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

Magnetite-producing magnetotactic bacteria collected from the oxic-anoxic transition zone of chemically stratified marine environments characterized by O-2/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 O-2-gradient media with H2S or thiosulfate (S2O32-) as electron sources and O-2 as electron acceptor or anaerobically with S2O32- and N2O as electron acceptor, with bicarbonate (HCO3-)/CO2 as sole C source. Cells grown with H2S contained S-rich inclusions. Cells oxidized S2O32- to sulfate (SO42-). Both strains grew microaerobically with formate. Neither grew microaerobically with tetrathionate (S4O62-), methanol, or Fe2+ as FeS, or siderite (FeCO3). Growth with S2O32- and radiolabeled C-14-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.