Handprints in Manganese: The Morphology and Attributes of Manganitrophus noduliformans and its Associated Manganese Oxides

Author: Way, Hannah Virginia

Year: 2027

Degree: Dissertation (Ph.D.)

Advisor: Leadbetter, Jared R.

Committee Members: Fischer, Woodward W.; Leadbetter, Jared R.; Newman, Dianne K.; Orphan, Victoria J.

Option: Geobiology

Abstract

Through the direct and indirect catalysis of redox reactions, microorganisms facilitate the deposition of manganese oxide minerals and drive the global manganese cycle. The overwhelming majority of these organisms are heterotrophic in nature. Thus far, the only species that have demonstrated the ability to chemolithoautotrophically oxidize Mn are members of a small and discrete phylogenetic group, the Manganitrophaceae. Manganitrophus noduliformans demonstrates chemolithoautotrophic manganese-oxidation dependent growth when cultured with a partner species. The entirety of their microbial biomass is encapsulated within millimeter-scale spheroidal manganese oxide nodules or continuous crusts that settle to the bottom of the culture media. Owing in large part to their comparatively recent discovery (2020), long doubling times, and the obscurant nature of the manganese oxides, much remains unknown about Mn oxidizing chemolithoautotrophs. This thesis seeks to meticulously characterize the ultrastructure of M. noduliformans and the biogenic manganese oxide minerals that it encapsulates itself in, and to further investigate the impact of the culture and oxides on the soluble metal content of surrounding waters. Chapter 2 describes the current state of knowledge regarding manganese oxides, Mn oxidizing bacteria, and their geological and biological context. In Chapter 3 we combined deep agar cultivation, cryofixation, and Transmission Electron Microscopy to describe the ultrastructural characteristics of Manganitrophus noduliformans and its progenitive manganese oxide nodules, documenting for the first time that they contain putative membrane vesicles and manganese oxide nanoribbons. High resolution tomograms reveal that the manganese oxide nodules consist of tangles of flat manganese oxide nanoribbons of approximately 5 nm thickness and variable width and length. Individual cells of M. noduliformans have an outer and inner membrane, are pleomorphic in form and are contacted by bundles of manganese oxide at discrete but seemingly random points on the outer membrane. Closely associated with the manganese oxide nanoribbons at the periphery of the nodules were abundant putative membrane vesicles in a range of sizes. In Chapter 4 we determined that a Mn oxidizing co-culture containing M. noduliformans and a fungal partner species is capable of generating manganese oxides at concentrations of metal salts many times greater than US regulatory limits and global averages in groundwater. Both the actively deposited and mature biogenic manganese oxides removed more metal cations from solution than the MnCO₃ substrate, media alone, or commercially available MnO₂, demonstrating potential as a tool of remediation. This work improves the collective understanding of the full breadth of structures and characteristics exhibited by biologically produced manganese oxide minerals and takes a step forward in the journey towards comprehension of the morphological features involved in the chemolithoautotrophic oxidation of manganese, as well as their potential as a tool of bioremediation.