Endosymbiotic Bacteria in the Parasitic Ciliate Ichthyophthirius multifiliis

Abstract

Endosymbiotic bacteria were identified in the parasitic ciliate Ichthyophthirius multifiliis, a common pathogen of freshwater fish. PCR amplification of DNA prepared from two isolates of I. multifiliis, using primers that bind conserved sequences in bacterial 16S rRNA genes, generated an ϳ1,460-bp DNA product, which was cloned and sequenced. Sequence analysis demonstrated that 16S rRNA gene sequences from three classes of bacteria were present in the PCR product. These included Alphaproteobacteria (Rickettsiales), Sphingobacteria, and Flavobacterium columnare. DAPI (4,6-diamidino-2-phenylindole) staining showed endosymbionts dispersed throughout the cytoplasm of trophonts and, in most, but not all theronts. Endosymbionts were observed by transmission electron microscopy in the cytoplasm, surrounded by a prominent, electron-translucent halo characteristic of Rickettsia. Fluorescence in situ hybridization demonstrated that bacteria from the Rickettsiales and Sphingobacteriales classes are endosymbionts of I. multifiliis, found in the cytoplasm, but not in the macronucleus or micronucleus. In contrast, F. columnare was not detected by fluorescence in situ hybridization. It likely adheres to I. multifiliis through association with cilia. The role that endosymbiotic bacteria play in the life history of I. multifiliis is not known.

“Candidatus Sonnebornia yantaiensis”, a member of candidate division OD1, as intracellular bacteria of the ciliated protist Paramecium bursaria (Ciliophora, Oligohymenophorea)

“…More recently, our knowledge of the diversity of bacteria associated with ciliates has increased significantly, primarily as a result of extensive molecular investigations of some commonly occurring species of the genera Paramecium and Euplotes. These studies have demonstrated that most bacterial symbionts belong to one of four classes of the phylum Proteobacteria, namely Alphaproteobacteria (including pathogenic Rickettsia) [2,8,9,18,19,21,22,51,59,60,62,64,67,69], Betaproteobacteria [58,63,66,68], Gammaproteobacteria [4,10,48,53] and Deltaproteobacteria [15]. Associations between ciliates and bacteria of other phyla seem to be infrequent, for example, Verrucomicrobia [42] and Firmicutes [54].…”

The use of nitazoxanide against the pathogens Ichthyophthirius multifiliis and Aeromonas hydrophila in silver catfish (Rhamdia quelen)

“…Bacteria of this genus are typically opportunistic and manifest themselves in hosts attacked and weakened by other etiological agents (Pavanelli et al, 2002). Ich is a potential vector for pathogenic bacteria of fish, such as Flavobacterium columnare (Sun et al, 2009) and Ewardsiella ictaluri (Xu et al, 2012b). Silver catfish parasitized treated with the lowest NTZ concentration did not present natural infection by Aeromonas sp.…”

Hemato-immunological and biochemical parameters of silver catfish Rhamdia quelen immunized with live theronts of Ichthyophthirius multifiliis

“…For each test in this study, new fish were collected to obtain the theronts once the infective activity of the parasite decreases along the hours and some bacteria could be observed. Analyzing the genomic sequencing of the parasite endosymbiontic bacteria in the I. multifiliis cytoplasm was reported [26]. These bacteria are relatively common in free living ciliates [27] and until the present it is not known the virulence of the bacteria on theronts survival [28].…”

“…In fish, this period can reach 10e12 weeks and can compromise the vaccine efficacy [35]. The mechanisms of the interaction between I. multifiliis and their hosts have been studied using the serum immobilization titer that involves specific cells from the humoral response [26,36,37]. It must be emphasized that biochemical analysis has not been used yet and the hematological parameters are little explored [11,13,17].…”