Identification and phylogenetic analysis of morphologically similar naked amoebae using the ssRNA

[摘要] Flat, fan-shaped amoebae are common in many aquatic habitats where they play an important role in microbial food webs. This is particularly true for benthic sediments where they are major consumers of bacteria. However, ecological studies are hindered by difficulties associated with detecting and identifying these small organisms. This project was the first molecular study to examine phylogenetic relationships among these morphologically similar amoebae, and to assess the utility of a molecular marker for identification purposes. Restriction analyses of the small-subunit ribosomal rRNA (ssrRNA) gene from 15 strains demonstrated that there was a high degree of sequence diversity among fan-shaped amoebae, and this form of analysis may prove to be a useful ecological tool for the unambiguous identification of these organisms. The primary and secondary structure of the ssrRNA gene from one representative fan-shaped amoeba, Vannella anglica, was determined. The ssrRNA was 1962 nucleotides in length with a low G+C content of 37.1%. Several regions were recognised which may be targeted by oligonucleotide probes for rapid identification in mixed cultures. Phylogeny inference programs using sequence data suggest that the fan-shaped amoebae branched from the eukaryotic tree before the divergence of the alveolates, fungi, plants and animals. Vannella anglica did not associate with Acanthamoeba or Hartmannella which indicates that the fan-shaped amoebae form a separate amoeboid lineage, and the subclass Gymnamoebia is polyphyletic. Phylogenetic analysis of 12 morphologically similar fan-shaped Vannella and Platyamoeba, using partial ssrRNA sequence analysis, suggested that the cell surface structure may not be a rigid diagnostic feature for the classification of these organisms. Moreover, the molecular and ultrastructural data suggest that one common, small, unidentified fan-shaped amoeba is not related to other Vannella and Platyamoeba species, and probably represents a new genus.

[发布机构] University:University of Glasgow

[关键词] Microbiology