The effects of acetate and glucose on carbon fixation and carbon utilization in mixotrophy of Haematococcus pluvialis.

The culture method using sodium acetate and glucose, widely used as organic carbon sources in the mixotrophy of Haematococcus pluvialis, was compared with its autotrophy. In the 12-day culture, mixotrophy using sodium acetate and glucose increased by 40.4% and 77.1%, respectively, compared to autotrophy, but the mechanisms for the increasing biomass were different. The analysis of the mechanism was divided into autotrophic and heterotrophic metabolism. The mixotrophy with glucose increased the biomass by directly supplying the substrate and ATP to the TCA cycle while inhibiting photosynthesis. Gene expressions related to glycolysis and carbon fixation pathway were confirmed in autotrophy and mixotrophy with glucose and acetate. The metabolism predicted in the mixotrophy with acetate and glucose was proposed via autotrophic and heterotrophic metabolism analysis. The mechanism of Haematococcus pluvialis under mixotrophic conditions with high CO2 concentration was confirmed through this study.

Waste mitigation and resource recovery from food industry wastewater employing microalgae-bacterial consortium.

Wastewater generated by the food industry is rich in nitrogen and phosphorus with possible presence of heavy metals. Physical and chemical methods of treatment, although effective, are expensive and may cause secondary environmental pollution damaging aquatic and human life. Traditional biological methods are eco-friendly and cost-effective but involve standalone microorganisms that pose risk of contamination and are not as effective. This review discusses the application of novel microalgal-bacterial consortium as a solution for the resource recovery and treatment of dairy, starch and aquaculture wastewater. Use of biofilm reactors containing anaerobic and aerobic sludge has shown 80-90% and > 90% COD and nutrient removal efficiency in treatment of dairy and starch processing wastewater, respectively. The treatment of aquaculture processing wastewater can be challenging due to high sality and requires salt-tolerant bacteria-microalgae consortium. In this regard, the identification of dominant microalgae and bacteria using 16S rRNA and 18S rRNA genes is recommended.

Algal glycobiotechnology: omics approaches for strain improvement.

Microalgae has the capability to replace petroleum-based fuels and is a promising option as an energy feedstock because of its fast growth, high photosynthetic capacity and remarkable ability to store energy reserve molecules in the form of lipids and starch. But the commercialization of microalgae based product is difficult due to its high processing cost and low productivity. Higher accumulation of these molecules may help to cut the processing cost. There are several reports on the use of various omics techniques to improve the strains of microalgae for increasing the productivity of desired products. To effectively use these techniques, it is important that the glycobiology of microalgae is associated to omics approaches to essentially give rise to the field of algal glycobiotechnology. In the past few decades, lot of work has been done to improve the strain of various microalgae such as Chlorella, Chlamydomonas reinhardtii, Botryococcus braunii etc., through genome sequencing and metabolic engineering with major focus on significantly increasing the productivity of biofuels, biopolymers, pigments and other products. The advancements in algae glycobiotechnology have highly significant role to play in innovation and new developments for the production algae-derived products as above. It would be highly desirable to understand the basic biology of the products derived using -omics technology together with biochemistry and biotechnology. This review discusses the potential of different omic techniques (genomics, transcriptomics, proteomics, metabolomics) to improve the yield of desired products through algal strain manipulation.

Enhanced biomass production through a repeated sequential auto-and heterotrophic culture mode in Chlorella protothecoides.

A repeated sequential auto-and heterotrophic (RSAH) culture mode was designed to enhancebiomass ofChlorella protothecoides. Based on the result that the photosynthesis system may receive damage if the light period is more than 16 h, autotrophy was applied in the 16 h of the light cycle and mixotrophy using acetic acid and glucose in the 8 h of dark cycle. In the dark cycle, an organic carbon source was added according to the Monod equation to maintain activation of the TCA cycle and organic carbon source-to-cell conversion. When acetic acid and glucose were used as organic carbon sources, this culture method was found to be 32.3% and 12.6% higher in biomass, 2.59 and 2.67 times higher in the organic carbon source-to-cell conversion factor, and 2.17 and 2.32 times higher in ATP/ADP ratio, respectively, compared to mixotrophy. Through this new culture method, economic feasibility and carbon reduction capabilities in large-scale cultures can be achieved.

A sustainable mixotrophic microalgae cultivation from dairy wastes for carbon credit, bioremediation and lucrative biofuels.

Globally, high CO2-emitting dairy industry obligated to treat waste and improve its carbon-footprints. Mixotrophic cultivation strategy (MCS) of microalgae enables to treat dairy wastes and mitigate CO2 for sustainable dairy economy. This study developed a biochemical process for organic whey with minimum dilution to avoid environmental burden. To make whey suitable for algae cultivation, it was pre-treated to remove polymers, unwanted solid fractions, opacity, and organic and inorganic overloads via acid hydrolysis, chemical flocculation and struvite formations with lowest dilution possible. 40% pretreated whey was most productive for biomass and lipid fractions respectively 4.54 and 1.80 gl-1 with daily productivities 0.50 and 0.20 gl-1d-1, however 25% to reach adequate treatment. Overall, biochemical treatment was effective to remove respectively 99.7 and 91-100% of organic and inorganic pollutants, however algal treatment alone exhibited maximum 92.6 and 48.5-98.4% removals from both treatment ratios which is promising finding of this work.

Split mixotrophy: A novel cultivation strategy to enhance the mixotrophic biomass and lipid yields of Chlorella protothecoides.

Mixotrophy (M) assumes sum of autotrophic (A) and heterotrophic (H) growths. In this study, a novel split-mixotrophic cultivation strategy (SMCS) developed as better mixotrophy via offering mutual-benefits through gas-exchange at both headspaces while splitting both trophic modes. To quantify synergistic-growth effects in combined-autotrophy and combined-heterotrophy (CA&CH) of SMCS, gross O2-evolution, DIC and DO concentrations were compared with A, H and M. Average 12-14% and 26-32% increase in DIC and DO concentrations were determined respectively in CA and CH than A, H and M. Biomass yield in CA + CH was increased approx.1.5-folds higher than yields of A + H and M regimes. These results show SMCS as better cultivation strategy than the M by increased biomass and lipid yields. Challenges associated with organic carbon can be solved by SMCS viz. chlorophyll loss, organic carbon uptake inhibition. SMCS could be a breakthrough to integrate bacterial process with algae for better bioprocess economy and energy recovery.