Carpospore early development and callus-like tissue induction of <Emphasis Type="Italic">Chrysymenia wrightii</Emphasis> (Rhodymeniaceae,Rhodophyta) under laboratory conditions

Morphological and culture studies of germlings derived from carpospores of Chrysymenia wrightii (Harvey) Yamada were carried out under various treatments combining temperature and irradiance. Basal, main, and tip branches were applied for inducing callus-like tissue. Focus was on how carpospores develop into germlings, how callus-like tissues are induced from explants, and how temperature and irradiance affect carpospore germination and discoid crust growth. Results show that carpospore development can be divided into three stages: division stage, discoid crust stage, and erect juvenile germling stage. Discoid crusts, even more than ten, might coalesce into a big discoid crust, and then developed into germlings. Filamentous fronds, formed on the rims of discoid crusts, exhibited in self-existence or co-existence form with germlings, could form spherical tufts if cultured separately. Filamentous callus-like tissues appeared on the tip branches after 13 days. PES is suitable for filament induction and culture, and filaments have potential use in germplasm preservation and vegetative propagation. Temperature (10, 15, 20, 25°C) and irradiance (8 and 36 μmol photons m⁻² s⁻¹) significantly influenced carpospore germination rate and discoid crust diameter. Carpospores germinated normally under 36 μmol photons m⁻² s⁻¹, 15~25°C, and maximum growth of discoid crusts was at 25°C, 36 μmol photons m⁻² s⁻¹; 10°C and 8 μmol photons m⁻² s⁻¹ did not favor carpospore germination or discoid crust growth.     

Optimization of photosynthesis,growth, and biochemical composition of the microalga <Emphasis Type="Italic">Rhodomonas salina</Emphasis>—an established diet for live feed copepods in aquaculture

The cryptophyte Rhodomonas salina is widely used as feed for copepod cultures. However, culturing conditions to obtain high-quality algae have not yet been efficiently optimized. Therefore, we aimed to develop a cultivation protocol for R. salina to optimize its nutritional value and provide technical recommendations for later large-scale production in algal photobioreactors. We studied photosynthesis, growth, pigments, fatty acid (FA) and free amino acid (FAA) composition of R. salina cultured at different irradiances (10–300 μmol photons m^?2 s^?1) and nutrient availability (deficiency and excess). The optimal range of irradiance for photosynthesis and growth was 60–100 μmol photons m^?2 s^?1. The content of chlorophylls a and c decreased with increasing irradiance while phycoerythrin peaked at irradiances of 40–100 μmol photons m^?2 s^?1. The total FA content was maximal at optimal irradiances for growth, especially under nutrient deficiency. However, highly unsaturated fatty acids, desired components for copepods, were higher under nutrient excess. The total FAA content was highest at limiting irradiances (10–40 μmol photons m^?2 s^?1) but a better composition with a higher fraction of essential amino acids was obtained at saturated irradiances (60–140 μmol photons m^?2 s^?1). These results demonstrate that quality and quantity of FA and FAA of R. salina can be optimized by manipulating the irradiance and nutrient conditions. We suggest that R. salina should be cultivated in a range of irradiance 60–100 μmol photons m^?2 s^?1 and nutrient excess to obtain algae with high production and a balanced biochemical composition as feed for copepods.     

Photosynthetic characteristics of female vegetative tissues of Porphyra katadai var. hemiphylla (Bangiales, Rhodophyta) in culture

In this study, chlorophyll fluorescence parameters (?F/F _m′, F _v/F _m) and oxygen evolution of female vegetative tissues of Porphyra katadai var. hemiphylla in unisexual culture (FV) and in mixed culture with male vegetative tissues (FV-M) were followed at 5–20 °C, 10 and 80 μmol photons m^?2 s^?1. The formation of reproductive tissues was closely correlated with decreasing photosynthetic activities. At the same temperature the tissues cultured under 80 μmol photons m^?2 s^?1 showed a greater extent of maturation than those under 10 μmol photons m^?2 s^?1, and their decrease in photosynthesis was also larger. Under the same light intensity the extent of maturation increased with increasing temperature, and both cultures showed higher values of ?F/F _m′ and F _v/F _m at 10 and 15 °C, while their oxygen evolution became negative at 15–20 °C during the later period. Under the same culture condition the maturation of FV-M culture was relatively faster than that of FV culture, while their photosynthetic activity, especially ?F/F _m′, was lower.     

