Biology subjects

Berthold, M.

Publications and source records attributed to Berthold, M..

7 recordsLinked to original sources

bioRxiv2025

Inter-strain diversity among coastal picocyanobacteria across salinity gradients

Strains of the picocyanobacteria genera Synechococcus and Cyanobium occur in cold-temperate zones from coastal waters to the open ocean, spanning a range of salinities and water depths. To thrive across different salinities, picocyanobacteria strains acclimate internal turgor by expending metabolic energy to accumulate compatible solutes and extrude inorganic ions. We grew five picocyanobacterial strains, derived from a range of source habitat salinities, under a matrix of light and salinity levels. Although Chl is a general proxy for phytoplankton biomass, Chl/cell is itself a key component of acclimation. Indeed, for all strains, except the brackish water CZS48M, the conditions supporting the highest Biovolume-specific growth rates shifted upwards towards higher salinities and PAR, compared to conditions for maximum Chl-specific growth. Therefore, the apparent optimal niche for a strain varies depending upon the metric used to track growth. Strains CZS48M and CZS25K derived from brackish lagoons of the Baltic Sea may be true brackobionts, with maximal growth at brackish salinities and high PAR, coinciding with their maximal metabolic capacities. CZS48M and CZS25K both also show high metabolism under higher salinity and low PAR, suggesting a situation of rapid metabolism, but lower achieved growth, under stress at the edges of their environmental tolerance ranges. Conversely, NIES981 (full marine, East China Sea) shows rapid metabolism under high, but also under low, salinities. The preferred salinity of each strain is consistent with its genome-encoded capabilities to synthesize different compatible solutes. In general, across strains, maximal metabolic rate is often offset from growth rate optima, showing conversion of metabolic electrons to biomass varies widely depending upon strain and condition, likely partly reflecting the costs of turgor regulation at the limits of salinity tolerance.

microbiology↗

bioRxiv2025

Fast or slow - light climate modulates intra-population sinking velocities in small phytoplankton

The global carbon cycle depends heavily on the carbon sequestration rates of aquatic ecosystems. Sinking of phytoplankton is a rapid mediator of carbon sequestration, because phytoplankton are globally abundant photoautotrophs that grow rapidly. Pico- and nano-phytoplankton sinking velocities vary depending on their growth state, viability, clumping, and distribution in the water column. We introduced high throughput fluorescence microscopy of well-plates, to measure sinking velocities of three diatom strains, and three cyanobacteria strains, with cell radii spanning an order of magnitude, all grown under three different light levels. Cultures were measured for sinking velocities repeatedly across their growth trajectories. Tracking multiple fluorescence wavebands allowed us to simultaneously determine sinking velocities for living vs. dead cells. Sinking velocities varied strongly across growth light levels, and across growth stages. These monoclonal cultures furthermore show distinct sub-populations of slow- and fast-sinking cells. Our results departed widely from simple Stokes Law estimates of sinking based upon radii and mass density of cells. Complex, heterogeneous phytoplankton communities likely show more complicated sinking patterns than are currently expressed in biogeochemical ocean models. Our well-plate microscopy approach using parallel imaging of many samples generates high-throughput measures of cell sinking at population- or community-scales, to in turn improve modelling of carbon export to deeper layers.

ecology↗

bioRxiv2024

SILAC-based quantification reveals modulation of the immunopeptidome in BRAF and MEK inhibitor sensitive and resistant tumor cells

