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Title: An investigation into microbial biotransformations of antimony
Author: Smith, Louise Michele
ISNI:       0000 0001 3449 5628
Awarding Body: De Montfort University
Current Institution: De Montfort University
Date of Award: 2001
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Interactions of microorganisms, both prokaryotic and eukaryotic, with the metal antimony were studied. Of particular interest was the process of biomethylation. Volatilisation of trimethylantimony from inorganic antimony substrate by mixed inoculum (of environmental source) enrichment cultures was demonstrated to occur. Trimethylantimony was the sole volatile antimony species detected in incubations designed to promote the growth of clostridia, no stibine or other volatile methylated species were detected. Two Clostridium sp. were isolated from environmental enrichment incubations and three characterised Clostridium sp. were demonstrated to possess a biomethylating capability. Up to 21 μg. 1-1 involatile methylantimony species were detected in the culture medium of monoseptic incubations of the characterised Clostridium sp. The relative quantities of involatile mono-, di- and trimethylantimony species produced during the course of the cultivation period is consistent with trimethylantimony oxide being a final product of antimony biomethylation, with monoand dimethylantimony species appearing transiently in the cultures as intermediates of an antimony biomethylation pathway. The fungi Cryptococcus humicolus, Candida boidinii, Candida tropicalis, Geotrichum candidum and Saccharomyces cerevisiae were all demonstrated to possess a similar antimony biomethylating capability. Volatile and involatile methylantimony species were detected, with involatile species being the predominant form. Both stibine and trimethylantimony were detected in culture headspace gases of fungal incubations. Levels of trimethylantimony were higher in incubations supplied with antimony III substrate, whilst stibine was the predominant volatile antimony species in incubations supplied with V valency substrate. S. cerevisiae demonstrated the highest stibine generating capability with up to 0.3% substrate being transformed. Regardless of substrate, overall antimony biomethylation efficiency (to both volatile and involatile species) was low, indicating that this biotransformation does not form the primary mode of resistance to the metal. Less than 0.1% of antimony III substrate was biomethylated by C. humicolus, the most productive species in terms of formation of methylantimony compounds. The intracellular accumulation of methylated antimony species further belies the theory that antimony biomethylation constitutes a resistance mechanism. Study of C. humicolus revealed the biomethylation process to be enzymatic and inducible by arsenic but not by antimony. This may indicate that the enzymes of the arsenic biomethylation pathway are the likely biocatalysts for the biomethylation of antimony. The low efficiency of antimony biomethylation indicates that this is most likely a fortuitous process. A number of Gram-positive cocci isolated from soil and sediment were demonstrated to bioreduce antimonate to an unknown inorganic antimony III compound concurrently with lactate oxidation and biomass formation (as measured by protein). Up to 48% of the supplied antimonate was bioreduced. The demonstration of dissimilatory antimonate respiration adds this metal to the increasing list of known "unusual" electron acceptors such as uranium, arsenic, selenium, iron and manganese. These studies reveal some of the microbial interactions of microorganisms with the metal antimony, demonstrating the potential that microorganisms have to contribute to the biogeochemical cycling of antimony through biotransformation processes
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Cryptococcus humicolus; Biomethylation; Clostridia; Stibine formation