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A Chlorella sp. was isolated from a brackish water high-altitude lake of the Northern-Western Himalayas and selected on the basis of its ability to secrete substantial amount of exopolysaccharide (EPS). The purified EPS was estimated to have molecular weight (Mw) of approximately 1.52 × 105 Da with polydispersity of 2.315 and showed amorphous dense morphology. The production of the EPS was maximized to ≅ 460 mg L−1 through nutrient optimisation. The monosaccharide composition of EPS showed the presence of hexose (glucose, galactose mannose), pentose (xylose, arabinose), deoxy (rhamnose), amino (galactosamine) and acid (galacturonic acid and glucuronic) sugars. The one-dimensional proton NMR and FT-IR analysis confirmed the presence of aliphatic groups. The pseudo-plastic rheology and the antioxidant activity of the EPS suggested its suitability for industrial applications. Importantly, the isolated polysaccharide exhibits its potential for easy and single pot biosynthesis of polysaccharide-capped gold-nanoparticles (AuNPs). The polysaccharide-capped AuNPs displayed exceptional stability at extended pH range and high salinity and suggest that this algal EPS can be utilized for its biotechnological application.

Spirulina is known to produce high protein and phycocyanin of commercial importance with concomitant CO2 utilisation. The pH is one of the most important factors for cell growth, CO2 utilisation and controlling contamination. In this study, an indigenously developed automated system for Spirulina cultivation was used at pilot scale, where CO2 supply was aimed to provide carbon source and to control culture pH. Among all the studied pH (7.5 ± 0.1,8.5 ± 0.1, 9.5 ± 0.1), pH 8.5 was found to be the best where biomass productivity, CO2 bio-fixation rate, protein and phycocyanin content were noted as 72 mg L−1 d-1, 0.13 g L-1 d-1, 64%, and 14%, respectively. Though the culture at pH 9.5 experienced late CO2 feeding, it was healthy and showed almost similar metabolite content compared to pH 8.5. The pilot scale automation system developed here can be employed to enhance CO2 fed pH control based performance of Spirulina or any microalgae cultivation.

Microalgae are sources of high-value metabolites such as lipids, carbohydrates, proteins and pigments. Microalgal metabolites are considered to be sustainable bioproducts with a great significance in food and fuel applications. However, the industrial/large scale production of these metabolites is challenging due to the lack of comprehensive knowledge of metabolic pathways and the aspects of energy conversion. In this chapter we provide an overview of the metabolic pathways involving the biosynthesis of high-value metabolites. Several aspects of metabolism confined exclusively to microalgal species are focused upon. In addition, this chapter also gives a brief description of various strategies for the enhancement of metabolite production.

In the present study, bacterial mixture (Rhizobium and Agrobacterium) and axenic Chlorella were cultivated individually, in a mixed (co-cultured) form, and through headspace connections to study volatile organic compounds (VOCs) profile and their effect on growth. Results indicated that VOCs produced by the axenic microalgae and microalgae co-cultured with bacteria were significantly different. Axenic Chlorella predominantly produced a flavouring organic compound 2-pentadecanone (69.54%), bacterial mixed culture produced 1-decanone, 1,2,3-butanetriol, and quinoline (15-20%), and direct co-culturing of Chlorella with bacteria predominantly produced 2-pentadecanone (32.4 %). When they were allowed to communicate distantly through headspace connection, highly diversified VOCs in large numbers but low quantities were noted, predominantly 1,2-propanediol (28.82 %). In addition, growth of the co-cultured Chlorella was 1.5 times higher, while Chlorella in headspace connection with bacterial mixture exhibited ∼ 3.2 times increase in growth compared to the axenic Chlorella, indicating the essential role of VOCs in growth and communication.

For efficient downstream processing, harvesting remains as one of the challenges in producing Nannochloropsis biomass, a microalga with high-value omega-3 oils. Flocculation is an effective, low-energy, low-cost method to harvest microalgae. Chitosan has been shown to be an effective food-grade flocculant; however, commercial chitosan is sourced from crustaceans, which has disadvantages including concerns over heavy-metal contamination. Thus, this study tests the flocculation potential of mushroom chitosan. Our results indicate a 13% yield of chitosan from mushroom. The identity of the prepared chitosan was confirmed by Fourier-transform infrared (FTIR) spectroscopy. Furthermore, results show that mushroom chitosan can be an alternative flocculant with >95% flocculation efficiency when tested in 100-mL jar and 200-L vertical column photobioreactor. Applications in a 2000-L raceway pond demonstrated that thorough mixing of mushroom chitosan with the algal culture is required to achieve efficient flocculation. With proper mixing, mushroom chitosan can be used to produce food-grade Nannochloropsis biomass suitable for the production of vegan omega-3 oils as a fish oil alternative.

