Biology subjects

Gerrits, R.

Publications and source records attributed to Gerrits, R..

9 recordsLinked to original sources

bioRxiv2026

Biophysical properties of material-colonizing fungal biofilms: multiscale structural and mechanical characterization

Black extremotolerant fungi form persistent biofilms on a wide range of natural and engineered substrates. Able to weather minerals, affect stone monument surfaces, and colonize solar panels, they demonstrate a strong capacity to interact with and modify material surfaces, even under most extreme conditions. In this study, we establish a methodological workflow for the structural and mechanical characterization of melanized biofilms formed by the black fungus Knufia petricola. This species represents a broader group of resilient surface colonizers and provides a model for in-depth investigation. When grown on solid agar/air interface, this species predominantly forms a compact biofilm, composed of spherical cells, while retaining the capacity for filamentous growth, providing a suitable framework to explore morphology-dependent biomechanical responses. The proposed toolbox combines complementary analytical techniques spanning multiple spatial scales, including shear-rheology to quantify bulk viscoelastic behavior, micro-indentation to resolve local stiffness of the biofilm surface, micro-computed tomography for non-destructive three-dimensional visualization of biofilm architecture, and cryogenic preparation methods and electron microscopy for high-resolution ultrastructural analysis. As a case study, we applied this workflow to compare biofilms grown on two nitrogen sources (NO3- vs. NH4+). Our results reveal that the nitrogen source plays a key role in biofilm morphology across multiple hierarchical levels - ranging from cell division patterns and distribution of extracellular polymeric substances (EPS) to overall mechanical properties, where NO3- leads to budding-dominated growth and increased stiffness, whereas NH4+ promotes meristematic growth and softer biofilms. The successful transfer and integration of methods originally developed for bacterial biofilm research highlights the feasibility of quantitative mechanical analyses in fungal systems. This multiscale toolbox provides a foundation for advancing the mechanistic understanding of fungal biofilms and biofilm-material interactions, with implications for geomicrobiology, material biodeterioration, and the design of bio-inspired functional materials. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=147 SRC="FIGDIR/small/720134v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@7fd08borg.highwire.dtl.DTLVardef@15476c2org.highwire.dtl.DTLVardef@40be50org.highwire.dtl.DTLVardef@8e9410_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2026

Carbon and nitrogen availability affect biofilm growth and morphology of the extremotolerant fungus Knufia petricola

Rock-inhabiting fungi thrive in subaerial oligotrophic environments such as desert rocks, solar panels and marble monuments where organic carbon and nitrogen are scarce. We tested whether the rock-inhabiting fungus Knufia petricola showed a preference regarding nitrogen ([Formula] or [Formula]) and carbon (glucose or sucrose) sources and whether it was sensitive towards carbon and nitrogen limitation. As this fungus produces the carbon-rich, nitrogen-free 1,8-dihydroxynaphthalene (DHN) melanin, we tested whether a melanin-deficient mutant would be less sensitive to carbon limitation. The carbon and nitrogen concentrations were the primary predictors of growth, with a broad optimum partially explained by an optimal fungal C:N ratio. Limiting carbon or nitrogen supply decreased biomass formation, CO2 production and biofilm thickness but promoted substratum penetration through filamentous growth. The nitrogen content of the biomass was flexible within limits, increasing upon increasing nitrogen supply or decreasing carbon supply. The carbon use efficiency was fairly constant, whereas melanization correlated with a higher nitrogen content of the biomass despite melanin being nitrogen-free. In conclusion, in vitro, K. petricola switches to explorative growth under nutrient limitations, like fast-growing fungi, revealing universal fungal resource-acquisition patterns. Graphical abstract text and imageCarbon and nitrogen availability affect biofilm growth and morphology of the extremotolerant fungus Knufia petricola Abolfazl Dehkohneh, Julia Schumacher, Bastiaan J. R. Cockx, Karin Keil, Tessa Camenzind, Jan-Ulrich Kreft, Anna A. Gorbushina, Ruben Gerrits Growth of the rock-inhabiting fungus Knufia petricola was studied by varying carbon and nitrogen sources and concentrations. Overall, growth was best predicted by the carbon and nitrogen concentrations. Carbon and nitrogen limitation promoted substratum penetration through filamentous growth. O_FIG O_LINKSMALLFIG WIDTH=158 HEIGHT=200 SRC="FIGDIR/small/712823v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@6d98bdorg.highwire.dtl.DTLVardef@146aac5org.highwire.dtl.DTLVardef@757fa8org.highwire.dtl.DTLVardef@ff709_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Iron acquisition strategies of the rock-inhabiting fungus Knufia petricola reveal vulnerability to chelator-based mitigation

