Biology subjects

Traxler, M. F.

Publications and source records attributed to Traxler, M. F..

10 recordsLinked to original sources

bioRxiv2025

A widespread Actinobacterial G Protein System regulates production of specialized metabolites in Streptomyces coelicolor

Actinobacterial G protein systems (AGPSs), also known as conservons, are regulatory systems that are broadly distributed within Actinomycetota. AGPSs are composed of a minimum of four proteins, including a sensor histidine kinase, a small Ras-like GTPase, a roadblock/MglB protein (likely a GTPase activating protein), and protein with a domain of unknown function that likely functions as a guanine-nucleotide exchange factor (GEF). While progress has been made in understanding AGPS function at the mechanistic level, the phylogenetic distribution of individual AGPSs, and the genes and processes they regulate, remain largely unmapped. Previously, the Cvn8 AGPS of Streptomyces coelicolor was found to influence expression of genes in multiple specialized metabolic pathways during interspecies interactions with other actinomycetes. However, the impact of the Cvn8 AGPS on specialized metabolism has not been assessed at the chemical level. Here, we investigated the phylogenetic distribution of the Cvn8 AGPS clade,and assessed the impact of the Cvn8 AGPS on natural product biosynthesis using untargeted metabolomics. In a set of 485 actinobacterial genomes, we found that members of the clade that includes the Cvn8 AGPS from S. coelicolor are widely distributed in the lineages known to produce specialized metabolites. We also found that in S. coelicolor, the pattern of specialized metabolite production varied in mutants lacking specific components of the Cvn8 AGPS. Specifically, normal production of the pigmented antibiotic actinorhodin during interspecies interactions required cvnA8 and cvnF8, while a{Delta} cvnD8 overproduced undecylprodigiosin. Together, these results connect a widespread AGPS to control of specialized metabolism in a model actinomycete. ImportanceActinobacterial G protein systems (AGPSs) are found widely in bacteria in the phylum Actinomycetota, including genera like Streptomyces that produce many useful molecules and pathogens such as Mycobacterium tuberculosis. The genes and functions regulated by these regulatory systems are largely unknown. Here we investigated the role of the Cvn8 AGPS in controlling the production of specialized metabolites, like antibiotics, in the model actinomycete Streptomyces coelicolor. We found that specific components of the Cvn8 AGPS were required for normal production of the antibiotic actinorhodin during interactions between S. coelicolor and another actinomycete. We also show that Cvn8 belongs to a group of AGPSs that is found broadly in the genus Streptomyces and in more distantly related orders of Actinomycetota such as the Pseudonorcardiales and Micromonosporales. Together, these results raise the possibility that this group of AGPSs may influence specialized metabolism across a broad range of Actinomycetota lineages.

microbiology↗

bioRxiv2025

The accessory protein CvnF8 modulates histidine kinase activity in an Actinobacterial G protein system in Streptomyces coelicolor

Conservons are regulatory systems found in bacteria of the phylum Actinomycetota. These regulatory systems are composed of four core proteins: a sensor histidine kinase-like protein (CvnA homolog), an MglA-type roadblock protein (CvnB homolog), a protein containing a domain of unknown function (CvnC homolog), and small Ras-like GTPase (CvnD homolog). Based on their conserved small GTPase components and their phylogenetic distribution, we propose that conservons should be known as Actinobacterial G protein systems (AGPSs). The signal transduction path through AGPSs remains poorly understood, and some AGPSs have additional accessory proteins (CvnE and CvnF homologs) of unknown function. In this work, we show that AGPS accessory proteins are present when the cognate histidine kinase protein (CvnA homolog) lacks an extracytoplasmic sensory domain. It was previously shown that the Cvn8 AGPS of Streptomyces coelicolor controls expression of multiple pathways for specialized metabolism and that the Cvn8 AGPS contains an accessory protein, CvnF8. Through protein modeling, we found that CvnF8 may share an interaction interface with the histidine kinase CvnA8, prompting the hypothesis that CvnF8 may serve as a modulator of CvnA8 activity. We found that in a purified system, CvnF8 strongly stimulated the ATPase activity and autophosphorylation of CvnA8. Taken together, these findings indicate that CvnF family accessory proteins likely serve as sensors and/or modulators of histidine kinases of AGPSs found broadly in Actinomycetota. Importance StatementMany lineages of bacteria in the phylum Actinomycetota contain conserved operons (conservons) that encode an unusual type of regulatory system whose function is poorly understood. These lineages include pathogens such as Mycobacterium tuberculosis and members of the genus Streptomyces that produce valuable natural products. These regulatory systems are composed of four proteins, including a sensor histidine kinase, a small Ras-like GTPase, a likely GTPase activating protein, and a protein containing a domain of unknown function. Given this composition, we propose that these regulatory modules be known as Actinobacterial G protein systems (AGPSs). We show that some AGPSs include accessory proteins that are only found with partner histidine kinases that lack sensory domains. We demonstrate that one such accessory protein can control the activity of its cognate histidine kinase. Together this work indicates that these CvnF-family accessory proteins likely serve as sensory inputs for AGPSs found broadly in Actinomycetota.

