Martocello
Donald E., III
Martocello
Donald E., III
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ArticleDiscovering hydrothermalism from afar: In Situ methane instrumentation and change-point detection for decision-making(Frontiers Media, 2022-10-25) Preston, Victoria Lynn ; Flaspohler, Genevieve Elaine ; Kapit, Jason ; Pardis, William A. ; Youngs, Sarah ; Martocello, Donald E., III ; Roy, Nicholas ; Girguis, Peter R. ; Wankel, Scott ; Michel, Anna P. M.Seafloor hydrothermalism plays a critical role in fundamental interactions between geochemical and biological processes in the deep ocean. A significant number of hydrothermal vents are hypothesized to exist, but many of these remain undiscovered due in part to the difficulty of detecting hydrothermalism using standard sensors on rosettes towed in the water column or robotic platforms performing surveys. Here, we use in situ methane sensors to complement standard sensing technology for hydrothermalism discovery and compare sensors on a towed rosette and an autonomous underwater vehicle (AUV) during a 17 km long transect in the Northern Guaymas Basin in the Gulf of California. This transect spatially intersected with a known hydrothermally active venting site. These data show that methane signalled possible hydrothermal-activity 1.5–3 km laterally (100–150 m vertically) from a known vent. Methane as a signal for hydrothermalism performed similarly to standard turbidity sensors (plume detection 2.2–3.3 km from reference source), and more sensitively and clearly than temperature, salinity, and oxygen instruments which readily respond to physical mixing in background seawater. We additionally introduce change-point detection algorithms—streaming cross-correlation and regime identification—as a means of real-time hydrothermalism discovery and discuss related data supervision technologies that could be used in planning, executing, and monitoring explorative surveys for hydrothermalism.
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ArticleRatio of electron donor to acceptor influences metabolic specialization and denitrification dynamics in Pseudomonas aeruginosa in a mixed carbon medium(Frontiers Media, 2021-09-10) Zhang, Irene H. ; Mullen, Susan ; Ciccarese, Davide ; Dumit, Diana ; Martocello, Donald E., III ; Toyofuku, Masanori ; Nomura, Nobuhiko ; Smriga, Steven ; Babbin, Andrew R.Denitrifying microbes sequentially reduce nitrate (NO3–) to nitrite (NO2–), NO, N2O, and N2 through enzymes encoded by nar, nir, nor, and nos. Some denitrifiers maintain the whole four-gene pathway, but others possess partial pathways. Partial denitrifiers may evolve through metabolic specialization whereas complete denitrifiers may adapt toward greater metabolic flexibility in nitrogen oxide (NOx–) utilization. Both exist within natural environments, but we lack an understanding of selective pressures driving the evolution toward each lifestyle. Here we investigate differences in growth rate, growth yield, denitrification dynamics, and the extent of intermediate metabolite accumulation under varying nutrient conditions between the model complete denitrifier Pseudomonas aeruginosa and a community of engineered specialists with deletions in the denitrification genes nar or nir. Our results in a mixed carbon medium indicate a growth rate vs. yield tradeoff between complete and partial denitrifiers, which varies with total nutrient availability and ratios of organic carbon to NOx–. We found that the cultures of both complete and partial denitrifiers accumulated nitrite and that the metabolic lifestyle coupled with nutrient conditions are responsible for the extent of nitrite accumulation.
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ThesisThe impact of metals and other stress factors on microbial ammonia oxidation physiology and isotope effects(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2024-06) Martocello, Donald E., III ; Wankel, ScottMicrobially-mediated cycling processes play central roles in regulating the speciation and availability of nitrogen, a vital nutrient with wide implications for agriculture, water quality, ecosystem health, and climate change. Ammonia (NH3) oxidation, the first and rate-limiting step of nitrification, is carried out by bacteria (AOB) and archaea (AOA). Despite more than a century of research into the physiology of AOB, and only more recently AOA, fundamental questions remain about the ammonia oxidation reaction mechanism and relevant stress factors that regulate environmental rates. Ammonia oxidizing organisms (AOO) require the trace metal micronutrients copper (Cu) and iron (Fe) for growth and metabolic catalysis. Ammonia oxidation is directly affected by pH in regulating the relative availability of ammonium (NH4+) and NH3. Also, photoinhibition of AOO is widely reported. The mechanism is unknown, although links to reactive oxygen species (ROS) cycling seem likely. We present detailed investigations of three environmentally relevant AOO stress factors: metal micronutrient limitation, pH changes, and ROS. Central to these studies were analyses of stable isotope fractionation and how changes in AOO physiology impact expression of these isotope effects. In turn, these tools facilitate probing of the ammonia oxidation reaction mechanism and we propose an initial obligatory coordinated NH4+-NH3 uptake step based on isotope mass balance. In addition, we studied nitrification and related environmental chemistry in the Northern Guaymas hydrothermal vent basin in the Gulf of California. This region hosts a unique juxtaposition of hydrothermal vent emissions enriched in NH4+ underlying an extensive regional oxygen deficient zone (ODZ). Most environmental studies of nitrification have focused on the mesopelagic (high oxygen, comparably warmer temperatures, low NH4+, and low metal micronutrient availability). The Northern Guaymas Basin is functionally the opposite. We suggest ultimate limitation by temperature and, surprisingly, potential proximal limitation by NH4+, Fe, and Cu. In total, this work emphasizes the recently recognized role of Fe and Cu in environmental limitation of nitrification, challenges key axioms of AOO cell culturing and physiology, and proposes revisions to canonical ammonia oxidation reaction mechanisms.
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DatasetDiscovering hydrothermalism from afar: in situ methane instrumentation and change-point detection for decision-making(Woods Hole Oceanographic Institution, 2022-10-06) Michel, Anna P. M. ; Wankel, Scott D. ; Preston, Victoria Lynn ; Flaspohler, Genevieve Elaine ; Kapit, Jason ; Pardis, William A. ; Youngs, Sarah ; Martocello, Donald E. ; Girguis, Peter R. ; Roy, NicholasSeafloor hydrothermalism plays a critical role in fundamental interactions between geochemical and biological processes in the deep ocean. A significant number of hydrothermal vents are hypothesized to exist, but many of these remain undiscovered due in part to the difficulty of detecting hydrothermalism using standard sensors on rosettes towed in the water column or robotic platforms performing surveys. Here, we use in situ methane sensors to complement standard sensing technology for hydrothermalism discovery and compare sensing equipment on a towed rosette and autonomous underwater vehicle (AUV) during a 17 km long transect in the Northern Guaymas Basin. This transect spatially intersected with a known hydrothermally active venting site. These data show that methane signaled possible hydrothermal activity 1.5-3 km laterally (100-150m vertically) from a known vent. Methane as a signal for hydrothermalism performed similarly to standard turbidity sensors (plume detection 2.2-3.3 km from reference source), and more sensitively and clearly than temperature, salinity, and oxygen instruments which readily respond to physical mixing in background seawater. We additionally introduce change-point detection algorithms---streaming cross-correlation and regime identification---as a means of real-time hydrothermalism discovery and discuss related data monitoring technologies that could be used in planning, executing, and monitoring explorative surveys for hydrothermalism.