Firmicutes are Gram-positive bacteria with a low mole% G+C content (less than 50%) and they constitute one of the main phyla within the Bacteria. This lineage is highly diverse in their morphology (rod, coccoid, spiral), physiology (anaerobic, aerobic), lifestyle (endospore-forming, nonspore-forming) and so on. Many species from the class Bacilli and Clostridia are characterized by the formation of heat-resistant and desiccation-resistant endospores. However, these phenotypic characteristics tend to be less conserved above family level, thus they are not reliable indicators of phylogenetic relationships. Our current understanding of the taxonomy and evolutionary relationships of Firmicutes divisions is mainly based on the branching patterns of these species in the 16S rRNA trees. Currently, Firmicutes encompass 3 classes, Bacilli, Clostridia, and Mollicutes, including 164 genera. However, except for their distinct clustering in the 16S rRNA trees, presently no other reliable biochemical or molecular characteristics are known which can clearly distinguish species belonging to this phylum from other bacteria. Furthermore, the monophyletic nature of the Firmicutes phylum and interrelationships among different families and orders within this phylum also remains to be determined with certainty.

 

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1. Phylogenetic Trees

2. Conserved Indels

3. Signature Proteins