The amino acid sequences of the cytochromes c553 from Porphyridium cruentum and Aphanizomenon flos-aquae

The amino acid sequences of cytochrome c₅₅₃ from the eukaryotic red alga Porphyridium cruentum and from the prokaryotic cyanobacterium Aphanizomenon flos-aquae have been determined from the tryptic and cyanogen bromide peptides. The results indicate that a charged region of these proteins has evolved with special rapidity to accomodate a rapid evolution of a binding site in the P₇₀₀ electron acceptor complex.     

CHANGES IN PHOTOSYNTHESIS IN RESPONSE TO COMBINED IRRADIANCE AND TEMPERATURE STRESS IN CYANOBACTERIAL SURFACE WATERBLOOMS1

Buoyant cyanobacteria, previously mixed throughout the water column, float to the lake surface and form a surface waterbloom when mixing subsides. At the surface, the cells are exposed to full sunlight, and this abrupt change in photon irradiance may induce photoinhibition; at the same time, temperature rises as well. This study investigated the damaging effects of this increase in temperature as well as the ecologically more relevant combination of both an increased temperature and a high photon irradiance. Analysis of surface blooms with oxygen microelectrodes showed that integrated oxygen contents that are dependent on the balance of photosynthetic oxygen evolution and respiratory oxygen uptake decreased when temperature was raised above the lake temperature. Gross rates of photosynthesis were unaffected by temperatures up to of 35°C; hence, a moderate increase in temperature mainly stimulated oxygen uptake. Preincubation of cells of the cyanobacterium Anabaena flos-aquae (Lyngb.) de Brébisson at temperatures up to 35°C did not affect the subsequent measurement of rates of net photosynthesis. Another 5°C rise in temperature severely damaged the photosynthetic apparatus. Failure to restore net rates of photosynthesis was coupled to a strong quenching of the ratio of variable to maximum fluorescence, F_v/F_m, that was the result of a rise in F_o. A combination of high temperature and high photon irradiance was more damaging than high temperature alone. In contrast, low photon irradiances offered substantial protection against heat injury of the photosynthetic apparatus. I conclude from this study that because cyanobacteria usually are acclimated to low average irradiance prior to bloom formation, there is a reasonable risk of chronic photoinhibition. The increase in temperature will enhance the photodamage of cells in the top layer of the bloom. Low photon irradiances in subsurface layers will offer protection against heat injury. If the high temperatures extend to the deepest, dark layers of the bloom, damage in those layers is likely to occur.     

KINETICS OF CELL DEATH IN THE CYANOBACTERIUM ANABAENA FLOS-AQUAE AND THE PRODUCTION OF DISSOLVED ORGANIC CARBON1

Kinetics of cell death and the production of dissolved organic carbon (DOC) were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown on three different N sources (N₂nitrate, and ammonium) in a phosphorus (P)-limited chemostat. The fraction of live cells in the total population increased as growth rate increased with decreasing P limitation. Cell death was less in nitrate and ammonium media than in N₂. The specific death rate (γ), when calculated as the slope ofv^?1_x vs. D^?1, where v_xand D are live cell fraction (or cell viability) and dilution rate, respectively, was 0. 0082 day^?1 in N₂and 0.0042 day^?1 in nitrate. The slope of the plot in ammonium culture was not significant; however, the value of the live cell fraction was within the range for the NO^?₃culture. The fraction of live vegetative cells in N₂ culture was constant at all growth rates and the increase in the overall live cell fraction with growth rate was due entirely to an increase in live heterocysts. Live heterocysts comprised 3.5% of the total cells at a growth rate of 0.25 day^?1 and increased to 6.3% at 0.75 day^?1 with the ratio of live heterocysts to live vegetative cells linearly increasing with growth rate. The fraction of live vegetative cells was invariant in nitrate cultures us in N₂cultures. The live heterocysts fraction also increased with growth rate in nitrate cultures, along with the live heterocysts : live vegetative cells ratio, but the level was lower than in N₂cultures. DOC released from dead cells increased inversely with growth rate in N₂from 36.4% of the total DOC at a growth rate of 0.75 day^?1 to 54.15% at 0.25 day^?1. The contribution of cell death to the total DOC production in nitrate and ammonium media was significantly less than that under N₂DOC from dead cells consisted mainly of high-molecular-weight compounds, whereas DOC excreted from live cells was largely of low molecular weight.     

Notes on the growth and sporulation of a natural population of Aphanizomenon flos-aquae

Aphanizomenon flos-aquae contributed regularly to the summer phytoplankton in Kinnego Bay, a highly eutrophic part of Lough Neagh. Growth of the alga was variable in different years, and was apparently related to the duration of depletion of dissolved nitrate-nitrogen in the water. Although four growth pulses occurred during the study period, sporulation was only observed during one of these, when the population was very dense although evenly distributed down the water column. It seems that Aphanizomenon overwintered in Kinnego Bay as vegetative filaments and that production of akinetes was not necessary for perennation of the species. The observed sporulation in 1973 may have been induced by the high pH values caused by dense phytoplankton crops; no other measured environmental factors were particularly unfavourable to growth of Aphanizomenon at this time.     

