Biology subjects

Kohl, L.

Publications and source records attributed to Kohl, L..

5 recordsLinked to original sources

bioRxiv2026

Soil nitrogen dynamics in riparian zones of two Arctic rivers

Riparian zones act as protective buffers, filtering land-to-river nutrient inputs through retention and nitrogen (N) gas losses. While rapid Arctic warming and permafrost thaw may enhance terrestrial nutrient inputs to aquatic systems, comprehensive assessments of N cycling in Arctic riparian soils are lacking. Conventionally, these zones are considered inactive due to N limitation of Arctic soils and low temperatures, leaving their N cycling unexplored. To address this, we investigated N pools and turnover processes in riparian zones of two Arctic rivers in Finland and Greenland. We combined measurements of the extractable N pool and in-situ nitrous oxide (N2O) flux with 15N-labeling techniques to quantify gross mineralization, nitrification, potential denitrification, and potential dissimilatory nitrate reduction to ammonium (DNRA). Our findings reveal that mineral N cycling in high-latitude riparian zones is more active than previously assumed. Despite low temperatures and low to intermediate soil organic carbon content, we found high gross N mineralization rates, alongside detectable rates of gross nitrification and potential DNRA. We attribute the unexpectedly high N activity in C-poor soils to low C/N ratios, which create a stoichiometric imbalance, thereby enhancing N mineralization. The presence or absence of vegetation largely determined the dominance and magnitude of these pathways. While dense vascular plant cover was associated with higher extractable N pools and gross mineralization rate, low nitrification rates and elevated DNRA potential indicated a tight N cycle. Conversely, sparsely vegetated patches with cryptogamic biocrusts acted as N2O hotspots. In bare sandy soils adjacent to the river, we found high gross nitrification rate and detectable N2O losses, possibly driven by riverine organic N inputs. Taken together, this research shows that Arctic riparian zones may play an important role in reducing terrestrial N inputs to the rivers, which should be considered when studying the fate of N in the rapidly changing Arctic.

ecology↗

bioRxiv2025

Host environment shapes filarial parasites fitness and Wolbachia endosymbionts dynamics

Filarial nematodes, responsible for diseases like lymphatic filariasis and onchocerciasis, depend on symbiotic Wolbachia bacteria for reproduction and development. Using the Litomosoides sigmodontis rodent model, we investigated how host type-2 immunity influences Wolbachia dynamics and parasite development. Type-2 immune environments selectively reduce germline Wolbachia in female filariae from wild-type mice, a change associated with disrupted oogenesis, embryogenesis, and microfilarial production, while somatic Wolbachia remain unaffected. Antibiotic treatments achieving systemic Wolbachia clearance result in similar reproductive impairments. Notably, Wolbachia-free microfilariae are observed shortly after Wolbachia depletion, suggesting that early-stage embryogenesis can proceed temporarily before progressive germline dysfunction ensues. Wolbachia-free microfilariae develop into infective larvae in the vector, but stall beyond the L4 stage in vertebrate hosts, showing arrested growth and reproductive organ maturation defects in both male and female larvae. These findings highlight the variable dependency on Wolbachia across life stages and provide insights into host-parasite-endosymbiont interactions shaped by environmental pressures. Graphical abstract. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/632327v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@98e008org.highwire.dtl.DTLVardef@9c32a7org.highwire.dtl.DTLVardef@c19000org.highwire.dtl.DTLVardef@1d523ad_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

CH4 transport in wetland plants under controlled environmental conditions: untangling the impacts of phenology

