Direct adherence of Fe(III) particles onto sheaths of Leptothrix sp. Strain OUMS1 in culture

Leptothrix species, one of the Fe/Mn-oxidizing bacteria, oxidize Fe(II) and produce extracellular, microtubuar, Fe-encrusted sheaths. Since protein(s) involved in Fe(II) oxidation is excreted from Leptothrix cells, the oxidation from Fe(II) to Fe(III) and subsequent Fe(III) deposition to sheaths have been thought to occur in the vicinity or within the sheaths. Previously, Fe(III) particles generated in MSVP medium amended with Fe(II) salts by abiotic oxidation were directly recruited onto cell-encasing and/or -free sheaths of L. cholodnii SP-6. In this study, whether this direct Fe(III) adherence to sheaths also occurs in silicon-glucose-peptone (SGP) medium amended with Fe(0) (SGP + Fe) was investigated using another strain of Leptothrix sp., OUMS1. Preparation of SGP + Fe with Fe powder caused turbidity within a few hours due to abiotic generation of Fe(III) particles via Fe(II), and the medium remained turbid until day 8. When OUMS1 was added to SGP + Fe, the turbidity of the medium cleared within 35 h as Fe(III) particles adhered to sheaths. When primitive sheaths, cell-killed, cell-free, or lysozyme/EDTA/SDS- and proteinase K-treated sheath remnants were mixed with Fe(III) particles, the particles immediately adhered to each. Thus, vital activity of cells was not required for the direct Fe(III) particle deposition onto sheaths regardless of Leptothrix strains.