SPECIFIC ASSOCIATIONS OF THE BLUEGREEN ALGAE ANABAENA AND APHANIZOMENON WITH BACTERIA IN FRESHWATER BLOOMS1

Scanning electron micrographs and autoradiographs of Anabaena circinalis Rabenh. and Aphanizomenon flos-aquae (L.) Ralfs in samples from fresh-water communities show that bacteria are attached specifically at the polar region of heterocysts of these known N₂ fixers. This algal-bacterial association occurs most frequently during bloom conditions. The possible roles of this association in maintaining nuisance bloom conditions are discussed.     

Studies on marine algae of the British Isles. 8. Cystoseira tamariscifolia (hudson) papenfuss

The fine structure of the zoospores of Urospora penicilliformis (Roth) Aresch. (Chlorophyceae) is described. Of special interest is the flagellar apparatus. The proximal part of each of the 4 flagella is ribbon-shaped and contains nine wings attached to the peripheral double tubules. The flagellar root system originates from the flagellar bases and includes striated fibrous roots, passing close to the nucleus, and cruciate nine-stranded microtubular roots along the four corners of the cell. The Golgi bodies produce numerous vesicles, concentrating apically in the cell; they are presumed to be of importance for the attachment of the zoospore.     

Effects of thermal acclimation and photoacclimation on lipophilic pigments in an invasive and a native cyanobacterium of temperate regions

The freshwater cyanobacterium Cylindrospermopsis raciborskii spreads from tropical to temperate regions worldwide. This entails acclimation to varied light and temperature conditions. We studied the thermal and light acclimation of the photosynthetic machinery of C. raciborskii by monitoring alteration of the chlorophyll a and carotenoid content in German strains of C. raciborskii, in African and Australian strains of C. raciborskii, and in German strains of Aphanizomenon gracile, a native cyanobacterium belonging to the same order (Nostocales). Our results showed that temperate and tropical C. raciborskii strains did not differ in pigment acclimation to light and temperature. In contrast, the ratio of photoprotective carotenoids (namely the carotenoid glycoside 4-hydroxymyxol glycoside [aphanizophyll]) to chlorophyll a increased significantly more in C. raciborskii in comparison with A. gracile (1) with decreasing temperatures from 20 to 10°C and a moderate light intensity of 80?µmol photons m^?2?s^?1 and (2) with increasing light intensities at a suboptimal temperature of 15°C, compared to 20°C. We conclude that below 20°C photoinhibition is avoided by greater photoprotection in the invasive species C. raciborskii compared to the native species A. gracile.     

MONOSPECIFIC AGGREGATIONS OF TWO CYANOPHYTES IN A EUTROPHIC LAKE1

Microcystis incerta Lemmerman, and Lyngbya versicolor (Wartmann) Gomont, formed large monospecific aggregations on the surface of a lake rich in Aphanizomenon flos-awuae (L.) Ralfs. Neither of the two algae in the aggregations was found in the water beneath.     

Importance of interspecific competition in the abundance of Aphanizomenon flos-aquae (Cyanophyceae)

The population dynamics of Aphanizomenon flos-aquae var. klebahnii Elenk. (Cyanophyceae) was studied in an artificial pond for 32 months from May 2002 to December 2004. Our previous in vitro study showed that the lower limits of water temperature and pH for its growth are within the ranges of 11°–14°C and 7.1–7.4, respectively, and it appeared that these findings are applicable to the emergence and disappearance of Ap. flos-aquae in the pond. Based on the change in the water temperature, the emergence of Ap. flos-aquae in 2004 was expected to be in late April, whereas emergence occurred after a 1-month lag period. During this period, Ankistrodesmus falcatus (Corda) Ralfs (Chlorophyceae) dominated the phytoplankton assemblage, which raised the possibility that the growth of Ap. flos-aquae was restricted by the existence of An. falcatus. We conducted mixed cultures of Ap. flos-aquae and An. falcatus at four temperatures (14°, 19°, 24°, and 29°C). After 18 days of incubation, An. falcatus dominated at 14° and 29°C whereas Ap. flos-aquae dominated at 19°C. This result indicates that a slightly higher water temperature than the growth threshold value is needed for Ap. flosaquae to outcompete An. falcatus, which agrees with the field observation. Contrary to the results of the mixed culture, the summer phytoplankton assemblage was dominated by Ap. flos-aquae, and the population of An. falcatus was less or almost absent. This variation seemed to be partly caused by the difference in nutrient conditions; concentrations of dissolved inorganic nitrogen and phosphorus in the pond were far lower than those in the culture medium. The lack of nitrogen fixation of An. falcatus seemed to be a growth disadvantage during the summer when the concentration of dissolved inorganic nitrogen was low.     

The formation and degradation of cyanobacterium Aphanizomenon flos-aquae blooms: the importance of pH, water temperature, and day length

Investigation of annual changes in phytoplankton community structure in a small artificial eutrophic pond was carried out from May 2002 to April 2003. A heavy bloom of Aphanizomenon flos-aquae var. klebahnii Elenk. (Cyanobacteria) persisted in most of the water column from June to the end of October. In November, the A. flos-aquae bloom suddenly crashed and green algae were predominant until the end of spring. Weekly monitoring suggested strong involvement of the changes in abiotic factors in the cyanobacterial bloom degradation. To clarify the effects of pH, water temperature, and day length on the growth of A. flos-aquae, laboratory batch experiments were conducted. The results showed that A. flos-aquae could not grow below pH 7.1 and 11°C, and the growth tended to be suppressed under a 10L:14D photoperiod. pH, water temperature, and day length are vital factors in the growth of A. flos-aquae and, additionally, grazing by cyclopoid copepods also seemed important in bloom collapse.