Selection of native freshwater microalgae and cyanobacteria for CO2 biofixation

Performance and mechanism of carbon dioxide fixation by a newly isolated chemoautotrophic strain Paracoccus denitrificans PJ-1

CO₂ is regarded as a major contributor to the global warming. CO₂ utilization is promising to reduce the CO₂ emissions. Currently, the biofixation of CO₂ using chemoautotrophs has markedly gain interest in CO₂ utilization. In this study, a newly isolated chemoautotroph, Paracoccus denitrificans PJ-1, was used for the biofixation of CO₂ under anaerobic condition. Experimental results revealed that Paracoccus denitrificans PJ-1 achieved a high carbon fixation rate (13.25 mg·L^-1·h^-1) which was ∼10 times faster than the previous reported chemotrophic bacteria using thiosulfate as electron donor. The best CO₂ fixation activity of Paracoccus denitrificans PJ-1 was achieved at the pH value of 9.0 and CO₂ concentration of 20 vol%. Meanwhile, a high CO₂ fixation yield of 106.03 mg·L^-1 was reached. The presence of oxygen was adverse to the biofixation, indicating that strain PJ-1 was more suitable for CO₂ fixation in anaerobic environments. Carbon mass balance analysis revealed that the carbon from CO₂ was mainly fixed into the extracellular organic carbon rather than the biomass. GC-MS analysis and cbbL gene test revealed that Paracoccus denitrificans PJ-1 fixed CO₂ through the Calvin-Benson-Bassham cycle and mainly converted CO₂ to oxalic acid and succinic acid. Overall, the excellent CO₂ fixation capacity of Paracoccus denitrificans PJ-1 suggests that it had potential for CO₂ utilization.

Modification and improvement of microalgae strains for strengthening CO2 fixation from coal-fired flue gas in power plants

Biological CO₂ capture using microalgae is a promising new method for reducing CO₂ emission of coal-fired flue gas. The strain of microalgae used in this process plays a vital role in determining the rate of CO₂ fixation and characteristics of biomass production. High requirements are put forward for algae strains due to high CO₂ concentration and diverse pollutants in flue gas. CO₂ can directly diffuse into the cytoplasm of cells by extra- and intracellular CO₂ osmotic pressure under high CO₂ concentrations. The flue gas pollutants, such as SO_x, NO_x and fly ashes, have negative effects on the growth of microalgae. This work reviewed the state-of-the-art advances on microalgae strains used for CO₂ fixation, focusing on the modification and improvement of strains that are used for coal-fired flue gas. Methods such as genetic engineering, random mutagenesis, and adaptive evolution have the potential to facilitate photosynthesis, improve growth rate and reduce CO₂ emission.

Utilization of Non-Living Microalgae Biomass from Two Different Strains for the Adsorptive Removal of Diclofenac from Water

In the present work, the adsorptive removal of diclofenac from water by biosorption onto non-living microalgae biomass was assessed. Kinetic and equilibrium experiments were carried out using biomass of two different microalgae strains, namely Synechocystis sp. and Scenedesmus sp. Also, for comparison purposes, a commercial activated carbon was used under identical experimental conditions. The kinetics of the diclofenac adsorption fitted the pseudo-second order equation, and the corresponding kinetic constants indicating that adsorption was faster onto microalgae biomass than onto the activated carbon. Regarding the equilibrium results, which mostly fitted the Langmuir isotherm model, these pointed to significant differences between the adsorbent materials. The Langmuir maximum capacity (Qmax) of the activated carbon (232 mg∙g−1) was higher than that of Scenedesmus sp. (28 mg∙g−1) and of Synechocystis sp. (20 mg∙g−1). In any case, the Qmax values determined here were within the values published in the recent scientific literature on the utilization of different adsorbents for the removal of diclofenac from water. Still, Synechocystis sp. showed the largest KL fitted values, which points to the affinity of this strain for diclofenac at relative low equilibrium concentrations in solution. Overall, the results obtained point to the possible utilization of microalgae biomass waste in the treatment of water, namely for the adsorption of pharmaceuticals.

