Transmembrane proteins rickettsia-like organisms (RLO) in aquatic animals: Adhesion, invasion and infection factors

Abstract

Besides participating in the transport of essential compounds and as recipients of phages, transmembrane proteins of rickettsia-like organisms (RLO), play an important role in the infection process of commercially important organisms such as fish, mollusk and crustaceans. Recently a new classification of RLO which divides them into four groups was reported: ancestral, typhus, the spotted fever and transitional. To date, only the typhus (TG) and spotted fever (SFG) groups have been reported as pathogenic of marine organisms. The outer membrane surface of the TG group has antigens type 0, 1, 2, 4, 5 (Sca0, Sca1, Sca2, Sca4, Sca5). Sca0 are also known as outer membrane proteins A (OmpA) and Sca5 as outer membrane proteins B (OmpB). Other outer membrane proteins such as enzymes called translocase (Tlc) have been detected, including translocase 1, 4 and 5 (Tlc1, Tlc4 and Tlc5). All these proteins (except for Sca0) have been detected in the SFG group. These proteins vary in features and functions. However, the information of RLO affecting marine organisms is not as common as that of terrestrial mammals. An analysis of the state of the art on the study of transmembrane proteins of RLO in marine organisms is performed in this review; additionally, the hypothetical infection mechanism of these RLO is inferred by using this information together with that reported of RLO affecting terrestrial organisms.