Coccoid Green Algae Research Articles

INFERRING TAXONOMIC POSITIONS AND TESTING GENUS LEVEL ASSIGNMENTS IN COCCOID GREEN LICHEN ALGAE: A PHYLOGENETIC ANALYSIS OF 18S RIBOSOMAL RNA SEQUENCES FROM DICTYOCHLOROPSIS RETICULATA AND FROM MEMBERS OF THE GENUS MYRMECIA (CHLOROPHYTA, TREBOUXIOPHYCEAE CL. NOV.)1

ABSTRACT Complete nuclear‐encoded small‐subunit ribosomal RNA (18S rRNA) coding sequences were determined for the coccoid green algae Dictyochloropsis reticulata (Tschermak‐Woess) Tschermak‐Woess, Myrmecia astigmatica Vinatzer, and M. bisecta Reisigl, to investigate the taxonomic position of Dictyochloropsis Geitler and of the genus Myrmecia Printz. Phylogenies inferred from these data revealed a sister‐group relationship between D. reticulata and certain coccoid green algae that lack motile stages (autosporic coccoids) within the order Microthamniales. The monophyletic origin of the Microthamniales, including autosporic coccoids previously classified in the Chlorophyceae, is clearly resolved by the rRNA sequence data. This finding. shows the considerable taxonomic breadth of that order, whose taxonomic position has been unclear so far. A new class, Trebouxiophyceae, is proposed for this group of green algae. Phylogenetic inferences from the rRNA sequences show paraphyly of the genus Myrmecia. The 18S rRNA sequence data suggest that, among taxa that share similar vegetative cell morphologies, the zoospore characters resolve better the actual genus and species boundaries. Within identical zoospore types, the rRNA data allow further resolution of taxonomic relationships. On the basis of the.se findings, I propose that the genus Friedmannia Chantanachat ± Bold be merged into Myrmecia and that only those species be left in the genus Myrmecia that are identical in particular zoospore characters (i.e. those described in detail for M. israeliensis (Chantanachat ± Bold) comb, nov.), namely M. astigmatica, M. biatorellae (Tschermak‐Woess ± Ptesst) Petersen, and M. israeliensis. Myrmecia bisecta has to be excluded from Myrmecia; its taxonomic position within the Trebouxiophyceae is unclear.

Effects of nitrogen, phosphorus and carbon enrichment on planktonic and periphytic algae in a softwater, oligotrophic lake in Florida, USA

The objective of this study was to investigate nutrient limitation of algal abundance in Anderson-Cue Lake, a softwater clear oligotrophic lake in north-central Florida. Nutrient diffusing clay pots and cylindrical enclosures were used in the field to test effects of different combinations of nitrogen, phosphorus, silica, and carbon on algal standing crop and composition of periphytic and planktonic algae, respectively. Effects of nutrient enrichment on periphytic algae were examined in two studies conducted 31 May – 8 July and 10 June – 15 July 1991. Nutrient effects on planktonic algae were examined in one study from 13 June – 1 July 1991. Planktonic and periphytic algal biovolume was significantly higher (p<0.05) when nitrogen and carbon were added in combination than with treatments without nitrogen, carbon, or nitrogen and carbon. Treatments with nitrogen and carbon combined resulted in lower algal diversity and dominance by coccoid green algae andScenedesmus. Results indicate that carbon and nitrogen can be limiting factors to algal growth in Anderson-Cue Lake and possibly other lakes of similar water quality.

The ultrastructure of cellular division (autosporogenesis) in the coccoid green alga,Trebouxia aggregata, revealed by rapid freeze fixation and freeze substitution

Adequate ultrastructural preservation of cells of the green algaTrebouxia aggregata is achieved by immersion freeze fixation using liquid propane followed by freeze substitution and resin embedding at ambient temperature. Despite differential staining of membranes, using this method we have been able to study plasma membrane biogenesis during cellular division. Daughter protoplasts are separated by an ingrowing septum of plasma membrane that extends into the cell from a particular site at the peripheral plasma membrane marked by centrioles. Septum development involves tip growth followed by lateral growth. This growth seems to involve transfer of membrane from an adjacent partially coated reticulum to the septum plasma membrane. The reticulum which extends from nearby Golgi stacks to the area of septum growth is associated with an extensive array of microtubules. After daughter protoplasts are completely separated, each one becomes surrounded by a cell wall which is distinct from the persisting mother wall. The ultrastructural evidence suggests that cells ofT. aggregata are autospores rather than vegetative cells.

