'Candidatus Tisiphia' is a widespread Rickettsiaceae symbiont in the mosquito Anopheles plumbeus (Diptera: Culicidae).

Symbiotic bacteria can alter host biology by providing protection from natural enemies, or alter reproduction or vectoral competence. Symbiont-linked control of vector-borne disease in Anopheles has been hampered by a lack of symbioses that can establish stable vertical transmission in the host. Previous screening found the symbiont 'Candidatus Tisiphia' in Anopheles plumbeus, an aggressive biter and potential secondary vector of malaria parasites and West Nile virus. We screened samples collected over 10-years across Germany and used climate databases to assess environmental influence on incidence. We observed a 95% infection rate, and that the frequency of infection did not fluctuate with broad environmental factors. Maternal inheritance is indicated by presence in the ovaries through FISH microscopy. Finally, we assembled a high-quality 1.6 Mbp draft genome of 'Ca. Tisiphia' to explore its phylogeny and potential metabolic competence. The infection is closely related to strains found in Culicoides biting midges and shows similar patterns of metabolism, providing no evidence of the capacity to synthesize B-vitamins. This infection offers avenues for onward research in anopheline mosquito symbioses. Additionally, it provides future opportunity to study the impact of 'Ca. Tisiphia' on natural and transinfected hosts, especially in relation to reproductive fitness and vectorial competence and capacity.