Strigomonas culicis

S. culicis spends its life cycle in mosquitos. It migrates from the mosquito midgut and enter the body cavity (haemocoel) and finally reside in the salivary glands.^[10] Unlike other trypanosomatids, S. culicis does not produce some amino acids such as methionine, histidine, and arginine; and vitamins such as thiamin, nicotinamide, and riboflavin.^[8] The bacterium provides these nutrients. In addition, it also provides enzymes required by the host for amino acid synthesis, lipid and purine/pyrimidine metabolism, urea cycle, haeme biosynthesis,^[11] protein synthesis, and protein folding. It can not reproduce on its own and relies on signals from the protist's nucleus.^[6] Isolated bacteria cannot survive on their own.^[11] When the bacteria are removed by antibiotic treatment, the protist survives but can not infect mosquitos.^[6]

S. culicis has about 12,162 open reading frames (ORFs).^[11]

The bacterium Ca. Kinetoplastibacterium blastocrithidii is a ß-proteobacterium of the family Alcaligenaceae. It is enclosed in two layers of cell membranes, and unlike typical bacterial membrane, peptidoglycan is greatly reduced.^[11] It acts as a cell organelle not only by supplying essential enzymes, but also by replacing paraflagellar rod associated to the axoneme, thus, intimately associated with the kinetoplast.^[12] In addition, it provides surplus supply of ATP molecules for increased metabolic activities.^[13] During cell division, as the kinetoplast of the host divides so do the bacterium.^[14] The host cell controls the number of bacterial division.^[1] This coordinated mitosis results in even distribution of one bacterium in each daughter cell.^[14]

Strigomonas culicis can be found in several mosquito genera, such as Anopheles, Culex, Aedes^[8] and Coquillettidia.