microbiology↗

bioRxiv2025

Uncovering the hidden diversity and functional roles of root endophytic Streptomyces under drought stress

The genus Streptomyces has consistently been found to be enriched in drought-stressed plant root microbiomes, yet the ecological basis and functional variation underlying this enrichment at the strain and isolate level remain unclear. Using two 16S rRNA sequencing methods with different levels of taxonomic resolution, we confirmed drought-associated enrichment of Streptomyces in field-grown sorghum roots and identified five closely related but distinct ASVs belonging to the genus with variable drought enrichment patterns. From a culture collection of sorghum root endophytes, we selected 12 Streptomyces isolates representing these ASVs for phenotypic and genomic characterization. Whole-genome sequencing revealed substantial variation in gene content, even among closely related isolates, and exometabolomic profiling showed distinct metabolic responses to media supplemented with drought-versus well-watered root tissue. Traits linked to drought survival, including osmotic stress tolerance, siderophore production, and carbon utilization, varied widely among isolates and were not phylogenetically conserved. Using a broader panel of 48 Streptomyces, we demonstrate that drought enrichment (DE) scores, determined through mono-association experiments in gnotobiotic sorghum systems, showed high variability and lacked correlation with plant growth promotion. Pangenome-wide association identified gene clusters involved in osmolyte transport (e.g., proP) and membrane biosynthesis (e.g., fabG) as positively associated with DE, though most associations lacked phylogenetic signal. Collectively, these results demonstrate that Streptomyces enrichment under drought is not a conserved genus-level trait but is instead strain-specific and functionally heterogeneous. Furthermore, enrichment in the root microbiome does not predict beneficial effects on plant growth. This work underscores the need to resolve functional traits at the strain level and highlights the complexity of microbe-host-environment interactions under abiotic stress. ImportanceUnderstanding how beneficial microbes respond to drought is critical for developing microbiome-based strategies to enhance crop resilience. The Streptomyces genus is consistently enriched in drought-stressed root microbiomes, yet our study reveals that this enrichment is not a uniform isolate-level response. Instead, we show that drought enrichment is highly strain-specific and functionally diverse, with key associated traits like osmotic stress tolerance and siderophore production varying independently of phylogeny. Importantly, enrichment does not predict a microbes ability to promote plant growth under stress. By integrating high-resolution taxonomic, genomic, and metabolomic approaches, we uncover the ecological and functional complexity underlying Streptomyces responses to drought. These findings emphasize the importance of resolving microbial function at the strain level and caution against assuming functional traits based on taxonomic identity itself.

microbiology↗

bioRxiv2023

Surface-active antibiotic production is a multifunctional adaptation for postfire microbes

Wildfires affect soils in multiple ways, leading to numerous challenges for colonizing microbes. While it is thought that fire-adapted microbes lie at the forefront of postfire ecosystem recovery, the specific strategies that these microbes use to thrive in burned soils remain largely unknown. Through bioactivity screening of bacterial isolates from burned soils, we discovered that several Paraburkholderia spp. isolates produced a set of unusual rhamnolipid surfactants with a natural methyl ester modification. These rhamnolipid methyl esters (RLMEs) exhibited enhanced antimicrobial activity against other postfire microbial isolates, including pyrophilous Pyronema fungi and Amycolatopsis bacteria, compared to the typical rhamnolipids made by organisms such as Pseudomonas spp. RLMEs also showed enhanced surfactant properties and facilitated bacterial motility on agar surfaces. In vitro assays further demonstrated that RLMEs improved aqueous solubilization of polycyclic aromatic hydrocarbons, which are potential carbon sources found in char. Identification of the rhamnolipid biosynthesis genes in the postfire isolate, Paraburkholderia caledonica str. F3, led to the discovery of rhlM, whose gene product is responsible for the unique methylation of rhamnolipid substrates. RhlM is the first characterized bacterial representative of a large class of integral membrane methyltransferases that are widespread in bacteria. These results indicate multiple roles for RLMEs in the postfire lifestyle of Paraburkholderia isolates, including enhanced dispersal, solubilization of potential nutrients, and inhibition of competitors. Our findings shed new light on the chemical adaptations that bacteria employ in order to navigate, grow, and outcompete other soil community members in postfire environments. Significance StatementWildfires are increasing in frequency and intensity at a global scale. Microbes are the first colonizers of soil after fire events, but the adaptations that help these organisms survive in postfire environments are poorly understood. In this work, we show that a bacterium isolated from burned soil produces an unusual rhamnolipid biosurfactant that exhibits antimicrobial activity, enhances motility, and solubilizes potential nutrients derived from pyrolyzed organic matter. Collectively, our findings demonstrate that bacteria leverage specialized metabolites with multiple functions to meet the demands of life in postfire environments. Furthermore, this work reveals the potential of probing perturbed environments for the discovery of unique compounds and enzymes.

microbiology↗

bioRxiv2023

A Taxonomically-informed Mass Spectrometry Search Tool for Microbial Metabolomics Data

MicrobeMASST, a taxonomically-informed mass spectrometry (MS) search tool, tackles limited microbial metabolite annotation in untargeted metabolomics experiments. Leveraging a curated database of >60,000 microbial monocultures, users can search known and unknown MS/MS spectra and link them to their respective microbial producers via MS/MS fragmentation patterns. Identification of microbial-derived metabolites and relative producers, without a priori knowledge, will vastly enhance the understanding of microorganisms role in ecology and human health.

microbiology↗

bioRxiv2023

Soil carbon mineralization and microbial community dynamics in response to PyOM addition

Wildfires can either negatively impact soil carbon (C) stocks through combustion or increase soil carbon stocks through the production of pyrogenic organic matter (PyOM), which is highly persistent and can affect non-pyrogenic soil organic carbon (SOC) mineralization rates. In this study, we used fine-resolution 13CO2 flux tracing to investigate PyOM-C mineralization, soil priming effects, and their impacts on soil microbial communities in a Californian mixed conifer forest Xerumbrept soil burned in the 2014 King Fire. We added PyOM produced from pine biomass at 350 {degrees}C and 550 {degrees}C to the soil and separately traced the mineralization of 13C-labeled water-extractable and non-water-extractable PyOM-C fractions in a short-term incubation. Our results indicate that the water-extractable fraction is 10-50x more mineralizable in both 350 {degrees}C and 550 {degrees}C PyOM treatments than the SOC or non-water-extractable PyOM fraction. 350 {degrees}C PyOM addition led to a short-term positive priming effect, likely due to co-metabolism of easily mineralizable PyOM-C and the SOC, whereas 550 {degrees}C PyOM addition induced negative priming, potentially due to physical protection of SOC. We observed significant shifts in bacterial community composition in response to both 350 {degrees}C and 550 {degrees}C PyOM, with positive PyOM responders belonging to the genera Noviherbaspirillum, Pseudonocardia, and Gemmatimonas. In contrast, fungal communities were less responsive to PyOM additions. Our findings expand our understanding of the post-fire cycling of PyOM and SOC, providing insights into the microbial mineralization of different PyOM-C fractions and their influence on soil C dynamics in fire-affected ecosystems.

ecology↗

bioRxiv2022

Prescribed fire selects for a pyrophilous soil subcommunity in a northern California mixed conifer forest.

Low intensity prescribed fire is a critical strategy for mitigating the effects of catastrophic wildfires. The above-ground response to fire has been well-documented, including many ecosystem benefits associated with prescribed burning, but fewer studies have directly addressed the effect of prescribed fire on soil organisms. We aimed to understand how soil microbial communities respond to prescribed fire and to determine the ecological processes driving their dynamics. We extensively sampled four plots for 17 months in a mixed conifer forest in northern California, USA; immediately following a low-intensity prescribed fire, a higher-intensity prescribed fire, and two no-burn control plots. We found that prescribed fire significantly altered the community structure for both fungi (ITS) and bacteria (16S), which was sustained throughout the time-series. By comparing our community profiling results with a model of neutral community assembly, we found that the presence of most taxa across all experimental conditions could be explained by neutral processes. However, combining threshold indicator taxa analysis and correlation network analysis with the neutral model identified a cohort of taxa that responded deterministically to prescribed fire. The subcommunity identified through this series of analyses includes both known and new pyrophilous taxa. Beyond this, our analyses revealed network modules within postfire communities which were responsive to fire-intensity. Taken together, these results lay the foundation for building a process-driven understanding of microbial community assembly in the context of the classical disturbance regime of fire.

