With an elegant and flexible electron transport chain, Shewanella oneidensis strain MR-1, is the most versatile respiratory organism known to date. MR-1 is a diverse respiratory heterotroph that lives in complex aquatic communities, often in association with other microorganism or eukaryotes, such as fish and algae. Fish produce TMAO as an osmoprotector, which also serve as a respiratory substrate for Shewanella isolates that are able to respire it. Although, TMAO is readily found in the aquatic environments where MR-1 is known to be found, MR-1 metabolism under TMAO respiring conditions is not fully understood. In addition, bacteria are usually studied as monocultures in laboratory conditions, however, microorganisms exist in nature as members of communities that interact with each other. Therefore, the factors that shape microbial behavior and interactions in communities remain largely undefined. The work presented in this thesis aims to further elucidate the metabolic strategy of MR-1 under TMAO respiring conditions, as well as, in a commensal interaction with Geobacter sulfurreducens. Coupled to the reduction of terminal electron acceptors, MR-1 has an aerobic branch, as well as, an anaerobic branch for the oxidation of carbon sources. However, in conditions where TMAO is the sole electron acceptor, the oxidation pathway for carbon sources is not fully understood. Furthermore, at the electron transport chain level, TMAO is reduced differently from other anaerobic compounds. Therefore, we aim to understand electron and carbon flux under growth conditions with this important electron acceptor. We have made gene deletions of key enzymes in both aerobic and anaerobic metabolic pathways in MR-1, and assayed for growth under conditions where TMAO is the sole terminal electron acceptor. We aim to begin to explore MR-1 metabolism in a more complex system with two organisms instead of one. For this purpose, we have engineered a close physical associationbetween S. oneidensis and Geobacter sulfurreducens. G. sulfurreducens is an anaerobic subsurface bacterium and another well-characterized organism capable of metal reduction and extracellular electron transfer. By performing laboratory evolution of this synthetic co-culture we aim to identify genes implicated in community interaction and understand how these genes influence their metabolism.
University of Minnesota M.S. thesis.August 2017. Major: Biochemistry, Molecular Bio, and Biophysics. Advisor: Jeffrey Gralnick. 1 computer file (PDF); vi, 39 pages.
Maysonet Sanchez, Rebecca.
Anaerobic Shewanella physiology: An unusual respiratory substrate and an unusual respiratory partner.
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