Stuart D. Sym

Microalgal fatty acid composition: implications for biodiesel quality

The fuel properties of microalgal biodiesel are predicted using published microalgal fatty acid (FA) compositions and predictive fuel models. Biodiesels produced from the microalgae investigated are predicted to have extremely poor oxidative stabilities and the majority also have poor cold-flow properties. The cetane number in most cases is out of specification, but less so than the oxidative stability and cold flow. These findings support the idea that feedstocks rich in monounsaturated fatty acids (MUFAs) are desirable for biodiesel but the composition of the saturated fatty acids (SFAs) is also shown to be of great importance. There is an apparent relationship between algal class and the percentage of FAs represented by MUFA. This potentially allows for the identification of high-MUFA algal classes, or at least provides some basis for researchers to make initial selections of target classes for bioprospecting. Comparisons of FA groups between algal classes also show that the SFAs of Mediophyceae contain significantly higher proportions of C14:0, which is in contrast to the normally abundant C16:0 and the Mediophyceae therefore have better cold-flow characteristics than other classes with similar total SFA contents. Certain particularly promising cases for biodiesel production are presented as species level examples of feedstocks that are close to satisfying the biodiesel standards and to further illustrate the challenges that remain. Variation in FA composition as a response to changes in certain environmental variables forms another important facet to feedstock selection and is briefly considered, with suggestions for further research.

Karenia cristata sp. nov. and Karenia bicuneiformis sp. nov. (Gymnodiniales, Dinophyceae): two new Karenia species from the South African coast

Abstract In 1988 and 1989, an undescribed gymnodinioid dinoflagellate species turned the waters of the largest bay in South Africa, False Bay, to a dirty olive-green colour. The bloom was accompanied by extensive abalone (Haliotis midae) mortalities and noxious gases causing eye, nose, skin and throat irritations in humans. In 1995, another undescribed gymnodinioid species bloomed in the same bay but with no adverse effects on marine fauna or humans. These two species form an established component of the phytoplankton assemblage on the south coast of South Africa. They are described here as Karenia cristata Botes, Sym & Pitcher and K. bicuneiformis Botes, Sym & Pitcher. Karenia cristata has a straight apical groove elevated into an apical crest and extending down immediately to the right of the sulcal extension on the ventral side. The hypocone is asymmetrical, with the right lobe larger and more rounded than the left; the nucleus is central, with the bulk situated in the hypocone. Its pigment content is similar to that of K. mikimotoi and K. brevis. Other than K. brevis, K. bicuneiformis is significantly larger than the other Karenia species and is distinctly dorso-ventrally flattened. The hypocone is w-shaped and the epicone is conical, giving the cell a distinctly angular outline. Pairwise distance comparisons of partial large subunit (28S) rDNA sequences indicate that these two species are clearly different from other species within the genus.

Phosphorus limitation and starvation effects on cell growth and lipid accumulation in Isochrysis galbana U4 for biodiesel production

The effect of varying levels of phosphorus (P) on Isochrysis galbana U4 growth, pigmentation and lipid accumulation were investigated. A reduction in the P content to 25% of the recommended level for f/2 medium did not lead to declines in cell growth rates or lipid accumulation levels relative to the cultures maintained on medium supplemented with the normal P dose. Evidence suggesting that the recommended P supply in f/2 exceeds the requirements for maximal algal growth has obvious economic implications for the mass production of I. galbana for biodiesel production. When P supply was in excess this species was also found to accumulate intracellular levels of P that exceeded by up to 6 times its P requirements for growth and cell division. The reduction in P concentration to levels below 25% resulted in P starvation stimulated chlorophyll reductions and carotenoid and lipid accumulation in this species.

Ultrastructure of Pyramimonas norrisii sp. nov. (Prasinophyceae)

The ultrastructure of Pyramimonas norrisii sp. nov. is described, based on material collected from Cape Town. This species displays characters consistent with the subgenus Vestigifera, but is unique in its scale morphology and flagellar apparatus configuration. The cell body is covered by four scale types, whilst the flagellar surfaces have three scale types, and the structures of these are outlined. The flagellar apparatus is basically of the rhombic type, but displays characters not previously recorded. This species is compared with other members of the genus having only a light microscope description.

Ultrastructure of Calyptrosphaera radiata, sp. nov. (Prymnesiophyceae, Haptophyta)

A novel member of the Calyptrosphaeraceae surrounded by a hyaline sheath, with only one chloroplast and without an emergent haptonema, is tentatively described as a species of Calyptrosphaera Lohmann. It has an interrupted body to its single pyrenoid and a unique microtubular root complement with only one crystalline root (CR) nucleating on root 2 (R2). At preprophase it produces a CR1, lending support to the idea that these crystalline roots contribute to the mitotic spindle. It shares numerous ultrastructural traits with the heterococcolithophorid Cruciplacolithus neohelis but, although it is tempting to consider it a haploid phase of this organism, is distinct from it.

