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Title: Novel respiratory flavocytochromes of Shewanella oneidensis MR-1
Author: Bilsland, Morag
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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Shewanella oneidensis MR-1 is a Gram-negative bacterium isolated from anaerobic freshwater lake sediments of Lake Oneida that exhibits remarkable respiratory versatility. In the absence of molecular oxygen, S. oneidensis MR-1 couples anaerobic growth to the reduction of various substrates, including ferric iron (FeIII), thiosulfate (S2O32-), sulfite (SO32-), trimethylamine N-oxide (TMAO), nitrate (NO3-), nitrite (NO2-) and organic substrates such was fumarate. The metabolic flexibility of S. oneidensis MR-1 is coupled to a complex and branched anaerobic respiratory chain. The respiratory enzymes of the fumarate reduction pathway have been extensively studied in S. oneidensis MR-1 and the related marine bacterium, S. frigidimarina NCIMB400. The terminal fumarate reductase of Shewanella is a soluble periplasmic flavocytochrome c3 (Fcc3) that catalyses the unidirectional production of succinate. The X-ray crystal structure of Fcc3 solved to high resolution provided the first detailed insight into the catalytic mechanism of fumarate reduction. In this work, the Fcc3 X-ray crystal structure provided a structural template to construct homology models of related flavoenzymes of unknown structure and function. The novel flavoenzymes were identified by sequence analysis of the S. oneidensis MR-1 genome and were shown to comprise separately encoded flavin (FccA54, FccA56 and FccA342) and cytochrome subunits (FccB54, FccB56 and FccB342), respectively, that were related by sequence to the corresponding domains in Fcc3. Molecular modelling of the catalytic flavin-binding subunits led to the suggestion that these related enzymes catalyse the reduction of acrylate-like substrates. Several biologically relevant plant metabolites, including phenylacrylates incorporated into lignin, were identified as potential substrates of the Fcc3-like enzymes. An fccA54 and fccB54 knockout strain of S. oneidensis MR-1 (MB5415) was constructed and grown anaerobically with each of the candidate acrylates to ascertain the biological function of FccA54.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available