Revealing the role of phosphorus supply on the phosphorus distribution and lipid production in Scenedesmus obliquus UTEX 393 during nitrogen starvation.

Microalgal-based processes offer promise for addressing two sustainability challenges: recovering phosphorus (P) from wastewater and producing biofuel feedstock. This study investigated the role of phosphorus supply on microalgal growth, lipid yield, and P distribution for Scenedesmus during nitrogen starvation. Extracellular polymeric substances and intracellular polymeric substances were the most important pools for inorganic phosphorus (IP) and organic phosphorus (OP), respectively. The main P pool for microalgae with low phosphorus supply was EPS, which accounted for 57 % of the total biomass phosphorus; while under high P concentrations, 79 % of the phosphorus was stored in IPS. A high concentration of orthophosphate stimulated rapid P uptake as IP and promoted the transformation of IP to OP associating with biomass synthesis. The highest P content of microalgal biomass was 6.5 % of dry weight when the phosphorus concentration in medium was 113 mg/L, and the OP content was 4.9 % of dry weight. High phosphate-P enhanced the biomass's lipid content by 60 %, and the distribution of fatty acid methyl esters was not altered by P concentrations. Collectively, high phosphate-P availability could promote microalgal biomass synthesis, lipid production and P accumulation.

Achieving superior carbon transfer efficiency and pH control using membrane carbonation with a wide range of CO2 contents for the coccolithophore Emiliania huxleyi.

The economic viability of microalgal-derived products relies on rapid CO2 transfer in a cost-effective manner. Many industrial gas streams contain concentrated CO2 that, if converted to useful products, would lower greenhouse gas emissions and valorize the wasted CO2. Membrane carbonation (MC) uses non-porous hollow-fiber gas-transfer membranes to deliver CO2 without bubble formation, which makes it possible to achieve a high carbon-transfer efficiency (CTE). However, inert gasses in the industrial streams (e.g., N2, O2, and H2O) can significantly lower the CO2-delivery rate. The means to overcome the buildup of inert gases in the membrane lumen is to manage the distal end of the membranes to sweep out inert gases while not wasting significant CO2. A MC-venting strategy was evaluated for CO2 inputs from 5% to 100%. Abiotic tests using a restricted exit flow could achieve >95% CTEabiotic for industrial CO2 streams. When integrated with semi-continuous cultivation of a marine coccolithophore, Emiliania huxleyi, CO2 delivery and venting were on-demand based on a pH set points and pH-actuated feed and venting valves. MC using the venting strategy achieved 100% CTEbiotic when delivering 100% and 50% CO2, which was better than 50% CTEbiotic obtained from pH-controlled sparging of 100% CO2-sparging. E. huxleyi consistently fixed ~80% of the delivered CO2 into biomass, and the remaining ~20% to calcite coccoliths. The compact size of MC modules, stable pH control, and no shear forces from bubble agitation during the CO2 delivery made MC an ideal match for cultivation of coccolithophores, which are sensitive to shear forces and pH fluctuations.

Evaluation of co-culturing a diatom and a coccolithophore using different silicate concentrations.

Globally, the demand for sustainable energy production and high-value biological compounds have become intertwined in an attempt to improve the feasibility of sustainable algal cultivation. Marine microalgae, especially diatoms and coccolithophores, represent viable cultures that can produce biofuels and high-value compounds. Growing them in co-culture offers the potential to produce lipids and pigments, while also generating CaCO3 for C sequestration. The main objective of this work was to investigate competition or co-existence of the diatom Chaetoceros gracilis and the coccolithophore Pleurochrysis Carterae. The focus was on the effects of silicate and co-culturing on the growth rate, productivity, pigment production, and ash production for C. gracilis and P. carterae in laboratory conditions. The results showed that, in monoculture, 2-mM Si enhanced the specific growth rate of C. gracilis, but did not affect P. carterae. Regardless of silicate concentration, C. gracilis was more productive than P. carterae. In co-culture, P. carterae had a slower growth rate, indicating an inhibitory effect of C. gracilis on P. carterae. Neither silicate concentration nor co-culturing had an impact on the contents of pigments fucoxanthin, chlorophyll-a, and chlorophyll-c, which means that pigment productivity was proportional to biomass productivity. Finally, the ash content increased in all cultures with the lower silicate concentration (0.2 mM) in the medium. With one exception, the ash content was dominated by SiO2 regardless of silicate amount, and CaCO3 was a major part of the ash only when P. carterae was grown separately with the higher silicate level. These results highlight that co-culturing did not provide an advantage for improving biomass, pigments, or CaCO3 productivity.

Phosphate depletion controls lipid content and accumulation of heterotrophic bacteria during growth of Synechocystis sp. PCC 6803.

