Biology subjects

Pfister, C. A.

Publications and source records attributed to Pfister, C. A..

4 recordsLinked to original sources

bioRxiv2026

Bacterial vitamin sharing emerges from a balance between release and uptake

Vitamin availability often shapes microbial communities, as many microbes use vitamins they cannot synthesize. Yet how vitamins become available to users remains poorly understood. To explore this process, we quantified vitamin B12 synthesis, uptake, and extracellular accumulation across hundreds of diverse soil, freshwater, and marine bacterial isolates. These measurements revealed distinct source-sink phenotypes and showed that producers vary substantially in the amount of B12 they provide extracellularly. B12 synthesis was predictable across divergent bacterial lineages from genome content, whereas uptake and extracellular accumulation were not. Controlled cell-death experiments and independently parameterized models showed that extracellular B12 could be quantitatively predicted from release by dead cells and reuptake by surviving cells. Thus, extracellular B12 availability is governed not by synthesis alone, but by the balance between release and uptake, with producer reuptake acting as a previously overlooked sink.

microbiology↗

bioRxiv2022

The diversity and functional capacity of microbes associated with coastal phototrophs

Coastal marine phototrophs exhibit some of the highest rates of primary productivity in the world. They have been found to host a diverse set of microbes, many of which may impact the biology of their phototroph hosts through metabolisms that are unique to microbial taxa. Here we characterized the metabolic functions of phototroph-associated microbial communities using metagenomes collected from 2 species of kelp (Laminaria setchellii and Nereocystis luetkeana) and 3 marine angiosperms (Phyllospadix scouleri, P. serrulatus and Zostera marina), including the rhizomes of two surfgrass species (Phyllospadix spp.) and the seagrass Zostera marina, and the sediments surrounding P. scouleri and Z. marina. Using metagenomic sequencing, we describe 72 metagenome assembled genomes (MAGs) that potentially benefit from being associated with macrophytes and may contribute to macrophyte fitness through their metabolic gene content. All host-associated metagenomes contained genes for the use of dissolved organic matter from hosts and vitamin (B1, B2, B7, B12) biosynthesis. Additionally, we found a range of nitrogen metabolism genes that transform dissolved inorganic nitrogen into forms that may be more available to the host. The rhizosphere of surfgrass and seagrass contained genes for anaerobic microbial metabolisms, including nifH genes associated with nitrogen fixation, despite residing in a well-mixed and oxygenated environment. The range of oxygen environments engineered by macrophytes likely explains the diversity of both oxidizing and reducing microbial metabolisms, and contributes to the functional capabilities of microbes and their influence on carbon and nitrogen cycling in nearshore ecosystems. ImportanceKelps, seagrasses and surfgrasses are ecosystem engineers on rocky shorelines where they show remarkably high levels of primary production. Through analysis of their associated microbial communities, we found a variety of microbial metabolisms that may benefit the host, including nitrogen metabolisms and the production of B vitamins. In turn, these microbes have the genetic capability to assimilate the dissolved organic compounds released by their phototroph hosts. We describe a range of oxygen environments associated with surfgrass, including low-oxygen microhabitats in their rhizomes that host genes for nitrogen fixation. The tremendous productivity of coastal phototrophs is likely due in part to the activities of associated microbes and an increased understanding of these associations is needed.

ecology↗

bioRxiv2020

Spatial organization of the kelp microbiome at micron scales

Macroalgae are colonized by complex and diverse microbial communities that are distinct from those on inert substrates, suggesting intimate symbioses that likely play key roles in both macroalgal and bacterial biology. Canopy-forming kelp fix teragrams of carbon per year in coastal kelp forest ecosystems, yet little is known about the structure and development of their associated microbial communities. We characterized the spatial organization of bacterial communities on blades of the canopy-forming kelp Nereocystis luetkeana using fluorescence in situ hybridization and spectral imaging with a probe set combining phylum, class and genus-level probes to target >90% of the microbial community. We show that kelp blades host a dense microbial biofilm, generally less than 20 m thick, in which disparate microbial taxa live in close contact with one another. The biofilm is spatially differentiated, with tightly clustered cells of the dominant symbiont Granulosicoccus sp. (Gammaproteobacteria) close to the kelp surface and filamentous Bacteroidetes and Alphaproteobacteria relatively more abundant near the biofilm-seawater interface. Further, a community rich in Bacteroidetes colonized the interior of kelp tissues. Microbial community structure and cell density increased along the length of the kelp blade, from sparse microbial colonization of newly produced tissues at the meristematic base of the blade to an abundant microbial biofilm on older tissues at the blade tip. Finally, kelp from a declining population hosted fewer microbial cells compared to kelp from a stable population, indicating that biofilms are characteristic of health and that biofilm loss may be related to the condition of the host. ImportanceThe microbial community coating the surfaces of macroalgae may play a key but underexplored role both in the biology of the macroalgal host and in the biogeochemistry of the coastal ocean. We show that photosynthetic blades of the canopy-forming kelp Nereocystis luetkeana host a complex microbial biofilm that is both dense and spatially differentiated. Microbes of different taxa are in intimate cell-to-cell contact with one another; microbial cells invade the interior of kelp cells as well as cover their external surfaces; and a subset of the surface microbiota projects into the water column. These results highlight the potential for metabolic interactions between key members of the kelp microbiome as well as between microbes and their host. The dense layer of microbes coating the surface of the kelp blade is well-positioned to mediate interactions between the host and surrounding organisms and to modulate the chemistry of the surrounding water column.

microbiology↗

bioRxiv2019

Cryptic genetic variation underpins rapid adaptation to ocean acidification

Global climate change has intensified the need to assess the capacity for natural populations to adapt to abrupt shifts in the environment. Reductions in seawater pH constitute a conspicuous stressor associated with increasing atmospheric carbon dioxide that is affecting ecosystems throughout the worlds oceans. Here, we quantify the phenotypic and genetic modifications associated with rapid adaptation to reduced seawater pH in the marine mussel, Mytilus galloprovincialis. We reared a genetically diverse larval population in ambient and extreme low pH conditions (pHT 8.1 and 7.4) and tracked changes in the larval size and allele frequency distributions through settlement. Additionally, we separated larvae by size to link a fitness-related trait to its underlying genetic background in each treatment. Both phenotypic and genetic data show that M. galloprovincialis can evolve in response to a decrease in seawater pH. This process is polygenic and characterized by genotype-environment interactions, suggesting the role of cryptic genetic variation in adaptation to future climate change. Holistically, this work provides insight into the processes underpinning rapid evolution, and demonstrates the importance of maintaining standing variation within natural populations to bolster species adaptive capacity as global change progresses.

evolutionary biology↗