Single cell transcriptomes of five nanociliates isolated from Cretan Sea (Greece)
Nanociliates play an important role in the microbial food web of oligotrophic marine systems as grazers of picoplankton on one side, and as prey for microplankton, on the other. However, knowledge on their taxonomy, phylogeny and trophic strategies is very limited, as well as their role as mixotrophs. In the present study, we investigated the transcriptomes of six marine planktonic nanociliates belonging to the three most abundant groups found in the Eastern Mediterranean Sea: Oligotrichida, Choreotrichida and Tintinnida. Our aim was to: 1) characterize the phylogenetic placement of these cellsusing concatenated phylotranscriptomic; 2) to compare those cells with ciliates from the literature, to identify genes potentially involved in mixotrophy. The concatenated phylogenetic tree surprisingly showed that two out of five cells, clustered with Tintinnida group, while the other three clustered in Oligotrichida group. Reciprocal best hits (RHBs) BlastP results showed that most of the homologous genes strictly related to the oligotrich of the present study and the mixotrophic Strombidium rassoulzadegani were related to phagosome, lysosome and metabolism, suggesting that the main differences between mixotrophs and heterotrophs might be hidden in this pattern. The results of the present study show that these transcriptomes, together with the identification of genes related to mixotrophy will help to establish a basis for the evaluation of differential gene expression in Oligotrichida, Choreotrichida and Tintinnida.