Search

The genus Rhizomastix is a poorly known group of amoeboid heterotrophic flagellates living as intestinal commensals of insects, amphibians or reptiles, and as inhabitants of organic freshwater sediments. Eleven Rhizomastix species have been described so far, but DNA sequences from only a single species have been published. Recently, phylogenetic analyses confirmed a previous hypothesis that the genus belongs to the Archamoebae; however, its exact position therein remains unclear. In this study we cultured nine strains of Rhizomastix, both endobiotic and free-living. According to their light-microscopic morphology and SSU rRNA and actin gene analyses, the strains represent five species, of which four are newly described here: R. bicoronata sp. nov., R. elongata sp. nov., R. vacuolata sp. nov. and R. varia sp. nov. In addition, R. tipulae sp. nov., living in the intestine of crane flies, is separated from the type species, R. gracilis. We also examined the ultrastructure of R. elongata sp. nov., which revealed that it is more complicated than the previously described R. libera. Our data show that either the endobiotic lifestyle of some Rhizomastix species has arisen independently from other endobiotic archamoebae, or the free-living members of this genus represent a secondary switch from the endobiotic lifestyle. [ABSTRACT FROM AUTHOR]

Ancyromonas was first described in 1882 by Saville Kent, with the modern concept of the genus dating from 1979 with the work of Hänel. Since then, organisms assigned to Ancyromonas have been found to be common in diverse ecosystems, and the group's isolated phylogenetic placement renders it of considerable evolutionary interest. However, in 2008 Cavalier-Smith et al. concluded that all modern accounts of Ancyromonas were of a different organism from that described by Saville Kent, and erected the new genus Planomonas to encompass modern observations of Ancyromonas, and several new species. We critique the rationale for creating this new genus, reexamining the original sources and making additional observations using light and electron microscopy. We find that almost all the differences between the genera are mistaken or insubstantial. In particular, (1) Cavalier-Smith et al. characterized Ancyromonas sensu Saville Kent as anchoring and Planomonas as gliding, while we find that each type of organism actually does both, and (2) it was claimed that Planomonas is flattened while Ancyromonas sensu Saville Kent is not, but this argument is inconsistent. We treat Planomonas as a junior synonym of Ancyromonas, and Planomonas mylnikovi as a junior synonym of Ancyromonas sigmoides. We transfer Planomonas cephalopora, Planomonas micra, Planomonas howeae and Planomonas limna to Ancyromonas. The genus Ancyromonas therefore includes: A. sigmoides, Ancyromonas cephalopora n. comb., Ancyromonas melba, Ancyromonas sinistra, Ancyromonas micra n. comb., Ancyromonas howeae n. comb., and Ancyromonas limna n. comb. [ABSTRACT FROM AUTHOR]

Endosomal sorting complexes required for transport (ESCRTs) are heteromeric protein complexes required for multivesicular body (MVB) morphogenesis. ESCRTs I, II, III and III-associated are ubiquitous in eukaryotes and presumably ancient in origin. ESCRT 0 recruits cargo to the MVB and appears to be opisthokont-specific, bringing into question aspects of the current model of ESCRT mechanism. One caveat to the restricted distribution of ESCRT 0 was the previous limited availability of amoebozoan genomes, the supergroup closest to opisthokonts. Here, we significantly expand the sampling of ESCRTs in Amoebozoa. Our electron micrographic and bioinformatics evidence confirm the presence of MVBs in the amoeboflagellate Breviata anathema. Searches of genomic databases of amoebozoans confirm the ubiquitous nature of ESCRTs I-III-associated and the restriction of ESCRT 0 to opisthokonts. Recently, an alternate ESCRT 0 complex, centering on Tom1 proteins, has been proposed. We determine the distribution of Tom1 family proteins across eukaryotes and show that the Tom1, Tom1L1 and Tom1L2 proteins are a vertebrate-specific expansion of the single Tom1 family ancestor, which has indeed been identified in at least one member of each of the major eukaryotic supergroups. This implies a more widely conserved and ancient role for the Tom1 family in endocytosis than previously suspected. [ABSTRACT FROM AUTHOR]