Effect of oxidative stress on the growth of magnetic particles in Magnetospirillum magneticum

Authors

  • Radu Popa Biology Department Portland State University
  • Wen Fang Biology Department Portland State University
  • Kenneth H. Nealson University of Southern California, Los Angeles, California, USA
  • Virginia Souza-Egipsy Center for Astrobiology, Torrejón de Ardoz, Madrid, Spain
  • Thelma S. Berquó University of Minnesota, Minneapolis, Minnesota, USA
  • Subir K. Banerjee University of Minnesota, Minneapolis, Minnesota, USA
  • Lee R. Penn University of Minnesota, Minneapolis, Minnesota, USA

Keywords:

Magnetospirillum magneticum AMB-1, magnetotactic bacteria, magnetosomes, biomineralization, magnetite, dwarf MMP

Abstract

Individual magnetosome-containing magnetic mineral particles (MMP) from magnetotactic bacteria grow rapidly such that only a small fraction (< 5%) of all magnetosomes contain dwarf (≤20 nm) MMP. Studies of the developmental stages in the growth of MMP are difficult due to the absence of techniques to separate dwarf from mature particles and because the former are sensitive to extraction procedures. Here, O2 stress was used to inhibit MMP expression in Magnetospirillum magneticum strain AMB-1. In addition, defined growth conditions not requiring chemical monitoring or manipulation of the gas composition during growth resulted in the production of cells containing high numbers of dwarf MMP. Cells exposed to different incubation treatments and cells with dwarf MMP were compared to cells with normal MMP with respect to growth, respiration, iron content, and relative magnetite load (RML). The cells were examined by electron microscopy, low temperature magnetometry, X-ray diffraction (XRD), and Mössbauer spectroscopy. In the 0–110 μM O2(aq) range, growth was positively correlated with [O2] and negatively correlated with RML. Most MMP formed during exponential growth of the cells. At 50–100 μM O2(aq) with stirring (150 rpm) and < 30% O2 loss during incubation, MMP expression was strongly inhibited whereas MMP nucleation was not. Cells highly enriched (~95%) in dwarf MMP were obtained at the end of the exponential phase in stirred (150 rpm) cultures containing 45 μM O2(aq). Only one dwarf MMP formed in each MMP vesicle and the chain arrangement was largely preserved. O2-stress-induced dwarf MMP consisted of non-euhedral spheroids (~25 nm) that were similar in shape and size to immature MMP from normal cells. They consisted solely of magnetite, with a single domain signature, no superparamagnetic behavior, and magnetic signatures, Fe(II)/Fe(III) ratios, and XRD patterns very similar to those of mature MMP. These results show that O2 stress in liquid cultures amended with an inorganic redox buffer (S2O32–/S0) can be used to produce abundant dwarf  MMP that are good proxies for studying MMP development. [Int Microbiol 2009; 12(1):49-57]

Author Biographies

Radu Popa, Biology Department Portland State University

Biology Department Portland State University

Wen Fang, Biology Department Portland State University

Biology Department Portland State University

Kenneth H. Nealson, University of Southern California, Los Angeles, California, USA

University of Southern California,
Los Angeles, California, USA

Virginia Souza-Egipsy, Center for Astrobiology, Torrejón de Ardoz, Madrid, Spain

Center for Astrobiology,
Torrejón de Ardoz, Madrid, Spain

Thelma S. Berquó, University of Minnesota, Minneapolis, Minnesota, USA

University of Minnesota, Minneapolis, Minnesota, USA

Subir K. Banerjee, University of Minnesota, Minneapolis, Minnesota, USA

University of Minnesota, Minneapolis, Minnesota, USA

Lee R. Penn, University of Minnesota, Minneapolis, Minnesota, USA

University of Minnesota, Minneapolis, Minnesota, USA

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Published

2010-09-20

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Section

Research Articles