Maximizing Biomass and Lipid Production in Heterotrophic Culture of Chlorella vulgaris: Techno-Economic Assessment

Background: Nowadays, chlorophycean microalgae have attained a broad-spectrum attention as a potential candidate for biomass and bioenergy production. Despite their appreciated benefits, one of major problems is their low biomass and lipid productivity. Here we investigated the heterotrophic culture in shake flasks and stirred tank bioreactor to improve the lipid and biomass production in a naturally isolated strain of Chlorella vulgaris. Methods: A naturally isolated C. vulgaris strain was cultivated in BG-11 medium in shake flask and bioreactor. Its biochemical composition and growth kinetic parameters were investigated. Results: The biomass productivity was improved (3.68 fold) under heterotrophic culture compared to basal autotrophic culture condition in shake flask experiment. The total lipid content increased to 44% of total Dry Cell Weight (DCW) during heterotrophic growth after 21 days. Moreover, a great Fatty Acid Methyl Esters (FAME) yield was observed under heterotrophic cultivation. Total biomass and lipid content of microalgae in bioreactor experiment increased to 4.95 and 2.18 g L-1 respectively, during 5 days of the experiment compared to its basic autotrophic culture. Conclusion: The techno-economic aspects of exploiting C. vulgaris as a biodiesel feedstock werealso evaluated. The results imply that heterotrophic cultivation could compensate the low biomass productivity in microalgae for green energy production. Ever growing rates of established patents on application of various genetic and bioengineering-based methods have made it possible to achieve higher lipid contents with reduced total costs for microalgal biodiesel production as well.

Bioprocess Engineering Aspects of Biopolymer Production by the CyanobacteriumSpirulinaStrain LEB 18

Microbial biopolymers can replace environmentally damaging plastics derived from petrochemicals. We investigated biopolymer synthesis by the cyanobacteriumSpirulinastrain LEB 18. Autotrophic culture used unmodified Zarrouk medium or modified Zarrouk medium in which the NaNO3content was reduced to 0.25 g L−1and the NaHCO3content reduced to 8.4 g L−1or increased to 25.2 g L−1. Heterotrophic culture used modified Zarrouk medium containing 0.25 g L−1NaNO3with the NaHCO3replaced by 0.2 g L−1, 0.4 g L−1, or 0.6 g L−1of glucose (C6H12O6) or sodium acetate (CH3COONa). Mixotrophic culture used modified Zarrouk medium containing 0.25 g L−1NaNO3plus 16.8 g L−1NaHCO3with the addition of 0.2 g L−1, 0.4 g L−1, or 0.6 g L−1of glucose or sodium acetate. The highest biopolymer yield was 44% when LEB 18 was growing autotrophically in media containing 0.25 g L−1NaNO3and 8.4 g L−1NaHCO3.

Evaluación de un sistema para la micorrización in vitro en plantas de mora de castilla (Rubus glaucus, Benth)

<strong>Objective</strong>. Obtain an in vitro mycorrhization system in autotrophic culture systems of blackberry plants (Rubus glaucus, Benth). <strong>Materials and methods</strong>. We used spores and root fragments with vesicles of Arbuscular Mycorrhizal Fungus (AMF) Glomus sp (GEV02). We established an autotrophic culture system of blackberry plantlets comparing two methods of direct inoculation of the AMF. We measured the number of spores produced, the length of the extraradical mycelium as well as the percentage of colonization of the AMF. Additionally, we measured the shoot and root length, and the fresh and dry weight of the leaf and root parts to determine the plant development. <strong>Results</strong>. The autotrophic culture system was successful for blackberry plants (Rubus glaucus, Benth; an optimal shoot and root growth was observed. Additionally, we obtained a system that allowed the development of Glomus sp. in in vitro conditions, with the formation of structures typical of the symbiosis as well as a good intraradical colonization, with the production of arbuscules and vesicles, development of extraradical mycelium with branched hyphae, and formation of new spores. <strong>Conclusion</strong>. For the first time, micropropagated blackberry plants associated successfully with an AMF under in vitro conditions, enabling the development of the symbiotic system AMF Glomus sp. associated to roots of micropropagated blackberry plantlets.<br /><strong>Key words</strong>: arbuscular mycorrhizal fungi (AMF), autotrophic culture, Rubus glaucus Benth, Glomus sp. (GEV02), in vitro mycorrhization.

Effects of heavy metals on nitrifying bacteria

Laboratory evaluations were conducted to study the toxic responses of heavy metals such as copper and nickel of an autotrophic culture of strict nitrifiers (Nitrosomonas sp. and Nitrobacter sp.) in continuous flow stirred tank reactors (CSTR). One of the CSTRs was operated as a suspended growth (SG) system while the other was operated as an attached & suspended growth (A&SG) system. Nitrification inhibition in a SG and A&SG systems was investigated with the emphasis on the effect of shock loading of copper and nickel. As a result of the copper and nickel test, Nitrosomonas sp. was found to be equally or more sensitive than Nitrobacter sp. However, a higher influent nickel concentration of 50 mg/L was needed to cause a similar percent inhibition of ammonium oxidation than the copper concentration of 5 mg/L. A geochemical equilibrium speciation model, MINTEQA2/PRODEFA2, was used to compute the concentrations of various chemical species present in the wastewater for both systems. The high correlations of Cu(NH3)4+2 and Ni(NH3)4+2 with percent inhibition were found and it was thought that they were probably the species responsible for the inhibition of ammonia oxidation.