Identification of a Tetrahymena species infecting guppies, pathology, and expression of beta-tubulin during infection.

Tetrahymenosis is caused by the ciliated protozoan Tetrahymena and is responsible for serious economic losses to the aquaculture industry worldwide. However, information regarding the molecular mechanism leading to tetrahymenosis is limited. In previous transcriptome sequencing work, it was found that one of the two ß-tubulin genes in T. pyriformis was significantly expressed in infected fish, we speculated that ß-tubulin is involved in T. pyriformis infecting fish. Herein, the potential biological function of the ß-tubulin gene in Tetrahymena species when establishing infection in guppies was investigated by cloning the full-length cDNA of this T. pyriformis ß-tubulin (BTU1) gene. The full-length cDNA of T. pyriformis BTU1 gene was 1873 bp, and the ORF occupied 1134 bp, whereas 5' UTR 434 bp, and 3' UTR 305 bp whose poly (A) tail contained 12 bases. The predicted protein encoded by T. pyriformis BTU1 gene had a calculated molecular weight of 42.26 kDa and pI of 4.48. Moreover, secondary structure analysis and tertiary structure prediction of BTU1 protein were also conducted. In addition, morphology, infraciliature, phylogeny, and histopathology of T. pyriformis isolated from guppies from a fish market in Harbin were also investigated. Furthermore, qRT-PCR analysis and experimental infection assays indicated that the expression of BTU1 gene resulted in efficient cell proliferation during infection. Collectively, our data revealed that BTU1 is a key gene involved in T. pyriformis infection in guppies, and the findings discussed herein provide valuable insights for future studies on tetrahymenosis.

Size dependent uptake and trophic transfer of polystyrene microplastics in unicellular freshwater eukaryotes.

Microplastics (MP) have become a well-known and widely investigated environmental pollutant. Despite the huge amount of new studies investigating the potential threat posed by MP, the possible uptake and trophic transfer in lower trophic levels of freshwater ecosystems remains understudied. This study aims to investigate the internalization and potential trophic transfer of fluorescent polystyrene (PS) beads (0.5 µm, 3.6 × 108 particles/mL; 6 µm, 2.1 × 105 particles/mL) and fragments (<30 µm, 5 × 103 particles/mL) in three unicellular eukaryotes. This study focuses on the size-dependent uptake of MP by two freshwater Ciliophora, Tetrahymena pyriformis, Paramecium caudatum and one Amoebozoa, Amoeba proteus, serving also as predator for experiments on potential trophic transfer. Size-dependent uptake of MP in all three unicellular eukaryotes was shown. P. caudatum is able to take up MP fragments up to 27.7 µm, while T. pyriformis ingests particles up to 10 µm. In A. proteus, small MP (PS0.5µm and PS6µm) were taken up via pinocytosis and were detected in the cytoplasm for up to 14 days after exposure. Large PS-MP (PS<30µm) were detected in A. proteus only after predation on MP-fed Ciliophora. These results indicate that A. proteus ingests larger MP via predation on Ciliophora (PS<30µm), which would not be taken up otherwise. This study shows trophic transfer of MP at the base of the aquatic food web and serves as basis to study the impact of MP in freshwater ecosystems.