Optimization of cultivation conditions for fatty acid composition and EPA production in the eustigmatophycean microalga Trachydiscus minutus

We determined the effects of cultivation conditions (nitrogen source, salinity, light intensity, temperature) on the composition of polyunsaturated fatty acids (PUFAs) and the production of eicosapentaenoic acid (EPA) in the laboratory cultured eustigmatophycean microalga, Trachydiscus minutus. T. minutus was capable of utilizing all nitrogen compounds tested (potassium nitrate, urea, ammonium nitrate, ammonium carbonate) with no differences in growth and only minor differences in fatty acid (FA) compositions. Ammonium carbonate was the least appropriate for lipid content and EPA production, while urea was as suitable as nitrates. Salinity (0.2 % NaCl) slightly stimulated EPA content and inhibited growth. Increasing salinity had a marked inhibitory effect on growth and PUFA composition; salinity at or above 0.8 % NaCl was lethal. Both light intensity and temperature had a distinct effect on growth and FA composition. The microalga grew best at light intensities of 470–1,070 μmol photons m^?2 s^?1 compared to 100 μmol photons m^?2 s^?1, and at 28 °C; sub-optimal temperatures (20, 33 °C) strongly inhibited growth. Saturated fatty acids increased with light intensity and temperature, whereas the reverse trend was found for PUFAs. Although the highest level of EPA (as a proportion of total FAs) was achieved at a light intensity of 100 μmol photons m^?2 s^?1 (51.1?± 2.8 %) and a temperature of 20 °C (50.9?±?0.8 %), the highest EPA productivity of about 30 mg L^?1?day^?1 was found in microalgae grown at higher light intensities, at 28 °C. Overall, for overproduction of EPA in microalgae, we propose that outdoor cultivation be used under conditions of a temperate climatic zone in summer, using urea as a nitrogen source.     

Ecophysiological analysis of moss-dominated biological soil crusts and their separate components from the Succulent Karoo, South Africa

Biological soil crusts, formed by an association of soil particles with cyanobacteria, lichens, mosses, fungi and bacteria in varying proportions, live in or directly on top of the uppermost soil layer. To evaluate their role in the global carbon cycle, gas exchange measurements were conducted under controlled conditions. Moss-dominated soil crusts were first analyzed as moss tufts on soil, then the mosses were removed and the soil was analyzed separately to obtain the physiological response of both soil and individual moss stems. Net photosynthetic response of moss stems and complete crusts was decreased by insufficient and excess amounts of water, resulting in optimum curves with similar ranges of optimum water content. Light saturation of both sample types occurred at high irradiance, but moss stems reached light compensation and saturation points at lower values. Optimum temperatures of moss stems ranged between 22 and 27°C, whereas complete crusts reached similar net photosynthesis between 7 and 27°C. Under optimum conditions, moss stems reached higher net photosynthesis (4.0 vs. 2.8 μmol m^?2 s^?1) and lower dark respiration rates (?0.9 vs. ?2.4 μmol m^?2 s^?1). Respiration rates of soil without moss stems were high (up to ?2.0 μmol m^?2 s^?1) causing by far lower absolute values of NP/DR ratios of soil crusts as compared to moss stems. In carbon balances, it therefore has to be clearly distinguished between measurements of soil crust components versus complete crusts. High rates of soil respiration may be caused by leaching of mosses, creating high-nutrient microsites that favor microorganism growth.     

Irradiance optimization of outdoor microalgal cultures using solar tracked photobioreactors

