Patterns of sheath elongation, cell proliferation, and manganese(II) oxidation in Leptothrix cholodnii

Leptothrix cholodnii is a Mn(II)-oxidizing and sheath-forming member of the class β-Proteobacteria. Its sheath is a microtube-like filament that contains a chain of cells. From a chemical perspective, the sheath can be described as a supermolecule composed of a cysteine-rich polymeric glycoconjugate, called thiopeptidoglycan. However, the mechanism that controls the increase in sheath length is unknown. In this study, we attempted to detect sheath elongation through microscopic examination by using conventional reagents. Selective fluorescent labeling of preexisting or newly formed regions of the sheath was accomplished using combinations of biotin-conjugated maleimide, propionate-conjugated maleimide, and a fluorescent antibiotin antibody. Epifluorescence microscopy indicated that the sheath elongates at the terminal regions. On the bases of this observation, we assumed that the newly secreted thiopeptidoglycan molecules are integrated into the preexisting sheath at its terminal ends. Successive phase-contrast microscopy revealed that all cells proliferate at nearly the same rate regardless of their positions within the sheath. Mn(II) oxidation in microcultures was also examined with respect to cultivation time. Results suggested that the deposition of Mn oxides is notable in the aged regions. The combined data reveal the spatiotemporal relationships among sheath elongation, cell proliferation, and Mn oxide deposition in L. cholodnii.