Biology subjects

Gautam, I.

Publications and source records attributed to Gautam, I..

4 recordsLinked to original sources

bioRxiv2024

Aspergillus nidulans cell wall integrity kinase, MpkA, impacts cellular phenotypes that alter mycelial-material mechanical properties

Mycelial materials are an emerging, natural material made from filamentous fungi that have the potential to replace unsustainable materials used in numerous commercial applications (e.g., packaging, textiles, construction). Efforts to change the mechanical properties of mycelial-materials have typically involved altering growth medium, processing approaches, or fungal species. Although these efforts have shown varying levels of success, all approaches have shown there is a strong correlation between phenotype (of both fungal mycelia and mycelial materials assembly) and resultant mechanical properties. We hypothesize that genetic means can be used to generate specific fungal phenotypes, leading to mycelial materials with specific mechanical properties. To begin to test this hypothesis, we used a mutant of the model filamentous fungus, Aspergillus nidulans, with a deletion of the last kinase in the cell wall integrity (CWI) signaling pathway, mpkA. We generated one set of mycelial materials from the {Delta}mpkA deletion mutant (A1404), and another from its isogenic parent (A1405; control). When subjected to tensile testing, and compared to material generated from the control, {Delta}mpkA material has similar elastic modulus, but significantly increased ultimate tensile strength, and strain at failure. When subjected to a fragmentation assay (i.e., resistance to shear-stress), the {Delta}mpkA material also had higher relative mechanical strength. To determine possible causes for this behavior, we carried out a comprehensive set of phenotype assessments focused on: three-dimensional structure, hyphal morphology, hyphal growth behaviors, and conidial development. We find, compared to the control, material generated from the {Delta}mpkA mutant manifests significantly less development, a modified cell wall composition, larger diameter hyphae, more total biomass, higher water capacity and more densely packed material, which all appear to impact the altered mechanical properties.

bioengineering↗

bioRxiv2024

Comparative Analysis of Polysaccharide and Cell Wall Structure in Aspergillus nidulans and Aspergillus fumigatus by Solid-State NMR

Invasive aspergillosis poses a significant threat to immunocompromised patients, leading to high mortality rates associated with these infections. Targeting the biosynthesis of cell wall carbohydrates is a promising strategy for antifungal drug development and will be advanced by a molecular-level understanding of the native structures of polysaccharides within their cellular context. Solid-state NMR spectroscopy has recently provided detailed insights into the cell wall organization of Aspergillus fumigatus, but genetic and biochemical evidence highlights species-specific differences among Aspergillus species. In this study, we employed a combination of 13C, 15N, and 1H-detection solid-state NMR, supplemented by Dynamic Nuclear Polarization (DNP), to compare the structural organization of cell wall polymers and their assembly in the cell walls of A. fumigatus and A. nidulans, both of which are key model organisms and human pathogens. The two species exhibited a similar rigid core architecture, consisting of chitin, -glucan, and {beta}-glucan, which contributed to comparable cell wall properties, including polymer dynamics, water retention, and supramolecular organization. However, differences were observed in the chitin, galactosaminogalactan, protein, and lipid content, as well as in the dynamics of galactomannan and the structure of the glucan matrix.

biophysics↗

bioRxiv2023

Structural Remodeling of Fungal Cell Wall Promotes Resistance to Echinocandins

The insufficient efficacy of existing antifungal drugs and the rise in resistance necessitate the development of new therapeutic agents with novel functional mechanisms1,2. Echinocandins are an important class of antifungals that inhibit {beta}-1,3-glucan biosynthesis to interfere with cell wall structure and function3,4. However, their efficacy is limited by the fungistatic activity against Aspergillus species and the trailing effect during clinical application. Here, we describe how echinocandins remodel the supramolecular assembly of carbohydrate polymers in the fungal cell wall in an unexpected manner, possibly resulting in a subsequent inhibition of the activity of these drugs. Solid-state nuclear magnetic resonance (ssNMR) analysis of intact cells from the human pathogenic fungus Aspergillus fumigatus showed that the loss of {beta}-1,3-glucan and the increase of chitin content led to a decrease in cell wall mobility and water-permeability, thus enhancing resistance to environmental stresses. Chitosan and -1,3-glucan were found to be important buffering molecules whose physical association with chitin maintained the wall integrity. These new findings revealed the difficult-to-understand structural principles governing fungal pathogens response to echinocandins and opened new avenues for designing novel antifungal agents with improved efficacy.

biophysics↗

bioRxiv2022

Genomic profiling of climate adaptation in Aedes aegypti along an altitudinal gradient in Nepal indicates non-gradual expansion of the disease vector

BackgroundDriven by globalization, urbanization and climate change, the distribution range of invasive vector species has expanded to previously colder ecoregions. To reduce health-threatening impacts on humans, insect vectors are extensively studied. Population genomics can reveal the genomic basis of adaptation and help to identify emerging trends of vector expansion. ResultsBy applying whole genome analyses and genotype-environment associations to populations of the main dengue vector Ae. aegypti, sampled along an altitudinal temperature gradient in Nepal (200- 1300m), we identify adaptive traits and describe the species genomic footprint of climate adaptation to colder ecoregions. We found two clusters of differentiation with significantly different allele frequencies in genes associated to climate adaptation between the highland population (1300m) and all other lowland populations ([≤] 800 m). We revealed non-synonymous mutations in 13 of the candidate genes associated to either altitude, precipitation or cold tolerance and identified an isolation-by-environment differentiation pattern. ConclusionOther than the expected gradual differentiation along the altitudinal gradient, our results reveal a distinct genomic differentiation of the highland population. This finding either indicates a differential invasion history to Nepal or local high-altitude adaptation explaining the populations phenotypic cold tolerance. In any case, this highland population can be assumed to carry pre-adapted alleles relevant for the species invasion into colder ecoregions worldwide that way expanding their climate niche.

genomics↗