| This thesis consists of three chapters. The first chapter is an introduction, and provides a general overview of the history, mineralogy, chemistry, geochemistry, biology and biochemistry of the element manganese (Mn). It also provides background to the subject of biological manganese oxidation and discusses both scientific and industrial aspects of this phenomenon. It ends with an overview of the current knowledge of the mechanisms involved in bacterial Mn oxidation.; The second chapter describes the cloning, sequencing, and expression in Escherichia coli of the genes encoding a ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) from strain SI85-9A1, a novel marine manganese-oxidizing bacterium. When the genes were introduced into an E. coli host strain, ribulose 1,5-bisphosphate-dependent CO{dollar}sb2{dollar} fixation occurred under control of a lac promoter, indicating that the protein is functional in E. coli. Although their function is unknown, this is the first direct evidence for the presence of RubisCO genes in a manganese oxidizing bacterium. Phylogenetic analysis of the RubisCO genes showed that the genes of strain SI85-9A1 are divergent, but are more related to the group containing RubisCO genes from non-chlorophyte algal chloroplasts than to the groups containing other bacterial RubisCO genes. The fact that this RubisCO sequence is not closely related to any other published RubisCO sequence suggests that this protein may be valuable for studies of the function and evolution of the RubisCO enzyme.; The third chapter describes the use of transposon mutagenesis to construct mutants of the freshwater Mn oxidizing bacterium Pseudomonas putida strain MnB1, that have lost their ability to oxidize manganese, and the characterization of some of these mutants. The majority of the non-oxidizing mutants had transposon insertions either in an operon involved in the biogenesis of c-type cytochromes, or in genes that encode key enzymes of the TCA cycle. In both cases the mutants were cytochrome c oxidase negative, and did not contain c-type cytochromes. The correlation between c type cytochromes and Mn oxidation suggests that in this organism Mn oxidation is mediated by the electron transfer chain. This finding supports earlier works that suggested that the oxidation of Mn may provide energy for mixotrophic growth. |
