Biology subjects

Weber, P. K.

Publications and source records attributed to Weber, P. K..

14 recordsLinked to original sources

bioRxiv2026

Oxidative stress reshapes diatom-microbiome interactions by shifting benefits from mutualistic to opportunistic bacteria

The roles of reactive oxygen species (ROS) as signaling molecules and inhibitors of phytoplankton growth are well documented. While phytoplankton physiological mechanisms for ROS detoxification are well characterized, the role of heterotrophic bacterial partners in ROS alleviation and outcomes for these bacteria remain poorly understood. Here, we examined how extracellular hydrogen peroxide (H2O2) shapes nutrient exchange between the diatom Phaeodactylum tricornutum and two phycosphere bacteria. From an initial screen of 20 bacteria, we identified a "helper" (Muricauda sp.) that enabled P. tricornutum to survive acute H2O2 stress and a "non-helper" (Algoriphagus sp.) that did not. Using nanoscale secondary ion mass spectrometry (nanoSIMS), we tracked diatom-derived carbon and nitrogen (13C and 15N) transfer to each bacterial partner under ROS stress. Oxidative stress disrupted diatom metabolism and altered nutrient transfer: diatom-derived carbon and nitrogen incorporation was significantly reduced in the helper but increased in the non-helper under H2O2 stress. Growth assays revealed that the helper preferentially utilized exudates from healthy, intact hosts, whereas the non-helper did not grow on exudates but thrived on lysates from damaged or lysed cells. Together, these findings indicate the helper was better adapted to accessing resources from living hosts, while the non-helper relied on nutrients released through ROS-induced host damage. Our results highlight oxidative stress as a key driver of algal-bacterial interactions and suggest that bacterial resource-acquisition strategy underlies host protection: bacteria utilizing healthy-host exudates are more likely to protect hosts from oxidative stress, while those benefiting from host damage are not, despite retaining ROS detoxification capacity.

microbiology↗

bioRxiv2026

Iron limitation alters diatom carbon flow through shifts in microbiome exometabolite consumption

Iron is required for photosynthesis, and thus affects biogeochemical cycling in widespread regions where its availability is limited. Turnover of aquatic photosynthetically-derived carbon is largely constrained by bacterial activity, but we lack a mechanistic understanding of how iron limitation influences this activity. We examined a bacterial enrichment community dependent on carbon from the diatom Phaeodactylum tricornutum to investigate how iron limitation alters the flow of carbon to bacteria, and exometabolite and community composition. Using stable isotope tracing, we quantified diatom exudate incorporation with single-cell-resolution. We identified a population of bacteria under iron limitation with high metabolic activity yet low incorporation of newly-fixed diatom carbon, indicating a shift in metabolism relative to the iron-replete control. Ultra-high-resolution exometabolomics revealed bacterial consumption of aromatics, lipid-like compounds, and purines and pyrimidines occurred under iron-limitation, when these compounds also exhibited increased exudation. We identified gene pathways for utilization of these compounds in taxa with increased abundance under iron limitation which may be responsible for carbon flow shifts. These results provide a mechanistic link between iron-limitation driven shifts in exudate composition and flow of carbon to the microbiome. This has important implications for predicting carbon flow in surface oceans and manipulating algal-bacterial interactions in engineered systems.

microbiology↗

bioRxiv2025

Marine bacteria cross-feeding controls the fate of extracellular glycolate carbon

Glycolate is a major product of phytoplankton photorespiration, but its fate in the microbial food web is not well constrained. Here, we used stable isotope probing and mass spectrometry combined with genomic analyses and microscopy to quantify glycolate metabolism by a taxonomically diverse set of heterotrophic marine bacteria. We found that 9 of 16 tested strains with the genomic capability to metabolize glycolate directly assimilated and respired glycolate carbon in monoculture. We next co-cultivated glycolate-incorporating strains with non-incorporating strains and found that several cross-feeders incorporated more glycolate carbon into their biomass than direct incorporators. Carbon use efficiency, reflecting proportional differences in movement of glycolate carbon into biomass versus into carbon dioxide, were distinct across co-cultures and ranged from 0.01 -3.15% depending on the strain mixtures. These results suggest that the fate of glycolate carbon is not limited to microbial taxa with the genetic capability for direct assimilation, and that bacterial metabolic interactions via cross-feeding play a critical role in influencing the efficiency of carbon transfer. Such information is critical to refine conceptual and numerical models of heterotrophic processing and transfer of organic carbon in an era of global change with predicted increases in photorespiration.

