Author(s):
Dragone, Giuliano 
; Fernandes, Bruno Daniel ; Abreu, Ana Paula ; Vicente, A. A. ; Teixeira, J. A.
Date: 2009
Persistent ID: http://hdl.handle.net/1822/10151
Origin: RepositóriUM - Universidade do Minho
Subject(s): Microalgae; Chlorella vulgaris; Starch; Urea; Nitrogen limitation
Description
Due to the limited stocks of fossil fuels and the production of greenhouse gas carbon dioxide on
their combustion alternative sources of energy are being investigated. Recently, microalgae have
received much attention as a renewable energy resource because these photosynthetic
microorganisms can convert sunlight, water and CO2 into potential biofuels (1). The microalga
Chlorella vulgaris, particularly, has been considered as a potential raw material for bioethanol
production because it can accumulates high levels of starch when grown under optimized culture
conditions (2).
The aim of the present work was to study the effect of nitrogen limitation on starch production
by the microalgae C. vulgaris.
C. vulgaris CCAP 211/1e (P12 strain) was obtained from the Culture Collection of Algal
Laboratory, Institute of Botany, Academy of Sciences of the Czech Republic. The original (nitrogen
sufficient) growth medium based on the elementary composition of algal biomass had the
following initial composition (mg l−1): 1,100 (NH2) 2CO, 237 KH2PO4, 204 MgSO4∙7H2O, 40
C10H12O8N2NaFe, 88 CaCl2, 0.83 H3BO3, 0.95 CuSO4∙5H2O, 3.3 MnCl2∙4H2O, 0.17 (NH4)
6Mo7O24∙4H2O, 2.7 ZnSO4∙7H2O, 0.6 CoSO4∙7H2O, and 0.014 NH4VO3 in distilled water (3). Nitrogen
limited growth medium was formulated by omitting urea from the original growth medium. The
microalgae were grown in 1 l Schott flasks with 0.4 l of medium. Cultures were maintained at
30ºC under continuous, cool white fluorescent lamps. Light intensity was approximately 100
mmol m‐2 s‐1 at the surface of the photobioreactors. The concentration of suspended algal
biomass was determined by optical density measurement at 700 nm. Starch content in the
microalgae was determined colorimetrically by the anthrone reaction.
The results showed that starch accumulation in C. vulgaris was strongly related to nitrogen
concentration. Under nitrogen limited growth conditions, starch constituted 36% of the algal
biomass after 118 h of cultivation, whereas nitrogen sufficient microalgae contained 8% of their
dry weight as starch. On the other hand, nitrogen sufficient condition led to an increase in
biomass concentration, with the highest biomass concentration of 2.06 g l‐1. It can be concluded
that accumulation of starch is enhanced in nitrogen limited cultures of C. vulgaris P12.
