Molecular Phylogenetic Analysis Places Percolomonas cosmopolites within Heterolobosea: Evolutionary Implications

An expanded phylogenomic analysis of Heterolobosea reveals the deep relationships, non-canonical genetic codes, and cryptic flagellate stages in the group

The phylum Heterolobosea Page and Blanton, 1985 is a group of eukaryotes that contains heterotrophic flagellates, amoebae, and amoeboflagellates, including the infamous brain-eating amoeba Naegleria fowleri. In this study, we investigate the deep evolutionary history of Heterolobosea by generating and analyzing transcriptome data from 16 diverse isolates and combine this with previously published data in a comprehensive phylogenomic analysis. This dataset has representation of all but one of the major lineages classified here as orders. Our phylogenomic analyses recovered a robustly supported phylogeny of Heterolobosea providing a phylogenetic framework for understanding their evolutionary history. Based on the newly recovered relationships, we revised the classification of Heterolobosea to the family level. We describe two new classes (Eutetramitea cl. nov. and Selenaionea cl. nov) and one new order (Naegleriida ord. nov.), and provide a new delimitation of the largest family of Heterolobosea, Vahlkampfiidae Jollos, 1917. Unexpectedly, we unveiled the first two cases of genetic code alterations in the group: UAG as a glutamine codon in the nuclear genome of Dactylomonas venusta and UGA encoding tryptophan in the mitochondrial genome of Neovahlkampfia damariscottae. In addition, analysis of the genome of the latter species confirmed its inability to make flagella, whereas we identified hallmark flagellum-specific genes in most other heteroloboseans not previously observed to form flagellates, suggesting that the loss of flagella in Heterolobosea is much rarer than generally thought. Finally, we define the first autapomorphy of the subphylum Pharyngomonada, represented by a fusion of two key genes for peroxisomal β-oxidation enzymes.

Living in the cracks: Two novel genera of Variosea (Amoebozoa) discovered on an urban sidewalk

Biological soil crusts represent a rich habitat for diverse and complex eukaryotic microbial communities. A unique but extremely common habitat is the urban sidewalk and its cracks that collect detritus. While these habitats are ubiquitous across the globe, little to no work has been conducted to characterize protists found there. Amoeboid protists are major predators of bacteria and other microbial eukaryotes in these microhabitats and therefore play a substantial ecological role. From sidewalk crack soil crusts, we have isolated three naked amoebae with finely tapered subpseudopodia, and a simple life cycle consisting of a trophic amoeba and a cyst stage. Using a holistic approach including light, electron, and fluorescence microscopy as well as phylogenetics using the ribosomal small subunit rRNA gene and phylogenomics using 230 nuclear genes, we find that these amoeboid organisms fail to match any previously described eukaryote genus. However, we determined the amoebae belong to the amoebozoan lineage Variosea based on phylogenetics. The molecular analyses place our isolates in two novel genera forming a grade at the base of the variosean group Protosteliida. These three novel varioseans among two novel genera and species are herein named "Kanabo kenzan" and "Parakanabo toge."

Lighting lantern above Psalteriomonadidae: Unveiling novel diversity within the genus Psalteriomonas (Discoba: Heterolobosea)

Psalteriomonadidae are a small family of anaerobic free-living protists belonging to Heterolobosea, Discoba. We cultured 74 new strains of mostly amoeboid Psalteriomonadidae obtained from mainly freshwater habitats and sequenced their 18S rRNA gene. Based on the phylogenetic analysis and genetic distances, we report multiple novel species, four of which we formally describe based on the light-microscopic morphology (Psalteriomonas minuta, P. australis, P. fimbriata, and P. parva). We also examined the ultrastructure of two Psalteriomonas species using transmission electron microscopy. We transfer Sawyeria marylandensis into the genus Psalteriomonas and synonymize Sawyeria with Psalteriomonas. In addition, we studied the flagellate stage of P. marylandensis comb. nov. for the first time, using light and scanning electron microscopy.

