Gram-positive bacteria are generally divided into the
Actinobacteria and the
Firmicutes.
The Actinobacteria or actinomycetes are a group of
Gram-positive bacteria with high G+C ratio. They include some of the most common soil bacteria. Other Actinobacteria inhabit plants and animals and including some pathogens, such as
Mycobacterium,
Corynebacterium,
Nocardia,
Rhodococcus and a few species of
Streptomyces. Actinobacteria produce secondary metabolites and are important to the pharmacological and biotechnology industries.
Streptomyces species, for example, produce important antibiotics. Some Actinobacteria form branching filaments and some
Actinomycetes species produce endospores.
The majority of Firmicutes have Gram-positive cell wall structure. However some, the Mollicutes or mycoplasmas, lack cell walls altogether and therefore do not respond to Gram staining. They do however lack the second (outer) membrane found in Gram-negative bacteria. Others members of the group, such as
Megasphaera,
Pectinatus,
Selenomonas, and
Zymophilus have a porous pseudo-outer-membrane that causes them to stain Gram-negative. The Firmicutes are generally restricted to a core group of related bacteria, called the low G+C group in contrast to the Actinobacteria. Firmicutes can be cocci or rod-shaped forms. Many produce endospores. They are found in various environments and some members of the group are important pathogens.
Recommended reading:Clostridia: Molecular Biology in the Post-genomic Era Corynebacteria: Genomics and Molecular BiologyMycobacterium: Genomics and Molecular BiologyBacillus: Cellular and Molecular BiologyStaphylococcus: Molecular GeneticsLactobacillus Molecular Biology: From Genomics to ProbioticsGenomics of GC-Rich Gram-Positive BacteriaLabels: bacillus, bacteriology, bacterium, clostridia, clostridium, corynebacterium, lactobacillus