The immunopeptidome is constantly monitored by T cells to detect foreign or aberrant HLA peptides. It is highly dynamic and reflects the current cellular state, enabling the immune system to recognize abnormal cellular conditions, such as those present in cancer cells. To precisely determine how changes in cellular processes, such as those induced by drug treatment, affect the immunopeptidome, quantitative immunopeptidomics approaches are essential. To meet this need, we developed a pulsed SILAC-based method for quantitative immunopeptidomics. Metabolic labeling with lysine, arginine, and leucine enabled isotopic labeling of nearly all HLA peptides across all allotypes (> 90% on average). We established a data analysis workflow that integrates the de novo sequencing-based tool Peptide-PRISM for comprehensive HLA peptide identification with MaxQuant for accurate quantification. We employed this strategy to explore the modulation of the immunopeptidome upon MAPK pathway inhibition (MAPKi) and to investigate alterations associated with early cellular responses to inhibitor treatment and acquired resistance to MAPKi. Our analyses demonstrated significant changes in the immunopeptidome early during MAPKi treatment and in the resistant state. Moreover, we identified putative tumor-specific cryptic HLA peptides linked to these processes that might represent exploitable targets for cancer immunotherapy. SynopsisWe have developed a mass spectrometric method that allowed us to investigate the effects of common MAPK inhibitors on the immunopeptidome of melanoma cells. This approach has led to the discovery of new potential targets for cancer immunotherapy.

immunology↗

bioRxiv2024

Two serial filters determine P2X7R cation selectivity, Ser342 in the central pore and lateral acidic residues at the cytoplasmic interface

The human P2X7R (hP2X7R) is a homotrimeric cell surface receptor gated by extracellular ATP4- with two transmembrane helices per subunit, TM1 and TM2. A ring of three S342 residues, one from each pore-forming TM2 helix, located halfway across the membrane bilayer, functions to close and open the gate in the apo and ATP4- bound open states, respectively. The hP2X7R is selective for small inorganic cations, but can also conduct larger organic cations such as Tris+. Here, we show by voltage-clamp electrophysiology in Xenopus laevis oocytes that mutation of S342 residues to positively charged lysines decreases the selectivity for Na+ over Tris+, but maintains cation selectivity. Deep in the membrane, laterally below the S342 ring are nine acidic residues arranged as an isosceles triangle consisting of residues E14, D352, and D356 on each side, which do not move significantly during gating. When the E14K mutation is combined with lysine substitutions of D352 and/or D356, cation selectivity is lost and permeation of the small anion Cl- is allowed. Lysine substitutions of S342 together with D352 or E14 plus D356 in the acidic triangle convert the hP2X7R mutant to a fully Cl--selective ATP4--gated receptor. We conclude that the ion selectivity of wild-type hP2X7R is determined by two sequential filters in one single pathway: (1) a primary size filter, S342, in the membrane center and (2) three cation filters lateral to the channel axis, one per subunit interface, consisting of a total of nine acidic residues at the cytoplasmic interface. SignificancePore size and electrostatic interactions are key to the permeation selectivity of ion channels. Previous cysteine scanning mutagenesis identified a tri-serine-342 ring located halfway across the membrane as the gate and selectivity filter of the P2X7 receptor channel, accessible from the inside to cationic but not anionic reagents. Consistent with a downstream cation filter, we could now switch P2X7R from cation to anion selectivity by lysine substitution of acidic residues at the cytoplasmic interface. Our data show that two sequential selectivity filters control the cation selectivity of the P2X7R channel, a dynamic tri-serine-342 size filter and three conformationally static cation filters of three acidic residues each. We propose that the ion selectivity of P2X receptors involves the mechanism described here.

biophysics↗

bioRxiv2022

Mesopredator-mediated trophic cascade can break persistent phytoplankton blooms in coastal waters