Biogeography, autecology, and phylogeny of Percolomonads based on newly described species

Percolomonads (Heterolobosea) are aquatic heterotrophic flagellates frequently found in saline waters up to hypersaline environments. We isolated and cultivated seven strains of percolomonad flagellates from marine waters and sediments as well as from a hypersaline inland lake in the Atacama Desert. Morphological characterizations, comprising light and scanning electron microscopy, revealed only slight differences between the strains mainly limited to the cell shape, length of flagella, and length of the ventral feeding groove. Phylogenetic analyses of the 18S and 28S rDNA genes showed the formation of three fully supported clades within the Percolomonadida: the Percolomonadidae, the Barbeliidae fam. nov. and the Lulaidae fam. nov. We describe two new families (Barbeliidae fam. nov., Lulaidae fam. nov.), a new genus (Nonamonas gen. nov.), and five new species (Percolomonas adaptabilis sp. nov., Lula levis sp. nov., Barbelia pacifica sp. nov., Nonamonas montiensis gen. et sp. nov., Nonamonas santamariensis gen. et sp. nov.). Salinity experiments showed that P. adaptabilis sp. nov. from the Atlantic was better adapted to high salinities than all other investigated strains. Moreover, comparisons of our cultivation-based approach with environmental sequencing studies showed that P. adaptabilis sp. nov. seems to be globally distributed in marine surface waters while other species seem to be more locally restricted.

Accumulation patterns of intracellular salts in a new halophilic amoeboflagellate, Euplaesiobystra salpumilio sp. nov., (Heterolobosea; Discoba) under hypersaline conditions

Halophilic microbial eukaryotes are present in many eukaryotic lineages and major groups; however, our knowledge of their diversity is still limited. Furthermore, almost nothing is known about the intracellular accumulation of salts in most halophilic eukaryotes. Here, we isolate a novel halophilic microbial eukaryote from hypersaline water of 134 practical salinity units (PSU) in a solar saltern. This species is an amoeboflagellate (capable of the amoeba-flagellate-cyst transformation) in the heterolobosean group and belongs to the genus Euplaesiobystra based on morphological data and 18S rDNA sequences. However, the isolate is distinct from any of the described Euplaesiobystra species. Especially, it is the smallest Euplaesiobystra to date, has a distinct cytostome, and grows optimally at 75–100 PSU. Furthermore, the phylogenetic tree of the 18S rDNA sequences demonstrates that the isolate forms a strongly supported group, sister to Euplaesiobystra hypersalinica. Thus, we propose that the isolate, Euplaesiobystra salpumilio, is a novel species. E. salpumilio displays a significantly increased influx of the intracellular Na⁺ and K⁺ at 50, 100, and 150 PSU, compared to freshwater species. However, the intracellular retention of the Na⁺ and K⁺ at 150 PSU does not significantly differ from 100 PSU, suggesting that E. salpumilio can extrude the Na⁺ and K⁺ from cells under high-salinity conditions. Interestingly, actively growing E. salpumilio at 100 and 150 PSU may require more intracellular accumulation of Na⁺ than the no-growth but-viable state at 50 PSU. It seems that our isolate displays two salt metabolisms depending on the tested salinities. E. salpumilio shows a salt-in strategy for Na⁺ at lower salinity of 100 PSU, while it displays a salt-out strategy for Na⁺ at higher salinity of 150 PSU. Our results suggest that the novel halophilic E. salpumilio fundamentally uses a salt-out strategy at higher salinities, and the accumulation patterns of intracellular salts in this species are different from those in other halophilic microbial eukaryotes.

Evidence from the resurrected family Polyrhabdinidae Kamm, 1922 (Apicomplexa: Gregarinomorpha) supports the epimerite, an attachment organelle, as a major eugregarine innovation

Background

Gregarines are a major group of apicomplexan parasites of invertebrates. The gregarine classification is largely incomplete because it relies primarily on light microscopy, while electron microscopy and molecular data in the group are fragmentary and often do not overlap. A key characteristic in gregarine taxonomy is the structure and function of their attachment organelles (AOs). AOs have been commonly classified as “mucrons” or “epimerites” based on their association with other cellular traits such as septation. An alternative proposal focused on the AOs structure, functional role, and developmental fate has recently restricted the terms “mucron” to archigregarines and “epimerite” to eugregarines.

