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Project Progress

The biology of Iron Oxidation

• A genetic system has been developed for our model neutraphilic Fe-oxidizing bacterium, Marinobacter aquaeolei ;
• A fosmid library has been constructed for M. aquaeolei and screened for Fe-oxidizing clones. Pigmented clones contain HemA .
• The genome of M. aquaeolei has been sequenced and draft annotation completed. The genome is being closed and manually annotated.
• Biochemical studies have confirmed that Heme production increases under Fe-oxidizing conditions. A genbank screening of the genome revealed a putative operon which includes Di-heme cytochrome C peroxidase and four neighboring proteins with predicted functions in electron transfer; gene arrangement is distinct compared to other available genomes. A manuscript is in preparation reporting these results. We suspect that this operon plays an important role in iron oxidation and are now conducting studies to confirm this hypothesis.



Iron Isotopic Studies

• The Fe isotopic composition of sulfides in black shales has been measured for samples ranging in age from Precambrian to Late Cretaceous, with specific focus on Late Archean to early Paleoproterozoic time.
• Highly variable and negative Fe isotopes before 2.3 Ga were measured and reported in Science earlier this year.
• Our interpretation of these results is that the oceans were globally Fe-rich, their Fe isotope composition and Fe content were variable in response to the episodic establishment of an Fe-rich pool supplied by hydrothermal activity and deposition of Fe-oxides, either in BIFs or dispersed throughout sediments on continental shelves and in the deep sea. After the rise of atmospheric oxygen by ca. 2.3 Ga, Paleoproterozoic oceans became stratified and characterized by an increase of sulfide precipitation relative to Fe-oxide precipitation. The effect of the increased role of sulfide precipitation on the change of Fe isotope record by 2.3 Ga is presently uncertain since reliable estimates of isotope fractionation during pyrite, or its precursor formation in the water column are lacking.