Managing eutrophied systems only bottom-up (nutrient decreases) can be economically and ecologically challenging. Top-down controls (consumption) were sometimes found to effectively control phytoplankton blooms. However, mechanistic insights, especially on possible trophic cascades, are less understood in brackish, species-poor coastal waters, where large cladocera are absent. In this study, we set-up large mesocosms for three consecutive years during growth season. One set of mesocosms was controlled by mesopredator (gobies and shrimp), whereas the other mesocosms had no such mesopredator present. The results were standardized to monitoring data of the ecosystem to denote possible differences between treatments and the system. We found that mesopredator mesocosms showed lower turbidity, phytoplankton biomass, and nutrients compared to no-mesopredator mesocosms and the ecosystem. This decrease allowed macrophytes to colonize water depths only sparsely colonized in the ecosystem. Rotifer biomass increased in mesopredator mesocosms compared to the ecosystem and no-mesopredator mesocosms. Likewise, copepod biomass that potentially grazes upon rotifers and other microzooplankton decreased in mesopredator mesocosms. No-mesopredator mesocosms were colonized by an omnivorous mesograzer (Gammarus tigrinus), potentially creating additional pressure on macrophytes and increasing grazing-mediated nutrient release. Zooplankton was not able to control the non-nutrient limited phytoplankton. We propose a new mechanism, where a higher mesopredator density will increase grazing on phytoplankton by promoting microzooplankton capable of grazing on picophytoplankton. This proposed mechanism would contrast with freshwater systems, where a decrease of zooplanktivorous fish would promote larger phytoplankton grazer like cladocera. Biomanipulation in such species-poor eutrophic coastal waters may be more successful, due to less trophic pathways that can cause complex top-down controls. Stocking eutrophic coastal waters with gobies and shrimps may be an alternative biomanipulative approach rather than selectively remove large piscivorous or omnivorous fish from eutrophic coastal waters.

ecology↗

bioRxiv2021

Combined effects of salinity and temperature on grazing activity of invasive Gammarus tigrinus on charophytes

Charophytes are a refuge for zooplankton and stabilize sediments, but they are also a food source for various animal species (water birds, fishes, invertebrates). Especially the introduction of new species, like Gammarus tigrinus, into the Baltic Sea led to yet not understood changes in the food web. Furthermore, future projections point to increased water temperatures at lowered salinity levels affecting species capacity to acclimatize to changing abiotic factors. In this study we investigated the influence of temperature and salinity on the grazing pressure of Gammarus tigrinus on two charophyte species: Chara aspera and Chara tomentosa. The grazing experiments were conducted in a full factorial design with the factors salinity (3 - 13 g kg-1), temperature (5 - 30 {degrees}C), and charophyte species. Grazing rates were determined as mass deviation within 48 hours considering biomass changes in the presence and absence of gammarids. Grazing rate were further used to calculate charophyte losses in two coastal lagoons with different salinity concentrations for recent and future time periods. The potential grazing peak of about 24 {degrees}C is not yet reached in these coastal waters but may be reached in the near future as shown by our future projection results. However, the temperature increase, and desalination will cause a shift in seasonal individual grazing patterns from summer to spring and autumn. Desalination and temperature increase can lead to a shift in optimal habitats for G. tigrinus in the future.

ecology↗

bioRxiv2021

Dynamics of primary productivity in relation to submerged vegetation of a shallow, eutrophic lagoon: a field and mesocosm study

Aquatic ecosystems nowadays are under constant pressure, either from recent or historical events. In most systems with increased nutrient supply, submerged macrophytes got replaced by another stable state, dominated by phytoplankton as main primary producer. Yet, reducing the nutrient supply did not yield the aimed goal of restored habitats for submerged macrophytes in systems worldwide. The question arises, why submerged macrophytes do not re-colonize, and if they are actually competitive. Therefore, primary production assays were conducted in ex-situ bentho-pelagic mesocosms and compared to the actual ecosystem, a turbid brackish lagoon of the southern Baltic Sea. Mesocosm were either manipulated to be colonized by macrophytes, or stayed phytoplankton dominated. Oxygen evolution was monitored over a period of five months in 5 min (mesocosms) to 10 min (ecosystem) intervals. Surface and depth-integrated production was calculated to analyse seasonal and areal resolved production patterns. It was found that macrophyte mesocosms were more stable, when considering only surface O2 production. However, calculating depth-integrated production resulted in net-heterotrophy in both shallow mesocosms approaches and the actual ecosystem. This heterotrophy is likely mediated by sediment respiration and POC accumulation in mesocosms, and a low share of productive to respiring water column in the actual ecosystem. Therefore, it seems unlikely that macrophytes will re-settle, as constant net-heterotrophy may allow for high-nutrient turnover at sediment-water interfaces and within the water column, favouring phytoplankton. Changes within the ecosystem cannot be expected without further restoration measures within and in the systems proximity.

ecology↗