Methods

Light microscopy and scanning and transmission electron microscopy, molecular phylogenetic analyses of ribosomal RNA genes.

Results

We obtained the first data on fine morphology of aseptate eugregarines Polyrhabdina pygospionis and Polyrhabdina cf. spionis, the type species. We demonstrate that their AOs differ from the mucron in archigregarines and represent an epimerite structurally resembling that in other eugregarines examined using electron microscopy. We then used the concatenated ribosomal operon DNA sequences (SSU, 5.8S, and LSU rDNA) of P. pygospionis to explore the phylogeny of eugregarines with a resolution superior to SSU rDNA alone. The obtained phylogenies show that the Polyrhabdina clade represents an independent, deep-branching family in the Ancoroidea clade within eugregarines. Combined, these results lend strong support to the hypothesis that the epimerite is a synapomorphic innovation of eugregarines. Based on these findings, we resurrect the family Polyrhabdinidae Kamm, 1922 and erect and diagnose the family Trollidiidae fam. n. within the superfamily Ancoroidea Simdyanov et al., 2017. Additionally, we re-describe the characteristics of P. pygospionis, emend the diagnoses of the genus Polyrhabdina, the family Polyrhabdinidae, and the superfamily Ancoroidea.

Diversity and phylogeny of percolomonads based on newly discovered species from hypersaline and marine waters

Percolomonads are common freshwater, marine and hypersaline tetraflagellated organisms. Current phylogenetic analyses of eukaryotes comprise only two species of this underinvestigated family. Here, we studied the morphology, salinity tolerance and 18S rDNA gene-based phylogeny of seven percolomonad cultures. We describe three new genera and five novel species of Percolomonadida based on phylogenetic distances and morphological characteristics: Barbelia atlantica, B. abyssalis, Lula jakobsenorum, Nakurumonas serrata and Percolomonas doradorae. The new species show features typical for percolomonads, one long flagellum for skidding, three shorter flagella of equal length and a ventral feeding groove. The new species comprise organisms living in marine and athalassic hypersaline waters with salinity ranging from 10 to 150 PSU. Based on these novel taxa, the taxonomy and phylogeny of Percolatea was extended and further resolved.

Morphology and Ecology of Two New Amoebae, Isolated From a Thalassohaline Lake, Dziani Dzaha

Dziani Dzaha is a hypersaline lake (Mayotte island), whose microbial community is dominated by photosynthetic microorganisms. Here, we describe two new free-living heteroloboseans. One belonging to the Pharyngomonas genus and the other, whose 18S rRNA gene sequence shares only 85% homology to its closest relatives Euplaesiobystra hypersalinica, was proposed as a new species of this genus being called Euplaesiobystra dzianiensis. Both strains were salt tolerant to 75‰ and grew between 25 and 37°C. Their distribution patterns varied seasonally and depended also on depth. Noticeably, both free-living amoebae isolates were able to graze on Arthrospira filaments, which are found within the same water layer. In conclusion, we document for the first time the presence and ecology of free-living amoebae in the thalassohaline lake Dziani Dzaha, and describe a new species of the Euplaesiobystra genus.

Ecological and evolutionary patterns in the enigmatic protist genus Percolomonas (Heterolobosea; Discoba) from diverse habitats

The heterotrophic flagellate Percolomonas cosmopolitus (Heterolobosea) is often observed in saline habitats worldwide, from coastal waters to saturated brines. However, only two cultures assigned to this morphospecies have been examined using molecular methods, and their 18S rRNA gene sequences are extremely different. Further the salinity tolerances of individual strains are unknown. Thus, our knowledge on the autecology and diversity in this morphospecies is deficient. Here, we report 18S rRNA gene data on seven strains similar to P. cosmopolitus from seven geographically remote locations (New Zealand, Kenya, Korea, Poland, Russia, Spain, and the USA) with sample salinities ranging from 4‰ to 280‰, and compare morphology and salinity tolerance of the nine available strains. Percolomonas cosmopolitus-like strains show few-to-no consistent morphological differences, and form six clades separated by often extremely large 18S rRNA gene divergences (up to 42.4%). Some strains grow best at salinities from 75 to 125‰ and represent halophiles. All but one of these belong to two geographically heterogeneous clusters that form a robust monophyletic group in phylogenetic trees; this likely represents an ecologically specialized subclade of halophiles. Our results suggest that P. cosmopolitus is a cluster of several cryptic species (at least), which are unlikely to be distinguished by geography. Interestingly, the 9 Percolomonas strains formed a clade in 18S rRNA gene phylogenies, unlike most previous analyses based on two sequences.