Photosynthetic activity and temperature regulation of microalgal cultures (Chlorella vulgaris and Scenedesmus obliquus) under different irradiances controlled by a solar tracker and different cell densities were studied in outdoor flat panel photobioreactors. An automated process control unit regulated light and temperature as well as pH value and nutrient concentration in the culture medium. CO₂ was supplied using flue gas from an attached combined block heat and power station. Photosynthetic activity was determined by pulse amplitude modulation fluorometry. Compared to the horizontal irradiance of 55 mol photons m^?2 d^?1 on a clear day, the solar tracked photobioreactors enabled a decrease and increase in the overall light absorption from 19 mol photons m^?2 d^?1 (by rotation out of direct irradiance) to 79 mol photons m^?2 d^?1 (following the position of the sun). At biomass concentrations below 1.1 g cell dry weight (CDW) L^?1, photoinhibition of about 35 % occurred at irradiances of ≥1,000 μmol photons m^?2 s^?1 photosynthetic active radiation (PAR). Using solar tracked photobioreactors, photoinhibition can be reduced and at optimum biomass concentration (≥2.3 g CDW L^?1), the culture was irradiated up to 2,000 μmol photons m^?2 s^?1 to overcome light limitation with biomass yields of 0.7 g CDW mol photons^?1 and high photosynthetic activities indicated by an effective quantum yield of 0.68 and a maximum quantum yield of 0.80 (F _v/F _m). Overheating due to high irradiance was avoided by turning the PBR out of the sun or using a cooling system, which maintained the temperature close to the species-specific temperature optima.     

Biomass and terpenoids produced by mutant strains of <Emphasis Type="Italic">Arthrospira</Emphasis> under low temperature and light conditions

The filamentous Cyanobacterium Arthrospira is commercially produced and is a functional, high-value, health food. We identified 5 low temperature and low light intensity tolerant strains of Arthrospira sp. (GMPA1, GMPA7, GMPB1, GMPC1, and GMPC3) using ethyl methanesulfonate mutagenesis and low temperature screening. The 5 Arthrospira strains grew rapidly below 14?°C, 43.75 μmol photons m^?2 s^?1 and performed breed conservation at 2.5?°C, 8.75 μmol photons m^?2 s^?1. We used morphological identification and molecular genetic analysis to identify GMPA1, GMPA7, GMPB1 and GMPC1 as Arthrospira platensis, while GMPC3 was identified as Arthrospira maxima. Growth at different culture temperatures was determined at regular intervals using dry biomass. At 16?°C and 43.75 μmol photons m^?2 s^?1, the maximum dry biomass production and the mean dry biomass productivity of GMPA1, GMPB1, and GMPC1 were 2057?±?80 mg l^?1, 68.7?±?2.5 mg l^?1 day^?1, 1839?±?44 mg l^?1, 60.6?±?1.8 mg l^?1 day^?1, and 2113?±?64 mg l^?1, 77.7?±?2.5 mg l^?1 day^?1 respectively. GMPB1 was chosen for additional low temperature tolerance studies and growth temperature preference. In winter, GMPB1 grew well at mean temperatures <10?°C, achieving 3258 mg dry biomass from a starting 68 mg. In summer, GMPB1 grew rapidly at mean temperatures more than 28?°C, achieving 1140 mg l^?1 dry biomass from a starting 240 mg. Phytonutrient analysis of GMPB1 showed high levels of C-phycocyanin and carotenoids. Arthrospira metabolism relates to terpenoids, and the methyl-d-erythritol 4-phosphate pathway is the only terpenoid biosynthetic pathway in Cyanobacteria. The 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) gene from GMPB1 was cloned and phylogenetic analysis showed that GMPB1 is closest to the Cyanobacterium Oscillatoria nigro-viridis PCC711. Low temperature tolerant Arthrospira strains could broaden the areas suitable for cultivation, extend the seasonal cultivation time, and lower production costs.     

The effect of irradiance and temperature responses and the phenology of a native alga,Undaria pinnatifida (Laminariales), at the southern limit of its natural distribution in Japan

Phenology, irradiance, and temperature characteristics of an edible brown alga, Undaria pinnatifida (Laminariales), were examined from the southernmost natural population in Japan, both by culturing gametophytes and examining the photosynthetic activity of sporophytes using dissolved oxygen sensors and pulse amplitude-modulated chlorophyll fluorometer (IMAGING-PAM). Our surveys confirmed that sporophytes were present between winter and early summer, but absent by July. IMAGING-PAM experiments were used to measure maximum effective quantum yield (ΦII at 0 μmol photons m^?2 s^?1) for each of 14 temperatures (8–36 °C). Oxygen production was also determined over a coarser temperature gradient. Net photosynthesis and ΦII (at 0 μmol photons m^?2 s^?1) were observed to be temperature-dependent; the maximum ΦII was estimated to be 0.67, occurred at 21.2 °C, and was nearly identical to the optimal temperature of the net photosynthetic rate (21.7 °C). A net photosynthesis–irradiance (P–E) model revealed that saturation irradiance (E _k) was 119.5 μmol photons m^?1 s^?1, and the compensation irradiance (E _c) was 17.4 μmol photons m^?1 s^?1. Culture experiments on the gametophytes revealed that most individuals could not survive temperatures over 28 °C and that growth rates were severely inhibited. Based on our observations, temperatures greater than 20 °C are likely to influence photosynthetic activity and gametophyte survival, and therefore, it is possible that this species might become locally extinct if seawater temperatures in this region continue to rise.     

