Biogeochemical cycles

Cyanobacteria are ancient prokaryotes that use photosynthesis and an accumulation of other adaptations to dominate aquatic ecosystems around the world. They are thus major contributors to biogeochemical cycling, a threat to human and environmental health, and an intriguing source for novel chemistry. We begin by providing an overview of bloom-forming cyanobacteria and their many toxic metabolites. We then discuss the characterization of some abundant extracellular pili of Microcystis aeruginosa, reporting a 2.4 Å cryoelectron microscopy pilus structure, revealing a novel class of pili that we have termed cyanobacterial tubular (CT) pili. The CT pili in M. aeruginosa were determined to be multi-functional, with a primary role in networking cells and enhancing colony formation, but also in controlling colony buoyancy, enriching iron, and accumulating toxins in the extracellular mucilage. Lastly, we explore the potential of heavy-labeling cyanobacterial cultures for the sake of isolating natural products that can be studied by vibrational spectroscopic imaging. The vibrational spectra of three classes of cyanopeptides along with their heavy-labeled counterparts are reported, and Density Functional Theory calculations are used to describe mode character, clarifying some unexpected changes in vibrational spectra upon heavy-labeling. As a whole, this work offers new insight into cyanobacterial physiology as well as a means to study cyanopeptides with imaging techniques and stable-isotope labeling.

Iron and manganese redox chemistry are important drivers of sulfur cycling in marine sediments. Florida Bay sediments are extremely sulfidic, having been attributed to mass mortality of seagrass and oxygen depletion in the water column. This research used conventional sediment analyses and a diagenetic model to infer the overall capacity for Florida Bay sediments to eliminate hydrogen sulfide and prevent high rates of sediment dissolved oxygen consumption via hydrogen sulfide reoxidation. Previous studies have suggested that iron is important for buffering hydrogen sulfide in Florida Bay sediments, while the results of this project show for the first time that this phenomenon is relevant only in specific locations and times of the year. However, my research indicates that Fe has the potential to sequester sulfides and minimize hypoxia in the Everglades system. Thus, under a scenario that greater amounts of Fe are delivered to Florida Bay sediments from freshwater flows under Everglades restoration, Fe could be a component of ecosystem management.

In plants, phenotypic plasticity, the ability to morphologically adapt to new or broad environmental conditions, is a consequence of long-term evolutionary genetic processes. Thus, plants adapted to low phosphate (P) environments exhibit only limited plasticity to take advantage of nutrient enrichment, a global phenomenon in terrestrial and aquatic environments. In the face of anthropogenic P-enrichment, low nutrient adapted resident plant species are frequently displaced by species with high morphological and genetic plasticity. However, it remains unclear whether plasticity is systemically expressed across molecular, biochemical, physiological, and morphological processes that ultimately contribute to the root and shoot phenotypes of plants. In this study, we demonstrated high plasticity in root-borne traits of sawgrass (Cladium jamaicense), the dominant plant species of the P-impoverished Everglades, and counter the idea of inflexibility in low P adapted species. However, sawgras s expressed inflexibility in processes contributing to shoot phenotypes, in contrast to cattail, which was highly plastic in shoot characteristics vii in response to P enrichment. In fact, plasticity in cattail shoots is likely a function of its growth response to P that was globally regulated by P-availability at the level of transcription. Plasticity and inflexibility in the growth of both species also diverged in their allocation of P to the chloroplast for growth in cattail versus the vacuole for P storage in sawgrass. In the Everglades, anthropogenic P-enrichment has changed the environment from a P-limited condition, where plasticity in root-borne traits of sawgrass was advantageous, to one of light-competition, where plasticity in shoot-borne traits drives competitive dominance by cattail.

In recent history, C. jamaicense has been displaced by another native monocot, T. domingensis, predominantly resulting from increased phosphorous enrichment in the Everglades. This study aimed to elucidate these two species responses to low and high [Pi] in terms of allocation, photosynthate partitioning and growth. C. jamaicense growth was independent of Pi, while T. domingensis growth increased with [Pi]. Under high [Pi], allocation to younger T. domingensis shoots occurred, while C. jamaicense shoots retained more [Pi], while low [Pi] resulted in homogeneous allocation patterns for both species. Additionally, Pi deficiencies induced carbohydrate levels in older shoots of T. domingensis, while [Pi] had no effect on photosynthate partitioning patterns in C. jamaicense. ACP activity was induced by Pi deficiency in all T. domingensis shoots and increased with shoot age, while no effect was observed in C. jamaicense. Results indicate these two species differ in allocation strategies when [Pi] is altered.