Biology subjects

Hofmockel, K. S.

Publications and source records attributed to Hofmockel, K. S..

6 recordsLinked to original sources

bioRxiv2025

Effects of matric versus osmotic potential changes on Variovorax beijingensis transcription

Soil microbes must continuously adapt to changes in water availability, which dynamically fluctuates with weather and irrigation, and these adaptations are closely linked to soil CO2 emissions. Soil water potential, which regulates microbe-available water, is controlled by both osmotic and matric potential, which both increase as soils dry. While both parameters can independently increase water potential, the genetic mechanisms underlying microbial responses to both are unknown, with potentially different mechanisms available for soil microbes to respond to these hydrologic parameters. To explore microbial responses to matric versus osmotic potential shifts, we evaluated the growth and transcription of Variovorax beijingensis in soils and liquid cultures of varying water potential. We find this microbe respires in dilute minimal medium (-240 {+/-}104 kPa), in liquid medium supplemented with sucrose (-1323 {+/-}20.8 kPa), and in a pair of matrices that span a similar range of pressures (-183 {+/-}55 and -1393 kPa {+/-}200 kPa). We show that the global gene expression patterns vary significantly across all four conditions, even when the matric potential and osmotic pressure are set to similar values. However, the direction of gene expression changes correlated for 68% of the transcripts arising from an increase in osmotic pressure within liquid medium and an increase in matric potential within the different soils. While a large overlap was observed in the Variovorax transcriptional response to shifts in both osmotic and matric potential, the responses were not identical, with matric potential shifts leading to 2.55-fold more genes exhibiting differential expression. IMPORTANCEIt remains hard to establish how changes in soil water properties affect microbial behaviors that regulate soil health, and the energy with which soil water is held is likely a holistic control on at least some of those microbial behaviors. This energy is controlled by parameters associated with soil saltiness (osmotic potential) and texture (matric potential), which both alter bioavailable water by contributing to total soil water potential. To investigate how the global transcriptional profile of a soil microbe changes when the microbe-available water is altered either by changing soil texture or by changing osmolyte concentrations, we varied osmotic and matric potential individually and performed RNA sequencing. We observe differences in the transcriptome across all conditions analyzed. A larger number of genes are differentially expressed as matric potential increases; however, many of the transcripts differentially expressed as osmotic pressure increases covary with those observed as the matrix potential increases.

systems biology↗

bioRxiv2023

Global Biogeography of the Soil Virosphere

Historically neglected by microbial ecologists, soil viruses are now thought to be critical to global biogeochemical cycles. However, our understanding of their global distribution, activities, and interactions with the soil microbiome remains limited. Here, we present the Global Soil Virus (GSV) Atlas, a comprehensive dataset compiled from 2,953 previously sequenced soil metagenomes and comprised of 616,935 uncultivated viral genomes (UViGs) and 38,508 unique viral operational taxonomic units (vOTUs). Rarefaction curves from the GSV Atlas indicate that most soil viral diversity remains unexplored, further underscored by high spatial turnover and low rates of shared vOTUs across samples. By examining genes associated with biogeochemical functions, we also demonstrate the viral potential to impact soil carbon and nutrient cycling. This study represents an extensive characterization of soil viral diversity and provides a foundation for developing testable hypotheses regarding the role of the virosphere in the soil microbiome and global biogeochemistry.

ecology↗

bioRxiv2023

Fungal organic acid uptake of mineral derived K is dependent on distance from carbon hotspot

Fungal mineral weathering processes regulate the bioavailability of inorganic nutrients from mineral surfaces to organic matter and increase the bioavailable fraction of nutrients. Fungal mineral weathering strategies can be classified as biomechanical (direct) or biochemical (indirect). In the case of fungal uptake of mineral nutrients through indirect weathering, it is widely hypothesized that uptake of mineral derived nutrients occurs through organic acid chelation, but such processes have not been directly visualized. This is in part due to challenges in probing the complex and heterogeneous soil environment. Here, using an epoxy-based mineral doped soil micromodel platform that we developed, which mimics soil mineralogy and structure, it permitted us to visualize and spatially probe the molecular mechanisms of mineral weathering. Mass spectrometry imaging revealed differences in the distribution of fungal exudates, citric acid and tartaric acid, on the soil micromodels in presence of minerals. Citric acid was detected closer to the nutrient rich inoculation point, whereas tartaric acid was highly abundant away from inoculation point. This suggested that the organic acid exuded by the fungi depended on the proximity from the carbon rich organic substrate at the point of inoculation. Using a combination of X-ray fluorescence and X-ray near edge structure analysis, we identified citric acid- and tartaric acid-bound K within fungal hyphae networks grown in the presence of minerals. Combined our results provide direct evidence that fungi uptake and transport mineral derived nutrient organic acid chelation. The results of this study provided unprecedented visualization of fungal weathering of soil minerals and hyphal K+ transport, while resolving the indirect weathering mechanism of fungal K uptake from mineral interfaces.