2-Methylisoborneol production characteristics of <Emphasis Type="Italic">Pseudanabaena</Emphasis> sp. FACHB 1277 isolated from Xionghe Reservoir,China

The cyanobacterium Pseudanabaena sp. FACHB 1277, a 2-methylisoborneol (2-MIB) producer isolated from Xionghe Reservoir, was identified by molecular biological methods based on the 16S rDNA sequence. Pseudanabaena sp. FACHB 1277 is a planktonic freshwater species with relatively high 2-MIB per cell density value (7.76?×?10^?6 ng cell^?1) and specific growth rate (0.25?±?0.01 d^?1). The effects of temperature and light intensity on 2-MIB production of Pseudanabaena sp. FACHB 1277 were investigated. Of the six temperatures tested, 10, 15, 20, 25, 30, and 35 °C, the maximum total 2-MIB per cell density and minimum cell density were observed at 10 °C, while the total 2-MIB and dissolved 2-MIB (including extracellular and dissolved intracellular 2-MIB) increased with increasing temperature. Among the six tested light intensities (10, 25, 40, 55, 70, and 85 μmol photons m^?2 s^?1), the minimum total 2-MIB per cell density and maximum cell density were observed at 25 μmol photons m^?2 s^?1. The total 2-MIB and extracellular 2-MIB increased with light intensity increasing from 10 to 40 μmol photons m^?2 s^?1, while no significant increase was observed when the light intensity was higher than 40 μmol photons m^?2 s^?1. The maximum intracellular 2-MIB (including dissolved and bound) occurred at 25 μmol photons m^?2 s^?1. The present study indicates that increasing temperature could favor the conversion of bound intracellular to dissolved 2-MIB, while increasing light intensity stimulates the release of dissolved intracellular 2-MIB into the environment.     

The effects of temperature and light intensity on growth,reproduction and EPS synthesis of a thermophilic strain related to the genus Graesiella

Tunisian microalgae are diverse and rarely been studied. This study reports a first investigation of thermophile Chlorophyta isolated from mats community colonizing the geothermal springs in the north of Tunisia at water temperature 60 °C. In the study, the combined effect of temperature and light intensity was investigated on the cell growth, the mother and daughter cells abundance and the extracellular polymeric substances synthesis in batch culture of the isolated species. Three levels were tested for each factor, 20, 30, 40 °C for temperature; and 20, 70, 120 μmol photons m^?2 s^?1 for light intensity, using full factorial design and response surface methodology. The thermophile strain was identified as a genus Graesiella and showed 99.8 % similarity with two Graesiella species: Graesiella emersonii and Graesiella vacuolata based on the 18S rDNA molecular identification. The optimal growth condition was found at 30 °C and 120 µmol photons m^?2 s^?1 (7 MC mL^?1 day^?1), with the abundance of vegetative cells (daughter cells). In contrast, the number of mother cells increased significantly as the growth decreased; consequently, the highest ratio of auto spore mother cells versus daughter cells (19.4) was obtained at 20 °C and 20 µmol photons m^?2 s^?1. The highest yield of EPS production (11.7 mg L^?1 day^?1) was recorded at the highest temperature (40 °C) and lowest light intensity (20 µmol photons m^?2s^?1). These results revealed how the species respond to high and low temperatures and suggest that the species should be considered as facultative thermophile.     