Der zönoblast als besondere Organisationsstufe der coccalen Grünalgen (chlorophyta)

Summary The multinuclear state in the microscopic coccoid green algae is a parallel to the siphonous state. Such “cells” which are in the main phase of development multinuclear are strictly not identical with the classic concept of a cell (algal cell) and do also not agree with the concept of a true coccoid habit. The coenoblast (coenocyt) presents a separate type of a habit and occurs not only in different classes of the green algae but also in the Chrysophyceae and Xanthophyceae. It is known that some uninucleate species of the Chlorococcales as well as of the Chlorellales are during sporogenesis for a very short time multinuclear as the mitoses precede the plasmatomy. But they remain in vegetative, trophic stage uninuclear before the reproduction is starting. The coenoblastic Chlorococcales and Chlorellales on the contrary are multinuclear during the whole vegetative phase (polyenergide during the trophic growth period) and the mitoses are progressive. Only the reproductive cells and the germlings are uninucleate. The characters of a coenoblast are given. The taxonomic value is that of an order or family as the mentioned state does not represent a natural group. On the contrary the usually given value of a genus would discredit the polyenergid habit.

CELL DIVISION IN THE GREEN MICROALGA MARVANIA GEMINATA: SEMI-EXOGENOUS AUTOSPOROGENESIS, ROLE OF COATED PIT-MICROTUBULE COMPLEXES, AND SYSTEMATIC SIGNIFICANCE

Cell division in the unicellular coccoid green alga M. geminata has been studied with transmission electron microscopy. Unlike the division cycle in other coccoid green algae, mitosis occurs not before the cell has expanded until about twice its original volume. Cell expansion involves the escape of part of the protoplast through a break in the cell wall. During mitosis the nuclear envelope remains intact. The spindle is not associated with centrioles, which seem to be absent throughout the cell cycle. The division site at the plasma membrane is marked by a short cortical microtubule which appears before division is initiated. The plasma membrane near the microtubule invaginates to form a coated pit-like structure. The latter continues to grow inward along with the short microtubule, and in effect constitutes the cleavage furrow. After furrowing, each daughter cell forms a wall layer at the new septum. Cells separate after the old, common wall layer is broken at the level of the septum. A model explaining cytokinetic events, in particular the furrowing mechanism, is presented. It is concluded that M. geminata may be considered as a member of a broadly conceived order Chlorococcales.

Chlorohippotes tenax gen. et sp. nov. (Chlorophyceae)

The genus Chlorohippotes is described on the only known species C. tenax. It is a coccoid green alga that becomes embedded in the gel of some multicellular Volvocales. Cells vary from spherical through mammiform to oblate-spheroidal with the morphologically anterior pole sunken into the host gel. They contain a parietal, initially 4-lobed, chloroplast with one to several pyrenoids. Asexual reproduction is by production of 4 or 8 zoospores per cell. The naked zoospore is oblanceolate and biflagellate, with two anterior contractile vacuoles and a cup-shaped but 4-lobed chloroplast with a basal pyrenoid. The stigma is anterio-lateral. The zoospore is rounded quadrate in cross-section. It becomes longitudinally 4-costate or also flattened when swimming but spherical upon attachment to a host. Sexual reproduction is unknown. Chlorohippotes tenax was first encountered on individuals of Volvox aureus Ehrenb. from a collection of shallow oxbow waters in the vicinity of Lawrence, Kansas (Thompson, 1979). It was also found epiphytic on V. carteri var. weissmannia (Powers) Iyengar and V. africanus West. The following summer this collection area was dry but the organism was again collected on V. carteri var. weissmannia from a stock pond ten miles west of Lawrence. In this pond it also occurred on Eudorina elegans Ehrenb. and E. plusicocca Smith. Infected and non-infected hosts from both collection sites were isolated into Volvox medium (Stein, 1973); thus permitting observations of the infection cycle. In nature and in culture, C. tenax was never observed attached to an inorganic substrate--i.e., culture flask. There appears to be an obligate association between the epiphyte and its Volvocalean hosts. The morphology of C. tenax has been consistent on all the hosts examined.

