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Title: Autotrophy in iron-oxidizing, acidophilic bacteria
Author: MacLean, Martin Robert
ISNI:       0000 0001 3615 7227
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1993
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Gram positive, moderately thermophilic, acidophilic bacteria which can oxidize mineral sulphides are likely to be used industrially in mineral processing. In comparison with the Gram negative Thiobacillus ferrooxidans which is currently used commercially, the best- characterized moderate thermophiles were shown to require enhanced concentrations of CO2 in air (i.e. greater than 0.033% (v/v)) for optimal growth. The influence of the supplied CO2 concentration was examined with growth of moderate thermophile strain BC1 and of T. ferrooxidans with ferrous iron as the substrate. Various aspects of CO2 utilization by these bacteria were examined with a view to explaining the requirement of the Gram positive thermophiles for a higher CO2 concentration. During autotrophic growth under C02~limitation (i.e. aeration with air, 0.033% (v/v) COo), strain BC1 and T. ferrooxidans both showed an approximate three-fold increase in RuBisCO synthesis and were capable of similar maximum RuBisCO and PRK activities. RuBisCO substrate affinities (A^,) for strain BC1 were 43.5 pM (CO2) and 67.5 pM (RuBP) and for T. ferrooxidans were 47 pM (CO2) and 85 pM (RuBP), again apparently indicating no major differences in the activity of these Calvin cycle enzymes. Both types also appeared to possess only the form I RuBisCO (LgSg). T. ferrooxidans was shown to induce a high affinity CO2 uptake system following growth under C02-limitation, which allowed the bacteria to show a maximum rate of CO2 uptake from air (0.03% (v/v) C02). The moderate thermophile strains BC1 and ALV did not induce a high affinity system under CO2 limitation, and required 0.1% (v/v) CO2 in air for the maximum rate of C02 uptake, which was a similar maximum rate to that of T. ferrooxidans. After harvesting and resuspension, strains BC1 and ALV, but not T. ferrooxidans had an obligate requirement for a "regeneration" period in the presence of an energy source (ferrous iron) before CO2 uptake could be demonstrated. This period may have been necessary for de novo protein synthesis. The presence of some unfixed carbon in the strain BC1 cytoplasm possibly indicated a less efficient utilization of accumulated CO2 in comparison with T. ferrooxidans. The presence of carboxysomes in T. ferrooxidans could have contributed to the efficient CO2 utilization; they were not observed in the Gram positive moderate thermophiles. Three membrane polypeptides (approximate molecular weight 93, 62 and 35 kDa) and two apparently soluble and potentially acid-stable polypeptides appeared to increase in concentration in T. ferrooxidans following growth under COo-limiting conditions. A recently obtained enrichment culture of moderate thermophiles from an Icelandic hot spring was found to be capable of relatively efficient growth on ferrous iron under air, in comparison with strain BC1. Electron microscopy revealed that attempts to isolate a pure culture which was capable of such growth had left a culture which comprised two types of bacteria. One of these bacteria appeared to be morphologically similar to strain BC1 whereas the other appeared to be a previously undescribed organism. A harvested and resuspended mixture of these two types (from growth under C02-limitation) possessed a high affinity CO2 uptake system (kinetically equivalent to that of T. ferrooxidans). The relative contribution of these two types to the efficient CO2 utilization awaits their separation. The correlation of good growth under air with the presence of high affinity transport systems, rather than with different "efficiencies" of CO2 fixation in the Calvin cycle, nevertheless appears established for the iron- oxidizing acidophiles.
Supervisor: Not available Sponsor: Science and Engineering Research Council ; Warren Spring Laboratory (Stevenage, England)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry ; QR Microbiology