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This work aimed to verify the effects of adding CO2 and irradiance to Kappaphycus alvarezii cultivation. Thalli were cultured in vitro for 2 weeks under low irradiance (50 μmol photons m−2 s−1) with the addition of CO2 according to the following concentrations: 142× 103 ppm (1CO2, 0.1 L min−1), 285 × 103 ppm (2CO2, 0.2 L min−1) and 428 × 103 ppm (3CO2, 0.3 L min−1), followed by culture under higher irradiance (200 μmol photons m−2 s−1) for 2 more weeks. Control had no CO2 addition. Afterwards, growth rate, chlorophyll a and carotenoid content were quantified. Samples were submitted to light microscopy and transmission electron microscopy. Growth rates of different treatments or control between experimental periods showed no significant differences, except for 2CO2 treatment at the end of each period. Kappaphycus alvarezii cultivated with CO2 addition showed cell wall thickening and increasing quantity of starch granules, chlorophyll a and carotenoids compared with control. Exposed to high irradiance, control samples showed signs of stress, such as changes in chloroplast, starch granules quantity decrease and total chlorophyll a and carotenoids increase. Samples cultivated with CO2 showed an increase in the quantity and size of the starch granules and an increase in the number of organelles (mitochondria) related to energy generation and cell construction (Golgi complex). Such alterations suggest cellular response after CO2 addition, such as the formation of starch reserves and cell wall thickening, which could make plants more tolerant to environmental stress during transport from indoor condition to sea farms. [ABSTRACT FROM AUTHOR]

Algal biomass refineries for sustainable transportation fuels, in particular biodiesel, will benefit from algal strain enhancements to improve biomass and lipid productivity. Specifically, the supply of inorganic carbon to microalgal cultures represents an area of great interest due to the potential for improved growth of microalgae and the possibility for incorporation with CO2 mitigation processes. Combinations of bicarbonate (HCO3−) salt addition and application of CO2 to control pH have shown compelling increases in growth rate and lipid productivity of fresh water algae. Here, focus was placed on the marine organism, Nannochloropsis gaditana, to investigate growth and lipid accumulation under various strategies of enhanced inorganic carbon supply. Three gas application strategies were investigated: continuous sparging of atmospheric air, continuous sparging of 5% CO2 during light hours until nitrogen depletion, and continuous sparging of atmospheric air supplemented with 5% CO2 for pH control between 8.0 and 8.3. These gas sparging schemes were combined with addition of low concentrations (5 mM) of sodium bicarbonate at inoculation and high concentration (50 mM) of sodium bicarbonate amendments just prior to nitrogen depletion. The optimum scenario observed for growth of N. gaditana under these inorganic carbon conditions was controlling pH with 5% CO2 on demand, which increased both growth rate and lipid accumulation. Fatty acid methyl esters were primarily comprised of C16:0 (palmitic) and C16:1 (palmitoleic) aliphatic chains. Additionally, the use of high concentration (50 mM) of bicarbonate amendments further improved lipid content (up to 48.6%) under nitrogen deplete conditions when paired with pH-controlled strategies. [ABSTRACT FROM AUTHOR]

The diatom Phaeodactylum tricornutum produces large quantities of lipids, especially triacylglycerols (TAGs) under nitrogen or phosphorus limitation. In this study, production of lipids and TAGs during this process was compared under conditions with different inputs of inorganic carbon. With an abundant supply of inorganic carbon, considerable accumulation of biomass, lipids, and TAGs was identified after a nitrogen/phosphorus-limiting 'induction incubation.' TAGs were still synthesized and accumulated even under inorganic carbon limitation with a cessation in the production of biomass and cellular lipids. This part of accumulated TAGs could be synthesized through recycling and transformation of other lipids such as glycolipids and phospholipids. Additionally, some alterations in the fatty acid profile following TAG accumulation were found. The content of the C16:0 fatty acid increased with decreases in C16:3 and C20:5, which could have been caused by enzymatic selectivity for these fatty acids during the process of TAG synthesis. It was concluded that nitrogen and phosphorus metabolism regulates the synthesis of TAG, while carbon metabolism promotes it by providing sufficient substrates. [ABSTRACT FROM AUTHOR]

