Date of Award


Document Type

Honors Thesis (Colby Access Only)


Colby College. Chemistry Dept.


D. Whitney King

Second Advisor

Rebecca R. Conry


Leptothix is an iron oxidizing bacteria that is ubiquitous in both marine and terrestrial environments. Living on a chemical gradient where reduced iron comes in contact with oxygen, these organisms use the iron as an energy source and as a building material for stocks and sheaths made of iron oxide. Historically these environments provided early settlers with bog iron, which was crucial in the production of tools. The purpose of this research is to define the chemical environment in which those organisms grow--specifically, the rate at which iron(II) is oxidized into iron (III) and the reactive oxygen species that are produced when oxygen is reduced. Reactive oxygen species, such as H2O2, oxidize both iron and potentially carbon, which presents a possible source of simple carbon compounds for growth. An acridinium ester (AE)-based chemiluminescence method was optimized for the analysis H2O2 measurements in high iron(II) environments. Using this analytical system, the H2O2 was measured at a number of fresh water seeps containing significant iron(II). The measurements indicate that there are unexpectedly high concentrations of H2O2 in these seeps suggesting that dissolved organic material or the iron(Il)oxyhydroxide solids in these samples is accelerating iron(II) oxidation by O2 and producing large fluxes of H2O2. In addition, elevated kinetic rates of iron(II) oxidation were observed in laboratory experiments consistant with the accelaration of iron(II) oxidation. This work shows that μM levels of H2O2 is present in some natural environments, is highly dynamic and is largely dependent on the interplay between water flow, heterogeneous soil iron chemistry, and the mixing of atmospheric oxygen with seep flows. These seeps provide a unique chemical environment that may play a role in defining the ecology of the organisms at this dynamic redox gradient.


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leptothix, iron, oxidation

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