Dominance of a 675?nm chlorophyll(ide) form upon selective 632.8 or 654?nm laser illumination after partial protochlorophyllide phototransformation

The phototransformation pathways of protochlorophyllide forms were studied in 8?C14-day-old leaves of dark-germinated wheat (Triticum aestivum L.) using white, 632.8?nm He?CNe laser and 654?nm laser diode light. The photon flux density (PFD) values (0.75?C360???mol photons?m^?2?s^?1), the illumination periods (20?ms?C10?s) and the temperature of the leaves (between ?60?°C and room temperature) were varied. The 77?K fluorescence spectra of partially phototransformed leaves showed gradual accumulation or even the dominance of the 675?nm emitting chlorophyllide or chlorophyll form at room temperature with 632.8?nm of PFD less than 200???mol photons?m^?2?s^?1 or with 654?nm of low PFD (7.5???mol photons?m^?2?s^?1) up to 1?s. Longer wavelength (685 or 690?nm) emitting chlorophyllide forms appeared at illuminations under ?25?°C with both laser lights or at room temperature when the PFD values were higher or the illumination period was longer than above. We concluded that the formation of the 675?nm emitting chlorophyllide form does not indicate the direct photoactivity of the 633?nm emitting protochlorophyllide form; it can derive from 644 and 657?nm forms via instantaneous disaggregation of the newly-produced chlorophyllide complexes. The disaggregation is strongly influenced by the molecular environment and the localization of the complex.     

Embryology of zygote and development of germling in Sargassum vachellianum Greville (Fucales,Phaeophyta)

Sargassum vachellianum Greville is one of the most important members in the subtidal seaweed flora along the coasts of the Eastern China Sea. In order to understand the embryology of zygotes and development of germlings in S. vachellianum, we performed artificial ripening, systematically observed the morphological changes and development of the fertilized eggs and germlings, and explored the effects of culture conditions on the growth of the germlings. The receptacles matured, and eggs and sperm were released after 1–5 days of culture at 21–24 °C under 60–90 μmol photons m^?2 s^?1 (14L:10D). Once fertilized, zygotes immediately detached from the female receptacles and began to germinate. Eight nuclei in the released fresh zygote soon begun to fuse, forming a large central nucleus, and underwent two horizontal divisions to produce a small “original rhizoid cell,” which eventually formed rhizoids after several divisions, and three other cells which eventually formed landmine-like germlings after several continuous divisions. The germlings then formed rhizoids and attached onto the bottom of the flask within 12 h of culture. The growth and development of the germlings younger than 20 days were significantly influenced by the culture temperature and light, with the optimal conditions being 21 °C and 40 μmol photons m^?2 s^?1. However, for germlings older than 30 days, the optimal conditions were 24 °C and 60 μmol photons m^?2 s^?1.     

A high-throughput method for measuring growth and loss rates in microalgal cultures

A miniaturized and low-cost assay for algal growth and loss rates, and estimation of compensation light was developed and optimized. Microalgal cultures were grown in white 96-well microplates to estimate specific growth rates at six temperatures, five salinities and eight light levels. Data from black 24-well microplates at six temperatures, five salinities and five light conditions were used in addition to estimate loss rates and compensation light. Absorption and reflection of light were different in the white and black microplates. Growth rates were estimated from daily in vivo fluorescence (IVF) measurements using a microplate reader fitted with a fluorometer. To validate the microplate algal growth assay, IVF was compared with cell counting by flow cytometry. Maximal growth rate for the test alga Pseudochattonella farcimen (Heterokonta) was estimated to 0.52?±?0.05 day^?1 at optimal temperatures ranging from 9 to 14°C and salinities 18–26 psu. Lowest value of compensation light as photosynthetic photon flux density (PPFD) was 4.2?±?1.2 μmol photons m^?2 s^?1, and lowest saturation light, 34.1?±?3.7 μmol photons m^?2 s^?1, was observed in the temperature range 5–11°C and salinity range 23–28 psu. Minimum loss rate was obtained at temperatures 5–8°C and salinities 26–31 psu. Blooms of P. farcimen have been recorded in nature under conditions similar to those minimizing loss rates rather than maximizing growth rates in this study. The microalgal assay described here allows for a large number of conditions to be tested, and accurate optimal conditions for growth and loss rates to be obtained.     

