Balantidium ctenopharyngodoni is identified as the sole ciliate species that exclusively resides within the hindgut of grass carp with high prevalence and intensity. In this study, the successful cultivation of B. ctenopharyngodoni enabled us to collect enough cells for genome sequencing. Consequently, we acquired a high-quality genome assembly spanning 68.66 Mb, encompassing a total of 22,334 nanochromosomes. Furthermore, we predicted 29,348 protein-coding genes, and 95.5% of them was supported by the RNA-seq data. The trend of GC content in the subtelomeric regions of single-gene chromosomes was similar to other ciliates containing nanochromosomes. A large number of genes encoding carbohydrate-binding modules with affinities for starch and peptidoglycans was identified. The identification of mitochondrion-related organelles (MROs) within genome indicates its well-suited adaptation to the anaerobic conditions in the hindgut environment. In summary, our results will offer resources for understanding the genetic basis and molecular adaptations of balantidia to hindgut of herbivorous fish.

BACKGROUND: Hosts, parasites, and microbiota interact with each other, forming a complex ecosystem. Alterations to the microbial structure have been observed in various enteric parasitic infections (e.g. parasitic protists and helminths). Interestingly, some parasites are associated with healthy gut microbiota linked to the intestinal eubiosis state. So the changes in bacteria and metabolites induced by parasite infection may offer benefits to the host, including protection from other parasitesand promotion of intestinal health. The only ciliate known to inhabit the hindgut of grass carp, Balantidium ctenopharyngodoni, does not cause obvious damage to the intestinal mucosa. To date, its impact on intestinal microbiota composition remains unknown. In this study, we investigated the microbial composition in the hindgut of grass carp infected with B. ctenopharyngodoni, as well as the changes of metabolites in intestinal contents resulting from infection.
RESULTS: Colonization by B. ctenopharyngodoni was associated with an increase in bacterial diversity, a higher relative abundance of Clostridium, and a lower abundance of Enterobacteriaceae. The family Aeromonadaceae and the genus Citrobacter had significantly lower relative abundance in infected fish. Additionally, grass carp infected with B. ctenopharyngodoni exhibited a significant increase in creatine content in the hindgut. This suggested that the presence of B. ctenopharyngodoni may improve intestinal health through changes in microbiota and metabolites.
CONCLUSIONS: We found that grass carp infected with B. ctenopharyngodoni exhibit a healthy microbiota with an increased bacterial diversity. The results suggested that B. ctenopharyngodoni reshaped the composition of hindgut microbiota similarly to other protists with low pathogenicity. The shifts in the microbiota and metabolites during the colonization and proliferation of B. ctenopharyngodoni indicated that it may provide positive effects in the hindgut of grass carp.

Anaerobic parasitic ciliates are a specialized group of ciliates that are adapted to anoxic and oxygen-depleted habitats. Among them, Balantidium polyvacuolum, which inhabits the hindgut of Xenocyprinae fishes, has received very limited scientific attention, so the molecular mechanism of its adaptation to the digestive tract microenvironment is still unclear. In this study, transmission electron microscopy (TEM) and single-cell transcriptome analysis were used to uncover the metabolism of B. polyvacuolum. Starch granules, endosymbiotic bacteria, and multiple specialized mitochondrion-related organelles (MROs) of various shapes were observed. The MROs may have completely lost the electron transport chain (ETC) complexes I, III, IV, and V and only retained succinate dehydrogenase subunit A (SDHA) of complex II. The tricarboxylic acid (TCA) cycle was also incomplete. It can be inferred that the hypoxic intestinal environment has led to the specialization of the mitochondria in B. polyvacuolum. Moreover, carbohydrate-active enzymes (CAZymes), including carbohydrate esterases, enzymes with a carbohydrate-binding module, glycoside hydrolases, and glycosyltransferases, were identified, which may constitute evidence that B. polyvacuolum is able to digest carbohydrates and starch. These findings can improve our knowledge of the energy metabolism and adaptive mechanisms of B. polyvacuolum.

UNASSIGNED: Balantidium coli is a protozoan that can infect humans and non-human primates, being the domestic pigs the animals most affected by this parasite. This study aimed to compare the performance of five coprological methods for diagnosis of Balantidium coli cysts in fecal samples from pigs.
UNASSIGNED: From September to December 2019, 558 fecal samples were collected from the rectum of backyard pigs in the Bucaramanga metropolitan area, Colombia. The average age of the sampled animals was 3-4 months. Fecal samples collected were tested using the following coprological techniques: Direct examination with Lugol\'s iodine solution, buffered saline, centrifugation/flotation and McMaster techniques, and Ziehl-Neelsen method.
UNASSIGNED: The results indicate that B. coli cysts were diagnosed most frequently through direct examination with Lugol\'s iodine solution (52.7% of the samples) followed by direct examination with a buffered saline solution (37.6%). Moderate concordance (k=0.41; p<0.05) was determined between direct method with Lugol\'s iodine and buffered saline solution, McMaster and buffered saline (k=0.35; p<0.05), and centrifugation/flotation and buffered saline (k=0.28; p<0.05) showed a fair degree of concordance. The rest of the comparisons were classified as poor. The flotation techniques (centrifugation/flotation and McMaster) did not show good recovery of cysts.
UNASSIGNED: It is concluded that the most efficient method for diagnosing this parasitosis was to an association between direct examination with Lugol\'s iodine solution and buffered saline.

