2024 O.N. Allen Soil and Environmental Microbiology Small Grants Program Awardees

Aldo Arellano (Bacteriology)

Exploring bacterial-fungal interactions, community assembly, and mosquito development in the Sarracenia purpurea microecosystem
The tripartite symbiosis of the purple pitcher plant, Sarracenia purpurea, the pitcher plant mosquito, Wyeomyia smithii, and their associated microbiota provides an ideal microecosystem to explore cross-trophic impacts on microbial function. Purple pitcher plants are carnivorous and reside in nutrient-depleted wetlands, where they produce water-filled leaves (pitchers) that act as pitfall traps for insect prey that supplement their nutrient requirements. S. purpurea do not produce several classes of enzymes required to digest prey and instead rely on inquiline macroinvertebrate and microbial communities present in pitcher fluid for the mechanical and hydrolytic enzymatic breakdown of captured insects, respectively. Both top-down (macroinvertebrate) and bottom-up (microbial) controls shape availability of key resources to promote ecosystem stability and function in the S. purpurea ecosystem. Research into the S. purpurea-associated microbial community has almost entirely focused on bacteria, and we have little to no understanding of how mosquito-mediated impacts on pitcher-associated fungal communities affect mosquito or plant fitness. This research will first aim to document the impacts of W. smithii larvae on fungal and bacterial community assembly and function in naturally occurring pitchers using field manipulations and paired ITS and 16S rRNA amplicon sequencing. Next, I will use gnotobiotic experiments to explore how monoculture and co-culture conditions impact community assembly and mosquito fitness. This work will integrate measures of function to attribute ecosystem services not only to specific taxa, but also to inferred interaction networks across taxonomic kingdoms and trophic levels.

Mauricio De La Parra Gurr & Stacy Nuryadi (Agroecology, Dept of Geography)

Characterization of microbial and viral diversity, metabolism, and biogeography in hydrothermal vents of the Galápagos
Tropical dry forests like those found on St. Croix, an island that is part of the US Virgin Islands, and Puerto Rico are severely understudied despite occupying over 40 percent of the tropics. Much of the tropical dry forest ecosystem is also influenced by hurricanes, which play a role in shaping belowground biogeochemical cycles due to shifts in organic matter and nutrient stock caused by debris deposition and canopy openings. Fungi are an important component of these nutrient fluxes as they decompose this newly fallen organic matter. The dual anthropogenic threats of climate change and land use change threaten the already fractured ecosystem which are tropical dry forests. Soil fungi are key to the health and preservation of this understudied ecosystem yet we know just as little about their diversity and response to climate change-related disturbance. By understanding the differences in fungal diversity, composition, and functional traits between native and non-native plant communities in tropical dry forests and comparing these fungal communities between tropical dry forests in St. Croix and Puerto Rico, we can better understand not only how to manage and protect the ecosystem in St. Croix and Puerto Rico but also tropical dry forest ecosystems throughout the Caribbean. Our research will not only bolster the lack of knowledge of fungal interactions in tropical dry forests, it will bolster our ability to conserve these vital ecosystems and help forest managers better predict nutrient dynamics across different tropical dry forests.

Dana Johnson & Josh Mirabella (Soil Science)

Effect of varying temperatures and durations of freeze on soil N2O emissions and the relative contributions of nitrifying and denitrifying bacteria
Increased nitrous oxide (N2O) production following freeze-thaw cycles are well-documented in agricultural soils in the midwestern United States, yet some research suggests that models routinely underestimate cold-season emissions. Efforts to quantify N2O emissions after freezing events have focused on temperatures just below 0˚C, while temperatures as low as -30˚C can be reached during midwestern winters. Ice density increases as temperatures continue to drop below 0˚C, and it follows that the impacts of freezing on soil structure and soil microbial mortality may intensify at increasingly cold temperatures. Another unknown facet of N2O dynamics following freezing events is the relative contributions of nitrifying and denitrifying bacteria. Nitrifiers and denitrifiers occupy distinct ecological niches from each other, differing in efficiency of N2O production in the face of differing levels of oxygen and nitrogen substrate. If soil physical and microbial properties are disrupted by extreme cold events, the relative contributions of nitrifiers and denitrifiers to soil N2O emissions may shift. This project aims explore the impacts of freezing events of varying temperatures and durations on (1) soil N2O emissions, (2) microbial mortality, and (3) the relative contributions of nitrifiers and denitrifiers to N2O emissions. The experiment will compare two temperatures (0˚C vs. -20˚C) and two durations of freeze (one day vs. seven days) in a lab incubation. Following thawing to 4˚C, N2O emissions will be measured over a three-day incubation, and microbial biomass will be determined via chloroform fumigation. The contributions of nitrifiers and denitrifiers will be determined via stable isotope probing. The project will begin in 2024 and conclude in 2025.

Katherine Klier & Marguerite Langwig (Freshwater &Marine Sciences)

Characterization of microbial and viral diversity, metabolism, and biogeography in hydrothermal vents of the Galápagos
The Galápagos Spreading Center (GSC) is a mid-ocean ridge that hosts high and low temperature hydrothermal vent fields. Here, vent microorganisms fuel life in the absence of sunlight by utilizing reduced inorganic chemicals from hydrothermal vent fluids to produce energy. Viruses infect and lyse these microorganisms, releasing their contents to the environment, and utilize microbial-acquired genes to manipulate their metabolisms. Since its initial characterization, the microbial and viral communities of the GSC have remained unexplored. This inhibits comparative analyses of the GSC to other vent sites, which are known to differ significantly in composition of animal species, even among vents that are physically close, such as the East Pacific Rise. To address the absence of data on microorganisms and viruses from the GSC, our work will provide the first metagenomes and metatranscriptomes of this ecosystem. These samples include three previously identified vents on thewestern GSC (Iguanas, Pingüinos, and Navidad) and one vent that our team helped discover, el Sendero del Cangrejo, totaling 36 metagenomes and metatranscriptomes. With these data, we will reconstruct microbial and viral genomes to characterize the diversity of GSC organisms and conduct comparative analyses to understand how GSC community structure and activity compares to other hydrothermal vent environments. In addition, we will identify genes for key biogeochemical cycles (e.g., sulfur, methane, hydrogen, nitrogen, and carbon cycling) to determine how microbes and viruses impact GSC biogeochemistry. We predict that similarly to vent animals, a large portion of GSC microorganisms will be endemic to this site and represent novel organisms only observed in the GSC hydrothermal vent field. Furthermore, we expect community composition and metabolism to be more similar between vent sites Navidad and Sendero del Cangrejo, which are geographically closer, compared to Iguanas and Pingüinos. Characterizing the microbes and viruses of the GSC is crucial in the face of climate change and deep-sea mining, which threaten to disrupt these ecosystems. Thus, our work provides important baseline data that will be crucial to understand and predict changes that may occur in the future due to human influence.