variation in biosynthetic gene cluster (BGC) repertoires among the analysed strains. Strongly inhibitory isolates carried candidate BGCs with similarity to characterised bioactive pathways, including pyoluteorin, rhizoxin, pyrrolnitrin, DAPG, and orfamide, alongside with multiple uncharacterised clusters that were either shared among inhibitory isolates or restricted to individual strains. All analysed genomes also contained clusters related to siderophore and HCN biosynthesis. However, in vitro assays showed that siderophore production was not clearly associated with inhibitory activity and that inhibition was mediated mainly by diffusible rather than volatile compounds. Altogether, our results suggest that Pseudomonas anti-oomycete activity is species- and strain-dependent and likely reflects different combinations of multiple, predominantly diffusible metabolites rather than a single conserved mechanism. In conclusion, this study provides a foundation for future work aimed at resolving mechanisms underlying microbial antagonism toward aquatic oomycete pathogens.

microbiology↗

bioRxiv2025

Single-cell RNA sequencing reveals influences of rearing environment on cellular immunity in brown trout (Salmo trutta)

Vertebrate immune systems exhibit striking evolutionary diversity, yet our understanding remains biased toward mammalian models. Here, we generate a single-cell atlas of immune cells from the ecologically and economically important salmonid Salmo trutta (brown trout), a lineage characterized by an ancestral whole-genome duplication (WGD). Profiling over 83,000 kidney-derived immune cells, we resolved 34 transcriptionally distinct populations, identified core immune lineages, and uncovered novel markers in neutrophils, macrophages, T- and B-cells. We detected pervasive transcriptional divergence between WGD-derived ohnologue pairs, indicating putative sub- and neofunctionalization in immune gene regulation. We further show that the transcriptional identity of immune cells is shaped by rearing history: fish raised in hatcheries--whether for one or multiple generations--showed shifts in immune gene expression across cell types. These included genes involved in G protein-coupled receptor signalling, a process which has previously been implicated in domestication. Our findings provide insight into the evolution of vertebrate immunity and raise concerns about the immunological fitness of hatchery-reared fish released into the wild.

immunology↗

bioRxiv2024

Towards an eco-epidemiological framework for managing freshwater crayfish communities confronted with crayfish plague

Wildlife diseases figure prominently among the main causes of biodiversity loss worldwide. Especially fungal and fungus-like pathogens are on the rise, wreaking havoc across the tree of life by threatening species persistence and destabilizing ecosystems. A worrisome example are freshwater crayfish species in Eurasia and Oceania, facing the dual challenge of introduced competitive crayfish species and an introduced water mold (Aphanomyces astaci) causing crayfish plague. A. astaci locally extinguishes susceptible native crayfish populations, while non-native individuals (mostly from North America) remain largely unaffected. Despite its significant impact and its [~]150 years of presence in Europe, studies and disease management recommendations for crayfish plague that are firmly rooted in epidemiological theory are scarce. Here, we present a practical eco-epidemiological framework to understand how multi-species crayfish communities react to crayfish plague introductions. The framework is based on the observation that the dynamics of crayfish communities are mainly determined by life-history characteristics, within- and among-species competition, effects of generalist predators (including fishing), and host-pathogen interactions. From this ecological and epidemiological context, we derive fundamental epidemiological metrics, single-host species and community-level basic reproduction numbers (R0). We investigate how host species densities affect the likelihood of a disease outbreak in a crayfish community, and we demonstrate that a communitys R0 value is simply the sum of the communitys single-host species R0 values, adjusted for competition and predation. We further demonstrate how R0 can be used to guide preventative and mitigation actions for crayfish communities. For example, we show how R0 expressions - even without a detailed parametrization - can be used to construct regional risk rankings for different crayfish communities, for an effective allocation of resources to local conservation plans. Our eco-epidemiological framework will also be of interest to the management of other aquatic host-pathogen systems with water-borne pathogen transmission as the main route of pathogen spread.

ecology↗

bioRxiv2023

An adaptable, user-friendly score sheet to monitor welfare in experimental fish

Fish are increasingly used as experimental animals across research fields. Currently, a quarter of all experimental animals used in Europe are fish. Less than 20% of these are standard model species. Welfare assessments for experimental fish are in their infancy compared to rodents. This can be attributed to the diversity of species used, the relative recency of fish as go-to model for research, and challenges to assess welfare and pain in non-vocal underwater species. The lack of guidelines and tools presents a challenge for researchers (particularly, for newcomers), for ethics committees, and for implementing refinement measures. Here, we present an adaptable, user-friendly score sheet for fish. The parameters contained in the excel tool are based on a literature review, have been validated by expert interviews, and evaluated by a fish pathologist. The tool allows to score individuals as well as groups, calculates summary scores and visualizes trends. We provide the underlying literature, give use examples and provide instructions on the adaptation and use of the score sheet. We hope that this tool will empower researchers to include welfare assessment in their routines, foster discussions on fish welfare parameters among scientists, facilitate interactions with ethics committees, and most importantly, enable the refinement of fish experiments.

animal behavior and cognition↗