The concomitant generation of renewable energy and material resources with distinct environmental applications for CO2 mitigation and wastewater treatment is one of the hallmarks of microalgal research. Microalgae are photoautotrophic microorganisms with simple growth requirements (light, CO2, N, P, and K) that can synthesize commodity biomolecules (lipids, proteins, and carbohydrates) and high-value metabolites in large amount over a short period of time. Requirement of microalgae for C, N, P, and K is usually met by providing technical grade chemicals which ultimately increases the cost of biomass production. However, since microalgae have the potential to utilize CO2 as well as N, P, and K from wastewater, high-density cultivation of microalgae can be accomplished by utilizing wastewater and CO2.

In this study, the concentrations of MgSO4, salinity and light intensity were optimised for maximum biomass productivity and lipid content in Chlorella sp. Lipid synthesized at varied experimental conditions was also assessed in detail for biodiesel properties through FAME analysis. FAMEs mainly composed of C16:0, C16:1(9), C16:3(7, 10, 13), C18:0, C18:1(11), C18:2(9, 12), C18:3(9, 12, 15). The optimum biomass productivity (372.50mgL(-1)d(-1)) and lipid content (32.57%) was obtained at MgSO4-150ppm; salinity-12.5ppm, and light intensity-25μmolm(-2)s(-1). However, at this condition the cetane number, a major biodiesel property was not complying with worldwide biodiesel standard. Therefore, further optimisations were done to check the suitability of biodiesel fuel. The optimum biomass productivity (348.47mgL(-1)d(-1)) and lipid content (12.43%) with suitable biodiesel fuel properties was obtained at MgSO4-50ppm, salinity-25ppm and light intensity-100μmolm(-2)s(-1). The validation experiments confirmed the closeness of predicted and measured response values.

In the present study, effects of various cultivation conditions on biomass and lipid productivity, detail FAME signature, CO 2 biofixation and elemental composition of Chlorella sp. and Chlamydomonas sp. have been investigated. In Chlorella sp., N-depletion has enhanced the lipid productivity by 12.70–14.61%. In Chlamydomonas sp., though the lipid content has increased by 22–26% upon N-depletion, lipid productivity has not changed significantly due to concomitant decrease in biomass productivity by 18–25%. The presence of lipid was also confirmed by FTIR spectroscopic analysis of biomass. The characteristic bands observed at 1744.30 cm −1 ( Chlamydomonas sp.) and ( Chlorella sp.) were credited to lipids due to C–O mode of the side chain from ester carbonyl group. Extracted lipid was transesterified to FAMEs. Chlorella sp. at N-replete indoor condition has produced the highest weight percentage of C16:0 (26.64%), C18:0 (3.77%) and C18:1 (27.94%). In Chlamydomonas sp., N-replete indoor condition has resulted in maximum content of MUFA (30.12%), LUFA (53.35%), second highest SFA (29.22%) and DUFA (23.23%). Inverse relationship was observed between MUFA and PUFA at all cultivation conditions. In both the microalgae, C16:0, C18:1 (9), C18:2 (9, 12), C18:3 (9, 12, 15) were identified as the major FAMEs which are suitable to be used as biodiesel components.

Microalgae are eukaryotic (e.g. green algae, diatoms) photosynthetic organisms capable of utilizing carbon dioxide and light for the synthesis of carbohydrates as energy compounds. They have been known since many years, but their large-scale cultivation has started a few decades ago. They have the potential to grow in open systems such as raceway ponds, circular ponds and lakes and also in controlled condition like closed photobioreactors. Microalgae are advantageous considering their higher productivity than terrestrial oilseed plants and ease of cultivation in wastewater and saline water. Microalgae do not compete with agricultural land for cultivation. They have dual role such as utilization of CO2 from atmosphere as well as remediation of wastewater by utilizing nutrients from wastewater to grow into biomass. Microalgae contain different types of major metabolites and high-value products such as proteins, lipids, carbohydrates, vitamins, pigments, antioxidants, minerals, etc. (Gupta et al. 2016; Mata et al. 2010; Rawat et al. 2011; Shriwastav et al. 2014; Francavilla et al. 2015). Their major metabolites are rich in essential amino acids and essential fatty acids, e.g. omega-3 fatty acids. Productivity of these major metabolites can be increased through mode of cultivation and nutrient limitation/stresses. Commonly, the lipids from microalgae are converted into biodiesel by the process of transesterification. After lipid extraction, a huge amount of residual biomass is left that is known as lipid-extracted algae (LEA). LEA still contains the high-value metabolites like proteins and carbohydrates in residual biomass (Ansari et al. 2015; Ju et al. 2012). Lipid-extracted algae can also serve as a good resource for biomethane, bioethanol and syngas production. In addition, protein fraction of LEA has promising potential as food and feed additive for animal and aquaculture. LEA biomass due to rich nitrogen content can also be employed as a fertilizer. Therefore, considering the rich chemical composition of microalgae, it can be considered as a good feedstock for the biorefinery.