ecology↗

bioRxiv2021

Fungal Mineral Weathering Mechanisms Revealed Through Direct Molecular Visualization

Soil fungi facilitate the translocation of inorganic nutrients from soil minerals to other microorganisms and plants. This ability is particularly advantageous in impoverished soils, because fungal mycelial networks can bridge otherwise spatially disconnected and inaccessible nutrient hotspots. However, the molecular mechanisms underlying fungal mineral weathering and transport through soil remains poorly understood. Here, we addressed this knowledge gap by directly visualizing nutrient acquisition and transport through fungal hyphae in a mineral doped soil micromodel using a multimodal imaging approach. We observed that Fusarium sp. DS 682, a representative of common saprotrophic soil fungi, exhibited a mechanosensory response (thigmotropism) around obstacles and through pore spaces ([~]12 {micro}m) in the presence of minerals. The fungus incorporated and translocated potassium (K) from K-rich mineral interfaces, as evidenced by visualization of mineral derived nutrient transport and unique K chemical moieties following fungal induced mineral weathering. Specific membrane transport proteins were expressed in the presence of minerals, including those involved in oxidative phosphorylation pathways and transmembrane transport of small molecular weight organic acids. This study establishes the significance of fungal biology and nutrient translocation mechanisms in maintaining fungal growth under water and nutrient limitations in a soil-like microenvironment.

microbiology↗

bioRxiv2019

Untapped viral diversity in global soil metagenomes

Viruses outnumber every other biological entity on Earth, and soil viruses are particularly diverse compared to other habitats. However, we have limited understanding of soil viruses because of the tremendous variation in soil ecosystems and because of the lack of appropriate screening tools. Here, we determined the global distribution of more than 24,000 soil viral sequences and their potential hosts, including >1,600 sequences associated with giant viruses. The viral sequences, derived from 668 terrestrial metagenomes, greatly extend existing knowledge of soil viral diversity and viral biogeographical distribution. We screened these sequences to identify a suite of cosmopolitan auxiliary metabolic genes (AMGs) encoding enzymes involved in soil organic carbon decomposition across soil biomes. Additionally, we provide evidence for viral facilitation of multi-domain linkages in soils by locating a fungal chitosanase in bacteriophages, generating a new paradigm of how viruses can serve as exchange vectors of carbon metabolism across domains of life.

microbiology↗

bioRxiv2019

Selection, succession and stabilization of soil microbial consortia

Soil microorganisms play fundamental roles in cycling of soil carbon, nitrogen and other nutrients, yet we have a poor understanding of how soil microbiomes are shaped by their nutritional and physical environment. Here we investigated the successional dynamics of a soil microbiome during 21-weeks of enrichment on chitin and its monomer, N-acetylglucosamine. We examined succession of the soil communities in a physically heterogeneous soil matrix as well as a highly mixed liquid medium. The guiding hypothesis was that the initial species richness would influence the tendency for the selected consortia to stabilize and maintain relatively constant community structure over time. We also hypothesized that long term, substrate-driven growth would result in consortia with reduced species richness as compared to the parent microbiome and that this process would be deterministic with relatively little variation between replicates. We found that the initial species richness does influence the long-term community stability in both liquid media and soil and that lower initial richness results in a more rapid convergence to stability. Despite use of the same soil inoculum and access to the same major substrate, the resulting community composition differed greatly in soil compared to liquid medium. Hence, distinct selective pressures in soils relative to homogenous liquid media exist and can control community succession dynamics. This difference is likely related to the fact that soil microbiomes are more likely to thrive, with fewer compositional changes, in a soil matrix compared to liquid environments. IMPORTANCEThe soil microbiome carries out important ecosystem functions, but interactions between soil microbial communities have been difficult to study due to the high microbial diversity and complexity of the soil habitat. Here we successfully obtained stable consortia with reduced complexity that contained species found in the original source soil. These consortia and the methods used to obtain them can be a valuable resource for exploration of specific mechanisms underlying soil microbial community ecology. The results of this study also provide new experimental context to better inform how soil microbial communities are shaped by new environments and how a combination of initial taxonomic structure and physical environment influences stability.

microbiology↗