Biology subjects

Mittag, M.

Publications and source records attributed to Mittag, M..

18 recordsLinked to original sources

bioRxiv2026

The enemy of my enemy: A bacterial antagonist rescues Chlamydomonas by inactivating a toxin from a rival

Microbial interactions are shaped by multiple community members, yet the underlying mechanisms remain poorly understood. Here, we investigated a tripartite interaction between the microalga Chlamydomonas reinhardtii and two Pseudomonas bacteria that coexist in the same soil habitat. In pairwise cultures, all three interactions are amensalistic (-like): Pseudomonas protegens Pf-5 antagonizes both C. reinhardtii and Pseudomonas fluorescens HKI0770 without benefit, while P. fluorescens inhibits C. reinhardtii without profiting from the alga. However, in a tripartite culture, P. fluorescens protects C. reinhardtii from P. protegens and promotes algal recovery. This protection is not stopped when the used carbon source, acetate, is supplemented. The P. fluorescens rescue effect is associated with reduced levels of the polyyne toxin protegencin produced by P. protegens. Protegencin levels, detected by Raman microspectroscopy, are decreased by application of spent medium or protein extracts from P. fluorescens, while heat- and protease-treatment abolish this activity. A heat-sensitive, proteinaceous factor, likely an enzyme(s), appears to contribute to protegencin inactivation. Our results show that P. fluorescens rescues C. reinhardtii by inactivating protegencin, despite being inhibited by P. protegens. These findings demonstrate the importance of investigating higher-order effects, since additional community members can transform pairwise antagonistic interactions into conditional protection through toxin inactivation.

microbiology↗

bioRxiv2026

Hippocampal granule cells balance energy and function along the Pareto optimal front

The dentate gyrus' principal neuron, the granule cell (GC), plays a key role in pattern separation, transforming similar inputs into dissimilar outputs. We used a new measure based on information theory to evaluate this transformation in an experimentally derived in silico GC model with realistic ion channel distributions across its dendrites. We found that model performance aligned well with current-clamp recordings from mouse brain slices. However, it was also possible to find artificial parameter combinations in the model that functionally outperformed the recorded cells while matching their action potential shapes. Rather than maximising computational power, the biologically realistic GC model balanced energy efficiency against increased functionality in a Pareto optimal way: No possible parameter combination was found to improve one of the objectives without impairing the other. Interestingly, immature GCs adopted a different weighted trade-off with a stronger emphasis on energy efficiency than pattern separation, but they remained Pareto optimal over their putative developmental trajectory. Our results support the idea that evolution favours neurons that can satisfy functional and energetic demands simultaneously.

neuroscience↗

bioRxiv2026

Tripartite synergy - Metabolic crosstalk between two bacterial mutualists and a marine microalga promotes algal fitness

Marine microalgae form major parts of phytoplankton and are highly relevant for global CO2 fixation. Although microalgae have lived together with bacteria in the oceans for billions of years, these ecosystem-relevant interactions remain largely uncharacterized. Here, we have studied biotic interactions between two marine bacteria and a marine microalga. We show that an N2-fixing Vibrio provides ammonium for Chlamydomonas sp. and a Marinobacterium. Both microorganisms cannot survive in an ammonium-free environment. In exchange, the microalga promotes the growth of both bacteria, via secretion of heat-resistant metabolites in case of Marinobacterium. Reciprocally, the Marinobacterium releases heat-resistant metabolites that stimulate algal growth and increase its photosynthetic pigments, Photosystem II quantum yield, and starch accumulation. Electron microscopy reveals a strengthened starch sheath around the algal pyrenoid and indicates a modified periplasmic space for metabolic exchange. Our data highlight a tight synergy of a marine microbial trio promoting each others growth and algal fitness.

microbiology↗

bioRxiv2026

A light-labile signal molecule acts as a photoregulator of secondary metabolite biosynthesis in a heterotrophic bacterium

While light is essential for many phototrophic organisms, our knowledge of the light-dependent regulation in heterotrophic organisms is scarce. Here, we found that the heterotrophic soil bacterium Pseudomonas protegens differentially accumulated 234 secreted metabolites depending on the light conditions. These metabolites included important antimicrobials such as pyoluteorin, 2,4-diacetylphloroglucinol, pyrrolnitrin, and rhizoxin analogs. Pyoluteorin, for instance, was 140-fold more abundant in the dark, due to a strong upregulation of the transcript of the pyoluteorin biosynthesis gene pltL. We discovered that 2,4-dichlorophloroglucinol (PG-Cl2), an activator of pyoluteorin biosynthesis, acts as a photoregulator that degrades much faster in the presence of light than in the dark. The resulting higher PG-Cl2 levels activate the pltL promoter in the dark. These findings reveal a novel mode of regulation in which light instability of a signal molecule allows the producing organism to sense and transmit light information to regulate the biosynthesis of a secondary metabolite.

