This dissertation represents a diversified study of the biochemical, physiological, and genetic traits of members of the low G+C subdivision of the Gram-type positive bacteria, also known as the'Firmicutes'. The phylum 'Firmicutes' contains a diverse array of taxa that are not easily separated into coherent phylogenetic groups by any one physiological trait, such as endospore-formation or dissimilatory iron reduction. This dissertation considers numerous contemporary, and highly convergent in providing breadth and scope of the subject matter, methods of study. The principle aim was to examine the lineage'Firmicutes' by a) a genomic study of the occurrence or absence of endosporulation genes in numerous members of the lineage, b) classic biochemical studies of the enzymes responsible for biotic iron reduction, and c) culture-dependent studies and isolations of various'Firmicutes' to both identify new iron-reducers and better resolve the taxonomy of the lineage. The work with endosporulation genes has shown there might not be a distinct set of "endosporulation-specific" genes. This raises several new questions about this exceptionally complex process. The work described here on "ferric reductases" suggests there are enzymes capable of iron reduction that also have additional activities. The isolation of novel bacteria presented here have added to the diversity of the'Firmicutes' but have also added to the phylogenetic and taxonomic complexity of this group. Traditional boundaries for families and genera have been weakened or shown to be in need of further studies.