Why Sequence Freshwater Iron-Oxidizing Bacteria?

The goal of this project is to obtain complete genome sequences for six different freshwater iron (Fe)-oxidizing bacteria (FeOB). Four of these are oxygen-dependent iron-oxidizing β-proteobacteria, and three of these, Sideroxydans lithotrophicus, Gallionella capsiferriformans, and strain TW-2, are capable of chemolithoautotrophic growth (that is, obtaining energy by the oxidation of inorganic compounds) using Fe(II) as sole energy source under microaerobic (low-oxygen) conditions. The fourth organism, Leptothrix cholodnii, is a sheath-forming heterotrophic (i.e., using complex organic compounds for nutrition) organism that oxidizes both Fe(II) and Mn(II) and deposits a ferromanganic coating on its sheath. In addition, we will sequence two oxygen-independent α-proteobacteria that utilize Fe(II) as an electron donor to carry out anoxygenic (oxygen-free) photosynthesis coupled to photolithoautotrophic growth (i.e., growth involving photosynthesis and oxidation). These latter two organisms, Rhodopseudomonas palustris TIE-1, and Rhodobacter sp. SW2, are currently being used to elucidate both genetic pathways and biochemical mechanisms of Fe(II) oxidation coupled to anoxygenic photosynthesis.

While iron oxidation is reckoned to be a very ancient metabolism on Earth, it is only recently that we have been able to grow these iron-oxidizing organisms in the laboratory in ways that allow us to study them in detail. As a result, very little is known about their basic physiology. For this reason, draft genomes will be immensely useful in understanding the organisms’ fundamental biology, especially with regard to the use of Fe(II) as an energy source and basic carbon flow. This research will aid human understanding of the coupling of iron oxidation to electron transport. The results can be of use in remediation of soils, sediments, or groundwater contaminated with radionuclides or metals such as strontium, uranium, cadmium, and arsenic. Iron-oxidizing bacteria play an important role in the iron cycle as it influences not only the carbon cycle, but also the sulfur and phosphorus cycles. Additionally, five of the six bacteria proposed for sequencing in this project link iron oxidation to carbon dioxide fixation, which is important for environmental carbon sequestration.

Principal Investigators: David Emerson (Amer. Type Culture Collection), Dianne K. Newman (Caltech), and Eric Roden (Univ. of Wisconsin-Madison)