microbiology↗

bioRxiv2025

Small shifts, big ripples: multi-omics studies reveal how ambient temperatures govern Chlamydomonas cellular responses

Photosynthetic protists, known as microalgae, face increasing temperatures due to climate change. The green biflagellate alga Chlamydomonas reinhardtii serves as a model for thermoregulation. While responses to thermal stress are well characterized, much less is known about the impact of ambient temperature shifts. Understanding microalgal responses to environmental temperature changes is critical, as these primary producers drive ecosystem productivity and food web dynamics. Here, C. reinhardtii grew mixotrophically at ambient temperatures from 18 {degrees}C to 33 {degrees}C. Transcriptomic profiling revealed extensive reorganization, with over 5,000 transcripts significantly affected, including those involved in algal-bacterial interactions, photoreception, lipid metabolism, photosynthesis, cilia formation, and the secretome. CO2 transfer rates and acetate levels measured at 18 {degrees}C and 28 {degrees}C suggest decreased photoautotrophic algal growth at 28 {degrees}C at first. Antagonistic bacterial activity was sustained longer at lower temperatures. Proteomic analyses of isolated cilia and secreted proteins corroborate major abundance changes within these sub-proteomes, particularly in ciliary intraflagellar transport complexes and mating-related proteins in the secretome. Together, these molecular alterations resulted in pronounced changes in growth, the lengths of cells and cilia swimming behavior, mating ability and bacterial antagonism. These data reveal major cellular responses caused by ambient, even short-term temperature shifts.

cell biology↗

bioRxiv2024

PinkyCaMP a mScarlet-based calcium sensor with exceptional brightness, photostability, and multiplexing capabilities

Genetically encoded calcium (Ca2+) indicators (GECIs) are widely used for imaging neuronal activity, yet current limitations of existing red fluorescent GECIs have constrained their applicability. The inherently dim fluorescence and low signal-to-noise ratio of red-shifted GECIs have posed significant challenges. More critically, several red-fluorescent GECIs exhibit photoswitching when exposed to blue light, thereby limiting their applicability in all-optical experimental approaches. Here, we present the development of PinkyCaMP, the first mScarlet-based Ca2+ sensor that outperforms current red fluorescent sensors in brightness, photostability, signal-to-noise ratio, and compatibility with optogenetics and neurotransmitter imaging. PinkyCaMP is well-tolerated by neurons, showing no toxicity or aggregation, both in vitro and in vivo. All imaging approaches, including single-photon excitation methods such as fiber photometry, widefield imaging, miniscope imaging, as well as two-photon imaging in awake mice, are fully compatible with PinkyCaMP.

neuroscience↗

bioRxiv2024

Deficiency of actin depolymerizing factors ADF/Cfl1 in microglia decreases motility and impairs memory

Microglia are highly motile cells that play a crucial role in the central nervous system in health and disease. Here we show that actin depolymerizing factors ADF and Cofilin1 (Cfl1) are key factors of microglia integrity and function. We found a profound morphological phenotype in absence of ADF and Cfl1 in microglia. In vivo two-photon imaging of microglia with ADF/Cfl1-KO revealed reduced microglial fine processes motility and impaired microglia migration towards a laser-induced lesion. We found increased accumulation of stabilized F-actin and altered microtubule dynamics in ADF/Cfl1-KO microglia, indicating that ADF/Cfl1 are necessary for microglial cytoskeleton dynamics. Interestingly, microglial ADF/Cfl1-deficiency decreased learning and memory, suggesting that impaired microglial cytoskeleton dynamics affect neuronal functions relevant for cognition. Our results reveal a fundamental role of ADF/Cfl1 in microglia function and underscore the importance of these innate immune cells for higher cognitive functions.

