The largest group of bacteria but somewhat less diverse than the proteobacteria. Firmicutes play an important role in beer, wine, and cider spoilage and are present in greater numbers in obese individuals (vs Bacteroidetes). The group is typically divided into the Clostridia, which are anaerobic, the Bacilli, which are obligate or facultative aerobes, and the Mollicutes. It contains approximately 2475 species, 40% of which are aggregated in just 6 genera; Lactobacillus - 100 sp., Mycoplasma - 110 sp., Bacillus - 114 sp, Clostridium 146 sp and Streptomyces 509. The Firmicutes are all gram-positive bacteria unlike the Proteobacteria which are gram-negative. The Firmicutes are further divided according to their GC ratios. This is the ratio of Guanine and Cytosine to Guanine, Cytosine, Adenine and Thymine in the cell, thus a GC ratio = G+C divided by G+C+A+T times 100. Fermicutes are either High GC or Low GC. Each of these categories contains 3 major groups.
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