A New Halophilic Heterolobosean Flagellate, Aurem hypersalina gen. n. et sp. n., Closely Related to the Pleurostomum-Tulamoeba Clade: Implications for Adaptive Radiation of Halophilic Eukaryotes

Halophilic protozoa are independently scattered across the molecular phylogeny of eukaryotes; most of which are assigned to Heterolobosea. Here, we isolated a biflagellate from a hypersaline water of 342‰ salinity. This isolate shared several morphological features with typical halophilic heterolobosean flagellates. In addition, molecular phylogenetic trees of the 18S rRNA gene sequences clearly indicated flagellate is a heterolobosean species closely related to the halophilic Tulamoebidae. However, the flagellate was not accommodated to any described genus. Cells were ovoid-shaped, and no amoebae were observed. The two unequal flagella beat heterodynamically. An ear-like bulge at the margin of a cytostomal groove was observed. Flagellates could grow at 100-200‰ salinity, suggesting an obligately halophilic species. Currently, it appears that the new halophilic Aurem hypersalina forms a strong clade with Tulamoebidae, and is sister to the Tulamoebidae, indicating that this new clade is composed almost entirely of obligate halophilic taxa. Thus, A. hypersalina and the Tulamoebidae clade currently represent a unique adaptive radiation of halophilic eukaryotes.

Dactylomonas gen. nov., a Novel Lineage of Heterolobosean Flagellates with Unique Ultrastructure, Closely Related to the Amoeba Selenaion koniopes Park, De Jonckheere & Simpson, 2012

We report the discovery of a new genus of heterolobosean flagellates, Dactylomonas gen. nov., with two species, D. venusta sp. nov. and D. crassa sp. nov. Phylogenetic analysis of the SSU rRNA gene showed that Dactylomonas is closely related to the amoeba Selenaion, the deepest-branching lineage of Tetramitia. Dactylomonads possess two flagella, and ultrastructural studies revealed an unexpected organization of the flagellar apparatus, which resembled Pharyngomonada (the second lineage of Heterolobosea) instead of Tetramitia: basal bodies were orthogonal to each other and a putative root R1 was present in the mastigont. On the other hand, Dactylomonas displayed several features uncommon in Heterolobosea: a microtubular corset, a distinctive rostrum supported by the main part of the right microtubular root, a finger-like projection on the proximal part of the recurrent flagellum, and absence of a ventral groove. In addition, Dactylomonas is anaerobic and seems to have lost mitochondrial cristae. Dactylomonas and Selenaion are accommodated in the family Selenaionidae fam. nov. and order Selenionida ord. nov. The taxonomy of Tetramitia is partially revised, and the family Neovahlkampfiidae fam. nov. is established.

Survey on diversity of marine/saline anaerobic Heterolobosea (Excavata: Discoba) with description of seven new species

Diversity of the anaerobic Heterolobosea (Excavata: Discoba) is only poorly understood, especially in marine environments. We have isolated and cultured 16 strains of anaerobic heteroloboseid amoebae and flagellates from brackish, marine and saline anoxic habitats worldwide. Phylogenetic analyses of SSU rDNA sequences and light-microscopic observations showed that all the strains belong to the family Psalteriomonadidae, the main anaerobic lineage of Heterolobosea, and that they represent eight species from the genera Monopylocystis, Harpagon and Pseudoharpagon. Seven species are newly isolated and described here as Monopylocystis minor n. sp., Monopylocystis robusta n. sp., Monopylocystis elegans n. sp., Monopylocystis disparata n. sp., Harpagon salinus n. sp., Pseudoharpagon longus n. sp. and Pseudoharpagon tertius n. sp. Amoebae, cysts and the ultrastructure of the genus Pseudoharpagon are presented for the first time.