Programmed Cell Death and Complexity in Microbial Systems

Programmed cell death (PCD) is central to organism development and for a long time was considered a hallmark of multicellularity. Its discovery, therefore, in unicellular organisms presents compelling questions. Why did PCD evolve? What is its ecological effect on communities? To answer these questions, one is compelled to consider the impacts of PCD beyond the cell, for death obviously lowers the fitness of the cell. Here, we examine the ecological effects of PCD in different microbial scenarios and conclude that PCD can increase biological complexity. In mixed microbial communities, the mode of death affects the microenvironment, impacting the interactions between taxa. Where the population comprises groups of relatives, death has a more explicit effect. Death by lysis or other means can be harmful, while PCD can evolve by providing advantages to relatives. The synchronization of death between individuals suggests a group level property is being maintained and the mode of death also appears to have had an impact during the origin of multicellularity. PCD can result in the export of fitness from the cell to the group level via re-usable resources and PCD may also provide a mechanism for how groups beget new groups comprising kin. Furthermore, PCD is a means for solving a central problem of group living - the toxic effects of death - by making resources in dying cells beneficial to others. What emerges from the data reviewed here is that while PCD carries an obvious cost to the cell, it can be a driver of complexity in microbial communities.

AN ADDITIONAL PUNCTATE SPECIES OF PYRAMIMONAS, P. FORMOSA, SP. NOV., AND ITS IMPACT ON THE SUBGENERA PUNCTATAE AND PYRAMIMONAS (PRASINOPHYCEAE, CHLOROPHYTA)

A new punctate species of Pyramimonas Schmarda from South Africa is described. This species is somewhat anomalous and, like P. chlorina Sym et Pienaar (subgenus Pyramimonas McFadden), has characters that bridge the divide between the subgenera Pyramimonas and Punctatae McFadden. Features of these two species, together with the lack of exclusive character sets for either subgenus derived from other species of these subgenera, lead to the conclusion that Punctatae now should be subsumed formally into the subgenus Pyramimonas.

Influence of nitrogen stress on Isochrysis galbana strain U4, a candidate for biodiesel production.

Lipid accumulation has been investigated in numerous microalgal species to assess their potential with respect to biodiesel production. The present work determines the effect of nitrogen stress on physiological and ultrastructural changes in Isochrysis galbana U4. This study is unique in showing the correlations between growth, lipid production, pigmentation and ultrastructural changes in Isochrysis cells undergoing nitrogen starvation. The continuation of algal growth after the complete depletion of external nitrogen was shown to be supported by internal nitrogen stores, possibly in the pyrenoid. Cell growth ceased and lipid accumulation was initiated after the internal store of nitrogen had become exhausted. The depletion of intracellular nitrogen reservoirs to critical thresholds initiated the onset of the stationary phase, a decline in chlorophyll content and the initiation of lipid and carotenoid accumulation. The most notable ultrastructural changes, upon nitrogen stress, were the accumulation of plastidial and cytoplasmic lipid bodies and the dismantling of the chloroplast. The size of the pyrenoid when external nitrogen became depleted was found to decrease significantly, up to four‐fold. This was attributed to the remobilization of nitrogen from Rubisco. The level of expression of heterochromatin was found to increase when cells were nitrogen starved. This is thought to favor long‐term dormancy in this species because aging cells have been noted to recover rapidly when returned to conditions favorable for growth. The observations of this study are consistent with the hypothesis that the responses of Isochrysis cells to nitrogen starvation are regulated by the internal reserves of nitrogen, and the depletion of these reserves is an important trigger for lipid accumulation in this species. The findings of this study also indicate that Isochrysis galbana U4 is a promising candidate for biodiesel lipid production.

Fine structure and systematics of Prymnesium radiatum sp. nov. (Prymnesiophyceae) from False Bay and Franskraal, South Africa

A novel colonial prymnesiophyte from the inshore waters of South Africa, which is reminiscent of the genus Corymbellus, is described at light and electron microscope levels. It differs from the only species of this genus, Corymbellus aureus, in scale structure, cell shape and colony morphology and has a complement of unusual morphological features that link it most with members of the Prymnesiales. Phylogenetic analyses of the nuclear-encoded SSU and LSU ribosomal DNA sequences indicate that this organism is closely related to members of the genus Prymnesium sensu lato and it is thus considered as a novel species, here named P. radiatum. The closest relative to P. radiatum in the SSU rDNA phylogenetic tree was Prymnesium neolepis (formerly Hyalolithus neolepis). The reconfiguration of the cytoskeleton during cell division in this organism is also novel, with a progressive elaboration of existing elements, rather than the massive reorganization expected in the prymnesiophytes.

Taxonomy of Pyramimonas obovata and other observations on the subgenus Vestigifera of Pyramimonas (Prasinophyceae, Chlorophyta)

A vestigiferan species commonly referred to as Pyramimonas obovata N. Carter has been redescribed as P. melkonianii sp, nov. Characters of this species and a further six (P. disomata Butcher ex McFadden, Hill et Wetherbee, P. mantoniae Moestrup et Hill, P. mitra Moestrup et Hill. P. moestrupii McFadden, P. aff. nephroidea McFadden, P. orientalis Butcher ex McFadden, Hill et Wetherbee) isolated from South African waters are used to define further the subgenus Vestigifera McFadden. This includes a unique chloroplast shape and basal hyaline region with stellate or cruciform vacuoles, a transitional plate‐like structure in the flagellum, and a different microtubular root system. The proximal set of basal body connectives were found to be remarkably symmetrical and like those of the subgenus Trichocystis McFadden, and a duct fibre was found associated with the Id root in all currently investigated species. The validity of the larger body (box and crown) scales as taxonomic markers at a fine level is also questioned.