Thesis

Preliminary elucidation of the methanogenic fermentations of veratric and syringic acids by interacting microbial associations isolated from anoxic freshwater sediment

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Awarding institution
  • University of Strathclyde
Date of award
  • 1986
Thesis identifier
  • T5491
Qualification Level
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Department, School or Faculty
Abstract
  • Lignia is the second most abundant natural polymer after cellulose and since it is semi-recalcitrant in the environment, it tends to accumulate. After pretreatment, however, labile molecules may be released from which, for example, methane, value-added products and chemical feedstocks may be generated. In this study ground pine (Pinus sylvestris) sawdust was used as a source of lignocellulose. Two pretreatment methods, acid and alkali hydolysis, were examined and the variables of cencentration, temperature and time optimised. Biomethanation of the two pretreatment products, hydrolysates and residual solids, in closed cultures by isolated microbial associations, resulted in 8.5-fold increases in total methane generation compared to untreated controls. Closed culture methods were used to enrich and isolate microbial associations from freshwater sediment capable of catabolising selected monomers under anoxic conditions. In all 20 associations were isolated of which two, a veratric acid-catabolising and a syringic acid-catabolising culture, were chosen for further study. Although initially both associations dissimilated the respective substrates to the terminbal product, nethane, the metabolic activity of the veratric acid-catabolising association changed such that catechol accumulated. A second veratric acid-catabolising association was then isolated which, like the syringic acid-catabolising association, was stable during repeated subcultivations. During open culture cultivations however, in which inceasing dilution rate regemes were applied, species displaced from both associations were apparent. Closed culture studies demonstrated optimum culture conditions of a temperature of 35 °C and a pH of 7.0. Dissimilations of both substrates were accompanied by concomitant sulphate reduction and methane production as the major terminal product. Determination of Ks values from both open and closed culture data showed that higher affinities were apparent in the case of the former. The validity of such determinations and comparisons was, however questioned. For both associations, inhibitions of methanogenesis by an analogue of coenzyme M, 2-bromoethanesulfonic acid, resulted in the accumulation of metabolic intermediates, which were subsequently identified by the use of HPLC, TLC, GLC, and UV spectrophotometry. Based on these identifications tentative breakdown pathways were formulated. Preliminary species isolations indicated that each association contained a minimum of ine sulphate reducer, two methanogens and two to three faculative anaerobes.
Advisor / supervisor
  • Senior, Eric
Resource Type
DOI
EThOS ID
  • uk.bl.ethos.381514

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