Abundance of picophytoplankton in the subsurface chlorophyll maximum layer in subtropical and tropical waters

A distinctive chlorophyll maximum was detected around 60-m depth in the western North Pacific Ocean and the South China Sea, and almost 55% of the total chlorophyll in the entire water column was found within 50 m around the subsurface chlorophyll maximum (SCM) layer. More than 70% of the chlorophyll was contained in picoplankton which passed through a 3-μm Nuclepore but retained on 0.22-μm Millipore filters at the SCM as well as the surface layers. By transmission electron microscopic observations, the picoplankton were identified as aChlorella-like coccoid green alga having a section size of 1.2 to 1.5 μm and cyanobacteria of 0.5 to 2 μm. No obvious difference in these two dominant groups was observed in the SCM and the surface samples except in numerous and heavily stacked thylakoids in the former samples.

Nutritional value of micro-algal mass cultures to the oyster Ostrea edulis L.

Mass cultures of natural phytoplankton were bloomed in outdoor tanks following nutrient enrichment. Once a bloom developed, tanks were enriched with nutrients daily and renewed at rates of 20%, 45% and 70% day −1. The 20% flow rate culture was grown without silicon and with an organic nutrient source. 70% flow rate cultures were predominantly Skeletonema costatum; 45% flow rate cultures contained a mixture of Chaetoceros species and Nitzschia and 20% flow rate cultures, which lacked silicon enrichment, were dominated by a coccoid green alga. Growth trials with Ostrea edulis showed that for supporting growth and maintaining condition index (Ci) the three diets could be ranked as follows: 70% flow rate > 45% > 20% (−silicon; +organic nutrient) The 70% flow rate culture was a significantly better diet than a reference laboratory culture of Skeletonema costatum for supporting growth and Ci, and the 45% diet maintained a higher oyster Ci than a reference laboratory culture of Chaetoceros calcitrans. The results are discussed, and the hypothesis is proposed that nutritional value of phytoplankton species is related to their reproductive strategy.

Effects of Burning on the Algal Communities of a High Desert Soil near Wallsburg, Utah

Effects of Burning on the Algal Communities of a High Desert Soil near Wallsburg, Utah

Nanochlorum eucaryotum: a Very Reduced Coccoid Species of Marine Chlorophyceae

Nanochlorum eucaryotum was isolated from a sea water aquarium housing different sponge species, cucumarias, small crustaceans and annelids. This bright green marine alga differs from all other known coccoid species. Its most prominent features are its very small cell size (1.5 pm) and its reduced cellular organization. Its cell contains one nucleus, one chloroplast, one mitochondrium and small vacuoles. Sometimes a Golgi apparatus can be seen. No other subcellular features have been observed. The cell wall is thin and smooth and does not contain any material of high electron density; only dividing cells show a rougher surface. The cells split into two daughter cells. No sexual reproduction has been observed in this organism. We have analyzed the ultrastructural cell organization, the amount of total DNA and RNA per cell, the pigment composition, the growth requirements and the sensitivity towards different inhibitors (chloramphenicol, cycloheximid, penicillin, lysozym and cellulase). The results afford the introduction of a new species; a new family or suborder of coccoid green algae is discussed.