microbiology↗

bioRxiv2024

Spatially structured competition and cooperation alters algal carbon flow to bacteria

Microbial communities regulate the transformations of carbon in aquatic systems through metabolic interactions and food-web dynamics that can alter the balance of photosynthesis and respiration. Direct competition for resources is thought to drive microbial community assembly in algal systems, but other interaction modes that may shape communities are more challenging to isolate. Through untargeted metabolomics and metabolic modeling, we predicted the degree of resource competition between bacterial pairs when growing on model diatom Phaeodactylum tricornutum-derived substrates. In a subsequent sequential media experiment, we found that pairwise interactions were consistently more cooperative than predicted based on resource competition alone, indicating an unexpected role for cooperation in algal carbon processing. To link this directly to algal carbon fate, we chose a representative cooperative and competitive influencer isolate and a model recipient and applied single-cell isotope tracing in a custom porous microplate cultivation system. In the presence of live algae, the recipient drew down more algal carbon in the presence of the cooperative influencer compared to the competitive influencer, supporting the sequential experiment results. We also found that total carbon assimilation into bacterial biomass, integrated over influencer and recipient, was significantly higher for the cooperative interaction. Our findings support the notion that non-competitive interactions are critical for predicting algal carbon fate. Significance StatementMicrobial interactions have widely been studied in the context of host resources but testing and measuring direct interactions in a lab has been particularly challenging. By combining untargeted metabolomics, sequential/(co-)culture, and metabolic modeling, we demonstrate that the presence of an unexpected interaction mode in a live system and show how it impacts the flow of host-derived resources. This top-down approach can help identify novel bacterial interactions that play a crucial role in microbial community-host ecosystems, which may have an impact in holobiont phenotypes including alga, fungal, or plant systems.

microbiology↗

bioRxiv2024

Coastal bacteria and protists assimilate viral carbon and nitrogen

Free viruses are the most abundant type of biological particles in the biosphere, but the lack of quantitative knowledge about their consumption by heterotrophic protists and bacterial degradation has hindered the inclusion of virovory in biogeochemical models. Here, using isotope-labeled viruses added to three independent microcosm experiments with natural microbial communities followed by isotope measurements with single-cell resolution and flow cytometry, we quantified the flux of viral C and N into virovorous protists and bacteria and compared the loss of viruses due to abiotic vs biotic factors. We found that some protists can obtain most of their C and N requirements from viral particles and that viral C and N get incorporated into bacterial biomass. We found that bacteria and protists were responsible for increasing the daily removal rate of viruses by 33% to 85%, respectively, compared to abiotic processes alone. Our laboratory incubation experiments showed that abiotic processes removed roughly 50% of the viruses within a week, and adding biotic processes led to a removal of 83% to 91%. Our data provide direct evidence for the transfer of viral C and N back into the microbial loop through protist grazing and bacterial breakdown, representing a globally significant flux that needs to be investigated further to better understand and predictably model the C and N cycles of the hydrosphere.

ecology↗

bioRxiv2024

Scarcity of fixed carbon transfer in a model microbial phototroph-heterotroph interaction

Although the green alga Chlamydomonas reinhardtii has long served as a reference organism, few studies have interrogated its role as a primary producer in microbial interactions. Here, we quantitatively investigated C. reinhardtiis capacity to support a heterotrophic microbe using the established coculture system with Mesorhizobium japonicum, a vitamin B12-producing -proteobacterium. Using stable isotope probing and nanoscale secondary ion mass spectrometry (nanoSIMS), we tracked the flow of photosynthetic fixed carbon and consequent bacterial biomass synthesis under continuous and diurnal light with single-cell resolution. We found that more 13C fixed by the alga was taken up by bacterial cells under continuous light, invalidating the hypothesis that the algas fermentative degradation of starch reserves during the night would boost M. japonicum heterotrophy. 15NH4 assimilation rates and changes in cell size revealed that M. japonicum cells reduced new biomass synthesis in coculture with the alga but continued to divide - a hallmark of nutrient limitation often referred to as reductive division. Despite this sign of starvation, the bacterium still synthesized vitamin B12 and supported the growth of a B12-dependent C. reinhardtii mutant. Finally, we showed that bacterial proliferation could be supported solely by the algal lysis that occurred in coculture, highlighting the role of necromass in carbon cycling. Collectively, these results reveal the scarcity of fixed carbon in this microbial trophic relationship (particularly under environmentally relevant light regimes), demonstrate B12 exchange even during bacterial starvation, and underscore the importance of quantitative approaches for assessing metabolic coupling in algal-bacterial interactions.