Present study describes the induction of carbonic anhydrase (CA) activity in Chlamydomonas sp. in presence of calcium carbonate. Results indicated that calcium carbonate increased the activity of extracellular CA enzyme by 14-fold compared to culture grown at 3 % CO2, and by fourfold compared to the culture grown at 0.03 % CO2. CA was purified by gel exclusion followed by ion exchange chromatography. Molecular weight of the purified CA was found to be approximately 28 kDa. The enzyme showed optimum stability in the pH range of 8.0–9.0 and temperature of 35 °C. CA activity was inhibited with Hg2+ and Pb2+, while Zn2+ was found to accelerate its activity. Purified CA was employed for carbonation reaction with CO2 and the calcite produced was characterized by scanning electron microscope and X-ray diffraction. The enhancement in CA activity was found to be reliable, convenient, and may be employed for CO2 sequestration using whole cells or immobilized bioreactor systems.

Cancer as an historical disease is known to occur since several hundred years and still prevails till date as one of the most feared diseases. Its occurrence and/or progression are considered as the outcome of the series of accumulated ocogenic changes in the cell those transform it from benign to invasive or metastatic. It has been observed that most of the metastatic cancers are not curable and the available drugs focus on steadying the tumour growth to prevent further metastasis. Metastasis remains the cause of around 90% of the cancer deaths. Fundamental understanding of metastasis and recent advancements in metastasis driven cancer research may help to strengthen and bring in practice the new and advanced approaches for cancer treatment. In view of this, we review in detail the molecular mechanism of metastasis, problems in diagnosing and treating metastasis, and recent developments in cancer biology. Future efforts in order to unveil the unpredicted and uncontrolled metastasis of cancer cells have also been summarised.

The authors reviews the advancements in carbonic anhydrase– driven processes for CO2 sequestration research and engineering. Historical and recent discoveries of carbonic anhydrase and idea behind using it for CO2 sequestration are elaborated as well as the uses of this enzyme in free and immobilized forms are thoroughly discussed. New concepts such as extension of immobilized enzyme systems for bioreactor approach with the aim of CO2 abatement at the source are also introduced briefly toward the end of the review. The authors also suggest the possible future directions to employ carbonic anhydrase for CO2 sequestration.

Present investigation entails carbonic anhydrase (CA) immobilization and its influence on transformation of CO2 to calcite. CA enzyme was immobilized in alginate beads, subsequently maintained its catalytic efficiency after sequential operational cycles. The immobilized beads showed better operational stability by retaining nearly 67% of its initial activity even after six cycles. Batch scale studies with free and immobilized enzyme revealed that the entrapped CA hydrates CO2 to bicarbonate and/or carbonate which was then made to react with Ca2+ ions to transform into calcite. Calcite was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The entrapped CA was employed for the performance evaluation with respect to several operational parameters including the influence of enzyme concentration in free and immobilized condition. It was concluded that immobilized CA in alginate beads would have the potential for CO2 sequestration by biomimetic route.

In this study, an attempt was made to use micro-algal system for the production of biodiesel precursors and simultaneous CO 2 mitigation. Chlorella sp. was found to have a higher growth rate as compared to the other algal species tested namely Chlamydomonas sp. and Synnecococcus sp. At different CO 2 concentrations (0.03%, 3%, 10% and 15%), the lipid productivity was 23.0, 20.0 and 27.3 mg/L/d respectively. Calcite produced was characterized using FT-IR, SEM and XRD. The FAME in crude biofuel was analyzed by GC-FID that found to contain palmitic acid (C16:0), docosapentaenoic acid (C22:5) and docosahexaenoic acid (C22:6). The calorific value of Chlorella sp. was found to be 29 kJ/g which is higher than values reported for fresh water microalgae making it a potential candidate to be used as an alternate fuel.