Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to gram-negative bacteria, which are not affected by the stain. The stain is caused by a high amount of peptidoglycan in the cell wall, which typically, but not always lacks the secondary membrane and lipopolysaccharide layer found in Gram-negative bacteria. Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus_Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Gram staining is a method for staining samples of bacteria that differentiates between the two main types of bacterial cell wall. ... Bacteria that are Gram-negative are not stained dark blue or violet by Gram staining, in contrast to Gram-positive bacteria. ... Peptidoglycan, also known as murein, is a homogenous layer lying outside the plasma membrane in prokaryotes. ... A cell wall is a more or less solid layer surrounding a cell. ... A lipopolysaccharide (LPS) is a large molecule that contains both lipid and a carbohydrate. ...

In the original bacterial phyla, the gram-positive forms made up the phylum Firmicutes, a name now used for the largest group. It includes many well-known genera such as Bacillus, Listeria, Staphylococcus, Streptococcus, Enterococcus, and Clostridium. It has also been expanded to include the Mollicutes, bacteria like Mycoplasma that lack cell walls and so cannot be stained by Gram, but are derived from such forms. Phylum is one of the levels of scientific classification of organisms; see the Phylum (biology) article. ... Classes Bacilli Clostridia Mollicutes The Firmicutes are a group of bacteria, most of which have Gram-positive stains. ... Species Bacillus anthracis Bacillus cereus Bacillus coagulans Paenibacillus larvae Bacillus natto Bacillus subtilis Bacillus thuringiensis The word bacillus is a descriptive term for the appearance of certain bacteria when viewed microscopically. ... Binomial name Listeria monocytogenes Listeria monocytogenes is a Gram-positive bacterium, in the division Firmicutes, named for Joseph Lister. ... Species S. aureus Staphylococcus (in Greek staphyle means bunch of grapes and coccos means granule) is a genus of gram-positive bacteria. ... Species S. pneumoniae S. pyogenes S. viridans Streptococcus is a genus of spherical, Gram-positive bacteria of the phylum Firmicutes. ... Species Enterococcus is a bacterium, of the phylum Firmicutes. ... Species Clostridium acetobutylicum Clostridium aerotolerans Clostridium botulinum Clostridium colicanis Clostridium difficile Clostridium formicaceticum Clostridium novyi Clostridium perfringens Clostridium tetani Clostridium is a genus of Gram positive anaerobic spore-forming bacteria. ... Species M. genitalium M. hominis M. pneumoniae etc. ...

The actinobacteria are another major group of gram-positive bacteria; they and the Firmicutes are referred to as the high and low G+C groups based on the guanosine and cytosine content of their DNA. If the second membrane is a derived condition, the two may have been basal among the bacteria, otherwise they are probably a relatively recent monophyletic group. They have been considered as possible ancestors for the archaeans and eukaryotes, both because they are unusual in lacking the second membrane and because of various biochemical similarities such as the presence of sterols. Orders Subclass Acidimicrobidae     Acidimicrobiales Subclass Actinobacteridae     Actinomycetales     Bifidobacteriales Subclass Coriobacteridae     Coriobacteriales Subclass Rubrobacteridae     Rubrobacterales Subclass Sphaerobacteridae     Sphaerobacterales The Actinobacteria are a group of Gram-positive bacteria. ... Guanosine is a molecule (known as a nucleoside) that is formed when guanine is attached to a ribose ring (also known as a ribofuranose) via a β-N9-glycosidic bond. ... Cytosine Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell. ... DNA replication Deoxyribonucleic acid (DNA) is a nucleic acid which is capable of carrying genetic instructions for the biological development of all cellular forms of life and many viruses. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea are a major group of prokaryotes. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Sterols are a subgroup of steroids with a hydroxyl group in the 3-position of the A-ring. ...

The Deinococcus-Thermus group of bacteria also have gram-positive stains, although they are structurally similar to gram-negative bacteria. Orders & Genera Deinococcales     Deinococcus Thermales     Thermus     Meiothermus     Marinithermus     Oceanithermus     Vulcanithermus The Deinococcus-Thermus are a small group of bacteria comprised of cocci highly resistant to environmental hazards. ...