microbiology↗

bioRxiv2024

A toxic environment selects for specialist microbiome in poison frogs

Shifts in microbiome community composition can have large effects on host health. It is therefore important to understand how perturbations, like those caused by the introduction of exogenous chemicals, modulate microbiome community composition. In poison frogs within the family Dendrobatidae, the skin microbiome is exposed to the alkaloids that the frogs sequester from their diet and use for defense. Given the demonstrated antimicrobial effects of these poison frog alkaloids, these compounds may be structuring the skin microbial community. To test this, we first characterized microbial communities from chemically defended and closely related non-defended frogs from Ecuador. Then we conducted a laboratory experiment to monitor the effect of the alkaloid decahydroquinoline (DHQ) on the microbiome of a single frog species. In both the field and lab experiments, we found that alkaloid-exposed microbiomes are more species rich and phylogenetically diverse, with an increase in rare taxa. To better understand the strain-specific behavior in response to alkaloids, we cultured microbial strains from poison frog skin and found the majority of strains exhibited either enhanced growth or were not impacted by the addition of DHQ. Additionally, stable isotope tracing coupled to nanoSIMS suggests that some of these strains are able to metabolize DHQ. Taken together, these data suggest that poison frog chemical defenses open new niches for skin-associated microbes with specific adaptations, including the likely metabolism of alkaloids, that enable their survival in this toxic environment. This work helps expand our understanding of how exposure to exogenous compounds like alkaloids can impact host microbiomes.

microbiology↗

bioRxiv2023

Differential substrate affinity and catabolite repression enable preferential use of urea by ammonia-oxidizing bacteria

Four distinct lineages of ammonia-oxidizing microorganisms (AOM) collectively contribute to one of the largest nitrogen fluxes in the global nitrogen budget. AOM possess widely different specific affinities for ammonia, thought to determine their niche differentiation. Nevertheless, ammonia-oxidizing archaea and bacteria (AOA, AOB), and complete ammonia oxidizers (comammox) co-occur in soils, freshwater sediments, and aquifers, suggesting that other factors must drive their coexistence. Here, we show that representatives of four AOM lineages employ distinct regulatory strategies for ammonia or urea utilization, thereby minimizing direct competition for either substrate. The tested AOA and comammox species preferentially used ammonia over urea, while beta-proteobacterial AOB favored urea utilization, repressed ammonia transport in the presence of urea, and showed higher affinity for urea than ammonia, whereas gamma-proteobacterial AOB co-utilized both substrates. Stable isotope tracing, kinetics, and transcriptomics experiments revealed that both assimilation and oxidation of ammonia are transport-dependent. These results reveal novel mechanisms of nitrogen metabolism regulation and transporter-based affinity underlying the contrasting niche adaptation and coexistence patterns among the major AOM lineages.

microbiology↗

bioRxiv2023

Arbuscular mycorrhiza convey significant plant carbon to a diverse hyphosphere microbial food web and mineral-associated organic matter

O_LIArbuscular mycorrhizal fungi (AMF) transport substantial plant carbon (C) that serves as a substrate for other soil organisms, a precursor of soil organic matter (SOM), and a driver of soil microbial dynamics. Using two-chamber microcosms where an air gap isolated AMF from roots, we 13CO2-labeled Avena barbata for six weeks and measured. the C Rhizophagus intraradices transferred to SOM and hyphosphere microorganisms. C_LIO_LINanoSIMS imaging, IRMS, 13C NMR, and SOM density fractionation showed hyphae and roots had similar 13C enrichment. AMF transferred 0.77 mg C per g of soil (increasing total C by 2%); 33% was found in occluded or mineral-associated pools, primarily as carbohydrates. C_LIO_LIIn the AMF hyphosphere, there was no overall change in community diversity but 36 bacterial ASVs significantly changed in relative abundance. With stable isotope probing (SIP)-enabled shotgun sequencing, we found taxa from the Solibacterales, Sphingobacteriales, Myxococcales and Nitrososphaerales (ammonium oxidizing archaea) were highly enriched in AMF-imported 13C (>20 atom%). Mapping 13C-enriched metagenome-assembled genomes to total ASVs showed at least 92 bacteria and archaea were significantly 13C-enriched. C_LIO_LIOur results illustrate the quantitative impact of hyphal C transport on the formation of potentially protective SOM pools and indicate microbial roles in the AMF hyphosphere soil food web. C_LI

microbiology↗

bioRxiv2022

Single cell carbon and nitrogen incorporation and remineralization profiles are uncoupled from phylogenetic groupings of diatom-associated bacteria

Bacterial remineralization of algal organic matter is thought to fuel algal growth, but this has not been quantified. Consequently, we cannot currently predict whether some bacterial taxa may provide more remineralized nutrients to algae than others, nor whether this is linked their incorporation. We quantified bacterial incorporation of algal-derived complex dissolved organic C (DOC) and N (DON) and net algal incorporation of remineralized C and N at the single cell level using isotope tracing and NanoSIMS for fifteen bacterial co-cultures growing with the diatom Phaeodactylum tricornutum. We found unexpected variability in the net C and N fluxes between algae and bacteria, including non-ubiquitous complex DON utilization and remineralization. We identified three distinct functional categories of metabolic interactions, which we termed macromolecule remineralizers, macromolecule users, and small-molecule users, the latter exhibiting efficient growth under low carbon availability. The functional categories were not linked to phylogeny and could not be elucidated strictly from metabolic capacity as predicted by comparative genomics. Using comparative proteogenomic analyses, we show that a complex DON incorporating strain expressed proteins related to growth and peptide transport, and a non-incorporator prioritized reactive oxygen species scavenging and inorganic nutrient uptake. Our analysis suggests that phylogeny does not predict the extent of algae-bacteria metabolite exchange, and activity-based measurements are indispensable to classify the high diversity of microbes into functional groups. These categorizations are useful for conceptual understanding and mechanistic numerical modeling to ultimately predict the fate of elemental cycles in response to environmental change.

microbiology↗

bioRxiv2022

A proton pump enhancing photosynthesis links phagocytosis to marine phytoplankton symbiogenesis

Diatoms, dinoflagellates, and coccolithophorids are the dominant groups of marine eukaryotic phytoplankton collectively responsible for the majority of primary production in the ocean1. These phytoplankton contain additional intracellular membranes around their chloroplasts derived from ancestral engulfment of red microalgae by unicellular heterotrophic eukaryotes that led to secondary endosymbiosis2. This symbiogenesis hypothesis for the origin of modern secondary endosymbiotic phytoplankton is supported by a wealth of palaeontologic, morphologic, and genomic evidence3-6. However, the selectable evolutionary advantage of these membranes and the physiological significance for extant phytoplankton are unknown. We report that the proton-pumping enzyme V-type H+-ATPase (VHA), ubiquitously used in eukaryotic intercellular digestion, is localized around the chloroplasts of centric diatoms and that VHA-activity significantly enhances photosynthesis over a wide range of oceanic irradiances. Similar results in pennate diatoms, dinoflagellates, and coccolithophorids, but not green or red microalgae, imply a mechanism resulting from the co-option of phagocytic VHA activity into a carbon concentrating mechanism that is common to secondary endosymbiotic phytoplankton. Furthermore, analogous VHA-dependent mechanisms in extant photosymbiotic marine invertebrates7-9 provide functional evidence for an adaptive advantage throughout the transition from endosymbiosis to symbiogenesis. Our results suggest that VHA-dependent enhancement of photosynthesis contributes at least 7% of primary production in the ocean, providing an example of a symbiosis-derived evolutionary innovation with global environmental implications.

evolutionary biology↗

bioRxiv2021

Active viral population dynamics in frozen Arctic peat soil revealed with H218O stable isotope probing metagenomics