Amoeba stages in the deepest branching heteroloboseans, including Pharyngomonas: evolutionary and systematic implications

The taxon Heterolobosea (Excavata) is a major group of protists well known for its diversity of life stages. Most are amoebae capable of transforming into flagellates (amoeboflagellates), while others are known solely as flagellates or solely as amoebae. The deepest-branching heterolobosean taxon confirmed previously, Pharyngomonas, was generally assumed to be a pure flagellate, suggesting that the amoeba form arose later in the evolution of Heterolobosea sensu lato. Here we report that multiple isolates of Pharyngomonas are actually amoeboflagellates that also have cyst stages, with only amoebae transforming into cysts. The amoeba form of Pharyngomonas showed heterolobosean characteristics (e. g. eruptive movement), but also possessed unusual morphological features like slow-flowing crenulated hyaline crescents with conical subpseudopodia, finger-like projections and branching posterior extensions. Furthermore, phylogenetic analyses of 18S ribosomal RNA gene sequences that included two undescribed species of amoebae showed that Pharyngomonas is not the only deep-branching heterolobosean to possess an amoeba stage. These results suggest that possession of an amoeba stage was ancestral for Heterolobosea, unifying this taxon as a group of species with amoeba stages in their lifecycle or derived from organisms with such stages.

Characterization of Selenaion koniopes n. gen., n. sp., an amoeba that represents a new major lineage within heterolobosea, isolated from the Wieliczka salt mine

A new heterolobosean amoeba, Selenaion koniopes n. gen., n. sp., was isolated from 73‰ saline water in the Wieliczka salt mine, Poland. The amoeba had eruptive pseudopodia, a prominent uroid, and a nucleus without central nucleolus. Cysts had multiple crater-like pore plugs. No flagellates were observed. Transmission electron microscopy revealed several typical heterolobosean features: flattened mitochondrial cristae, mitochondria associated with endoplasmic reticulum, and an absence of obvious Golgi dictyosomes. Two types of larger and smaller granules were sometimes abundant in the cytoplasm--these may be involved in cyst formation. Mature cysts had a fibrous endocyst that could be thick, plus an ectocyst that was covered with small granules. Pore plugs had a flattened dome shape, were bipartite, and penetrated only the endocyst. Phylogenies based on the 18S rRNA gene and the presence of 18S rRNA helix 17_1 strongly confirmed assignment to Heterolobosea. The organism was not closely related to any described genus, and instead formed the deepest branch within the Heterolobosea clade after Pharyngomonas, with support for this deep-branching position being moderate (i.e. maximum likelihood bootstrap support--67%; posterior probability--0.98). Cells grew at 15-150‰ salinity. Thus, S. koniopes is a halotolerant, probably moderately halophilic heterolobosean, with a potentially pivotal evolutionary position within this large eukaryote group.

A contemporary evaluation of the acrasids (Acrasidae, Heterolobosea, Excavata)

Sorocarpic protists are organisms that individually aggregate and work together to form a fungus-like fruiting body (sorocarp). The amoeboid forms are often colloquially referred to as "cellular slime molds" or "acrasids". We argue the latter term should be used only to refer to members of Acrasidae in Heterolobosea. Here we study the diversity of two Acrasidae genera, Acrasis and the closely similar Pocheina, using a combination of morphological characteristics and small subunit rRNA gene sequences. A total of eight isolates of Acrasis and an example of Pocheina were examined. Acrasis/Pocheina form a well-supported monophyletic group that is the highly supported sister to a clade containing Allovahlkampfia and several other amoebae. Four molecular lineages of Acrasis were resolved, each of which is characterized by a distinctive fruiting body morphology. Each lineage represents a species, two of which are novel, Acrasis kona n. sp. and Acrasis takarsan n. sp. An isolate identified as Pocheina rosea is nested within the clade containing isolates of the taxon Acrasis rosea, into which P. rosea is tentatively subsumed. One member of the tightly knit allovahlkampfid clade was induced to form a simple sorocarp, leading us to include this clade in Acrasidae.

