Respiratory Succession and Community Succession of Bacterioplankton in Seasonally Anoxic Estuarine Waters

Anoxia occurs in bottom waters of stratified estuaries when respiratory consumption of oxygen, primarily by bacteria, outpaces atmospheric and photosynthetic reoxygenation. Once water becomes anoxic, bacterioplankton must change their metabolism to some form of anaerobic respiration. Analysis of redox chemistry in water samples spanning the oxycline of Chesapeake Bay during the summer of 2004 suggested that there was a succession of respiratory metabolism following the loss of oxygen. Bacterial community doubling time, calculated from bacterial abundance (direct counts) and production (anaerobic leucine incorporation), ranged from 0.36 to 0.75 day and was always much shorter than estimates of the time that the bottom water was anoxic (18 to 44 days), indicating that there was adequate time for bacterial community composition to shift in response to changing redox conditions. However, community composition (as determined by PCR-denaturing gradient gel electrophoresis analysis of 16S rRNA genes) in anoxic waters was very similar to that in surface waters in June when nitrate respiration was apparent in the water column and only partially shifted away from the composition of the surface community after nitrate was depleted. Anoxic water communities did not change dramatically until August, when sulfate respiration appeared to dominate. Surface water populations that remained dominant in anoxic waters were Synechococcus sp., Gammaproteobacteria in the SAR86 clade, and Alphaproteobacteria relatives of Pelagibacter ubique, including a putative estuarine-specific Pelagibacter cluster. Populations that developed in anoxic water were most similar (<92% similarity) to uncultivated Firmicutes, uncultivated Bacteroidetes, Gammaproteobacteria in the genus Thioalcalovibrio, and the uncultivated SAR406 cluster. These results indicate that typical estuarine bacterioplankton switch to anaerobic metabolism under anoxic conditions but are ultimately replaced by different organisms under sulfidic conditions.     

Evaluation of Succession in an Estuarine Macrobenthic Soft-Bottom Community near Tampa,Florida

A subtidal macrobenthic infaunal community was quantitatively sampled monthly from February 1975 to July 1978 (42 months). During that period, complete defaunation (presumably due to hypoxia) occurred three times at approximately annual intervals. The recovery of the community was examined for successional patterns by quantitative and qualitative normal and inverse classification analyses and by rank-order analysis of the dominant species. There was no consistent pattern of succession from recovery to recovery. Samples taken just after defaunation were not similar to each other and no consistent suites of species were detected. Classical succession in which suites of species are successively replaced by other suites until a persisting suite of species occurs (faciliation model) was not found. Other models of succession are discussed.     

The Mitochondrial Genome of Protists

The data on the structure and functions of the mitochondrial genomes of protists (Protozoa and unicellular red and green algae) are reviewed. It is emphasized that mitochondrial gene structure and composition, as well as organization of mitochondrial genomes in protists are more diverse than in multicellular eukaryotes. The gene content of mitochondrial genomes of protists are closer to those of plants than animals or fungi. In the protist mitochondrial DNA, both the universal (as in higher plants) and modified (as in animals and fungi) genetic codes are used. In the overwhelming majority of cases, protist mitochondrial genomes code for the major and minor rRNA components, some tRNAs, and about 30 proteins of the respiratory chain and ribosomes. Based on comparison of the mitochondrial genomes of various protists, the origin and evolution of mitochondria are briefly discussed.     

Untangling the Phylogeny of Amoeboid Protists1

ABSTRACT. The amoebae and amoeboid protists form a large and diverse assemblage of eukaryotes characterized by various types of pseudopodia. For convenience, the traditional morphology‐based classification grouped them together in a macrotaxon named Sarcodina. Molecular phylogenies contributed to the dismantlement of this assemblage, placing the majority of sarcodinids into two new supergroups: Amoebozoa and Rhizaria. In this review, we describe the taxonomic composition of both supergroups and present their small subunit rDNA‐based phylogeny. We comment on the advantages and weaknesses of these phylogenies and emphasize the necessity of taxon‐rich multigene datasets to resolve phylogenetic relationships within Amoebozoa and Rhizaria. We show the importance of environmental sequencing as a way of increasing taxon sampling in these supergroups. Finally, we highlight the interest of Amoebozoa and Rhizaria for understanding eukaryotic evolution and suggest that resolving their phylogenies will be among the main challenges for future phylogenomic analyses.     

Soil Aggregates and Associated Organic Matter under Conventional Tillage,No-Tillage,and Forest Succession after Three Decades

Impacts of land use on soil organic C (SOC) are of interest relative to SOC sequestration and soil sustainability. The role of aggregate stability in SOC storage under contrasting land uses has been of particular interest relative to conventional tillage (CT) and no-till (NT) agriculture. This study compares soil structure and SOC fractions at the 30-yr-old Horseshoe Bend Agroecosystem Experiment (HSB). This research is unique in comparing NT and CT with adjacent land concurrently undergoing forest succession (FS) and in sampling to depths (15–28 cm) previously not studied at HSB. A soil moving experiment (SME) was also undertaken to monitor 1-yr changes in SOC and aggregation. After 30 years, enhanced aggregate stability under NT compared to CT was limited to a depth of 5 cm, while enhanced aggregate stability under FS compared to CT occurred to a depth of 28 cm and FS exceeded NT from 5–28 cm. Increases in SOC concentrations generally followed the increases in stability, except that no differences in SOC concentration were observed from 15–28 cm despite greater aggregate stability. Land use differences in SOC were explained equally by differences in particulate organic carbon (POC) and in silt-clay associated fine C. Enhanced structural stability of the SME soil was observed under FS and was linked to an increase of 1 Mg SOC ha⁻¹ in 0–5 cm, of which 90% could be attributed to a POC increase. The crushing of macroaggregates in the SME soil also induced a 10% reduction in SOC over 1 yr that occurred under all three land uses from 5–15 cm. The majority of this loss was in the fine C fraction. NT and FS ecosystems had greater aggregation and carbon storage at the soil surface but only FS increased aggregation below the surface, although in the absence of increased carbon storage.     

