J. C. Green

Phylogenetic reconstructions of the Haptophyta inferred from 18s ribosomal DNA sequences and available morphological data

Abstract Most haptophytes are unicellular, photosynthetic flagellates, although some have coccoid, colonial, amoeboid, or filamentous stages. Nearly all have a characteristic filamentous appendage, the haptonema, arising between the two flagella. The small subunit ribosomal RNA gene (l8S ribosomal DNA) from 18 haptophyte species has been sequenced, and the sequences aligned with those of more than 300 published and unpublished chlorophyll a + c algae. Phylogenies were constructed using maximum likelihood, neighbor-joining, and weighted maximum parsimony analyses. The high divergence (6%) between members of Pavlova and the remaining haptophytes supports the division of Haptophyta into two classes: Prymnesiophyceae and Pavlovophyceae. Three major clades that correspond to known taxa within the Prymnesiophyceae were identified: one clade embraces Phaeocystis spp.; the second includes members of the genera Chrysochromulina, Prymnesium, and Imantonia; and the third includes coccolithophorid genera and the genus Isochrysis. Two other clades contain taxa whose sequences were derived from a gene clone library. These taxa are not strongly related to any of the cultured taxa included in this study. Based on 18S ribosomal DNA sequence data and available information on morphological structure and ultrastructure, we propose that the class Prymnesiophyceae be divided into four orders: Phaeocystales ord. nov., Prymnesiales, Isochrysidales, and Coccolithales. A total of 1–2% divergence at this level in the 18S ribosomal RNA gene analysis warrants a separation above the level of family. Within the Pavlovophyceae, a new genus is established, Rebecca J.C. Green gen. nov., into which Pavlova salina and Pavlova helicata are moved.

LIPID BIOMARKER DIVERSITY IN THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) AND THE RELATED SPECIES GEPHYROCAPSA OCEANICA1

Twenty‐four strains of Emiliania huxleyi and two strains of Gephyrocapsa oceanica were grown at 15°C under identical culture conditions to assess genetic variability in key lipid biomarker profiles (C37‐C39 alkenones, C36 and C37 alkyl alkenoates, and C31‐C38 alkenes). Under our culture conditions, little divergence an biomarker composition was detected between E. huxleyi strains from different oceanic regions or between E. huxleyi and G. oceanica even though the strains originated from biogeographical regions as diverse as the subpolar North Atlantic and subtropical Western Pacific. The major differences observed were in tetraunsaturated alkenone abundance and alkene profiles, which tended to separate neritic from open ocean strains. Different strains from the same locality were as different as strains originating from widely separated ocean basins, indicating extreme genotypic diversity within a population. Replicate cultures of the same strain showed significant variability in their biomarker profiles even though the culture temperature varied by only ±0.3°C, indicating that their synthesis ratios are influenced by environmental and/or physiological variable(s), as yet unidentified, in addition to temperature. Strong covariance in C37 and C38 methyl alkenone unsaturation ratios (Uk37 and Uk38Mρ respectively) and, in coastal strains, C33, alkene and alkenone unsaturation ratios indicates that these compounds are biochemically linked.

Genetic characterisation of Emiliania huxleyi (Haptophyta)

Amongst the coccolithophorids, Emiliania huxleyi is the most successful and can form large scale blooms under a variety of environmental conditions. This implies extensive genetic variation within this taxon. Physiological, morphological and antigenic differences between clonal isolates support this suggestion. Our investigations into the level of genetic variation within the morphological species concept of E. huxleyi indicate that it is such a young taxon that sequence comparisons of both coding and non-coding regions cannot resolve the issue of how many separate taxonomic entities are involved. However, PCR-based genetic fingerprinting techniques do reveal extensive genetic diversity, both on a global scale and within major bloom populations in both space and time. Cell DNA content can also separate cells with morphotype A coccoliths from those with morphotype B coccoliths. Taken together with physiological and morphological evidence, these data suggest that the morphotypes of E. huxleyi should be separated at the variety level. We have used both nuclear and plastid rRNA sequence comparisons to confirm the place of E. huxleyi within the Haptophyta.

Calcium carbonate deposition in the motile (Crystallolithus) phase of Coccolithus pelagicus (Prymnesiophyceae)

Non-motile heterococcolith-bearing cells of Coccolithus pelagicus grown in clonal culture eventually give rise to motile cells of the “Crystallolithus” phase. Such motile cells have a complex periplast comprising layers of organic scales, holococcoliths of the crystallolith type and an outer investment referred to here as the envelope. Scales, crystallolith baseplates and discrete units of envelope are formed in Golgi-associated cisternae. The deposition of calcium carbonate does not appear to take place intracellularly as it does in the non-motile heterococcolithophorid phase. In order to locate the site of crystallolith synthesis, cells were treated with CO2 to remove the existing CaCO3. After resuspending decalcified cells in fresh medium, CaCO3 first appeared on crystallolith baseplates outside the plasmalemma, external to the mature cisternae of the Golgi apparatus and near to the flagellar bases. Crystalloliths apparently undergoing calcification are always closely associated with the envelope. The ...

