Search

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.

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.