Award: OCE-1459252

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 Submitted by: Peter Girguis