Characterization of Pharyngomonas kirbyi (= "Macropharyngomonas halophila" nomen nudum), a very deep-branching, obligately halophilic heterolobosean flagellate

The tetraflagellate Pharyngomonas is among the most commonly reported morphotypes of halophilic protozoa. We have established two cultures of Pharyngomonas kirbyi, SD1A and AS12B, from 300‰ and 210‰ salinity waters from the USA and Australia, respectively. 18S rRNA gene phylogenies confirm that Pharyngomonas is the same entity as 'Macropharyngomonas' (nomen nudum), and represents the deepest branch in the heterolobosean lineage. Pharyngomonas kirbyi (Strain SD1A) has flattened/discoidal cristae, and lacks conspicuous Golgi dictyosomes. It also has a heterolobosean 'double bikont' flagellar apparatus, with two right roots, each associated with an 'I' fibre and part of a rhizoplast-like complex. One right root splits shortly after its origin, and supplies most of the microtubules that support both the ventral groove, and the sub-anterior cytopharynx. Interestingly, Pharyngomonas has some potentially ancestral features not found in typical Heterolobosea, including elongated left roots associated with multilayered 'C' fibres, orthogonal basal bodies, and a spur structure that might represent a 'B' fibre homolog. Both isolates are obligate halophiles that grow best at 100-200‰ salinity and do not grow below 75‰ salinity. Pharyngomonas is therefore of considerable evolutionary importance, both as a deep-branching, plesiomorphic heterolobosean, and a borderline extreme halophile.

Oramoeba fumarolia gen. nov., sp. nov., a new marine heterolobosean amoeboflagellate growing at 54 °C

An amoeba strain was isolated from marine sediment taken from the beach near a fumarole in Italy. The trophozoites of this new marine species transforms into flagellates with variable numbers of flagella, from 2 to 10. The strain forms round to oval cysts. This thermophilic amoeboflagellate grows at temperatures up to 54°C. Molecular phylogenetic analysis of the small subunit ribosomal DNA (SSU rDNA) places the amoeboflagellate in the Heterolobosea. The closest relatives are Stachyamoeba sp. ATCC50324, a strain isolated from an ocean sample, and Vrihiamoeba italica, a recent isolate from a rice field. Like some other heterolobosean species, this new isolate has a group I intron in the SSU rDNA. Because of the unique place in the molecular phylogenetic tree, and because there is no species found in the literature with similar morphological and physiological characteristics, this isolate is considered to be a new genus and a new species, Oramoeba fumarolia gen. nov., sp. nov.

Marinamoeba thermophila, a new marine heterolobosean amoeba growing at 50 degrees C

Two amoeba strains were isolated from marine sediment taken at the same place with 18 months interval from a region of the sea floor heated by extended submarine hot springs and fumaroles. These thermophilic amoebae grow at temperatures up to 50 degrees C. Sequences of the internal transcribed spacer demonstrated that the two strains belong to the same species and are different from any genus for which sequences are known. Phylogeny using small subunit ribosomal RNA places the amoeba in the Heterolobosea. Their closest relatives are the hypersaline flagellate Pleurostomum flabellatum and the hypersaline amoeba Tulamoeba peronaphora. The freshwater amoeboflagellate genera Naegleria and Willaertia belong to the same phylogenetic clade in the Vahlkampfiidae. The new marine species does not transform into flagellates. It forms cysts, which are round to ellipsoidal with few pores. Because of their unique place in the molecular phylogenetic tree, and because there is no morphologically identical species found in the literature, these isolates are considered to be a new species and a new genus, Marinamoeba thermophila.

Unusual Mitochondrial Genome Structures throughout the Euglenozoa

Mitochondrial DNA of Kinetoplastea is composed of different chromosomes, the maxicircle (bearing 'regular' genes) and numerous minicircles (specifying guide RNAs involved in RNA editing). In trypanosomes [Kinetoplastea], DNA circles are compacted into a single dense body, the kinetoplast. This report addresses the question whether multi-chromosome mitochondrial genomes and compacted chromosome organization are restricted to Kinetoplastea or rather occur throughout Euglenozoa, i.e., Kinetoplastea, Euglenida and Diplonemea. To this end, we investigated the diplonemid Rhynchopus euleeides and the euglenids Petalomonas cantuscygni, Peranema trichophorum and Entosiphon sulcatum, using light and electron microscopy and molecular techniques. Our findings together with previously published data show that multi-chromosome mitochondrial genomes prevail across Euglenozoa, while kinetoplast-like mtDNA packaging is confined to trypanosomes.

Ultrastructure and Phylogenetic Placement within Heterolobosea of the Previously Unclassified, Extremely Halophilic Heterotrophic Flagellate Pleurostomum flabellatum (Ruinen 1938)

Although Pleurostomum was described almost a century ago, flagellates assigned to this taxon have been recorded only in very occasional faunistic studies of highly saline habitats, and their phylogenetic position has remained uncertain. We report the cultivation, ultrastructure, and phylogenetic relationships of Pleurostomum flabellatum isolated from a Korean saltern pond of 313 per thousand salinity. This isolate is biflagellated with a cytostomal groove, and is not distinguishable from previous accounts of P. flabellatum from saturated brines in India and Australia. Pleurostomum flabellatum shows ultrastructural features characteristic of many Heterolobosea: (1) a striated rhizoplast, (2) an absence of stacked Golgi bodies, (3) parallel basal bodies and flagella, and (4) a large number of peripheral microtubules supporting a rostrum. 18S rRNA gene phylogenies strongly confirm the affinities of P. flabellatum within Heterolobosea. Furthermore, the 18S rRNA gene of P. flabellatum has the heterolobosean-specific helix 17_1, and a group I intron in the same position as in Acrasis rosea. Within Heterolobosea, the 'amoeboflagellate' genera Naegleria and Willaertia were its closest relatives with high bootstrap support and posterior probability. P. flabellatum was observed only as a flagellate, and never as an amoeba. Since light microscopy and electron microscopy observations indicate that P. flabellatum flagellates are capable both of feeding and division, there might be no amoeba stage. Being morphologically distinct from its closest relatives and phylogenetically distant from other flagellate-only Heterolobosea, P. flabellatum cannot be moved into any previously described heterolobosean genus. Instead, we move Pleurostomum into Heterolobosea, and assign as the type species Pleurostomum salinum Namyslowski 1913, a species that closely resembles P. flabellatum. The optimal temperature for growth of P. flabellatum is 40 degrees C. Interestingly, P. flabellatum grows optimally at 300 per thousand salinity and fails to grow below 200 per thousand salinity, indicating that it is an 'extreme halophile'. The optimal salinity for growth is the highest for any eukaryote examined to date.

Andalucia (n. gen.)--the deepest branch within jakobids (Jakobida; Excavata), based on morphological and molecular study of a new flagellate from soil

A new heterotrophic flagellate (Andalucia godoyi n. gen. n. sp.) is described from soil. Earlier preliminary 18S rRNA analyses had indicated a relationship with the phylogenetically difficult-to-place jakobid Jakoba incarcerata. Andalucia godoyi is a small (3-5 mum) biflagellated cell with a ventral feeding groove. It has tubular mitochondrial cristae. There are two major microtubular roots (R1, R2) and a singlet root associated with basal body 1 (posterior). The microtubular root R1 is associated with non-microtubular fibres "I,""B," and "A," and divides in two parts, while R2 is associated with a "C" fibre. These structures support the anterior portion of the groove. Several features of A. godoyi are characteristic of jakobids: (i) there is a single dorsal vane on flagellum 2; (ii) the C fibre has the jakobid multilaminate substructure; (iii) the dorsal fan of microtubules originates in very close association with basal body 2; and (iv) there is no "R4" microtubular root associated with basal body 2. Morphological analyses incorporating the A. godoyi data strongly support the monophyly of all jakobids. Our 18S rRNA phylogenies place A. godoyi and J. incarcerata as a strong clade, which falls separately from other jakobids. Statistical tests do not reject jakobid monophyly, but a specific relationship between Jakoba libera and J. incarcerata and/or A. godoyi is rejected. Therefore, we have established a new genus Andalucia n. gen. with the type species Andalucia godoyi n. sp., and transfer Jakoba incarcerata to Andalucia as Andalucia incarcerata n. comb.