Elisabete Barbarino

Distribution of intracellular nitrogen in marine microalgae: Calculation of new nitrogen-to-protein conversion factors

Nitrogen budgets in microalgae are strongly affected by growth conditions and physiological state of the cultures. As a consequence, protein N (PN) to total N (TN) ratio may be variable in microalgae grown in batch cultures, and this may limit the usefulness of the nitrogen-to-protein conversion factors (N-Prot factors), the most practical way of determining protein content. The accuracy of protein determination by this method depends on the establishment of specific N-Prot factors, and experimental data are needed to fill this gap. Complementing a previous study, the present work was designed to quantify the fluctuations of the main nitrogenous compounds during the growth of 12 species of marine microalgae, as well as to determine N-Prot factors for them. The microalgae were cultured in two experimental conditions: (a) using a N-replete culture medium (initial N concentration, 1.18 mM) and aeration, and (b) with a N-depleted culture medium (initial N concentration, 235 μM) and no aeration. The distribution of intracellular nitrogen was studied by constructing budgets of different nitrogen pools in different growth phases of the cultures. In all species, large variations occurred in the distribution of PN and non-protein N (NPN) in the treatments tested and in different growth phases. Intracellular inorganic nitrogen (NO3  − , NO2  −  and NH3 + NH4  + ) was the most important NPN component (0.4 – 30.4% of TN) in all species, followed by nucleic acids (0.3 – 12.2% of TN), and chlorophylls (0.1 – 1.8% of TN). The relative importance of NPN was greater in the exponential phase, decreasing during growth. PN ranged from 59.3 to 96.8% of TN. N-Prot factors are proposed for each of the species studied, based on the ratio of amino acid residues to TN, with values ranging from 2.53 to 5.77. Based on current results and on the previous study, we establish an overall average N-Prot factor for all species, treatments and growth phases of 4.78 ± 0.62 (n = 354). This study confirms that the use of the traditional factor 6.25 is unsuitable for marine microalgae, and the use of the N-Prot factors proposed here is recommended.

Amino acid composition, protein content and calculation of nitrogen-to-protein conversion factors for 19 tropical seaweeds

The use of nitrogen‐to‐protein conversion factors (N‐Prot factors) is the most practical way of determining protein content. The accuracy of protein determination by this method depends on the establishment of N‐Prot factors specific to individual species. Experimental data are needed to allow the use of this methodology with seaweeds. The present study was designed to characterize the amino acid composition and to establish specific N‐Prot factors for six green, four brown and nine red marine algae. Mean values for individual amino acids tended to be similar among the three groups, but some differences were found. Green algae tended to show lower percentages of both aspartic acid and glutamic acid than the other two groups of algae. The percentages of both lysine and arginine were higher in red algae, while brown algae tended to show more methionine than green and red algae. The actual protein content of the species, based on the sum of amino acid residues, varied from 10.8% (Chnoospora minima, brown algae) to 23.1% (Aglaothamnion uru‐guayense, red algae) of the dry weight. Nitrogen‐to‐protein conversion factors were established for the species studied, based on the ratio of amino acid residues to total nitrogen, with values ranging from 3.75 (Cryptonemia seminervis, red algae) to 5.72 (Padina gymnospora, brown algae). The relative importance of non‐protein nitrogen is greater in red algae, and consequently lower N‐Prot factors were calculated for these species (average value 4.59). Conversely, protein nitrogen content in both green and brown algae tends to be higher, and average N‐Prot factors were 5.13 and 5.38, respectively. An overall average N‐Prot factor for all species studied of 4.92 ± 0.59 (n = 57) was established. This study confirms that the use of the traditional factor 6.25 is unsuitable for seaweeds, and the use of the N‐Prot factors proposed here is recommended.

Tissue nitrogen and phosphorus in seaweeds in a tropical eutrophic environment: What a long-term study tells us

Percentages of nitrogen and phosphorus in 10 species of seaweeds (6 green and 4 red algae) were monitored from 1997 to 2004 by seasonal sampling in Guanabara Bay, South-eastern Brazil. The species did not show consistent variations in tissue N, P and N:P that related to annual cycles. Throughout this study, higher percentages of tissue N and P were found in Bostrychia radicans and Grateloupia doryphora (red algae) and lower in Cladophora rupestris and Codium decorticatum (green algae). In November 1999, the Icaraí Submarine Sewage Outfall became operational, resulting in a reduction of visual pollution in the area and an improvement in the local quality of seawater for recreational use. Measurements of dissolved nutrients at the sampling site did not indicate significant changes in concentrations after the commissioning of the submarine sewage outfall; however, tissue P and N:P ratio of most of species were significantly lower than in the first two years of this survey. Variations in tissue nitrogen throughout this study were not significant, except for G. doryphora in some comparisons. Results show that seaweeds function very well as monitors of environmental changes in Guanabara Bay. Experimental data are needed to identify possible environmental processes which are promoting changes in chemical composition of the local seaweed populations.

Crescimento e composição química de dez espécies de microalgas marinhas em cultivos estanques

Microalgae show several economic applications, such as uses in aquaculture and in food industry, and there is a search for new uses, such as the biomass production to convert into biodiesel. All possible applications are directly linked to growth rate and the chemical profile of the species. Thus, the selection of conditions to promote a better use of algal biomass is fundamental for economic purposes. In this study, 10 species of marine microalgae were cultured and compared for growth and chemical composition. Remarkable differences of growth performance have been observed, with species with small cell volumes growing faster than species with large cell volumes. Levels of protein, carbohydrate, lipid and photosynthetic pigments varied widely, and proteins were identified as the most abundant substances. Some species showed high concentrations of fatty acids of economic importance, such as eicosapentaenoic and linoleic acids. The concentrations of amino acids were similar among species. In all microalgae, glutamic and aspartic acids were the most abundant amino acids. An overall evaluation of the results indicates that few general trends related to the taxonomy of algal groups were recognized.

Seasonal changes in population structure of the tropical deep-water kelp Laminaria abyssalis

Tropical kelp populations are rare and anomalous relicts of shallow‐water populations that existed during glacial periods of cooler oceanographic climate. The endemic Brazilian tropical kelp, Laminaria abyssalis Joly and Oliveira Filho, occurred at depths below 40 m. The seasonal variations in biological aspects of L. abyssalis sporophyte populations and local variations in seawater nutrients and temperature were evaluated. A population was sampled four times between the austral spring of 2005 to winter 2006. Seasonal variations in the population structure and in the tissue content of nitrogen (N), carbohydrate and pigments were observed. Higher density (6.3 individuals m−2), biomass (7.3 kg m−2) and blade area (13 221 cm2) were observed in summer, while the highest percentage of tissue total N (1.6%), carbohydrates (32.9%) and photosynthetic pigments (chlorophyll a = 1.9% and chlorophyll c = 0.4%) were observed in spring. The highest surface area of fertile tissue in L. abyssalis sporophytes (2.36%) was recorded in winter, indicating winter as the season when more investments are made in reproduction. The highest concentrations of total N (6.3 μM) and phosphate (0.6 μM) in seawater were observed in spring and summer, respectively. Seawater temperatures lower than 20°C, which are characteristic of upwelling waters, occurred every month and were most frequent in spring and summer. We show that L. abyssalis invests more in growth in spring and summer and reaches the greatest thallus size and population density in summer. The lower abundance during winter may be related to the lower frequency of temperatures below 20°C and the local seasonal storms that cause turnover of rhodoliths, the main substrate for L. abyssalis.