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Table 1 Comparison of basic features of endosymbiotic and free-living bacteria (ordered by genome size)

From: Genome degeneration affects both extracellular and intracellular bacterial endosymbionts

  Carsonella ruddii Sulcia muelleri Buchnera spp. Mycoplasma genitalium Blattabacterium spp. Baumannia cicadellinicola Wigglesworthia glossinidius
Phylum γ-Proteobacteria Bacteroidetes γ-Proteobacteria Mollicutes Bacteroidetes γ-Proteobacteria γ-Proteobacteria
Role as symbiont Obligate, primary, mutualistic Obligate, primary, mutualistic Obligate, primary, mutualistic Pathogen Obligate, primary, mutualistic Obligate, primary, mutualistic Obligate, primary, mutualistic
Host Psyllids Sharpshooters Aphids Human Cockroaches Sharpshooters Tsetse flies
Genome size (kbp) 160 245 422–686 580 Approximately 650 686 698
GC content (%) 16.5 22.4 20.1–26.2 31.7 Approximately 32 33.2 22.5
Biological function/disease Nutrition Nutrition Nutrition Genital infections Nutrition Nutrition Nutrition
Location Intracellular in bacteriocyte Intracellular in bacteriocyte* Intracellular in bacteriocyte Cell associated Intracellular in bacteriocyte Intracellular in bacteriocyte* Intracellular in bacteriocyte
Transmission Vertical Vertical Vertical Horizontal Vertical Vertical Vertical
  Blochmannia spp. Cadidatus Ishikawaella capsulata Cadidatus Rosenkranzia clausaccus Chlamydia trachomatis Sodalis glossinidius Escherichia coli K-12 Sorangium cellulosum
Phylum γ-Proteobacteria γ-Proteobacteria γ-Proteobacteria Chlamydiae γ-Proteobacteria γ-Proteobacteria Myxobacteria
Role as symbiont Obligate, primary, mutualistic Obligate, primary, mutualistic Obligate, primary, mutualistic Pathogen Facultative, secondary, commensal Commensal Environment
Host Carpenter ants Stinkbugs Stinkbugs Human Tsetse flies Mammalian intestine Free-living
Genome size (kbp) 705–792 820–830 900–960 1,043 4,170 (972 pseudogenes) 4,639 13,034
GC content (%) 27.4–29.6 38.9 (groEL)§ 36–38 (groEL)§ 41.3 54 51 71.4
Biological function/disease Nutrition Unknown Unknown Ocular, lung and genital infections Influences parasite load (Trypanosoma) of host   
Location Intracellular in bacteriocyte Extracellular in midgut crypts Extracellular in midgut crypts Intracellular Facultative intracellular Extracellular Extracellular
Transmission Vertical Vertical Vertical Horizontal Horizontal/vertical Horizontal  
  1. *S. muelleri lives with B. cicadellinicola in the same bacteriocyte. The genome size of S. glossinidius is comparable to that of free-living Enterobacteriaceae, but it is in an early state of degeneration, as exemplified by the massive presence of pseudogenes and a coding capacity of only 51%. §The GC content of the groEL genes is presented for the stinkbug endosymbionts. In the other sequenced endosymbionts the groEL gene has the highest GC content, indicating that the overall GC content of the stinkbug endosymbionts is probably significantly lower.