Structural Characterization of the Cell Division Cycle in Strigomonas culicis, an Endosymbiont- Bearing Trypanosomatid

Abstract

Strigomonas culicis (previously referred to as Blastocrithidia culicis) is a monoxenic trypanosomatid harboring a symbiotic bacterium, which maintains an obligatory relationship with the host protozoan. Investigations of the cell cycle in symbiont harboring trypanosomatids suggest that the bacterium divides in coordination with other host cell structures, particularly the nucleus. in this study we used light and electron microscopy followed by three-dimensional reconstruction to characterize the symbiont division during the cell cycle of S. culicis. We observed that during this process, the symbiotic bacterium presents different forms and is found at different positions in relationship to the host cell structures. At the G1/S phase of the protozoan cell cycle, the endosymbiont exhibits a constricted form that appears to elongate, resulting in the bacterium division, which occurs before kinetoplast and nucleus segregation. During cytokinesis, the symbionts are positioned close to each nucleus to ensure that each daughter cell will inherit a single copy of the bacterium. These observations indicated that the association of the bacterium with the protozoan nucleus coordinates the cell cycle in both organisms.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Fed Rio de Janeiro, Inst Biofis Carlos Chagas Filho, Lab Ultraestrutura Celular Hertha Meyer, BR-21941590 Rio de Janeiro, RJ, BrazilUniv Fed Rio de Janeiro, Inst Nacl Ciencia & Tecnol Biol Estrutural & Bioi, BR-21941590 Rio de Janeiro, RJ, BrazilInst Nacl Metrol, BR-25250020 Rio de Janeiro, RJ, BrazilUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, BR-04023062 São Paulo, BrazilInst Butantan, Lab Especial Ciclo Celular, BR-05503900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, BR-04023062 São Paulo, BrazilWeb of Scienc