Winter carbon loss in northern ecosystems is estimated to be greater than the average growing season carbon uptake. However, most ecosystem carbon measurements neglect winter months since carbon losses (primarily driven by microbial decomposers) are assumed to be negligible at low temperatures. We used stable isotope probing (SIP) targeted metagenomics to reveal the genomic potential of active soil microbial populations under winter conditions, with an emphasis on viruses and virus-host dynamics. Peat soils from the Bonanza Creek LTER site in Alaska were incubated under subzero anoxic conditions with H218O for 184 and 370 days. We identified 46 bacterial populations (MAGs; spanning 9 bacterial phyla) and 243 viral populations (vOTUs) that actively took up 18O and produced significant CO2 throughout the incubation. Active hosts, predicted for 33% of the active vOTUs, were some of the most abundant MAGs and capable of fermentation and organic matter degradation. Approximately three-quarters of the active vOTUs carried auxiliary metabolic genes that spanned five functional categories, including carbon utilization, highlighting the potential impact of viruses in this peat soils microbial biogeochemistry. These results illustrate significant bacterial and viral activity and interactions occur in frozen soils, revealing viruses are a major community-structuring agent throughout winter months.

microbiology↗

bioRxiv2019

Influence of light on particulate organic matter utilization by attached and free-living marine bacteria

While the impact of light on primary productivity in aquatic systems has been studied for decades, the role light plays in the degradation of photosynthetically-produced biomass is less well understood. We investigated the patterns of light-induced particle breakdown and bacterial assimilation of detrital C and N using 13C and 15N labeled freeze-thawed diatom cells incubated in laboratory microcosms with a marine microbial community freshly-collected from the Pacific Ocean. Particles incubated in the dark resulted in increased bacterial counts and dissolved organic carbon concentrations compared to those incubated in the light. Light also influenced the attached and free-living microbial community structure as detected by 16S rRNA gene amplicon sequencing. For example, bacterial taxa from the Sphingobacteriia were enriched on dark-incubated particles and taxa from the family Flavobacteriaceae and the genus Pseudoalteromonas were numerically enriched on particles in the light. Isotope incorporation analysis by phylogenetic microarray and NanoSIMS (a method called Chip-SIP) identified free-living and attached microbial taxa able to incorporate N and C from the particles. Some taxa, including members of the Flavobacteriaceae and Cryomorphaceae, exhibited increased isotope incorporation in the light, suggesting the use of photoheterotrophic metabolisms. In contrast, some members of Oceanospirillales and Rhodospirillales showed decreased isotope incorporation in the light, suggesting that their heterotrophic metabolism, particularly when occurring on particles, might increase at night or may be inhibited by sunlight. These results show that light influences particle degradation and C and N incorporation by attached bacteria, suggesting that the transfer between particulate and free-living phases are likely affected by external factors that change with the light regime, such as time of day, depth and season.

ecology↗

bioRxiv2017

Metagenomics reveals niche partitioning within the phototrophic zone of a microbial mat

Hypersaline photosynthetic microbial mats are stratified microbial communities known for their taxonomic and metabolic diversity and strong light-driven day-night environmental gradients. In this study of the upper photosynthetic zone of hypersaline microbial mats of Elkhorn Slough, California (USA), we show how reference-based and reference-free methods can be used to meaningfully assess microbial ecology and genetic partitioning in these complex microbial systems. Mapping of metagenome reads to the dominant Cyanobacteria observed in the system, Coleofasciculus (Microcoleus) chthonoplastes, was used to examine strain variants within these metagenomes. Highly conserved gene subsystems indicate a core genome for the species, and a number of variant genes and subsystems suggest strain level differentiation, especially for carbohydrate utilization. Metagenome sequence coverage binning was used to assess ecosystem partitioning of remaining microbes. Functional gene annotation of these bins (primarily of Proteobacteria, Bacteroidetes, and Cyanobacteria) recapitulated the known biogeochemical functions in microbial mats using a genetic basis, and also revealed evidence of novel functional diversity within the Gemmatimonadetes and Gammaproteobacteria. Combined, these two approaches show how genetic partitioning can inform biogeochemical partitioning of the metabolic diversity within microbial ecosystems.

microbiology↗