Carbon dioxide from geothermal gas converted to biomass by cultivating coccoid cyanobacteria

The Blue Lagoon is a geothermal aquifer with a diverse ecosystem located within the Reykjanes UNESCO Global Geopark on Iceland's Reykjanes Peninsula. Blue Lagoon Ltd., which exploits the aquifer, isolated a strain of coccoid cyanobacteria Cyanobacterium aponinum (C. aponinum) from the geothermal fluid of the Blue Lagoon more than two decades ago. Since then Blue Lagoon Ltd. has cultivated it in a photobioreactor, for use as an active ingredient in its skin care products. Until recently, the cultivation of C. aponinum was achieved by feeding it on 99.99% (4N) bottled carbon dioxide (CO₂). In this investigation, C. aponinum was cultivated using unmodified, non-condensable geothermal gas (geogas) emitted from a nearby geothermal powerplant as the feed-gas instead of the 4N-gas. The geogas contains roughly 90% vol CO₂ and 2% vol hydrogen sulfide (H₂S). A comparison of both CO₂ sources was made. It was observed that the use of geogas did enhance the conversion efficiency. A 13 weeks' average CO₂ conversion efficiency of C. aponinum was 43% and 31% when fed on geogas and 4N-gas, respectively. Despite the high H₂S concentration in the geogas, sulfur accumulation in the cultivated biomass was similar for both gas sources. Our results provide a model of a CO₂ sequestration by photosynthetic conversion of otherwise unused geothermal emission gas into biomass.

CXCR2 Inhibition Combined with Sorafenib Improved Antitumor and Antiangiogenic Response in Preclinical Models of Ovarian Cancer

Antiangiogenic therapy is important for the treatment of gynecological cancer. However, the therapeutic benefit derived from these treatments is transient, predominantly due to the selective activation of compensatory proangiogenic pathways that lead to rapid development of resistance. We aimed to identify and target potential alternative signaling to anti-vascular endothelial growth factor (VEGF) therapy, with a view toward developing a combination of antiangiogenic agents to provide extended therapeutic benefits. We developed a preclinical in vivo phenotypic resistance model of ovarian cancer resistant to antiangiogenic therapy. We measured dynamic changes in secreted chemokines and angiogenic signaling in tumors and plasma in response to anti-VEGF treatment, as tumors advanced from the initial responsive phase to progressive disease. In tumors that progressed following sorafenib treatment, gene and protein expression levels of proangiogenic CXC chemokines and their receptors were significantly elevated, compared with responsive tumors. The chemokine (C-X-C motif) ligand 8 (CXCL8), also known as interleukin-8 (IL-8) increase was time-dependent and coincided with the dynamics of tumor progression. We used SB225002, a pharmacological inhibitor of chemokine (C-X-C motif) receptor 2 (CXCR2), to disrupt the CXC chemokine-mediated functions of ovarian cancer cells in in vitro assays of cell growth inhibition, spheroid formation, and cell migration. The combination of CXCR2 inhibitor with sorafenib led to a synergistic inhibition of cell growth in vitro, and further stabilized tumor progression following sorafenib in vivo. Our results suggest that CXCR2-mediated chemokines may represent an important compensatory pathway that promotes resistance to antiangiogenic therapy in ovarian cancer. Thus, simultaneous blockage of this proangiogenic cytokine pathway using CXCR2 inhibitors and the VEGF receptor (VEGFR) pathway could improve the outcomes of antiangiogenic therapy.

Biomass and lipid accumulation of three new screened microalgae with high concentration of carbon dioxide and nitric oxide

Three species of indigenous microalgae species were isolated from an artificial lake. They were identified as Scenedesmus sp., through the molecular phylogenetic and morphological method and named SDEC-12, SDEC-13 and SDEC-14. To evaluate their tolerance to the harmful composition in the exhaust gas and the potential to produce biodiesel, they were cultured with 15% CO2 and 200 ppm NO. The SDEC-13 and SDEC-14 strains were able to grow well under 15% CO2 with the maximum biomass productivity of 0.087 and 0.090 g L(-1) d(-1), respectively. When cultured with 15% CO2, the three strains showed a similar total lipid content (25.7-28.25%) and the fatty acid of SDEC-14 strain showed the highest saturated level (76.59%). SDEC-13 was the only strain that could tolerate 200 ppm NO and 15% CO2, while its total lipid content remained unaffected by the NO, so the SDEC-13 strain had the potential to produce biodiesel with flue gas.

Flue-gas-influenced heavy metal bioaccumulation by the indigenous microalgae Desmodesmus communis LUCC 002

Desmodesmus communis LUCC 002 was cultivated using flue gas originating from a coal-fired power plant as a carbon dioxide (CO2) source. The flue gas contains various heavy metals. For investigating the fate of flue-gas-introduced metals on the cultivation system, bioaccumulation was measured in the microalgal biomass and milieu. The accumulated biomass was found to contain eight heavy metals: arsenic, chromium, barium, lead, selenium, silver, cadmium, and mercury. High heavy metal accumulations were also found in the control group of algae grown without the addition of flue gas at the same location. Further testing revealed that some of the heavy metals originated from well water used in the cultivation. The flue-gas-influenced bioaccumulation pattern of different heavy metals was observed. The responses of individual heavy metals and the influence of well water microbial flora on the algal growth were investigated, this study showed that hormesis was developed by the D. communis LUCC 002.