To achieve sustainable production of biofuel from microalgae, a well-optimized and sustained biomass production is prerequisite. The major factor determining the higher productivity of algae is the availability and uptake of CO for biomass growth. In this study, an improved CO sequestration method leading to improved biomass yields has been investigated. The ability of OH ions in fixing dissolved CO in form of HCO in algal growth medium was studied using a Chlorella sp. and scaled-up in a photobioreactor. It was observed that a critical concentration of 0.005 M OH is required for HCO formation and utilization by algae. HCO uptake was enhanced by 70.8% (in presence of 0.01 M NaOH) with a sixfold increase in growth rate compared with only CO system. In mineral carbon systems such as NaHCO and NaCO, increase in HCO uptake was enhanced by 65.4% and 63.4%, respectively. The maximum rate of CO fixation of 6.6 mg L h was obtained with 0.01 M NaOH which was 1.5 times compared with mineral carbon sources. The biomass from scale-up experiment contained 16.3% lipid (by weight) of which 75% is unsaturated fatty acids (in total lipids). This supports the idea that fixing the dissolved CO in the form of bicarbonate using alkali helps in increased biomass productivity rather than CO itself, forms a precursor for biodiesel, and increases CO sequestration in a cyclic process. [ABSTRACT FROM AUTHOR]

The leafy gametophytic phase of Porphyra torta Krishnamurthy(Rhodophyta), a candidate species for mariculture in Alaska, grows only inwinter and early spring and is restricted to the outer coast of southeastAlaska. To help determine specific environmental factors limiting theseasonal and geographic distribution of this species, culture experimentswere conducted using environmentally realistic levels of three physicalfactors. Growth and phycoerythrin concentration in juvenile gametophyteswere compared under combinations of nitrate, salinity, and inorganiccarbon representing the maximum and minimum levels of each factor in themarine environment. Recovery experiments were also conducted todetermine whether blades affected by low nutrient or salinity levels couldregain normal growth rates and pigment levels. To make statistically validcomparisons of growth rates among treatment groups, where repeatedmeasures were used, a two-stage analysis was tested and found to beappropriate. Low nitrate had a significant, negative effect on growth andphycoerythrin concentration. Salinity had a weak, negative effect on bladegrowth, while inorganic carbon had no observed effect on blade growth,and neither had a significant effect on phycoerythrin concentration. Bladesaffected by low nitrate were able to regain normal growth rates and higherthan normal pigment levels when nitrate was increased, after up to 6 weeksof exposure. The growth rate, modeled from the data, increased with timeinitially, dependent on nitrate level. [ABSTRACT FROM AUTHOR]

The effect of environmental parameters on the growthof Porphyra linearis gametophytes was examinedunder controlled conditions, and related to themultilinear regression growth model recently developedfor this seaweed under coastal conditions in theeastern Mediterranean. Growth chambers, a gradienttable, special culture devices and analytical methodswere combined for this culture study.The major factors significantly controlling thegrowth rate of the P. linearis gametophytein glass dishes were: photoperiod, temperature, agein culture, photosynthetic photon flux (PPF), salinityand water dynamics. Maximal growth occurred underdaylength of 12 h, medium temperature (15–20 °C), low PPF (70–140 μmol photon m-2s-1), ambient salinity (30–40 ppt), 1–3 h ofdaily air exposure, and water velocity of 4 cm s-1.Photosynthesis and respiration rates weredominantly affected by daylength and temperature,while the concentration of pigments was dominantlyaffected by PPF and temperature.These conditions correspond well to the optimalnatural growth environment of this local species andare in agreement with the optimum estimated throughthe recently developed outdoor mathematical growthmodel. [ABSTRACT FROM AUTHOR]