Preliminary results using the rapd analysis to screen bloom populations of Emiliania huxleyi (Haptophyta)

Abstract The feasibility of using the randomly amplified polymorphic DNA (RAPD) analysis to generate amplification fragment length polymorphism (AFLP) ‘fingerprints’ was investigated. The isolates examined originate from a bloom in the North Atlantic and from various stages of a mesocosm experiment at the Marine Biological Field Station, University of Bergen, Norway. Preliminary evidence suggests that not all individuals within either natural or mesocosm blooms are genetically identical. AFLP fingerprinting offers the possibility of tracing genotypes during the development of blooms in the natural environment.

The architecture of the flagellar apparatus ofPrymnesium patellifera (Prymnesiophyta)

The flagellar apparatus of the small prymnesiophytePrymnesium patellifera has been analysed and a reconstruction is presented. Externally, the cell carries two sub-equal flagella and a short non-coiling haptonema. Within the cell, there are four microtubular roots and a number of fibrous bands, the latter interconnecting the two basal bodies and the haptonema base. One of the roots (r1) consists of a sheet of up to 25 microtubules originating close to the proximal extremity of the haptonema base, but the other three roots are composed of between 1 and 4 microtubules only. Distally, a large striated fibrous auxiliary connecting root extends across the anterior part of the cell linking root r1 and a mitochondrial profile on the opposite side of the cell. The arrangement of the components of the flagellar apparatus ofP. patellifera is commensurate with the general pattern found in many prymnesiophytes other than members of the Pavlovales, but there are a number of differences in detail from the other species described hitherto.

STRUCTURE AND PHYSIOLOGY OF THE HAPTONEMA IN CHRYSOCHROMULINA (PRYMNESIOPHYCEAE). I. FINE STRUCTURE OF THE FLAGELLAR/HAPTONEMATAL ROOT SYSTEM IN C. ACANTHA AND C. SIMPLEX1

The intracellular structural relationships between the flagella and haptonema in Chrysochromulina acantha Leadbeater & Manton (Prymnesiophyceae) were studied in detail and a reconstruction is presented. Three micro‐tubular roots are associated with the flagellar apparatus. The largest, consisting of a sheet of approximately 20 microtubules, has its origins at the base of the left basal body. The main body of microtubules passes over the surface of a mitochondrion toward the left chloroplast and apparently terminates at a pair of microtubules oriented perpendicularly to it. Four microtubules diverge from the sheet and pass behind the left basal body. Two other roots–one consisting of a 2 + 2 + 1 arrangement of microtubules, the other of a single microtubule only—are associated with the right basal body. The two basal bodies are connected by distal and proximal fibers, and they are linked also to the base of the haptonema, three fibers extending from the haptonemal base to the right basal body, one only to the left. An additional fiber extending from the right basal body passes between the left basal body and the base of the haptonema, terminating at the largest microtubular root. Lateral extensions link this fiber to both the left basal body and the haptonematal base. Negative staining of isolated root systems of C. simplex Estep et al. shows that the arrangement of microtubules and fibrous connections is similar to that in C. acantha. The root system of C. acantha is compared to those of other members of the Prymnesiophyceae.

STRUCTURE AND PHYSIOLOGY OF THE HAPTONEMA IN CHRYSOCHROMULINA (PRYMNESIOPHYCEAE). II. MECHANISMS OF HAPTONEMATAL COILING AND THE REGENERATION PROCESS

The axoneme in the free part of the haptonema in Chrysochromulina acantha Leadbeater & Manton and C. simplex Estep et al. consists of seven single microtubules, except in the extreme distal swelling where, in C. simplex, there are only three microtubules. In the extended haptonema, the microtubules are arranged in a ring though they are not evenly spaced, the gap between two of the microtubules being larger than that between any other neighboring pairs. In the coiled haptonema, rearrangement of the microtubules occurs so that the ring becomes distorted and the microtubules form two superposed arcs. A sliding microtubule mechanism is considered as a means by which haptonematal movement might be affected, and this is discussed in relation to the fine structure of both embedded material and negatively stained demembranated cells. We show that haptonematal coiling is dependent on the presence of calcium ions and that an external concentration of between 10−6 and 10−7 M Ca2+ is the threshold below which the frequency of coiling on cell death is reduced. The results of experiments using ethylene bis‐(oxyethylenenitrilo)‐tetracetic acid (EGTA) and lanthanum ions to control extracellular and intracellular Ca2+ concentrations are discussed in terms of both external free calcium and intracellular pools. We also show that haptonematal regeneration following excision begins with a short lag phase. This is followed by a period of rapid growth, decreasing after approximately 4 h. Full haptonematal regrowth is not achieved until after 12–15 h. The rate of haptonematal regeneration is strongly affected when the flagella are regenerating simultaneously. These observations are interpreted in terms of competition for intracellular precursors.

Taxonomy (46 — or More — Protistan Phyla) — Session Summary

This session summarizes current thinking concerned with classification of protists and outlines a scheme for their presumed phylogenetic relationships. It is presented in three sections 1) a descriptive summary of the papers presented, 2) a discussion of current ideas concerning phylogeny and 3) a dendrogram of phylogenetic relationships among eukaryotic organisms.