Sachitra Kumar Ratha

Biochemical modulation of growth, lipid quality and productivity in mixotrophic cultures of Chlorella sorokiniana

The genus Chlorella is a widely employed microalga for biodiesel, as it can be grown using photo/mixo/heterotrophic mode of cultivation. The present investigation was undertaken with the hypothesis that addition of different substrates (amino acids, carbon sources, vitamins) along with reducing agents may aid in diverting Acetyl CoA to malonyl CoA or fatty acid biosynthesis, under mixotrophic conditions in Chlorella sorokiniana. Preliminary investigations undertaken with two reducing agents individually (sodium thiosulphate and methyl viologen) along with selected substrates revealed the promise of sodium thiosulphate (1%) in enhancing lipid accumulation significantly. Further, the role of inclusion of twelve substrates and sodium thiosulphate revealed that supplementation with tryptophan (0.1%) recorded 57.28% enhancement in lipid productivity on 4th day. Highest values of lipid productivity of 33% were recorded on 8th day in 0.1% glucose supplemented medium containing sodium thiosulphate. Fatty Acid Methyl Ester (FAME) profiles generated revealed significant reduction in the content of Poly unsaturated fatty acids (PUFA) and enhanced Mono unsaturated fatty acids (MUFA) (especially oleic acid) in the treatments involving tryptophan, Vitamin B12, sodium pyruvate and glucose. This study reveals the promise of using sodium thiosulphate along with selected substrate for enriching the quality and quantity of lipids, which can be valuable for exploiting algae as a source of biodiesel.

Exploring nutritional modes of cultivation for enhancing lipid accumulation in microalgae

The objective of this study was to identify the most promising nutritional mode of growth for enhanced biomass and lipid productivity in a set of twenty microalgal strains, grown under photoautotrophic and mixotrophic/heterotrophic conditions using 2% glucose as carbon source. These included four cyanobacterial strains (Cyanosarcina, Phormidium, Nostoc and Anabaena) and sixteen green algae belonging to six genera (five strains each of Chlorella and Chlorococcum, two of Scenedesmus and one each of Chlamydomonas, Kirchneria, Bracteacoccus and Ulothrix). Lipid productivity ranged from 2–13% under photoautotrophic conditions, 1.7–32% under mixotrophic conditions and 0.9–20% under heterotrophic conditions. MIC‐G5 Chlorella sp. followed by MIC‐G11 Chlorella sp. exhibited the highest cellular lipid content (355 and 271 μg/ml) and lipid productivity of 32% and 28% respectively in mixotrophic condition. In the glucose supplemented conditions (heterotrophic), a significant reduction in PUFA from 25.1 to 9.4, 29.2 to 12.4 and 44.7 to 10.2 was observed in MIC‐G4, MIC‐G5 and MIC‐G11, respectively. A remarkable enhancement of 33–70% in SFA was recorded under mixotrophic conditions. As the quality of biodiesel is based on high SFA and low PUFA, our results illustrate the significance of glucose supplemented condition as a promising strategy for generating high value biodiesel from algae.

NUTRIENT SEQUESTRATION, BIOMASS PRODUCTION BY MICROALGAE AND PHYTOREMEDIATION OF SEWAGE WATER

The present work was aimed at analysing the role of inoculated microalgae in nutrient dynamics, bioremediation and biomass production of sewage water. Preliminary microscopic analyses of sewage water revealed the presence of different algal groups, with predominance of Cyanophyta. Among the inoculated strains, Calothrix showed highest dry cell weight (916.67 mg L−1), chlorophyll and carotenoid content in tap water + sewage water (1:1) treatment. Significant removal of NO3-N ranging from 57–78% and PO4-P (44–91%) was recorded in microalgae inoculated tap water + sewage water. The total dissolved solids and electrical conductivity of tap water + sewage water after incubation with Calothrix sp. decreased by 28.5 and 28.0%, accompanied by an increase in dissolved oxygen from 4.4 to 6.4 mg L−1 on the 20th day. Our investigation revealed the robustness of Calothrix sp. in sequestering nutrients (N and P), improving water quality and proliferating in sewage water.

Bioprospecting and indexing the microalgal diversity of different ecological habitats of India

Our study reports the collection, biodiversity analyses, isolation and identification of microalgae from different habitats of India. Cyanophyceae and Chlorophyceae were the most dominant algal groups recorded, with the highest number being recorded for non-heterocystous cyanobacteria (48), followed by 44 unicellular forms. Sagar Island, Sunderbans recorded the greatest number of algae, and unicellular/colonial green algae were present in all the samples. Shannon’s Diversity Index was highest in Koikhali, Sunderbans, followed by Rushikulya River, Odisha. Selective enrichment, purification through serial dilution followed by plating and regular observations led to the isolation of sixteen strains. Identification was done by using microscopic observations, supported with standard monographs and classified as belonging to seven genera (Chlorella, Chlorococcum, Kirchneria, Scenedesmus, Chlamydomonas, Tetracystis and Ulothrix). 18S rDNA sequencing was undertaken for four strains. The set of sixteen strains were screened under standard cultural conditions for their growth kinetics and Chlorella sorokiniana MIC-G5, followed by Chlorella sp. MIC-G4 exhibited the highest growth rates. The strain Chlorococcum sp. MIC-G2 recorded highest chlorophyll, while MIC-G3 ranked highest for carbohydrates. The study aided in identifying the dominant microalgae in the diverse habitats and characterizing their growth rate and carbohydrate content, providing a valuable germplasm for further utilization in agriculture and industry.

Ecobiological aspects of algae cultivation in wastewaters for recycling of nutrients and biofuel applications

Algae-based wastewater treatment is an ecofriendly option, which involves complex interactions among the micro/macro flora and fauna. The use of consortia (algal polycultures, algae–bacteria/algae–fungi consortia and biofilms/mats) for wastewater treatment has proved more effective in nutrient recycling, bioremediation and biomass production. The present review focuses on ecobiological aspects of wastewaters, the interactions among the biotic components in natural and engineered aquatic systems, nutrient recycling, and the potential of algae-based wastewater treatment technologies for algae biomass and biofuel production. Although wastewater treatment coupled with production of biofuels is a promising option, concerted research efforts are needed in the future to develop commercial-scale technologies for biofuel production from algae cultivated in wastewaters.