ON THE MASS CULTURE OF ALGAE

Heterotrophy Compared to Photoautotrophy for Growth Characteristics and Pigment Compositions in Batch Cultures of Four Green Microalgae

Four strains of green microalgae (Scenedesmus acutus, Scenedesmus vacuolatus, Chlorella sorokiniana, and Chlamydomonas reinhardtii) were compared to determine growth and pigment composition under photoautotrophic or heterotrophic conditions. Batch growth experiments were performed in multicultivators with online monitoring of optical density. For photoautotrophic growth, light-limited (CO2-sufficient) growth was analyzed under different light intensities during the exponential and deceleration growth phases. The specific growth rate, measured during the exponential phase, and the maximal biomass productivity, measured during the deceleration phase, were not related to each other when different light intensities and different species were considered. This indicates species-dependent photoacclimation effects during cultivation time, which was confirmed by light-dependent changes in pigment content and composition when exponential and deceleration phases were compared. Except for C. reinhardtii, which does not grow on glucose, heterotrophic growth was promoted to similar extents by acetate and by glucose; however, these two substrates led to different pigment compositions. Weak light increased the pigment content during heterotrophy in the four species but was efficient in promoting growth only in S. acutus. C. sorokiniana, and S. vacuolatus exhibited the best potential for heterotrophic biomass productivities, both on glucose and acetate, with carotenoid (lutein) content being the highest in the former.

Nitrogen, phosphorus and high CO2 modulate photosynthesis, biomass and lipid production in the green alga Chlorella vulgaris

Climate change could impact nutrient bioavailability in aquatic environment. To understand the interaction of nutrient bioavailability and elevated CO₂, Chlorella vulgaris cells were grown in ambient air or 5% CO₂ in different concentrations of nitrogen and phosphorus in a photobioreactor. The chlorophyll content, photosynthesis and respiration rates increased in 5% CO₂ to support higher biomass production. The nutrient limitation in the growth media resulted in reduced photosynthetic rates of the algal cells and their PSI, PSII, and whole chain electron transport rates and biomass production. Conversely, their lipid content increased partly due to upregulation of expression of several lipid biosynthesis genes. The order of downregulation of photosynthesis and upregulation in lipid production due to nutrient limitation was in the order of N > P. The N-50 and 5% CO₂ culture had only 10% reduction in biomass and 32% increase in lipids having 85% saturated fat required for efficient biofuel production. This growth condition is ideal for generation of biodiesel required to reduce the consumption of fossil fuel and combat global warming.

Association between algal productivity and phycosphere composition in an outdoor Chlorella sorokiniana reactor based on multiple longitudinal analyses

Microalgae as a biofuel source are of great interest. Bacterial phycosphere inhabitants of algal cultures are hypothesized to contribute to productivity. In this study, the bacterial composition of the Chlorella sorokiniana phycosphere was determined over several production cycles in different growing seasons by 16S rRNA gene sequencing and identification. The diversity of the phycosphere increased with time during each individual reactor run, based on Faith's phylogenetic diversity metric versus days post-inoculation (R = 0.66, P < 0.001). During summer months, Vampirovibrio chlorellavorus, an obligate predatory bacterium, was prevalent. Bacterial sequences assigned to the Rhizobiales, Betaproteobacteriales and Chitinophagales were positively associated with algal biomass productivity. Applications of the general biocide, benzalkonium chloride, to a subset of experiments intended to abate V. chlorellavorus appeared to temporarily suppress phycosphere bacterial growth, however, there was no relationship between those bacterial taxa suppressed by benzalkonium chloride and their association with algal productivity, based on multinomial model correlations. Algal health was approximated using a model-based metric, or the 'Health Index' that indicated a robust, positive relationship between C. sorokiniana fitness and presence of members belonging to the Burholderiaceae and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade. Bacterial community composition was linked to the efficiency of microalgal biomass production and algal health.

Numerical Taxonomy of Heterotrophic Bacteria Growing in Association with Continuous-Culture Chlorella sorokiniana

Twenty-nine cultures isolated from nonaxenic growths of Chlorella sorokiniana (Shihira and Krauss) and eight reference cultures were tested for 150 morphological and biochemical characteristics. The taxonomic data were subjected to computer analysis from which five major clusters were identified. The bacterial isolates have been placed in the genera: Pseudomonas, Acinetobacter, Flavobacterium, and Bacillus. Amino acid requirements of four strains from the test set were determined.

