The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure.[2] 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 Bacillota 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 Actinomycetota. They have round cells, called cocci (singular coccus), or rod-like forms (bacillus).
Many Bacillota 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. Bacillota play an important role in beer, wine, and cider spoilage.
The group is typically divided into the Clostridia, which are anaerobic, and the Bacilli, which are obligate or facultative aerobes.
On phylogenetic trees, the first two groups show up as paraphyletic or polyphyletic, as do their main genera, Clostridium and Bacillus.[3] However, Bacillota as a whole is generally believed to be monophyletic, or paraphyletic with the exclusion of Mollicutes.[4]
This second phylogeny is based on 16S rRNA-based LTP release 132 by the All-Species Living Tree Project,[7] with the currently accepted taxonomy based on the List of Prokaryotic names with Standing in Nomenclature (LPSN),[8] National Center for Biotechnology Information (NCBI),[9] and some non-validated clade names from Genome Taxonomy Database.[10]
More than 274 genera were considered as of 2016[update] to be within the Bacillota phylum,[citation needed] notable genera of Bacillota include: