IOAN I. ARDELEAN12, CRISTINA MOISESCU1 AND DAN RAZVAN POPOVICIU2
'Center of Microbiology, Institute of Biology 060031 Bucharest, Romania
2"Ovidius" University Faculty of Natural Sciences Constantza, Romania
This paper is focused on magnetotactic bacteria and their possible contributions to the terraformation of Mars or other planets. The potential for terraformation is mainly based on their ability to carry out aerobic or anaerobic respiration with either nitrate or ferric iron, to fix carbon dioxide in the dark using the energy released through the oxidation of inorganic chemicals such as thiosulfate, and to use molecular nitrogen for cell growth. Furthermore, the magnetic assisted taxies, could help magnetotactic bacteria in their navigation toward optimum growth conditions, when a magnetic field is present.
Magnetotactic bacteria (MTB) are prokaryotes whose specific functional characteristic is magnetotaxis, the orientation and swimming along the Earth's geomagnetic field lines (Blakemore, 1975). Magnetotaxis is determined by the presence inside the cell of particles named magnetosomes. The discovery of MTB stimulated interest among microbiologists, physicists, engineers, geologists, chemists (Schüler and Frankel, 1999) and today the subject has become a bona fide field of research in microbiology (Bazylinski and Frankel, 2004).
The aim of this paper is to shortly review the present state of research on MTB in order to put forward that the structure and the functions of different MTB should be important in the process of terraformation. This focus on their possible role in the terraformation of Mars or other planets should take into account that other types of microorganisms, for example photoautotrophic and/ or extremophiles are already better known as the most important candidates for terraformation (Nienow et al., 1988; Friedmann et al., 1993; Nussinov et al., 1994; Haynes and McKay, 1992; Hiscox, 2000b). However, the so far known particularities of MTB argue that they have potential to participate to the process of terraformation.
Several comprehensive and authoritative reviews on MTB have been published (Blakemore, 1982; Frankel et al., 1998; Mann et al., 1990; Stolz, 1993; Schüler and Frankel, 1999; Bazylinski and Frankel, 2004; Frankel and Bazylinski, 2006; Stephens, 2006; Bazylinski et al., 2007) and their reading is highly recommended for a larger and deeper view on MTB. Terraforming "a process of planetary engineering, specifically directed at enhancing the capacity of an extra-terrestrial planetary environment to support life" (Fogg, 1995) evolved from a science-fiction story to a scientific domain (Sagan, 1961, 1973; Averner and MacElroy, 1976; Badescu, 2005; Jukes, 1991; McKay et al., 1991; Haynes and McKay, 1992; Hiscox and Thomas, 1995; Hancox, 1999; Nussinov et al., 1994; Hiscox, 2000a; Birch, 1992; Fogg, 1989, 1993, 1998; Zubrin and Wagner, 1996; Zubrin and McKay, 1997; McKay and Marinova, 2001; Marinova et al., 2000; Gerstell et al., 2001; Popoviciu, 2006).
2. Magnetotactic Bacteria - General Considerations
The morphology of single celled MTB ranges from spirilla, vibrioids, cocci, rods to ovoid. The reports on multi-celled magnetotactic prokaryote come with details about the life cycle of an isolated from a saline lagoon (Rodgers et al., 1990; Keim et al., 2004).
Magnetosomes are intracellular bodies which in Magnetospirillum strains (M. magnetotacticum or M. gryphiswaldense) consist of magnetic iron mineral particles enclosed within a membrane about 3-4 nm thick (Gorby et al., 1988). The size and morphology of magnetic crystals are species specific and uniform within a single cell. For example in M. gryphiswaldense the dimension of magne-tosomes is around 45 nm (Schüler, 2004). In many MTB strains the iron mineral particle consists of magnetite (Fe3O4), whereas in several MTB from marine, sulfidic environments, the iron mineral particles consist of greigite (Fe3S4). However, there are few reports concerning MTB that produce both magnetite and greigite (Bazylinski et al., 1995; Kasama et. al., 2006; Lins et al., 2007). The size of magnetite or greigite crystals found in different strains is between 35-120 nm which is within the permanent single-magnetic-domain (SD) size range for both minerals (Butler and Banerjee, 1975).
In the last few years the study of the proteins found in magnetosome membrane created special interest because it was expected that at least some of these proteins would enable the processes of mineral formation of nanocrystals to be regulated by biochemical pathways (Schüler and Baeuerlein, 1998; Schüler and
Frankel, 1999; Matsunaga et al., 2000; Schüler, 2004; Grünberg et al., 2004; Bazylinski and Frankel, 2004; Frankel and Bazylinski, 2006; Tanaka et al., 2006).
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