Influence of Various Nitrogen Sources on Biomass and Lipid Production by Chlorella vulgaris

Abstract

Chlorella vulgaris is a unicellular, photosynthetic fresh water green alga with high concentration of chlorophyll. This microalga synthesizes biomass by trapping energy from the sun. It has valuable components particularly pigments and protein thus, can be utilized in the nutraceutical, pharmaceutical and agricultural industry. The organism was obtained by blooming in a 10:90 mixture of cow dung extract and pond water from fresh water pond at the African Regional Aquaculture Centre [ARAC] at Aluu, Rivers State, Nigeria. Blooming was enhanced by intermittent manual aeration under natural illumination with a bank of fluorescent tubes emiting ca15 µE/m²/s each. The isolate was cultured using a synthetic medium and identified as Chlorella vulgaris on the basis of its molecular characteristics by Polymerase Chain Reaction [PCR] technique. The potential of producing biomass and lipid from Chlorella vulgaris using three different nitrogen sources namely potassium nitrate, urea and sodium nitrate in a synthetic medium were investigated. The best growth of about 279 mgL-1 cell dry matter and 5.27% lipid content was obtained with urea as compared to the other nitrogen sources. Potassium nitrate gave 68 mgL-1 cell dry matter with about 1.53% lipid content, while sodium nitrate resulted in 236 mgL-1 cell dry matter and 0.73% lipid content. The maximum specific growth rate (µ=0.198) with a doubling time of 5.05 was recorded with urea at a concentration of 0.055 mgL-1, NaNO3 at the same concentration with urea had (µ=0.182) and a doubling time of 5.5, but KNO3 showed the least specific growth rate             (µ= 0.169) with doubling time of 6.33. Overall, urea gave higher yields of biomass and lipid, caused small fluctuations with the medium during the algal growth.