Microbial iron reduction

Microorganisms play fundamental roles in the cycling of iron between its oxidized and reduced forms. Fe-reducing bacteria couple the oxidation of cytoplasmic electron donors with the reduction of Fe(III) found in soil and sediments. Reduction of solid phase metals, such as Fe-oxides, by these microorganisms relies on their remarkable ability to transfer electrons to extracellular electron acceptors. The mechanism of extracellular electron transfer has been studied in great detail in Gram-negative bacteria such as Shewanella and Geobacter but is not well understood in Gram-positive bacteria.
Iron reduction by Clostridium acetobutylicum 

Gram-positive bacteria are likely to contribute significantly to Fe(III) reduction in the environment, particularly under conditions unfavorable to Gram-negative bacteria. Whereas this process can be energy yielding, it may also serve as way of relieving the cell of excess electrons. We use Clostridium acetobutylicum as a model to study the process of iron reduction and extracellular electron transfer in a Gram-positive organism. Our goal is to understand the molecular mechanisms of electron transfer and the effect of iron reduction on the bacterial metabolism. We are using a combination of molecular biology, analytical chemistry, spectroscopy and microscopy tools to unravel the mechanistic details of this process. 

 Extracellular electron transfer in Shewanella oneidensis

Shewanella oneidensis is a very versatile bacterium with respect to its respiratory capabilities. When oxygen is not present, it can use a great range of alternative electron acceptors for respiration, including soluble and insoluble compounds. Central to this is the production of a large number of cytochromes involved in electron transfer to different electron acceptors. Whereas the electron transfer pathways have been characterized in some detail, much less is known about the signals and signal transducing pathways that ensure expression of specific cytochromes when they are needed. We use genetic and genomic approaches to address how this bacterium controls the expression of cytochromes involved in reduction of iron and other metals.

People: Karin Meibom (senior scientist), Cornelia List (Ph.D. student).