Firmicutes

The Firmicutes (Latin: firmus, strong, and cutis, skin, referring to the cell wall) are a phylum of bacteria, most of which have gram-positive cell wall structure. A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer membrane that causes them to stain gram-negative. Scientists once classified the Firmicutes to include all gram-positive bacteria, but have recently defined them to be of a core group of related forms called the low-G+C group, in contrast to the Actinobacteria. They have round cells, called cocci (singular coccus), or rod-like forms (bacillus). Many Firmicutes produce endospores, which are resistant to desiccation and can survive extreme conditions. They are found in various environments, and the group includes some notable pathogens. Those in one family, the heliobacteria, produce energy through anoxygenic photosynthesis. Firmicutes play an important role in beer, wine, and cider spoilage. The group is typically divided into the Clostridia, which are anaerobic, the Bacilli, which are obligate or facultative aerobes, and the Mollicutes, which are parasites. On phylogenetic trees, the first two groups show up as paraphyletic or polyphyletic, as do their main genera, Clostridium and Bacillus. The phylogeny is based on 16S rRNA-based LTP release 132 by the All-Species Living Tree Project, with the currently accepted taxonomy based on the List of Prokaryotic names with Standing in Nomenclature (LPSN), National Center for Biotechnology Information (NCBI), and some non-validated clade names from Genome Taxonomic Database. Notes:♥ Clade names not lodged at National Center for Biotechnology Information (NCBI) or listed in the List of Prokaryotic names with Standing in Nomenclature (LPSN) The family Synergistaceae (Clostridiales Family XV Incertae Sedis) and Thermodesulfobiaceae have been removed from Firmicutes based on the fact, they do not form a monophyletic clade with it. More than 274 genera were considered as of 2016 to be within the Firmicutes phylum, notable genera of Firmicutes include: