Ultrastructural analyses of the flagellar apparatus suggested that Sphaeroplea , Atractomorpha , the Hydrodictyaceae, and the Neochloridaceae, all of which produce biflagellate motile cells with directly opposed (DO) basal bodies, are allied in an order Sphaeropleales. Recent studies of 18S rDNA sequence data supported an alliance of the DO group, but no data from Sphaeroplea and its allies were included. This investigation presented a test of the phylogenetic hypothesis suggested by the flagellar apparatus evidence using sequence data from the nuclear-encoded small-subunit rDNA (18S) and large subunit rDNA (26S) genes, combined with additional taxon sampling. Results from phylogenetic analyses weakly supported monophyly of biflagellate DO taxa and indicated that pyrenoids with cytoplasmic invaginations are present in numerous distinct lineages. Analysis of both molecular data sets supported a class Chlorophyceae comprised of at least six major groups that generally correspond to currently recognized orders or families: Chaetophorales, Chaetopeltidales, Chlamydomonadales, Sphaeropleales, Sphaeropleaceae, and Oedogoniales. In addition, Cylindrocapsa , Elakatothrix , Treubaria , and Trochiscia formed a seventh chlorophycean clade that is new to science. This investigation demonstrated that the 26S rDNA gene provides more phylogenetic signal, per unit sequence, than the 18S rDNA gene and that combined analysis yields topologies with more robust support than independent analysis of either data set.
Considerable progress has been made recently, based on classical morphological characters and newly described ultrastructural features, in understanding the phylogenetic relationships of the tracheophytes to the green algae and bryophytes. Recent technological advances in molecular biology, particularly the advent of the polymerase chain reaction (PCR), have allowed nucleotide sequence data relevant to such large-scale phylogenetic questions to accumulate, especially ribosomal RNA gene sequences (both the large and small subunits) from the nucleus and the chloroplast. We present synthetic cladistic analyses of the green plants that combine and compare available morphological and molecular data sets. Although the resulting phylogenies are poorly resolved in some areas at present, certain conclusions are supported: (1) The green plants are composed of two major monophyletic groups, one containing the "charophyte green algae and the land plants (i.e., "bryophytes" plus tracheophytes), the other containing the bulk of the classically delimited "green algae" (chlorophytes, pleurastrophytes, and ulvophytes). ( 2) The land plants are a well-supported monophyletic group, but neither the specific outgroup for the land plants nor the precise relationships among basa lineages of land plants are clear. In many analyses (including the combined molecular and morphological analysis) the three major lineages (i.e., liverworts, hornworts, and mosses) appear to be paraphyletic with respect to the tracheophytes, with an indication that the mosses alone may be the sister group of the tracheophytes; however, in other analyses the "bryophytes" are supported as a monophyletic group. (3) The ulvophytes, chlorophytes, and pleurastrophytes are each supported as monophyletic (with the exception of a few taxa that may be misplaced m the current classification), with the topology: [ulvophytes [chlorophytes + pleurastrophytes]]. Combined analyses o! molecular and morphological data offer the greatest potential for resolving these relationships.
The Salt Plains National Wildlife Refuge (SPNWR) near Cherokee, Oklahoma, contains a barren salt flat where Permian brine rises to the surface and evaporates under dry conditions to leave a crust of white salt. Rainfall events dissolve the salt crust and create ephemeral streams and ponds. The rapidly changing salinity and high surface temperatures, salinity, and UV exposure make this an extreme environment. The Salt Plains Microbial Observatory (SPMO) examined the soil microbial community of this habitat using classic enrichment and isolation techniques and phylogenetic rDNA studies. Rich growth media have been emphasized that differ in total salt concentration and composition. Aerobic heterotrophic enrichments were performed under a variety of conditions. Heterotrophic enrichments and dilution plates have generated 105 bacterial isolates, representing 46 phylotypes. The bacterial isolates have been characterized phenotypically and subjected to rDNA sequencing and phylogenetic analyses. Fast-growing isolates obtained from enrichments with 10% salt are predominantly from the gamma subgroup of the Proteobacteria and from the low GC Gram-positive cluster. Several different areas on the salt flats have yielded a variety of isolates from the Gram-negative genera Halomonas, Idiomarina, Salinivibrio, and Bacteroidetes. Gram-positive bacteria are well represented in the culture collection including members of the Bacillus, Salibacillus, Oceanobacillus, and Halobacillus.
The hydrodictyacean green algal lineage has been the focus of much research due to the fossil record of at least some members, their ornamented cell walls, and their distinctive reproductive strategies. The phylogeny of the family was, until recently, exclusively morphology based. This investigation examines hydrodictyacean isolates from several culture collections, focusing on sequences from ribosomal data: 18S rDNA, 26S rDNA (partial), and internal transcribed spacer (ITS)-2 data. Results from phylogenetic analyses of independent and combined data matrices support the Hydrodictyaceae as a monophyletic lineage that includes isolates of Chlorotetraedron, Hydrodictyon, Pediastrum, Sorastrum, and Tetraedron. Phylogenetic analyses of rDNA data indicate that the three-dimensional coenobium of Hydrodictyon is evolutionarily distinct from the three-dimensional coenobium of Sorastrum. The more robust aspects of the ITS-2 data corroborate the 18S þ 26S rDNA topology and provide a structural autapomorphy for the Hydrodictyaceae and Neochloridaceae, that is, an abridgment of helix IV in the secondary structure. The rDNA data do not support monophyly of Pediastrum but rather suggest the existence of four additional hydrodictyacean genera: Monactinus, Parapediastrum, Pseudopediastrum, and Stauridium.
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