Chemolithoautotrophy in the marine, magnetotactic bacterial strains MV-1 and MV-2

Abstract

Magnetite-producing magnetotactic bacteria collected from the oxic-anoxic transition zone of chemically stratified marine environments characterized by O2/H2S inverse double gradients, contained internal S-rich inclusions resembling elemental S globules, suggesting they oxidize reduced S compounds that could support autotrophy. Two strains of marine magnetotactic bacteria, MV-1 and MV-2, isolated from such sites grew in O2-gradient media with H2S or thiosulfate (S2O3(2-)) as electron sources and O2 as electron acceptor or anaerobically with S2O3(2-) and N2O as electron acceptor, with bicarbonate (HCO3-)/CO2 as sole C source. Cells grown with H2S contained S-rich inclusions. Cells oxidized S2O3(2-) to sulfate (SO4(2-)). Both strains grew microaerobically with formate. Neither grew microaerobically with tetrathionate (S4O6(2-)), methanol, or Fe2+ as FeS, or siderite (FeCO3). Growth with S2O3(2-) and radiolabeled 14C-HCO3- showed that cell C was derived from HCO3-/CO2. Cell-free extracts showed ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity. Southern blot analyses indicated the presence of a form II RubisCO (cbbM) but no form I (cbbL) in both strains. cbbM and cbbQ, a putative post-translational activator of RubisCO, were identified in MV-1. MV-1 and MV-2 are thus chemolithoautotrophs that use the Calvin-Benson-Bassham pathway. cbbM was also identified in Magnetospirillum magnetotacticum. Thus, magnetotactic bacteria at the oxic-anoxic transition zone of chemically stratified aquatic environments are important in C cycling and primary productivity.

Magnetovibrio blakemorei gen. nov., sp. nov., a magnetotactic bacterium ( Alphaproteobacteria : Rhodospirillaceae ) isolated from a salt marsh

“…However, the final cell yield of these cultures was only 23-28 % of the high-iron-containing culture, based on direct cell counts, which suggests that cells in these lowiron cultures continue to produce magnetosomes, thereby starving themselves of iron and limiting their growth yield. This further indicates that magnetosome iron in this strain is not biologically available for growth, and thus magnetosomes are not used for iron storage (Dubbels et al, 2004).…”

“…Alternatively, the oxidation of Fe(II) might support N 2 O reduction during growth and the resulting Fe(III) could, in turn, cause the oxidation of resazurin and the change from colourless to pink. Strain MV-1 T is known to possess an Fe(II) oxidase (Dubbels et al, 2004 , distributed throughout the growth medium while the medium was still liquid (kept at about 44 u C). A carbon source was deemed positive for the support of aerobic growth of strain MV-1 T if three conditions were met: (i) a band of cells formed in the tube, (ii) the cell count after growth was significantly greater than the control containing no carbon source and (iii) cells continued to grow in the same medium in three successive transfers.…”

“…All acids used for iron determinations were trace-metal grade (Mallinckrodt Baker Inc.). Approximately 15 mg freeze-dried cells was acid-digested as described by Dubbels et al (2004). Samples of growth medium were acidified and diluted directly with concentrated HCl to a final concentration of 1 %.…”

Diversity of <i>Magnetospirillum</i> Sp. from the Southern Coast of India

“…Amplification of genes encoding RuBisCO in the CBB cycle demonstrated the presence of RuBisCO cbbM large-subunit (form II) gene and autotrophy pathway in all three strains of Magnetospirillum sp. The presence of cbbM gene shows that the isolated strains can grow in higher CO 2 : O 2 ratio 35 . Magnetotactic bacteria produce magnetosomes only when restricted to grow as microaerophiles with high CO 2 : O 2 ratio.…”

“…Magnetotactic bacteria produce magnetosomes only when restricted to grow as microaerophiles with high CO 2 : O 2 ratio. During microaerophillic growth and magnetosome formation the three isolated Magnetospirillum species rely on form-II RuBisCO enzyme for respiration 35 . The distribution of MTB across the southern Indian coast has been discussed in this study.…”