Balantioides coli is a known ciliated zoonotic protozoan that mainly causes diarrhea in humans and pigs. An efficient and reliable culture system for this parasite remains unavailable until now. In this study, a modified Dulbecco\'s modified eagle medium (DMEM) with pH 7.0-7.5, containing 5 mg/mL starch and 20% new calf serum, was optimized for propagation of B. coli at 28°C-32°C. At the growth-peaking stage, the average trophozoite density was up to 12,970 trophozoites per milliliter. A reproducible protocol for isolation and maintenance of this parasite was also developed based on the modified DMEM culture medium. Moreover, cloning results of B. colipopulations showed that 250 trophozoites in 3 mL modified DMEM medium were the minimal number of trophozoites that propagated to the growth-peaking stage, and finally obtained the individual population. However, less than 250 trophozoites failed to continuously grow in the modified DMEM culture medium under the optimal conditions for growth of B. coli. These data showed that the modified DMEM culture medium is an ideal and efficient medium for propagation and maintenance of B. coli in vitro and will help studies on its biology, genome, transcriptome, proteome, and drug screening.

Balantioides coli (=Balantidium coli) is the only ciliate that parasitizes humans. Pigs are the main reservoir. Other species, as camels, cattle, donkey, sheep and goat have been also proposed as reservoirs for human infections. The parasite has a direct life cycle, being transmitted by the faecal-oral route. This type of cycle and the large number of host species imply an important potential for zoonotic transmission of the parasite. Infections are most commonly found in tropical and temperate regions, with prevalence up to 100% in pigs; high prevalence values have been also recorded in some non-human primates and camels. In humans, prevalence is usually under 10% in the population at risk. The main epidemiological factors involved in the transmission of this parasite include close contact with pigs, lack of basic sanitation infrastructures (water supply, wastewater disposal) and hygiene. Individual health status, intestinal microbiota and diet are also important for the onset of the infection. Outbreaks caused by this parasite are rare; those reported to date were related to poor hygienic conditions or to catastrophic natural disasters. Balantioides coli infections can be asymptomatic and symptomatic, which can be chronic (with intermittent diarrhoea), or acute (a dysenteric form which can be life-threatening). Efective treatments include tetracycline, iodoquinol and 5-nitroimidazole compounds (metronidazole, secnidazole). The main effective individual preventive measure is the use of disinfected water for drinking and other uses. Adequate water supply infrastructures, proper disposal of wastewater and animal faeces, and regular monitoring programs on farms will help limit transmission.

Balantioides coli is a ciliated parasite that can cause diarrhea when inhabiting the colon and cecum of pigs and humans. However, information regarding the changes in structure and composition of the gut microbiome in piglets infected with B. coli remains scarce. In this study, 16S rDNA amplicon sequencing was conducted on fecal samples from both B. coli-positive piglets with diarrhea and B. coli-negative piglets without diarrhea. The results showed that Firmicutes and Bacteroidetes were the major phyla in the two groups, and the relative abundance of the phylum Firmicutes, including Ruminococcaceae and Clostridiaceae, was significantly lower in the B. coli-positive samples than in the B. coli-negative ones (p < 0.05). Compared with B. coli-negative samples, Alloprevotella and Faecalibacterium showed distinctly higher relative abundances (p < 0.05) in the B. coli-positive samples, and the abundances of some potential pathogenic bacteria, including Escherichia-Shigella and Campylobacter, were positively correlated with B. coli infection and diarrhea of weaned piglets. In addition, there were statistically significant differences in fecal microbiota diversity and abundances of predicted functional genes between B. coli-colonized and B. coli-negative samples (p <  0.05). Taken together, these findings suggest that there were significant differences in the bacterial community composition, diversity, and functions between the B. coli-positive and B. coli-negative piglets, and the colonization by B. coli may be associated with the dysbiosis of gut microbiota structure in weaned piglets.

BACKGROUND: Balantidium coli, a parasitic unicellular ciliate, often causes asymptomatic balantidiasis of the colon, but extraintestinal disease may occur rarely in immunosuppressed individuals. Renal balantidiasis associated with systemic lupus erythematosus has not been reported before.
METHODS: We present a case of a 48-year-old Thai woman who presented with nephrotic syndrome due to systemic lupus erythematosus-related nephritis. Initially, few B. coli cysts were found in urine sediment, but these increased substantially following treatment with prednisolone. She made an uneventful recovery with 10 days of oral tetracycline therapy. No B. coli cysts were found in her stool.
CONCLUSIONS: The route of infection in our patient was unclear but is likely to have been orofecal. Neither her infection nor its treatment caused a deterioration in her renal function.

Balantidium coli human infection predominantly occurs in tropical and subtropical regions in the world. Human case is extremely rare in China. This report details a case of B. coli infection in a 68-year-old man in China, who presented with history of abdominal pain, tenesmus, diarrhea with blood and was diagnosed as B. coli-caused dysentery. Our case indicates possible occurrence of Balantidium coli-related disease in cooler climates. This case is presented not only because of its rarity but also for future references.

The ciliate Balantidium ctenopharyngodoni is the most prominent protist in the guts of grass carp, where it mainly inhabits the creamy luminal contents of the hindgut. Ciliates are generally colonized by microorganisms via phagotrophic feeding. In order to study the intracellular bacteria in this ciliate, we have successfully established it in in vitro culture. Herein, we investigated and compared the bacterial community structures of cultured and freshly collected B. ctenopharyngodoni. The results showed that these two groups exhibited different bacterial communities. The most abundant bacterial family in freshly collected samples was Enterobacteriaceae, while in cultured samples it was Fusobacteriaceae. In addition, a key intracellular bacterium, Cetobacterium somerae, was identified in the cytoplasm of cultured ciliates using fluorescence in situ hybridization (FISH). This study shows that ciliates can retain the intracellular bacteria acquired in the natural habitat for quite a long time, but the bacterial community structure of ciliates eventually changes after a long period of cultivation.