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 Downloads PDF Published 2010-09-20 Issue Vol. 12 No. 1 (2009) Section Research Articles License Submission of a manuscript to International Microbiology implies: that the work described has not been published before, including publication in the World Wide Web (except in the form of an Abstract or as part of a published lecture, review, or thesis); that it is not under consideration for publication elsewhere; that all the coauthors have agreed to its publication. The corresponding author signs for and accepts responsability for releasing this material and will act on behalf of any and all coauthors regarding the editorial review and publication process.If an article is accepted for publication in International Microbiology, the authors (or other copyright holder) must transfer to the journal the right–not exclusive–to reproduce and distribute the article including reprints, translations, photographic reproductions, microform, electronic form (offline, online) or any other reproductions of similar nature. Nevertheless, all article in International Microbiology will be available on the Internet to any reader at no cost. The journal allows users to freely download, copy, print, distribute, search, and link to the full text of any article, provided the authorship and source of the published article is cited. The copyright owner's consent does not include copying for new works, or resale. In these cases, the specific written permission of International Microbiology must first be obtained.Authors are requested to create a link to the published article on the journal's website. The link must be accompanied by the following text: "The original publication is available on LINK at <http://www.im.microbios.org>. Please use the appropiate URL for the article in LINK. Articles disseminated via LINK are indexed, abstracted, and referenced by many abstracting and information services, bibliographic networks, subscription agencies, library networks, and consortia.