Fungal iron acquisition has mostly been studied for pathogens living in competitive environments where securing iron from the host is critical for proliferation. How fungi from stress-rich but competition-free material surfaces handle iron uptake is, however, unknown. We studied these processes in rock-inhabiting fungi, known for their constitutive melanin-production, extremotolerant lifestyle and colonization of exposed surfaces such as solar panels and marble monuments, by choosing Knufia petricola to represent this group. The characterization of targeted mutants showed that K. petricola produces an extracellular - yet undefined - siderophore on which it relies less than on the ferroxidase-iron permease complex for reductive iron assimilation. By disrupting melanin synthesis, it was demonstrated that this pigment can reduce and adsorb iron but nevertheless does not contribute significantly to iron acquisition. Moreover, growth towards an iron source was found to be siderophore-dependent. Ferric citrate could not be directly assimilated. Finally, it was found that K. petricola and other rock-inhabiting fungi exhibited high sensitivity to strong iron chelators such as EDTA. These observations not only offer a potential mitigation strategy for preventing fungal colonization of subaerial materials using iron chelators, but also highlight the specialized adaptations of these fungi to low-competition environments. ImportanceThe rock-inhabiting fungus Knufia petricola acquires iron primarily via reductive iron assimilation, independently of the iron-adsorbing and -reducing melanin. Its siderophore, although extracellular and allowing chemotropism towards an iron source, is not able to obtain iron from strong iron chelators such as BPS and EDTA. This sensitivity to iron sequestration opens avenues to mitigate the fungal colonization of materials such as solar panels.

microbiology↗

bioRxiv2025

The individual brain: mapping variability in hemispheric functional organization across cognitive domains in a representative sample

Several core cognitive networks in the human brain show marked left-right differences in their functional organization. While these asymmetries are well described at the level of individual functions, overarching patterns of variability in hemispheric functional organization across multiple domains have not been mapped in a representative sample. To address this gap, we conducted a large-scale neuroimaging study with 200 participants (100 left-handers and 100 right-handers) to map hemispheric phenotypes across four distinct cognitive domains: language, tool use, spatial attention, and face perception. We challenge the traditional one-size-fits-all view of hemispheric organization by showing that deviations from the typical pattern of functional segregation are more prevalent than generally assumed, in both left- and right-handers. As predicted, variation in asymmetry was more pronounced in the left-handed sample. Critically, we found no evidence that the prototypical, "textbook", pattern of brain organization confers any advantage in general cognitive ability or IQ. These results challenge the assumption of a single optimal brain organization and demonstrate that hemispheric functional segregation in humans is much more variable than anticipated.