Growth and Photosynthesis of Nanochlorum eucaryotum, a New and Extremely Small Eucaryotic Green Alga

Nanochlorum eucaryotum is a very small species of unicellular coccoid green algae (1.5 pm). The growth of Nanochlorum under different conditions of salinity, pH and light intensities was studied. Optimal growth rates were observed with normal sea water salinity and low light conditions at pH 7.0. The contents of chlorophylls, carotinoids, soluble proteins and the chlorophyll a to chlorophyll b ratio were measured. The light saturating curves of Nanochlorum cells grown under light intensities of 100 lx, 2000 lx and 10000 lx reveal a very narrow capacity of light adaptation. When cultured under higher light intensities, Nanochlorum was not able to reach high photosynthetic activities but underwent a photoinhibition of photosynthesis. The contents of cytochrome f, P-700 and ribulosebisphosphate carboxylase were low and comparable with those of low light adapted Chlorella cells. The analysis of the chlorophyll-protein complexes shows that about 80% of total chlorophyll is bound in the light harvesting chlorophyll protein complexes. All results indicate that Nanochlorum is a low light adapted marine organism with very narrow ecological flexibility.

Nitrogen fixation associated with a hotspring green alga

A unicellular alga which can grow in the light without a combined nitrogen source was isolated from a hot spring. The cells were almost spherical, usually 5–10 μm in diameter. Absorption spectra of the watersoluble pigments and of the acetone-extracted ones revealed the existence of chlorophyll a and b and the absence of phycobilins. Thin sections examined by electron microscopy revealed an eukaryotic organization with features typical of the coccoid green algae (the Chlorococcales). Cells divided by internal cytokinesis and subsequent liberation of daughter cells from the parental wall, in a way similar to Chlorella. The alga reduced acetylene to ethylene and incorporated 15N2 into cell protoplasm when incubated in a low oxygen atmosphere. Nitrogenase activity was light-dependent, microaerophilic and thermophilic. Although the association of symbiotic nitrogen fixing prokaryotes with the cells may still be possible, any such organisms have not so far been detected.

On the experimental silicification of microorganisms. III. Implications of the preservation of the green prokaryotic alga prochloron and other coccoids for interpretation of the microbial fossil record

Abstract Evidence for Precambrian fossil eukaryotic microorganisms has been based on: (1) the presence of internal ‘spots’ which have been variously interpreted to be remains of nuclei or pyrenoids of photosynthetic plastids or other organelles; (2) tetrahedral tetrad arrangement of cells; (3) trilete scars interpreted to be indicative of meiotic division: (4) large cell diameters; and (5) putative mitotic cell divisions. These features have been reported in fossils preserved in Precambrian cherts. We have studied modern microbial mats, thought to be analogues of Precambrian fossil communities, and found they may be silicified by laboratory procedures. In microbial mats from Baja California we have found many ‘spot cells’ that we could identify as remains of cyanophytes. We have silicified the newly discovered large prokaryotic coccoid green alga Prochloron and have found that it, like many cyanophytes previously silicified, preserves its structure and maintains its initial dimensions. In laboratory-silicified prokaryotic organisms we have found that all of the above criteria, supposedly characteristic of eukaryotes, can be observed. We conclude that there is no compelling morphological evidence for fossil eukaryotic microbes from Precambrian cherts.

Effects of petroleum pollutants on arctic microbial populations

Microorganisms encounter oil in the Arctic from natural seepages and accidental spillages. Incubation of Prudhoe crude oil with water from coastal ponds along Prudhoe Bay resulted in several changes in the microbial communities. Bacterial populations increased by several orders of magnitude; ameoboid protozoa were replaced by flagellated protozoa; coccoid green algae completely disappeared; diatoms increased and blue-green and green filamentous algae appeared to be unaffected. The microbial populations associated with a natural oil seepage at Cape Simpson were markedly different from those of the adjacent areas. The seep was devoid of vascular plant cover and, in some areas, of bacteria. Fungi were found to be abundant in the bacteria-free regions. Lichens flourished in the older sections. Underlying oil slicks experimentally floated in Prudhoe Bay, the bacterial population increased, in large part attributable to oil degrading Pseudomonads, but species diversity appeared to be unaffected.