TABLE 1.
Characteristics and culturability status of the selected bacterial symbionts of insectsa
| Symbiont | Phylum or class | Host | Association | Transmission | Available genomes (complete, total) | Genome size (Mb) | %GC | Culturability | Genetic engineering | Host recolonization |
|---|---|---|---|---|---|---|---|---|---|---|
| Intracellular obligate endosymbionts | ||||||||||
| Buchnera aphidicola | Gammaproteobacteria | Aphids | Obligate | Transovarial transfer | 38, 69 | 0.58 | 24.7 | − | − | − |
| Carsonella ruddii | Gammaproteobacteria | Psyllids | Obligate | Transovarial transfer | 8, 9 | 0.17 | 15.4 | − | − | − |
| Portiera aleyrodidarum | Gammaproteobacteria | Whiteflies | Obligate | Transovarial transfer | 5, 6 | 0.33 | 25.1 | − | − | − |
| Evansia muelleri | Gammaproteobacteria | Moss bugs | Obligate | Transovarial transfer | 1 | 0.36 | 25.3 | − | − | − |
| Tremblaya princeps | Betaproteobacteria | Scale insects | Obligate | Transovarial transfer | 7, 8 | 0.14 | 58.9 | − | − | − |
| Uzinura diaspidicola | Bacteroidetes | Scale insects | Obligate | Transovarial transfer | 1 | 0.26 | 30.2 | − | − | − |
| Sulcia muelleri | Bacteroidetes | Auchenorrhyncha | Obligate | Transovarial transfer | 34, 39 | 0.25 | 22.8 | − | − | − |
| Zinderia insecticola | Betaproteobacteria | Froghoppers | Obligate | Transovarial transfer | 1 | 0.21 | 13.5 | − | − | − |
| Nasuia deltocephalinicola | Betaproteobacteria | Leafhoppers | Obligate | Transovarial transfer | 3 | 0.12 | 16.3 | − | − | − |
| Baumannia cicadellinicola | Gammaproteobacteria | Leafhoppers | Obligate | Transovarial transfer | 3, 4 | 0.69 | 34.6 | − | − | − |
| Vidania fulgoroideae | Betaproteobacteria | Planthoppers | Obligate | Transovarial transfer | 1 | 0.14 | 18.2 | − | − | − |
| Purcelliella pentastirinorum | Gammaproteobacteria | Planthoppers | Obligate | Transovarial transfer | 1 | 0.48 | 21.1 | − | − | − |
| Hodgkinia cicadicola | Alphaproteobacteria | Cicadas | Obligate | Transovarial transfer | 18, 34 | 0.13 | 46.5 | − | − | − |
| Nardonella spp. | Gammaproteobacteria | Weevils | Obligate | Transovarial transfer | 4 | 0.22 | 16.7 | − | − | − |
| Sodalis pierantonius | Gammaproteobacteria | Weevils | Obligate | Transovarial transfer | 1 | 4.5 | 56.1 | − | − | − |
| Blochmania floridanus | Gammaproteobacteria | Ants | Obligate | Transovarial transfer | 1 | 0.71 | 27.4 | − | − | − |
| Blattabacterium spp. | Bacteroidetes | Cockroaches, termites | Obligate | Transovarial transfer | 21, 22 | 0.62 | 25.2 | − | − | − |
| Skilesia alterna | Bacteroidetes | Geopemphigus aphids | Obligate | Transovarial transfer | 1 | 1.32 | 37 | − | − | − |
| Wigglesworthia glossinidia | Gammaproteobacteria | Tsetse flies | Obligate | Milk gland | 2 | 0.71 | 23.8 | − | − | − |
| Arsenophonus melophagi | Gammaproteobacteria | Louse flies | Obligate | Milk gland | 0, 1 | 1.16 | 32.2 | − | − | − |
| Sodalis baculum | Gammaproteobacteria | Lygaeoid stinkbugs | Obligate | Plausible transovarial transfer | 1 | 1.62 | 36.8 | − | − | − |
| Serratia symbiotica clade B | Gammaproteobacteria | Lachinae aphids | Transitional obligate | Transovarial transfer, possible horizontal transfer | 2, 3 | 0.65–1.76 | 20.9–32.2 | − | − | − |
| Intracellular facultative endosymbionts | ||||||||||
| Asaia spp. | Gammaproteobacteria | Mosquitos, leafhoppers | Facultative | Vertical and horizontal transmission | 0, 6 | 3.55 | 60.2 | ✓ | ✓ | ✓ |
| Fritschea spp. | Chlamydiae | Scale insects | Facultative | Vertical and possible horizontal transmission | − | − | − | |||
| Fukatsuia symbiotica | Gammaproteobacteria | Aphids | Facultative | Vertical and horizontal transmission | 1, 2 | 2.96 | 43.6 | ✓ | − | − |
| Hamiltonella defensa | Gammaproteobacteria | Aphids, whiteflies | Facultative | Vertical and horizontal transmission | 8, 13 | 1.42–2.28 | 37.2–41.1 | ✓ | − | − |