Effects of flashing light-emitting diodes on algal biomass productivity

To reduce power consumption and enhance algal biomass productivity in a thin flat-plate bioreactor (called a sliver tank bioreactor), flashing (pulsing) light was used. Biomass productivity and power consumption were monitored in controlled experiments using various photon flux levels, including a constant (non-flashing) flux of 75 μmol photons m^?2 s^?1 and three flashing experiments with photon fluxes of 375, 275, and 175 μmol photons m^?2 s^?1. Flashing experiments were performed at 10 kHz and a duty cycle of 20 %. A sliver tank bioreactor with a chamber width of 6.4 mm was used for its short optical path. Data from the experiments where light was flashed with a photon flux of 375 μmol photons m^?2 s^?1 indicated 9.6 % less power and 2.86 times the biomass productivity compared to the constant photon flux experiments. Similar results were obtained for the other flashing light regimes, which had lower biomass yields but also less input power per unit biomass produced, indicating that a large fraction of the continuously applied photons are shed or wasted, even at levels approximately 1/30th the intensity of full sun.     

Effects of irradiance and salinity on the growth of carpospore-derived tetrasporophytes of Gracilaria edulis and Gracilaria tenuistipitata var liui (Rhodophyta)

Gracilaria edulis and Gracilaria tenuistipitata var liui are agarophytes with high commercial value which are currently cultivated in countries like India and Thailand. They have great potential for mariculture in Malaysia. Experiments were carried out to study carpospore germination and determine the effects of irradiance and salinity on the growth of these two species. Both species showed the Dumontia type of carpospore development. Both species showed increased daily growth rate (% day^?1) with increasing irradiance and tolerance for a wide range of salinity with a preference for low salinity. G. edulis grew best at 100 μmol photons m^?2 s^?1 and 15 psu while G. tenuistipitata var liui grew best at 60–130 μmol photons m^?2 s^?1 and 15 psu. The highest growth rate obtained for G. edulis and G. tenuistipitata var liui was 13.57 and 19.7 % day^?1 respectively. tenuistipitata var liui. ANOVA showed that both irradiance and salinity have significant effect on the growth of both species (P?<?0.05). The results showed that G. tenuistipitata var liui is a good candidate for mass cultivation in Malaysian brackish waters. Besides, this study also showed the feasibility of using spore culture to provide stocks for sustainable farming of Gracilaria.     

The effects of different light intensities on the culture of Gigartina skottsbergii (Rhodophyta,Gigartinales) tetrasporophytes and gametophytes in the Magellan region,Chile

Gigartina skottsbergii is a red seaweed used as raw material for extracting carrageenans, constituting an important economic resource for Chile. In 2009, extraction in the Magellan region reached 15,064 t. The growing demand has adversely affected the sustainability of natural beds, creating an interest in the culture of this resource. In order to provide information relevant to the culture and regeneration of this seaweed, the present study addresses the effects of different light intensities on the growth of G. skottsbergii gametophytes and tetrasporophytes during the early stages of development. Mature reproductive fronds were induced to release spores in the laboratory by a drying process. Gametophytes cultured at different light intensities showed an increase in diameter, which reached 519.13?±?108.95 μm with 4 μmol photons m^?2 s^?1, while tetrasporophytes showed a greater increase in diameter, reaching 714.11?±?116.45 μm with 8 μmol photons m^?2 s^?1. Results indicate that both stages of the reproductive cycle are influenced by different light intensities within a limited range. Therefore, both phases require different and specific ranges of light intensity.     

SHORT‐TERM EFFECT OF TEMPERATURE ON THE PHOTOKINETICS OF MICROALGAE FROM THE SURFACE LAYERS OF ANTARCTIC PACK ICE1

Microalgae growing within brine channels (85 psu salinity) of the surface ice layers of Antarctic pack ice showed considerable photosynthetic tolerance to the extreme environmental condition. Brine microalgae exposed to temperatures above ?5°C and at irradiances up to 350 μmol photons·m^?2·s^?1 showed no photosynthetic damage or limitations. Photosynthesis was limited (but not photoinhibited) when brine microalgae were exposed to ?10°C, provided the irradiance remained under 50 μmol photons·m^?2·s^?1. The highest level of photosynthetic activity (maximum relative electron transport rate [rETR_max]) in brine microalgae growing within the surface layer of sea ice was at approximately 18 μmol electrons·m^?2·s^?1, which occurred at ?1.8°C. Effective quantum yield of PSII and rETR_max of the halotolerant brine microalgae exhibited a temperature‐dependent pattern, where both parameters were higher at ?1.8°C and lower at ?10°C. Relative ETR_max at temperatures above ?5°C were stable across a wide range of irradiance.     