neuroscience↗

bioRxiv2025

Revisiting atypical language lateralization in dyslexia

Hemispheric lateralization has been central to developmental dyslexia research for over a century, yet its role in the etiology of reading and language deficits remains elusive. While altered asymmetries have long been implicated, evidence is inconsistent, with limited consideration given to individual variability in lateralization patterns. This study investigated hemispheric lateralization in 35 adults with dyslexia and 35 matched controls using functional MRI across three language tasks: word generation, rhyming decision, and lexical decision. Laterality indices (LIs) were calculated to comprehensively assess the strength, direction, and consistency of activation across global and regional task-specific brain areas. Significant group differences were not found in the absolute strength of lateralization for global measures or any regional measures, except in the fusiform gyrus, where people with dyslexia showed lower asymmetry. Directional asymmetry was similar across the two groups, except in the fusiform gyrus during the reading task, where dyslexic individuals showed a higher prevalence of right-hemisphere lateralization compared to controls. Interestingly, we found that dyslexic participants demonstrated greater inconsistency in regional lateralization during reading and rhyming tasks. Among individuals with dyslexia, those with inconsistent lateralization in the reading task had weaker fusiform lateralization, although fusiform LI strength itself did not predict reading outcomes. Our findings suggest that dyslexia is characterized by inconsistent, rather than universally weaker, lateralization patterns. Inconsistencies in task-related and regional lateralization may disrupt the efficiency of language networks, contributing to observed reading deficits. By highlighting the role of regional and task-specific inconsistencies, this study provides new insights into the neural mechanisms underlying dyslexia and underscores the importance of considering individual variability in hemispheric lateralization when investigating language disorders.

neuroscience↗

bioRxiv2024

Neural substrates and behavioral relevance of speech envelope tracking: evidence from post-stroke aphasia

Neural tracking of the low-frequency temporal envelope of speech has emerged as a prominent tool to investigate the neural mechanisms of natural speech processing in the brain. However, there is ongoing debate regarding the functional role of neural envelope tracking. In this context, our study aims to offer a novel perspective by investigating the critical brain areas and behavioral skills required for neural envelope tracking in aphasia, a language disorder characterized by impaired neural envelope tracking. We analyzed an EEG dataset of 39 individuals with post-stroke aphasia suffering a left-hemispheric stroke who listened to natural speech. Our analysis involved lesion mapping, where left lesioned brain voxels served as binary features to predict neural envelope tracking measures. We also examined the behavioral correlates of receptive language, naming, and auditory processing (via rise time discrimination task) skills. The lesion mapping analysis revealed that lesions in language areas, such as the middle temporal gyrus, supramarginal gyrus and angular gyrus, were associated with poorer neural envelope tracking. Additionally, neural tracking was related to auditory processing skills and language (receptive and naming) skills. However, the effects on language skills were less robust, possibly due to ceiling effects in the language scores. Our [fi]ndings highlight the importance of central brain areas implicated in language understanding, extending beyond the primary auditory cortex, and emphasize the role of intact auditory processing and language abilities in effectively processing the temporal envelope of speech. Collectively, these [fi]ndings underscore the signi[fi]cance of neural envelope tracking beyond mere audibility and acoustic processes. Signi[fi]cance statementWhile some studies have proposed that neural envelope tracking primarily relates to audibility and acoustic speech processes, others have suggested its involvement in actual speech and language comprehension. By investigating the critical brain areas and behavioral skills essential in aphasia, we argue for a broader signi[fi]cance of neural envelope tracking in language processing. Furthermore, our [fi]ndings highlight a speci[fi]city among individuals with aphasia, indicating its correlation with lesions in temporal brain regions associated with receptive language functions. This addresses the signi[fi]cant heterogeneity in lesion characteristics present among individuals with aphasia and suggests the potential of neural tracking as an EEG-based tool for speci[fi]cally assessing receptive language abilities in this population.

neuroscience↗

bioRxiv2024

Individualized functional localization of the language and multiple demand network in chronic post-stroke aphasia

