| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | February 18, 2015 |
| Latest Amendment Date: | February 18, 2015 |
| Award Number: | 1459252 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Michael Sieracki
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | March 1, 2015 |
| End Date: | February 28, 2019 (Estimated) |
| Total Intended Award Amount: | $396,186.00 |
| Total Awarded Amount to Date: | $396,186.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1033 MASSACHUSETTS AVE STE 3 CAMBRIDGE MA US 02138-5366 (617)495-5501 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
16 Divinity Avenue Cambridge MA US 02138-2020 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
Marine Geology and Geophysics, BIOLOGICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Iron is one of the most abundant elements on Earth and is an essential element for life. Despite its abundance, iron is not always biologically available. For example, in the water column of the ocean, iron is easily oxidized and precipitates or sinks to the sediments. This can result in there being such a deficit of iron in the open ocean that it is often the primary limiting nutrient for the growth of phytoplankton that form the base of the marine food web. Marine sediments can be a major source of iron to the ocean, when it is made biologically available. Interestingly, one group of bacteria, the iron-oxidizing bacteria (FeOB), can use iron directly as an energy source to fuel their growth, and may govern the availability of iron to other parts of the ocean. While this group can be abundant at hydrothermal vents, little is known about their abundance or activity in marine sediments. Are these bacteria playing an important role in controlling the flux of iron from the sediments to the water column? To answer this, sediments on the east and west coasts of the United States will be analyzed to characterize and quantitate the diversity and abundance of FeOB. In addition, a series of laboratory experiments will be aimed at understanding the specific role they play in controlling iron flux from the sediments to the ocean, as well as the technically challenging question of determining the lower limit of oxygen at which they can grow. This work has relevance to our understanding of how biological control of a seemingly minor constituent in seawater, iron, could have implications for productivity of the entire ocean. Notably, a predicted impact of climate change on marine environments is to decrease oxygen levels in the ocean. This could have a profound influence on the sedimentary iron cycle, and possibly lead to greater inputs of iron, which could in turn alleviate iron-limitation in some regions of the ocean, thereby enhancing the rate of CO2-fixation and draw down of CO2 from the atmosphere. This project will provide training for a postdoctoral scientist, graduate students and undergraduates. Public outreach will include a student initiated exhibit, entitled "Iron and the evolution of life on Earth" at the Harvard Museum of Natural History providing a unique opportunity for undergraduate training and outreach.
The central hypothesis of this proposal is that FeOB are more common in marine sedimentary environments than previously recognized, and play a substantive role in governing the iron flux from the sediments into the water column by constraining the release of dissolved iron (dFe) from sediments. A survey of near shore regions in the Gulf of Maine, and a transect along the Monterey Canyon off the coast of California will obtain cores of sedimentary muds and look at the vertical distribution of FeOB and putative Fe-reducing bacteria using sensitive techniques to detect their presence and relative abundance. Sediments will be used in a novel reactor system that will allow for precise control of O2 levels and iron concentration to measure the dynamics of the iron cycle under different oxygen regimens. Pure cultures of FeOB with different O2 affinities will be tested in a bioreactor coupled to a highly sensitive mass spectrometer to determine the lower limits of O2 utilization for different FeOB growing on iron, thus providing mechanistic insight into their activity and distribution in low oxygen environments.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
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This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Iron is the fourth most abundant element in the crust. It has been a key element in humankind's evolution (we would not exist without iron, as it is necessary for many of our key enzymes) and civilization (iron was so important to us that we call it out by name as the Iron Age: when humans started fashioning tools out of Iron).
Iron is equally critical to the rest of our biosphere. As in humans, Iron is important for the nearly all life on Earth. The oxygen in our atmosphere is made in large part by marine bacteria and alga, who depend on Iron to make the enzymes necessary for photosynthesis. Indeed, oxygen production on Earth is governed by the limited availability of Iron to these marine microorganisms, so it?s fair to say that Iron controls the amount of oxygen in our atmosphere.
Iron's relationship with oxygen is, however, a bit more complicated. Iron exists in two predominant forms on Earth: Iron(II), or "Iron two", and Iron(III), or "Iron three". Iron(II) was very common on early Earth, and remains common today in those parts of our world devoid of oxygen. Deep sea hydrothermal vents, acidic hot springs, and even deep sea sediments and deep terrestrial soils all harbor Iron(II). Iron(III) is very common wherever oxygen is present, which nearly all of the surface and deep ocean, nearly every river and lake, and nearly all the surface soils on all the continents. Notably, Iron(III) forms when Iron(II) encounters oxygen. More specifically, this fast and spontaneous reaction between Iron(II) and oxygen forms Iron(III) oxides, which are commonly known as "rust".
Humans typically don't think highly of rust. We associate it with the decay of our bridges, cars, and other objects. Rust is also problematic for the many organisms that need Iron for their enzymes. Iron(III) is not readily accessible to most organisms, so they have evolved different mechanisms to acquire scarce Iron(II) from the environment, or to convert Iron(III) back into Iron(II) for the biosynthesis of new enzymes.
The situation, however, is most dire for those microbes that make a living on Iron(II). On early Earth, before there was lots of oxygen in our atmosphere, there was an abundance of Iron (II) that microbes could use as a "fuel" source. As the oxygen in Earth's atmosphere continued to rise, these so-called "iron oxidizing bacteria" had to find ways to use the Iron(II) before is spontaneously reacted with oxygen to form Iron (III).
Today, we find these bacteria to be most abundant in areas where oxygen is sparse, such as the aforementioned vents, hot springs, and sediments. However, we also find them in areas where there is seemingly plenty of oxygen, and we do not yet know how they manage to "make a living". This project was aimed at understanding how iron-oxidizing bacteria (which we will call FeOB for short, as the letters "Fe" represent Iron on the periodic table of elements) compete with these spontaneous processes. We hypothesized that FeOB might somehow manage to control the oxygen in their environment, allowing them to better compete for Iron(II). We conducted a broad series of studies that revealed that they do, indeed, manage to influence the oxygen concentration around their Iron sources. They do this by forming a layer of polysaccharides, which is kind of like the mucus in the human nose. It covers the Iron(II) minerals and somehow keeps oxygen from accessing them. Also, FeOBs seems to use some tricks like changing the pH (activity) so that they can access Iron in ways that other organisms can't.
These studies were important for helping us understand how these organisms make a living on a well-oxygenated Earth. Equally important, these organisms do play a role in rusting away the many buildings, cars and other structures that we make out of Iron. This research might help our industry counterparts think broadly about how to minimize the role of these microbes in rusting away infrastructure. Finally, this project gave us a chance to train many early career scientists in microbiology, statistics, public communication, engineering, and writing. Some of the students from this project are going on to pursue careers in industry, while others are considering medicine, environmental law, and academics.
Last Modified: 06/26/2019
Modified by: Peter Girguis
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