UNLABELLED: Currently, new species of freshwater fish trypanosomes, which are economically important parasites, are being described based on subjectively selected features, i.e., their cell morphology and the host species. We have performed detailed phylogenetic and haplotype diversity analyses of all 18S rRNA genes available for freshwater fish trypanosomes, including the newly obtained sequences of Trypanosoma carassii and Trypanosoma danilewskyi. Based on a sequence similarity of 99.5%, we divide these trypanosomes into 15 operational taxonomic units, and propose three nominal scenarios for distinguishing T. carassii and other aquatic trypanosomes. We find evidences for the existence of a low number of freshwater fish trypanosomes, with T. carassii having the widest geographic and host ranges. Our analyses support the existence of an umbrella complex composed of T. carassii and two sister species. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s42995-023-00191-0.

• Keywords
• 18S rRNA, Freshwater fish trypanosomes, Morphology, Phylogeny,
• Publication type
• Journal Article MeSH

The mitochondrial DNA (mtDNA) of a primitive kinetoplastid flagellate Cryptobia helicis is composed of 4.2 kb minicircles and 43 kb maxicircles. 85% and 6% of the minicircles are in the form of supercoiled (SC) and relaxed (OC) monomers, respectively. The remaining minicircles (9%) constitute catenated oligomers composed of both the SC and OC molecules. Minicircles contain bent helix and sequences homologous to the minicircle conserved sequence blocks. Maxicircles encode typical mitochondrial genes and are not catenated. The mtDNA, which we describe with the term 'pankinetoplast DNA', is spread throughout the mitochondrial lumen, where it is associated with multiple electron-lucent loci. There are approximately 8400 minicircles per pankinetoplast-mitochondrion, with the pan-kDNA representing approximately 36% of the total cellular DNA. Based on the similarity of the C.helicis minicircles to plasmids, we present a theory on the formation of the kDNA network.

• MeSH
• Microscopy, Electron MeSH
• Kinetoplastida genetics   ultrastructure   MeSH
• DNA, Kinetoplast chemistry   genetics   ultrastructure   MeSH
• Nucleic Acid Conformation MeSH
• DNA, Circular analysis   MeSH
• DNA, Mitochondrial ultrastructure   MeSH
• Mitochondria genetics   ultrastructure   MeSH
• DNA, Protozoan analysis   chemistry   ultrastructure   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA, Kinetoplast MeSH
• DNA, Circular MeSH
• DNA, Mitochondrial MeSH
• DNA, Protozoan MeSH