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1 " Candidatus Midichloria mitochondrii " bacteria in an oocyte of the tick Ixodes ricinus. b indicates the bacteria, m indicates a mitochondrion. A group of five bacteria is clearly visible within one organelle, while other " Ca. M. mitochondrii " appear to be in the cytoplasm, engulfed by a host-derived membrane. Bar = 0.7 μm  

1 " Candidatus Midichloria mitochondrii " bacteria in an oocyte of the tick Ixodes ricinus. b indicates the bacteria, m indicates a mitochondrion. A group of five bacteria is clearly visible within one organelle, while other " Ca. M. mitochondrii " appear to be in the cytoplasm, engulfed by a host-derived membrane. Bar = 0.7 μm  

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“Candidatus Midichloriaceae” (order Rickettsiales) is a family that encompasses obligate intracellular bacteria present in a wide range of hosts, from parasitic arthropods (ticks, fleas, bedbugs) to aquatic animals (e.g. sponges and corals) and protists, including pathogenic amoebae (genus Acanthamoeba). In addition, multiple studies have detected...

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... In many cases, these emerging diseases appear as skin pathologies, as is the case of red mark syndrome (RMS) affecting rainbow trout Oncorhynchus mykiss (Ferguson et al., 2006;Lloyd et al., 2008;Oidtmann et al., 2013;Schmidt et al., 2018;Schmidt-Posthaus et al., 2009;Verner-Jeffreys et al., 2008). RMS is a disease consisting of single or multiple skin lesions usually localized on the trunk of fish approaching market size (Castelli et al., 2016a). Farmers are forced to downgrade the fish to highly manufactured items because of its reduced market value (e.g., fish balls and baby food), thus causing a substantial economic damage. ...
Article
Red mark syndrome (RMS) is a disease of farmed rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), one of the most widespread freshwater farmed species in Europe. The disease emerges at water temperatures below 16 °C and consists of one or more bright red skin lesions on the fish body. Mortality due to RMS is reportedly rare, but the disease leads to downgrading of the product and subsequent economic losses. Despite the disease impact, the causative agent for RMS is still formally undetermined although increasing evidence points to a bacterium ascribed to the Midichloriaceae family (order Rickettsiales), hereafter referred to as RMS-Midichloria like organism (RMS-MLO). Intriguingly, recently deposited sequences revealed the presence of RMS-MLO-like bacteria associated with Ichthyophthirius multifiliis, a common protozoan skin parasite of freshwater fish frequently harboring bacterial endosymbionts. Therefore, we hypothesized that I. multifiliis could be a vehicle for RMS-MLO. This was tested by infecting RMS-diseased rainbow trout with I. multifiliis theronts, and subsequently investigating the presence of RMS-MLO in tomonts detached from the fish. Real time PCR analyses showed clearly that I. multifiliis previously exposed to RMS-affected fish become positive to RMS-MLO suggesting that this bacterium can be at least transiently acquired and carried by the protozoan. Moreover, statistical analyses suggested a possible level of vertical transmission in I. multifiliis from one trophic stage to the next one. Further studies will be necessary to prove whether I. multifiliis has a role in the horizontal transfer of RMS-MLO bacteria from diseased RMS fish to healthy ones.