Recent research found a distinct dissociation between brain regions supporting domain-general cognitive processes and regions supporting core language functions. The question of whether individuals with post-stroke aphasia (IWA) exhibit a comparable dissociation remains debated, particularly as previous studies overlooked individual variability in functional network organization and aphasia heterogeneity. To address this gap, we employed an individualized functional localization approach to test the involvement of the domain-general multiple demand (MD) network during language processing in chronic aphasia. We collected functional MRI data in 15 IWA and 13 age-matched controls. Participants performed a spatial working memory task, triggering MD network activation, as well as a listening and reading task, triggering language network activation. We compared both groups individualized activation patterns and investigated the link with aphasia severity. Involvement of the MD network during language processing was examined by investigating language task activity within subject-specific regions that are active during the MD task. The language and MD network each generalized well across different task modalities, but exhibited robust spatial dissociation from each other in both groups. Moreover, there was no evidence of MD network activation during language processing in either group. Additionally, the language network showed weaker activation in IWA compared to controls in left-hemispheric brain regions, with higher activation values in the left correlating with improved language performance in IWA. In conclusion, our findings suggest that the MD network does not contribute to passive, receptive language functions in chronic aphasia or healthy older adults. Instead, our results align with previous research proposing that normalized left-hemispheric language activity supports language performance in chronic aphasia.

neuroscience↗

bioRxiv2020

Fibre-specific laterality of white matter in left and right language dominant people

Despite the typical symmetrical appearance of the human brain, several functional and structural asymmetries have been reported. Language is the most commonly described lateralised cognitive function, relying relatively more on the left hemisphere in over 90% of the population. This is in line with white matter studies which have revealed leftwards lateralisation of the arcuate fasciculus, a white matter tract that connects important language-related regions. Most research to date examining the structure-function relationship of language lateralisation only included people showing a left language hemisphere dominance. As such, the reported correlations do not allow for inferences of relationships between the directions of functional and structural lateralisation of language. In this work, we applied a state-of-the-art "fixel-based" analysis approach, which allows to statistically analyse white matter micro- and macrostructure on a fibre-specific level. To study lateralisation using this framework, we defined a bespoke fibre-specific laterality index which allowed us to examine whole-brain white matter asymmetries in samples of participants with left and right language dominance (LLD and RLD respectively). Both groups showed similar extensive and intricate patterns of significant white matter lateralisation. Few group differences were found between both groups, with a similar leftwards lateralisation of the arcuate fasciculus, regardless of functional language lateralisation of the participants. A significant group difference of lateralisation was detected in the forceps minor, with a leftwards lateralisation in LLD and rightwards lateralisation for the RLD group. In conclusion, we showed that fixel-based analysis of fibre-specific lateralisation indices is an effective approach to study white matter asymmetries. Our results suggest that the lateralisation of language functioning and the arcuate fasciculus are driven by independent biases. The exact relationship between forceps minor asymmetry and language dominance could be an interesting subject of future studies.

neuroscience↗

bioRxiv2017

Preparation for mental effort recruits Dorsolateral Prefrontal Cortex: an fNIRS investigation

Preparing for a mentally demanding task calls upon cognitive and motivational resources. The underlying neural implementation of these mechanisms is receiving growing attention, given the implications for professional, social, and medical contexts. While several fMRI studies converge in assigning a crucial role to a cortico-subcortical network including Anterior Cigulate Cortex (ACC) and striatum, the involvement of Dorsolateral Prefrontal Cortex (DLPFC) during mental effort anticipation has yet to be replicated. This study was designed to target DLPFC contribution using functional Near Infrared Spectroscopy (fNIRS), as a more cost-effective tool measuring cortical hemodynamics. We adapted a validated mental effort task, where participants performed easy and difficult mental calculation, while measuring DLPFC activity during the anticipation phase. As hypothesized, DLPFC activity increased during preparation for a hard task as compared to an easy task. Besides replicating a previous fMRI study, these results establish fNIRS as an effective tool to investigate cortical contributions to preparation for effortful behavior. This is especially useful if one requires testing large samples (e.g., to target individual differences), populations with contraindication for functional MRI (e.g., infants or patients with metal implants), or subjects in more naturalistic environments (e.g., work or sport).

neuroscience↗