neuroscience↗

bioRxiv2024

Dynamics of microglia-glioblastoma crosstalk at the far infiltration zone

The interaction of glioblastoma (GB) and microglia is critical due to its implications for tumor progression, immune response modulation, and potential therapeutic strategies. However, the role of microglia in GB pathogenesis remains unclear, especially regarding the in vivo dynamics of their interplay. Performing three-photon imaging in an autochthonous, immunocompetent mouse GB model, we examined tumor/microglia dynamics within previously inaccessible regions at the GB far infiltration zone in the corpus callosum. Initially, microglia increased tissue surveillance upon encountering GB-cells in sparsely infiltrated areas. In contrast, when GB-cell density increased, microglia reduced surveillance, suggesting a biphasic response to tumor invasion. Additionally, microglia were not uniformly attracted to infiltrating GB-cells; only a subset moved directionally toward them within a defined spatial range. This study provides insight into the heterogeneity of the immune response to tumor invasion and the dynamics of microglia-GB interactions in vivo. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=124 SRC="FIGDIR/small/614016v1_ufig1.gif" ALT="Figure 1"> View larger version (57K): org.highwire.dtl.DTLVardef@24b1d8org.highwire.dtl.DTLVardef@1180609org.highwire.dtl.DTLVardef@346dbforg.highwire.dtl.DTLVardef@1144dd_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2024

Three-photon in vivo imaging of neurons and glia in the medial prefrontal cortex with sub-cellular resolution

The medial prefrontal cortex (mPFC) is important for higher cognitive functions, including working memory, decision making, and emotional control. In vivo recordings of neuronal activity in the mPFC have been achieved via invasive electrical and optical approaches. Here we apply low invasive three-photon in vivo imaging in the mPFC of the mouse at unprecedented depth. Specifically, we measure neuronal and astrocytic Ca2+-transient parameters in awake head-fixed mice up to a depth of 1700 {micro}m. Furthermore, we longitudinally record dendritic spine density (0.41 {+/-}0.07 {micro}m-1) deeper than 1 mm for a week. Using 1650 nm wavelength to excite red fluorescent microglia, we quantify their processes motility (58.9 {+/-}2% turnover rate) at previously unreachable depths (1100 {micro}m). We establish three-photon imaging of the mPFC enabling neuronal and glial recordings with subcellular resolution that will pave the way for novel discoveries in this brain region.

neuroscience↗

bioRxiv2023

Aberrant hippocampal Ca2+ micro-waves following synapsin-dependent adenoviral expression of Ca2+ indicators

Genetically encoded calcium indicators (GECIs) such as GCaMP are invaluable tools in neuroscience to monitor neuronal activity using optical imaging. The viral transduction of GECIs is commonly used to target expression to specific brain regions, can be conveniently used with any mouse strain of interest without the need for prior crossing with a GECI mouse line and avoids potential hazards due to the chronic expression of GECIs during development. A key requirement for monitoring neuronal activity with an indicator is that the indicator itself minimally affects activity. Here, using common adeno-associated viral (AAV) transduction procedures, we describe spatially confined aberrant Ca2+ micro-waves slowly travelling through the hippocampus following expression of GCaMP6, GCaMP7 or R-CaMP1.07 driven by the synapsin promoter with AAV-dependent gene transfer, in a titre-dependent fashion. Ca2+ micro-waves developed in hippocampal CA1 and CA3, but not dentate gyrus (DG) nor neocortex, were typically first observed at 4 weeks after viral transduction, and persisted up to at least 8 weeks. The phenomenon was robust, observed across laboratories with various experimenters and setups. Our results indicate that aberrant hippocampal Ca2+ micro-waves depend on the promoter and viral titre of the GECI, density of expression as well as the targeted brain region. We used an alternative viral transduction method of GCaMP which avoids this artifact. The results show that commonly used Ca2+-indicator AAV transduction procedures can produce artefactual Ca2+ responses. Our aim is to raise awareness in the field of these artefactual transduction-induced Ca2+ micro-waves and we provide a potential solution. Impact statement: Common AAV transduction procedures induce artefactual spatially confined Ca2+ waves in the hippocampus.

neuroscience↗

bioRxiv2023

Skewed distribution of spines is independent of presynaptic transmitter release and synaptic plasticity and emerges early during adult neurogenesis

