Evidence of a role for copper in iron uptake for magnetosome synthesis in the marine, magnetotactic bacterium, strain MV-1

Dubbels, Bradley
Major Professor
Dennis A. Bazylinski
Committee Member
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Veterinary Microbiology and Preventive Medicine

The research in this dissertation represents the initial characterization in regards to iron uptake in the marine magnetotactic bacterium, strain MV-1. Cellular iron content differences between MV-1 and a non-magnetotactic mutant, designated MV-1nm1, suggested that MV-1nm1 is deficient in one or more iron acquisition systems present in MV-1. Protein profiles of MV-1 and MV-1nm1 showed the non-magnetotatic mutant did not produce several proteins observed in MV-1, including an iron regulated, periplasmic protein. This protein was designated p19 and is a homodimer with a subunit molecular mass of about 19,000 Da that binds copper in a 1:1 ratio. The structural gene for p19 as well as two putative upstream genes were cloned and sequenced. One of these genes encoded for a putative iron permease with similarities to Ftr1p from the yeast Saccharomyces cerevisiae, while the second encoded for a ferrodoxin-like protein of unknown function. Based on the model for a copper-dependent, high-affinity iron uptake in S. cerevisiae, the presence of a periplasmic, p19 dependent, iron oxidase was predicted to be present in MV-1. A periplasmic enzyme exhibiting this activity was subsequently identified and purified. Like Fet3p, the S. cerevisiae iron oxidase, this enzyme was iron-regulated and contained 4 atoms of copper per molecule. Though no function has been found for p19, all three components (p19, iron oxidase, iron permease) for a high-affinity iron transport system similar to that found in S. cerevisiae are present in MV-1 and may be important in providing iron for magnetosome biomineralization.;The magnetotactic bacterium strain MV-1 has been shown to grow microaerobically with sulfide or thiosulfate as electron donors and anaerobically with nitrous oxide (N2O) serving as the terminal electron acceptor. This magnetotactic strain is capable of growing autotrophically with HCO3- /CO2 supplied as the sole source of carbon in the growth media, utilizing the Calvin-Benson-Bassham pathway for CO2 fixation. Specifically, MV-1 possesses the form II RubisCO gene (cbbM). In this dissertation, the cloning and sequencing of a form II RubisCO gene (cbbM) in the magnetotactic spirillum, Magnetospirillum magnetotacticum is reported. Assessment of the magnetotactic spirilla M. gryphiswaldense and M. magneticum for the presence of cbbM was also performed.