Extracellular Polysaccharide Production by Thraustochytrid Protists

Four strains of marine stramenopilan protists, the thraustochytrids, were studied for their ability to produce extracellular polysaccharides (EPSs). Observations by light and scanning electron microscopy revealed the production of a matrix of EPS around groups of cells in stationary cultures. EPS in shake culture filtrates ranged from 0.3 to 1.1 g/L. EPS production, which was studied in greater detail in 2 isolates, SC-1 and CW1, increased with age of cultures, reaching a peak in the stationary phase. Anion exchange chromatography yielded a single fraction of the EPS of both species. The EPS contained 39% to 53% sugars, besides proteins, lipids, uronic acids, and sulfates. Molecular weight of the EPS produced by SC-1 was approximately 94 kDa, and that of CW1, 320 kDa. Glucose formed the major component in the EPS of both isolates—galactose, mannose, and arabinose being the other components. Cultures of both isolates survived air-drying up to a period of 96 hours, suggesting a role for EPS in preventing desiccation of cells.     

Early Evolution of Protists Introductory Remarks of Chairman

SYNOPSIS. Phylogenetic relations are ultimately determined by homologous relationships, including both structural and functional data. Following the establishment of those relationships, the direction of evolutionary change must be determined using paleontologic, developmental, and especially morphocline, data. From that perspective the direction of subsequent development becomes clearer and the problems of origins become more explicit. Using the foregoing methodology it has been possible to identify plausibly monophyletic groups of animal protists or protozoa. Allowing for attendant difficulties, there nevertheless emerges certain fairly convincing generalities: (a) the predominantly pseudopodial forms, with a few minor exceptions, have direct origins from apochlorotic algae; (b) the predominantly kinetidal forms (zooflagellates and ciliates), though also derived originally from apochlorotic algae, give evidence of extended evolutionary development with the especially noteworthy emergence of a permanent ingestatory structure; (c) both groups have increased size, a tendency towards multinuclearity and polyploidy, cytoplasmic differentiations of various sorts, and complex life cycles. In terms of further evolution, namely the emergence of multicellular animals, the pseudopodial forms are almost certainly a dead end while the kinetidal forms are arguably the ancestors of at least 2 metazoan phyla.     

Mixotrophic Protists In Marine and Freshwater Ecosystems

ABSTRACT Some protists from both marine and freshwater environments function at more than one trophic level by combining photosynthesis and panicle ingestion. Photosynthetic algae from several taxa (most commonly chrysomonads and dinoflagellates) have been reported to ingest living prey or nonliving particles, presumably obtaining part of their carbon and/or nutrients from phagocytosis. Conversely, some ciliates and sarcodines sequester chloroplasts after ingestion of algal prey. Plastid retention or "chloroplast symbiosis" by protists was first demonstrated < 20 years ago in a benthic foraminiferan. Although chloroplasts do not divide within these mixotrophic protists, they continue to function photosynthetically and may contribute to nutrition. Sarcodines and ciliates that harbor endosymbiotic algae could be considered mixotrophic but are not covered in detail here. the role of mixotrophy in the growth of protists and the impact of their grazing on prey populations have received increasing attention. Mixotrophic protists vary in their photosynthetic and ingestion capabilities, and thus, in the relative contribution of photosynthesis and phagotrophy to their nutrition. Abundant in both marine and freshwaters, they are potentially important predators of algae and bacteria in some systems. Mixotrophy may make a stronger link between the microbial and classic planktonic food webs by increasing trophic efficiency.     

138 Molecular Evolution of Glutamine Synthetase In Protists

The binding of fluorescein isothiocyanate (FITC) conjugated lectins to gametes of Aglaothamnion byssoides Itono during the fertilization was studied by the use of confocal microscope. The physiological effects of lectins and carbohydrates on gamete binding were also examined. Three lectins, concanavalin A (ConA), Soybean agglutinin (SBA) and wheat germ agglutinin (WGA) bound to the surface of spermatia, but each lectin labeled different region of the spermatium. SBA bound only to the spermatial appendages but ConA bound to the whole spermatial surface except spermatial appendages. WGA labeled narrow region which connects spermatial body and appendages. During fertilization, ConA and WGA specific substances on the spermatial surface moved towards the area contacting with trichogyne and accumulated on the surface of fertilization canal. Spermatial binding to trichogynes was inhibited by pre-incubation of spermatia with SBA, while trichogyne receptors were blocked by the complementary carbohydrate, N-acetyl-D-galactosamine. WGA and its complementary carbohydrate had little effect on gamete binding. For searching the step of sexual isolation, crossing experiment was performed between Aglaothamnion byssoides and twelve other red algal species. Results showed that the gamete recognition was genus-specific: the gametes bound freely with their partners of the same genus. When two species from same genus were crossed, sexual isolation occurs gradually during the fertilization process. Therefore, sexual isolation in red algae appears to be determined by multi-step process and gamete binding is the initial step.