Variation in cell size of the diatom <Emphasis Type="Italic">Coscinodiscus granii</Emphasis> influences photosynthetic performance and growth

Cell size has implications for the package effect in photon absorption as well as for metabolic scaling of metabolism. In this study, we have avoided species-related differences by using isolates of the marine planktonic diatom Coscinodiscus granii with cells of different sizes and grown at different light intensities to investigate their energy allocation strategies. To make full use of incident light, several fold variations in cellular chlorophyll a content were employed across cell size. This modulation of pigment-related light absorbance was deemed effective as similar light absorbing capacities were found in all treatments. Unexpected low values of O₂ evolution rate at the highest irradiance level of 450 μmol photons m^?2 s^?1 were found in medium and large cells, regardless of more photons being absorbed under these conditions, suggesting the operation of alternative electron flows acting as electron sinks. The growth rate was generally larger at higher irradiance levels except for the large cells, in which growth slowed at 450 μmol photons m^?2 s^?1, suggesting that larger cells achieved a balance between growth and photoprotection by sacrificing growth rate when exposed to high light. Although the ratio of carbon demand to rates of uncatalysed CO₂ diffusion to the cell surface reached around 20 in large cells grown under higher irradiance, the carbon fixation rate was not lowered, due to the presence of a highly effective carbon dioxide concentrating mechanism.     

Effects of light and temperature on the odor production of 2-methylisoborneol-producing Pseudanabaena sp. and geosmin-producing Anabaena ucrainica (cyanobacteria)

Frequent off-flavor events caused by geosmin and 2-methylisoborneol (MIB) have attracted research on the main producers, cyanobacteria. This study evaluated the effects of light and temperature on the odor production of MIB-producing Pseudanabaena sp. Lauterborn and geosmin-producing Anabaena ucrainica (Schhorb.) Watanabe. The maximum MIB production and lowest growth rate (indicated by the chlorophyll a (Chl a)) were observed at 35 °C compared with that at 10 °C and 25 °C. Cultures grown under a light intensity of 60 μmol photons m⁻² s⁻¹ demonstrated the highest MIB production and minimum growth rate, whereas the minimum MIB production and maximum growth rate were obtained under 10 μmol photons m⁻² s⁻¹. Similar patterns were observed for geosmin production. A. ucrainica had the highest geosmin production and lowest Chl a concentration under 10 °C and 60 μmol photons m⁻² s⁻¹. Moreover, greater proportions of geosmin and MIB were released into extracellular under growth-inhibiting temperatures and light intensities. An inverse correlation between odor production and the cell growth rate was suggested, and this relationship may reflect the competition for substrates of odor and Chl a synthesis. Thus, the accumulation of geosmin and MIB was probably the result of decreased cellular metabolic activity in cyanobacteria.     

First description of the environmental niche of the epibenthic dinoflagellate species Coolia palmyrensis,C. malayensis,and C. tropicalis (Dinophyceae) from Eastern Australia

Environmental variables such as temperature, salinity, and irradiance are significant drivers of microalgal growth and distribution. Therefore, understanding how these variables influence fitness of potentially toxic microalgal species is particularly important. In this study, strains of the potentially harmful epibenthic dinoflagellate species Coolia palmyrensis, C. malayensis, and C. tropicalis were isolated from coastal shallow water habitats on the east coast of Australia and identified using the D1‐D3 region of the large subunit (LSU) ribosomal DNA (rDNA). To determine the environmental niche of each taxon, growth was measured across a gradient of temperature (15–30°C), salinity (20–38), and irradiance (10–200 μmol photons · m^?2 · s^?1). Specific growth rates of Coolia tropicalis were highest under warm temperatures (27°C), low salinities (ca. 23), and intermediate irradiance levels (150 μmol photons · m^?2 · s^?1), while C. malayensis showed the highest growth at moderate temperatures (24°C) and irradiance levels (150 μmol photons · m^?2 · s^?1) and growth rates were consistent across the range of salinity levels tested (20–38). Coolia palmyrensis had the highest growth rate of all species tested and favored moderate temperatures (24°C), oceanic salinity (35), and high irradiance (>200 μmol photons · m^?2 · s^?1). This is the first study to characterize the environmental niche of species from the benthic harmful algal bloom genus Coolia and provides important information to help define species distributions and inform risk management.