Elemental balancing of biomass and medium composition enhances growth capacity in high-density Chlorella vulgaris cultures

The basic requirements for high-density photoautotrophic microalgal cultures in enclosed photobioreactors are a powerful light source and proper distribution of light, efficient gas exchange, and suitable medium composition. This article introduces the concept of balancing the elemental composition of growth medium with biomass composition to obtain high-density cultures. N-8 medium, commonly used for culturing Chlorella vulgaris was evaluated for its capacity to support high-density cultures on the basis of elemental stoichiometric composition of C. vulgaris. This analysis showed that the N-8 medium is deficient in iron, magnesium, sulfur, and nitrogen at high cell densities. N-8 medium was redesigned to contain stoichiometrically balanced quantities of the four deficient elements to support a biomass concentration of 2% (v/v). The redesigned medium, called M-8 medium, resulted in up to three- to fivefold increase in total chlorophyll content per volume of culture as compared to N-8 medium. Further experiments showed that addition of each of the four elements separately to N-8 medium did not improve culture performance and that balanced supplementation of all four deficient elements was required to yield the improved performance. Long-term (24 d) C. vulgaris culture in M-8 medium showed continuous increase in chlorophyll content and biomass throughout the period of cultivation. In contrast, the increase in chlorophyll content and biomass ceased after 7 and 12 d, respectively in N-8 medium, demonstrating the higher capacity of M-8 medium to produce biomass. Thus, the performance of high cell density photobioreactors can be significantly enhanced by proper medium design. The elemental composition of the biomass generated is an appropriate basis for medium design.

A new method for the preparation of uniformly 14C-labelled compounds by using Anacystis nidulans

1. Growth conditions were devised which enabled Anacystis nidulans to be grown on high specific radioactivity (14)CO(2) (at over 98% isotopic abundance of (14)C) in a closed system with greater than 85% substrate utilization. 2. The DNA and RNA content of A. nidulans was estimated by various methods and compared with that of Chlorella pyrenoidosa. 3. A procedure was developed for the quantitative extraction and separation of the DNA and RNA from A. nidulans. 4. The fractionation and analysis of the DNA and RNA includes methods for the preparation of the uniformly (14)C-labelled deoxyribonucleoside monophosphates and the uniformly (14)C-labelled ribonucleoside monophosphates. 5. The base 6-methylaminopurine was identified as a component of the DNA. 6. The preparation and total yield of uniformly (14)C-labelled amino acids from A. nidulans are also briefly described. The results are discussed in relation to the use of other micro-organisms for the preparation of compounds labelled with (14)C.

Absorption Coefficients of Chlorophyll Derivatives

Methods are described for the isolation of chlorophylls a and b, and for the preparation of 12 chlorophyll derivatives, including crystalline pheophorbide a, from these starting compounds. Laboratory cultures of Chlorella were fed C14O2. After 9 days growth the cells were heat-killed, their pigments extracted, and chlorophylls a and b isolated chromatographically. The following C14-labelled compounds were prepared: chlorophyll a, allomerized chlorophyll a, chlorophyllide a, pheophytin a, allomerized pheophytin a, pheophorbide a, methyl pheophorbide a, chlorophyll b, chlorophyllide b, methyl chlorophyllide b, allomerized chlorophyllide b, allomerized methyl chlorophyllide b, pheophorbide b, and allomerized pheophorbide b. Assuming uniform distribution of carbon-14 label in the parent chlorophyll molecules, specific and molar absorption coefficients were calculated from the specific radioactivities of these derivatives.

Growth of Scenedesmus obliquus in relation to the supply of iron

Equal amounts of iron in the form of iron citrate or Fe-EDTA were added to the mineral media. The effect of the two salts upon cell-, substance-and chlorophyll-production of Scenedesmus obliquus cultivated in light-dark-regimes of 15:9 hours was studied.In bubbling cultures at 75 000 Lux the number of cells and the dry substance increased by a factor of about 16-19 with Fe-EDTA and by a factor of 10-12 with iron citrate. With both salts it was possible to get a production of daughter cells twice within one light-dark-cycle of 24 hours.The chlorophyll content of cells and substance cultivated in Fe-EDTA-medium was smaller than that of those cultivated in iron citrate-medium. The possible relations between the amount of chlorphyll and the production of substance are discussed.