| Regiella insecticola | Gammaproteobacteria | Aphids | Facultative | Vertical and horizontal transmission | 0, 2 | 2.04 | 42.5 | (✓) | − | − |
| Rickettsiella viridis | Gammaproteobacteria | Aphids | Facultative | Vertical and probable horizontal transmission | 1 | 1.58 | 39.3 | − | − | − |
| Serratia symbiotica clade A | Gammaproteobacteria | Aphids | Facultative | Vertical and horizontal transmission | 2, 12 | 1.53–3.58 | 40.3–52.5 | ✓ | − | − |
| Sodalis glossinidius | Gammaproteobacteria | Tsetse flies | Facultative | Milk-gland | 2 | 4.30 | 54.4 | ✓ | ✓ | ✓ |
| Sodalis melophagi | Gammaproteobacteria | Louse flies | Facultative | Milk-gland | 0, 1 | 4.15 | 50.8 | ✓ | − | − |
| Reproductive manipulators | ||||||||||
| Arsenophonus spp. | Gammaproteobacteria | Various insects | Reproductive manipulator | Vertical and horizontal transmission | 8, 9 | 2.33–4.99 | 38.3 | ✓ | ✓ | ✓ |
| Cardinium spp. | Bacteroidetes | Various arthropods and nematodes | Reproductive manipulator | Vertical and horizontal transmission | 2, 8 | 0.89–1.48 | 33.7–39.2 | (✓) | − | − |
| Rickettsia spp. | Alphaproteobacteria | Various arthropods | Reproductive manipulator | Vertical and horizontal transmission | 0, 5 | 1.25–2.10 | 32.7 | (✓) | ✓ | ✓ |
| Spiroplasma spp. | Mollicutes | Various arthropods and plants | Reproductive manipulator | Vertical and horizontal transmission | 4, 9 | 0.71–2.30 | 23.7–29.3 | ✓ | ✓ | (✓) |
| Wolbachia spp. | Alphaproteobacteria | Various arthropods and nematodes | Reproductive manipulator | Vertical and horizontal transmission | 26, 1,249 | 0.47–2.55 | 26.4–38.3 | (✓) | − | − |
| Extracellular symbionts | ||||||||||
| Burkholderia gladioli | Betaproteobacteria | Lagria beetles | Context dependent | Egg smearing | 0, 2 | 2.08–8.56 | 59–67.9 | ✓* | − | − |
| Burkholderia spp. | Betaproteobacteria | Alydid stinkbugs | Facultative | Environmental | 1 | 6.96 | 63.15 | ✓* | ✓ | ✓ |
| Ishikawaella capsulata | Gammaproteobacteria | Plataspid stinkbugs | Obligate | Egg capsules | 1 | 0.75 | 30.2 | − | − | − |
| Pantoea spp. | Gammaproteobacteria | Pentatomid stinkbugs | Obligate | Egg smearing | 2 | 1.18 | 30.53 | ✓* | − | − |
| Rhodococcus rhodnii | Actinobacteria | Assassin bugs | Facultative | Coprophagy | 0, 3 | 4.44 | 69.7 | ✓ | ✓ | ✓ |
| Snodgrassella alvi | Betaproteobacteria | Bees, bumble bees | Facultative | Coprophagy | 1, 65 | 2.43 | 41.81 | ✓ | ✓ | ✓ |
| Streptomyces philanthi | Actinobacteria | Beewolves | Context dependent | Brood smearing | 0, 1 | 7.66 | 72.2 | ✓* | − | − |
| Tachikawaea gelatinosa | Gammaproteobacteria | Urostylidid stinkbugs | Obligate | Egg jelly | 1 | 0.71 | 25.1 | − | − | − |
a
The list is not exhaustive. Genome availability indicates the number of genomes published in the NCBI GenBank database in March 2020 and serves as an indication of the research attention for the model. A genome is considered complete if the assembly yielded a fully circularized chromosome with sufficient coverage. Indicated genome sizes and %GC are the average values of all complete published genomes of the species. Culturability status reads are the following: ✓, culturable in axenic medium; (✓), culturable on insect cell lines; −, not culturable in vitro. An asterisk indicates that the culturability status is valid for at least one strain of one species but might not be valid for the whole genus. Genetic engineering status reads are the following: ✓, at least a transformation with an exogenous plasmid has been achieved; −, no transformation has been reported in the literature. Host recolonization status reads are the following: ✓, in vitro-cultured endosymbionts can recolonize their natural host; (✓), in vitro-cultured wild-type endosymbionts can recolonize their natural host, but genetically modified endosymbionts have a colonization defect; −, recolonization has not been reported in the literature.