O_LIMethane (CH4) fluxes at plant surfaces are the net result of transport of soil-produced CH4 and within-plant CH4 production and consumption, yet factors and processes controlling these fluxes remain unclear. C_LIO_LIWe conducted high-frequency automated CH4 flux measurements from shoots of Carex rostrata (sedge), Menyanthes trifoliata (forb) and shrubs (Betula nana, Salix lapponum) during early, high and late summer in a climate-controlled environment to assess the effects of environmental variables, seasonality and CH4 cycling microbes in the CH4 flux. Measurements were conducted from intact plant-soil samples collected throughout growing seasons 2020 and 2021 from Lompolojankkafen, northern Finland. C_LIO_LIAll studied species showed seasonal variability in CH4 fluxes. The CH4 fluxes were not impacted by light level, while out of the studied species, porewater CH4 concentration increased fluxes from all but B. nana. Air temperature only and negatively affected CH4 flux from C. rostrata. Both methanogens and methanotrophs were detected in aboveground parts of S. lapponum and M. trifoliata, methanotrophs in B. nana, while neither were detected in C. rostrata. C_LIO_LIOur study demonstrates that the seasonal phase of the plants regulates CH4 flux they mediate across species, which was not observed in the field. The detection of methanogens and methanotrophs in herbs and shrubs suggests that microbial processes may contribute to their CH4 flux. C_LI

ecology↗

bioRxiv2022

Macrophages inhibit Coxiella burnetii by the ACOD1-itaconate pathway for containment of Q fever

Infection with the intracellular bacterium Coxiella (C.) burnetii can cause chronic Q fever with severe complications and limited treatment options. Here, we identify the enzyme cis- aconitate decarboxylase 1 (ACOD1 or IRG1) and its product itaconate as protective host immune pathway in Q fever. Infection of mice with C. burnetii induced expression of several anti-microbial candidate genes, including Acod1. In macrophages, Acod1 was essential for restricting C. burnetii replication, while other antimicrobial pathways were dispensable. Intratracheal or intraperitoneal infection of Acod1-/- mice caused increased C. burnetii burden, significant weight loss and stronger inflammatory gene expression. Exogenously added itaconate restored pathogen control in Acod1-/- mouse macrophages and blocked replication in human macrophages. In axenic cultures, itaconate directly inhibited growth of C. burnetii. Finally, treatment of infected Acod1-/-mice with itaconate efficiently reduced the tissue pathogen load. Thus, ACOD1-derived itaconate is a key factor in the macrophage-mediated defense against C. burnetii and may be exploited for novel therapeutic approaches in chronic Q fever.

immunology↗

bioRxiv2019

Vital role for Plasmodium berghei Kinesin8B in axoneme assembly during male gamete formation and mosquito transmission

SummarySexual development is an essential phase in the Plasmodium life cycle, where male gametogenesis is an unusual and extraordinarily rapid process. It produces 8 haploid motile microgametes, from a microgametocyte within 15 minutes. Its unique achievement lies in linking the assembly of 8 axonemes in the cytoplasm to the three rounds of intranuclear genome replication, forming motile microgametes, which are expelled in a process called exflagellation. Surprisingly little is known about the actors involved in these processes. We are interested in kinesins, molecular motors that could play potential roles in male gametogenesis. We have undertaken a functional characterization in Plasmodium berghei of kinesin-8B (PbKIN8B) expressed specifically in male gametocytes and gametes. By generating Pbkin8B-gfp parasites, we show that PbKIN8B is specifically expressed during male gametogenesis and is associated with the axoneme. We created a{Delta} Pbkin8B knockout cell line and analysed the consequences of the absence of PbKIN8B on male gametogenesis. We show that the ability to produce sexually differentiated gametocytes is not affected in{Delta} Pbkin8B parasites and that the 3 rounds of genome replication occur normally. Nevertheless, the development to free motile microgametes is halted and the life cycle is interrupted in vivo. Ultrastructural analysis revealed that intranuclear mitoses is unaffected whereas cytoplasmic microtubules, although assembled in doublets and elongated, fail to assemble in the normal axonemal \"9+2\" structure and become motile. Absence of a functional axoneme prevented microgamete assembly and release from the microgametocyte, severely reducing infection of the mosquito vector. This is the first functional study of a kinesin involved in male gametogenesis. These results reveal a previously unknown role for PbKIN8B in male gametogenesis, providing new insights into Plasmodium flagellar formation.

cell biology↗