During the culturing of cyanobacteria, heterotrophic bacteria can compete for nutrients, compromise the quality of the harvested biomass, or cause culture crashes. We systematically investigated the effects of depleting inorganic phosphate (Pi) on the growth of the cyanobacterium Synechocystis sp. PCC 6803, its community of heterotrophic bacteria, and the biomass's chemical composition. On the one hand, depleting Pi had minimal impact on total biomass, extracellular polymeric substances (ESP), soluble microbial products (SMP), and most types of intracellular organic polymers production. On the other hand, depleting Pi led to markedly less lipid content, less heterotrophic biomass, and a shift in the heterotrophic community from Burkholderiales to Sphingobacteriales and Saprospirales. The causes of the large impacts were that Synechocystis was much better at scavenging a very low Pi concentration and lowering the Pi available to the heterotrophs. This work lays a foundation for controlling the accumulation of heterotrophs and reducing their deleterious effects in cyanobacteria culturing.

Uptake of phosphate by Synechocystis sp. PCC 6803 in dark conditions: Removal driving force and modeling.

Rapid uptake of inorganic phosphate (Pi) by microalgae should occur through two processes operating in parallel: onto extracellular polymeric substances (EPS) and intracellular polymeric substances (IPS). Most previous studies focused only on overall Pi uptake and ignored the roles of EPS. We investigated the two-step removal of Pi by Synechocystis sp. PCC 6803 in dark conditions (i.e., without incorporation of Pi into newly synthesized biomass). We also developed a model to simulate both steps. Experimental results with Synechocystis confirmed that Pi in the bulk solution was removed by the two uptake mechanisms operating in parallel, but with different kinetics. All uptake rates decreased with time, and the Pi uptake rate by IPS was much higher than that by EPS at all times, but EPS had a larger maximum Pi-storage capacity -- 33-48 mgP/gCODEPS versus 15-17 mgP/gCODIPS. Synechocystis had a maximum Pi-storage capacity in the range of 22-28 mgP/g dry biomass. Protein in EPS and IPS played the key role for binding Pi, and biomass with higher protein content had greater Pi-storage capacity. Furthermore, biomass with low initial stored Pi had faster Pi-uptake kinetics, leading to more Pi removed from the bulk solution. This work lays the foundation for using microalgae as a means to remove Pi from polluted water and for understanding competition for Pi in microbial communities.

Enhancement mechanisms of short-time aerobic digestion for waste activated sludge in the presence of cocoamidopropyl betaine.

Cocoamidopropyl betaine (CAPB), which is a biodegradable ampholytic surfactant, has recently been found to dramatically enhance the aerobic digestion of waste activated sludge (WAS) in short-time aerobic digestion (STAD) systems. Therefore, it is important to understand the mechanisms in which CAPB enhances WAS aerobic digestion performance. Results showed that CAPB could dramatically enhance the solubilization of soluble proteins (PN), polysaccharides (PS), nucleic acids (NA) and humic-like substances (HS) in the STAD system within the initial 2 h. Then PN, PS and NA gradually decreased, while HS showed only minor decease. In addition, CAPB increased the proportion of low MW fractions (<20 kDa) from 4.22% to 39.4%, which are more biodegradable. Specific oxygen uptake rates and dehydrogenase enzyme activity results indicated that CAPB markedly improved the aerobic microorganism activities. Microbial community analyses and principle coordinate analyses (PCoA) revealed that CAPB increased the proportion of some functional microorganisms, including Proteobacteria, Planctomycetales, Acinetobacter, Pseudomonas and Aeromonas. The changes driven by CAPB could explain the enhanced performance of the STAD system for WAS aerobic treatment.

How myristyltrimethylammonium bromide enhances biomass harvesting and pigments extraction from Synechocystis sp. PCC 6803.

Myristyltrimethylammonium bromide (MTAB) is a cationic surfactant used to improve biomass harvesting and pigment extraction form microalgae, but the mechanisms underlying its effectiveness are poorly defined. We document the mechanisms for enhanced harvesting and pigment extraction for the cyanobacterium Synechocystis sp. PCC 6803 using measurements from flow cytometer, zeta potential, release of soluble components, and microscopy. Harvesting efficiency increased as the MTAB/Biomass dose increased from 0 to 40%. A low MTAB dose (≤ 8%) mainly brought about coagulation and flocculation, which led to aggregation that improved harvesting, but 40% MTAB had the highest harvesting efficiency, 62%. Adding MTAB above a MTAB/Biomass dose of 8% also increased cell-membrane permeability, which allowed the solvent (ethyl acetate) to pass into the cells and resulted in a large increase in extraction efficiency of pigments: An MTAB/Biomass ratio of 60% for 180 min achieved the highest extraction efficiencies of chlorophyll and carotenoids, 95% and 91%, respectively. Combining harvesting and extraction performances with results from flow cytometry, zeta potential, release of soluble components, and microscopy lead to the following mechanistic understandings. MTAB dose from 8% to 40% solubilized EPS, which lowered the biomass's negative charge, but caused breakup of the large aggregates. An increase of cell permeability also in this stage allowed ethyl acetate to pass into the cells and achieve better pigment extraction. MTAB >40% led to cell lysis and a large increase in soluble organics, but complete cell lysis was not required to achieve the maximum extraction efficiency. The MTAB/Biomass % ratio for optimizing harvest efficiency and pigment extraction lay in the range of 40%-60%.