Dendritic spines are crucial for excitatory synaptic transmission as the size of a spine head correlates with the strength of its synapse. The distribution of spine head sizes follows a lognormal-like distribution with more small spines than large ones. We analysed the impact of synaptic activity and plasticity on the spine size distribution in adult-born hippocampal granule cells from rats with induced homo- and heterosynaptic long-term plasticity in vivo and CA1 pyramidal cells from Munc-13-1-Munc13-2 knockout mice with completely blocked synaptic transmission. Neither induction of extrinsic synaptic plasticity nor the blockage of presynaptic activity degrades the lognormal-like distribution but changes its mean, variance and skewness. The skewed distribution develops early in the life of the neuron. Our findings and their computational modelling support the idea that intrinsic synaptic plasticity is sufficient for the generation, while a combination of intrinsic and extrinsic synaptic plasticity maintains lognormal like distribution of spines.

neuroscience↗

bioRxiv2022

Modelling the contributions to hyperexcitability in a mouse model of Alzheimer's disease

Neuronal hyperexcitability is a feature of Alzheimers disease (AD). Three main mechanisms have been proposed to explain it: i), dendritic degeneration leading to increased input resistance, ii), ion channel changes leading to enhanced intrinsic excitability, and iii), synaptic changes leading to excitation-inhibition (E/I) imbalance. However, the relative contribution of these mechanisms is not fully understood. Therefore, we performed biophysically realistic multi-compartmental modelling of excitability in reconstructed CA1 pyramidal neurons of wild-type and APP/PS1 mice, a well-established animal model of AD. We show that, for synaptic activation, the excitability promoting effects of dendritic degeneration are cancelled out by excitability decreasing effects of synaptic loss. We find an interesting balance of excitability regulation with enhanced degeneration in the basal dendrites of APP/PS1 cells potentially leading to increased excitation by the apical but decreased excitation by the basal Schaffer collateral pathway. Furthermore, our simulations reveal that three additional pathomechanistic scenarios can account for the experimentally observed increase in firing and bursting of CA1 pyramidal neurons in APP/PS1 mice. Scenario 1: increased excitatory burst input; scenario 2: enhanced E/I ratio and scenario 3: alteration of intrinsic ion channels (IAHP down-regulated; INap, INa and ICaT up-regulated) in addition to enhanced E/I ratio. Our work supports the hypothesis that pathological network and ion channel changes are major contributors to neuronal hyperexcitability in AD. Overall, our results are in line with the concept of multi-causality and degeneracy according to which multiple different disruptions are separately sufficient but no single disruption is necessary for neuronal hyperexcitability. In briefUsing a computational model, we find that changes in the extrinsic network and intrinsic biophysical neuronal properties rather than dendritic degeneration alone explain the altered firing behaviour observed in Alzheimers disease (AD). HighlightsO_LISimulations of synaptically driven responses in PCs with AD-related dendritic degeneration. C_LIO_LIDendritic degeneration alone alters PC responses to layer-specific input but additional pathomechanistic scenarios are required to explain neuronal hyperexcitability in AD. C_LIO_LIPossible scenario 1: Burst hyperactivity of the surrounding network can explain hyper-excitability of PCs during AD. C_LIO_LIPossible scenario 2: AD-related increased excitatory input together with decreased inhibitory input (E/I imbalance) can lead to hyperexcitability in PCs. C_LIO_LIPossible scenario 3: Changes in E/I balance combined with altered ion channel properties can account for hyperexcitability in AD. C_LI

neuroscience↗

bioRxiv2022

sDarken: Next generation genetically encoded fluorescent sensors for serotonin

We developed a new family of genetically encoded serotonin (5-HT) sensors (sDarken) on the basis of the native 5-HT1A receptor and circularly permuted GFP. sDarken 5-HT sensors are bright in the unbound state and diminish their fluorescence upon binding of 5-HT. Sensor variants with different affinities for serotonin were engineered to increase the versatility in imaging of serotonin dynamics. Experiments in vitro and in vivo showed the feasibility of imaging serotonin dynamics with high temporal and spatial resolution. As demonstrated here, the designed sensors showed excellent membrane expression, have high specificity, a superior signal-to-noise ratio, detect the endogenous release of serotonin and are suitable for two-photon in vivo imaging.

neuroscience↗

bioRxiv2021

Orfamide-A-mediated bacterial-algal interactions involve specific Ca2+ signalling pathways

The antagonistic bacterium Pseudomonas protegens secretes the cyclic lipopeptide orfamide A, which triggers a Ca2+ signal, causing the deflagellation of the green microalga Chlamydomonas reinhardtii. By investigating targeted synthetic orfamide A variants and inhibitors, we found that at least two Ca2+-signalling pathways and TRP channels are involved in this response.

