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Title: A survey of culturable methanogens in contrasting marine sediments, their substrates and physiological characteristics
Author: Watkins, Andrew
ISNI:       0000 0004 2733 2312
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2012
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Few culture-based surveys have been undertaken on methanogens in contrasting marine sediments. This project conducted a comprehensive study of methanogens in a range of marine sediments including tidal-flats, a shallow bay, deep-water mud volcanoes and Guaymas Basin hydrothermal sediments. Nine of the sixteen recognised methanogen genera were cultured ranging from only one methanogen genus at mud volcano sites to eight in tidal-flats. At a number of these sites, culture-independent techniques (16S rRNA and mcrA gene sequences) had either failed to detect the presence of methanogens or had under-estimated the methanogen diversity. Acetate and hydrogen utilizing methanogens (including two strains of the genus Methanococcus) were cultured from marine sediments with high sulphate content. But by far the most abundant genus was Methanococcoides being isolated from seven of the sites investigated, including the deepest (in terms of water depth) non-thermophilic methanogens so far isolated. Study of the isolated Methanococcoides strains has extended the substrate range of the genus by identifying of two new directly utilized methylated substrates (betaine and choline). The substrate range of this genus has been further extended by demonstrating dimethylsulphide utilization, a compound only previously known as a growth substrate in closely related genera. In addition to substrate tests, representative strains from each of the sites investigated were physiology characterized including temperature, pH and Na+ concentration ranges. Members of the genus Methanococcoides are mesophilic/ psychrotolerant, neutrophilic and halotolerant. Their substrates are limited to methylated compounds. For the first time strains of mesophilic methanogens (Methanococcoides) were tested for their ability to grow under elevated hydrostatic pressure, up to 70 MPa. In conclusion, methylotrophic methanogens play an important role in marine sediment methanogenesis with the methylotrophic genus Methanococcoides being widespread. The range of methylotrophic substrates is wider than previously described and further work is required to determine the full extant of methylated compounds as substrates for methanogenesis. Molecular based studies often fail to identify the presence of methanogens that are subsequently detected in culture-based studies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QE Geology