ecology↗

bioRxiv2021

Pyrolyzed substrates induce aromatic compound metabolism in the post-fire fungus, Pyronema domesticum

Wildfires represent a fundamental and profound disturbance in many ecosystems, and their frequency and severity are increasing in many regions of the world. Fire affects soil by removing carbon in the form of CO2 and transforming remaining surface carbon into pyrolyzed organic material (PyOM). Fires also generate substantial necromass at depths where the heat kills soil organisms but does not catalyze the formation of PyOM. Pyronema species strongly dominate soil fungal communities within weeks to months after fire. However, the carbon pool (i.e. necromass or PyOM) that fuels their rise in abundance is unknown. We used a Pyronema domesticum isolate from the catastrophic 2013 Rim Fire (CA, USA) to ask if P. domesticum is capable of metabolizing PyOM. P. domesticum grew readily on agar media where the sole carbon source was PyOM (specifically, pine wood PyOM produced at 750 {degrees}C). Using RNAseq, we investigated the response of P. domesticum to PyOM and observed a comprehensive induction of genes involved in the metabolism and mineralization of aromatic compounds, typical of those found in PyOM. Lastly, we used 13C-labeled 750 {degrees}C PyOM to demonstrate that P. domesticum is capable of mineralizing PyOM to CO2. Collectively, our results indicate a robust potential for P. domesticum to liberate carbon from PyOM in post-fire ecosystems and return it to the bioavailable carbon pool. IMPORTANCEFires are increasing in frequency and severity in many regions across the world. Thus, its critically important to understand how our ecosystems respond to inform restoration and recovery efforts. Fire transforms the soil, removing many nutrients while leaving behind both nutritious necromass and complex pyrolyzed organic matter, which is often recalcitrant. Filamentous fungi of the genus Pyronema strongly dominate soil fungal communities soon after fire. While Pyronema are key pioneer species in post-fire environments, the nutrient source that fuels their rise in abundance is unknown. In this manuscript, we used a P. domesticum isolate from the catastrophic 2013 Rim Fire (CA, USA) to demonstrate that P. domesticum metabolizes pyrolyzed organic material, effectively liberating this complex pyrolyzed carbon and returning it to the bioavailable carbon pool. The success of Pyronema in post-fire ecosystems has the potential to kick-start growth of other organisms and influence the entire trajectory of post-fire recovery.

microbiology↗

bioRxiv2020

Enhancement of antimicrobial diversity in situ through relaxed symbiont specificity in an insect/actinomycete partnership

Some insects form symbioses in which actinomycetes provide defense against pathogens by making antimicrobials. The range of chemical strategies employed across these associations, and how these strategies relate to insect lifestyle, remains underexplored. We assessed subsocial passalid beetles of the species Odontotaenius disjunctus, and their frass (fecal material) which is an important food resource within their galleries, as a model insect/actinomycete system. Through chemical and phylogenetic analyses, we found that O. disjunctus frass collected across eastern North America harbored multiple lineages of Streptomyces and diverse antimicrobials. Metabolites detected in frass displayed synergistic and antagonistic inhibition of a fungal entomopathogen, Metarhizium anisopliae, and multiple streptomycete isolates inhibited this pathogen when co-cultivated directly in frass. These findings support a model in which the lifestyle of O. disjunctus accommodates multiple Streptomyces lineages in their frass, resulting in a rich repertoire of antimicrobials that likely insulates their galleries against pathogenic invasion.

microbiology↗

bioRxiv2019

High Resolution Imaging Mass Spectrometry of Bacterial Microcolonies at Ecological Scales

Microbes interact with the world around them at the chemical level. However, directly examining the chemical exchange between microbes, and microbes and their environment, at ecological scales, i.e. the scale of a single bacterial cell or small groups of cells, remains a key challenge. Here we address this obstacle by presenting a methodology that enables Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) of bacterial microcolonies. By combining optimized sample preparation with sub-atmospheric pressure MALDI, we demonstrate that chemical output from groups of as few as ~50 cells can be visualized with MALDI-IMS. Application of this methodology to Bacillus subtilis and Streptomyces coelicolor revealed heterogeneity in chemical output across microcolonies, and asymmetrical metabolite production when cells grew within physiological gradients produced by Medicago sativa roots. Taken together, these results indicate that MALDI-IMS can readily visualize metabolites made by very small assemblages of bacterial cells, and that even these small groups of cells can differentially produce metabolites in response to local chemical gradients.

microbiology↗