G. H. M. Jaworski

Enumeration of natural Microcystis populations

Three methods for estimating the cell concentrations of natural, colonial Microcystis populations are described, and the results are compared statistically. Ultrasonic disruption of colonies is most conveniently applied to dense populations and gives results comparable with those obtained by alkaline hydrolysis. Excessive exposure to ultrasonic waves may destroy cells. A regression relating cell concentration to mean colony volume can, subject to conditions described, give crude estimates of Microcystis at low population densities or in mixed populations.

The viability of akinetes of blue-green algae recovered from the sediments of Rostherne Mere

Akinetes from species of blue-green algae were recovered from the recent sediments of Rostherne Mere. Gas vacuolate populations of Aphanizomenon and Anabaena were cultured from sediment up to 18 and 64 years old respectively. Akinetes of blue-green algae may not only have a temporary, or overwintering, function but may also ensure long term survival.

The influence of carbon dioxide-depletion on growth and sinking rate of two planktonic diatoms in culture

Growth in relation to CO2-depletion and CO2-enrichment was investigated for the freshwater diatoms Asterionella formosa and Fragilaria crotonensis in batch cultures. Algal concentration and pH were measured during growth cycles, and inorganic carbon quantities determined by potentiometric Gran titrations and from pH-alkalinity relationships. After the primary growth with CO2-depletion and pH increase, successive CO2-enrichments induced further such cycles and produced a final three- to fivefold increase in algal biomass over that of unenriched controls. The extent of CO2-depletion, and pH rise, was greater in later cycles, indicative of some cellular adaptation. Values of pH reached 9·7 for Asterionella and 9·9 for Fragilaria. The lowest residual quantities of free CO2 were 0·1 and 0·03 μmol 1-1 for Asterionella and Fragilaria respectively, which were less than 0·05% of the corresponding residual quantities of total CO2. The primary limitation of CO2-uptake and growth was probably related to the concentra...

Comparative ultrastructural ontogeny of zoosporangia of Zygorhizidium affluens and Z. planktonicum, chytrid parasites of the diatom Asterionella formosa

The fine-structural development of the small, 5–10 m, operculate zoosporangia of the monocentric chytrids Zygorhizidium affluens and Z. planktonicum , growing as epibionts on the planktonic diatom Asterionella formosa , is compared. In both species, following encystment and germination, the germ tube grows over the surface of the diatom frutule and penetrates the host cells by squeezing between the upper and lower girdle lamellae. As the cyst enlarges to form a sporangium, the single lipid globule breaks up and disperses, an operculum differentiates and the nucleus divides. In both species, cleavage of the cytoplasm into zoospore initials is mainly achieved by the infurrowing of the plasmamembrane, although there may be some contribution from internal cleavage vesicles. Flagellar axoneme profiles are not observed in the sporangia until cytoplasmic cleavage is well advanced. Specialized zoospore organelles, such as the rumposome fibrillar vesicles and endoplasmic reticulum-delimited ‘ribosome core’, do not form until the later stages of zoospore differentiation. The taxonomic and functional implications of these observations are discussed.

Sporangium differentiation and zoospore fine-structure of the chytrid Rhizophydium planktonicum, a fungal parasite of Asterionella formosa

Sporangium development in the fungal parasite Rhizophydium planktonicum has been followed by electron microscopy using dual clonal cultures. Following zoospore encystment on Asterionella , a fine germ-hypha is produced which penetrates the host via the girdle lamella. The sporangium develops directly from the cyst and becomes delimited from the germ-hypha by the formation of a septum. The pre-cleavage sporangium develops a thickened apical wall (a papilla) which ultimately gives rise to a vesicle which surrounds the emerging zoospores. This pattern of vesicle formation differs significantly from that so far described in other chytrid species. The nucleus undergoes mitosis before the sporangium cytoplasm becomes cleaved into uninucleate zoospore initials by the formation of an internal furrow system. Specialized zoospore organelles such as the lipid-associated rumposome and paracrystalline bodies are not formed until zoospore initial delimitation is almost completed. The fine-structure of the mature zoospore was used to evaluate the current taxonomic status of this species, particularly in relation to two other chytrid parasites of this host ( Zygorhizidium affluens and Z. planktonicum ). In zoospores of R. planktonicum , the ribosome aggregates typical of this genus are not delimited by endoplasmic reticulum. Zoospores of this species also contain paracrystalline bodies and dense occlusions in the region where the flagellum enters the spore body. These features have previously only been noted in other genera and therefore it is concluded that this species is probably not closely related to other Rhizophydium spp.

A simple separation technique for purifying micro-algae

A simple separation technique using polycarbonate membrane filters for purifying microalgae is described.

Ultrastructural study of operculation (discharge apparatus) and zoospore discharge in zoosporangia of Zygorhizidium affluens and Z. planktonicum, chytrid parasites of the diatom Asterionella formosa

The development of opercula in sporangia of two monocentric chytrids, Zygorhizidium affluens and Z. planktonicum , is one of the earliest specialized events during zoosporogenesis. The mode of operculum differentiation is significantly different in the two species. In Z. affluens the clearly demarked lid-like operculum differentiates by the annular rupture of the sporangium wall, which remains sealed by an underlying pad of amorphous material. In Z. planktonicum , the operculum shows no obvious structural differentiation from the rest of the sporangium wall and develops at the top of an apical papilla. At the time of zoospore discharge in Z. affluens the pad of sealing wall material presumably erodes allowing the operculum lid to spring open. In Z. planktonicum , the operculum wall disintegrates around its rim and eventually tears open to release the zoospores. Fully differentiated zoospores of Z. planktonicum are surrounded by a loose fibrillar matrix, which probably binds the liberated spores together for a minute or two before dispersing and allowing the spores to swim away.

Variability in sinking rate of the freshwater diatom Asterionella formosa Hass.: The influence of the excess density of colonies

Changes in the densities of live and killed colonies of Asterionella formosa Hass. from both exponentially increasing and stationary phase cultures, were investigated in relation to variation in cell size and mean sinking rates. The small variations in apparent excess colony density (range: 152–254 kg m-3) between exponential and senescent cells could not alone account for the two- to six-fold observed differences in sinking rate. Neither the sinking rate nor the density were greatly affected by the diminution in cell size brought about by frequent subculturing.