microbiology↗

bioRxiv2021

A polyyne toxin produced by an antagonistic bacterium blinds and lyses a green microalga

Microalgae are key contributors to global carbon fixation and the basis of many food webs. In nature, their growth is often supported or suppressed by other microorganisms. The bacterium Pseudomonas protegens Pf-5 arrests the growth of the green alga Chlamydomonas reinhardtii, deflagellates the alga by the cyclic lipopeptide orfamide A, and alters its morphology. Using a combination of Raman microspectroscopy, genome mining and mutational analysis, we discovered a novel polyyne toxin we name protegencin that is secreted by P. protegens and penetrates algal cells to destroy their primitive visual system, the eyespot. Together with secreted orfamide A, protegencin prevents the phototactic behavior of C. reinhardtii needed to perform optimal photosynthesis. A protegencin-deficient biosynthetic mutant of P. protegens does not affect growth or eyespot carotenoids of C. reinhardtii. Thus, protegencin acts in a direct and destructive way, and reveals at least a two-pronged molecular strategy used by algicidal bacteria.

plant biology↗

bioRxiv2020

The diagonal band of broca continually regulates olfactory-mediated behaviors by modulating odor-evoked responses within the olfactory bulb

Sensory perception is modulated in a top-down fashion by higher brain regions to regulate the strength of its own input resulting in the adaptation of behavioral responses. In olfactory perception, the horizontal diagonal band of broca (HDB), embedded in the basal forebrain modulates olfactory information processing by recruiting olfactory bulb (OB) interneurons to shape excitatory OB output. Currently, little is known about how specific HDB to OB top-down signaling affects complex olfactory-mediated behaviors. Here we show that the olfactory bulb is strongly and differentially innervated by HDB projections. HDB-silencing via tetanus toxin light chain led to reduced odor-evoked Ca2+-responses in glomeruli of the OB, underscoring HDBs role in odor response modulation. Furthermore, selective, light-mediated silencing of HDB to OB afferents completely prevented olfactory-mediated habituation and discrimination behaviors. Notably, also social habituation and discrimination behaviors were affected. Mono-transsynaptic tracing studies indicated a robust HDB innervation from the paraventricular nucleus (PVN). Here we provide evidence for a novel tri-synaptic PVN-HDB-OB axis responsible for modulating these types of behavior. Thus, HDB to OB projections constitute a central top-down pathway for olfactory-mediated habituation and discrimination behaviors.

neuroscience↗

bioRxiv2020

Hippocampal hyperactivity in a rat model of Alzheimers disease

Neuronal network dysfunction is a hallmark of Alzheimers disease (AD). However, the underlying pathomechanisms remain unknown. We analyzed the hippocampal micronetwork in a rat model of AD at an early disease stage at the beginning of extracellular amyloid beta (A{beta}) deposition. We established two-photon Ca2+-imaging in vivo in the hippocampus of rats and found hyperactivity of CA1 neurons. Patch-clamp recordings in brain slices in vitro revealed changes in the passive properties and intrinsic excitability of CA1 pyramidal neurons. Furthermore, we observed increased neuronal input resistance and prolonged action potential width in CA1 pyramidal neurons. Surprisingly, all parameters measured to quantify synaptic inhibition and excitation onto CA1 pyramidal neurons were intact suggesting a cell immanent deficit. Our data support the view that altered intrinsic excitability of CA1 neurons may precede inhibitory dysfunction at an early stage of disease progression.

neuroscience↗

bioRxiv2019

Microglia motility depends on neuronal activity andpromotes structural plasticity in the hippocampus

Microglia, the resident immune cells of the brain, play a complex role in health and disease. They actively survey the brain parenchyma by physically interacting with other cells and structurally shaping the brain. Yet, the mechanisms underlying microglia motility and their significance for synapse stability, especially during adulthood, remain widely unresolved. Here we investigated the impact of neuronal activity on microglia motility and its implication for synapse formation and survival. We used repetitive two-photon in vivo imaging in the hippocampus of awake mice to simultaneously study microglia motility and their interaction with synapses. We found that microglia process motility depended on neuronal activity. Simultaneously, more dendritic spines emerged in awake compared to anesthetized mice. Interestingly, microglia contact rates with individual dendritic spines were associated with their stability. These results suggest that microglia are not only sensing neuronal activity, but participate in synaptic rewiring of the hippocampus during adulthood, which has profound relevance for learning and memory processes.

neuroscience↗