(62c) Effects of Total Inorganic Carbon and Nitrogen Concentrations On Lipid Formation In Chlorella Vulgaris

Effects of total
inorganic carbon and nitrogen concentrations on lipid formation in Chlorella vulgaris

Jinsoo Kim¹,
Joo-Youp Lee¹, Kaniz F. Siddiqui²

¹ Chemical Engineering
Program, University of Cincinnati, OH 45221-0012

² The Metropolitan Sewer
District of Greater Cincinnati,
Cincinnati, OH
45204-2002

Microalgae have recently received great
attention as a promising alternative bioenergy source because they can produce a
substantial amount of triacylglycerols (e.g. 20-50 % dry cell weight) and can
be readily converted into biodiesel.  Chlorella vulgaris has been selected for
this growth kinetic study since it is one of the fastest growing microalgae and
contains a reasonable amount of triacylglycerols (e.g. 14-22 % dry cell weight).  Dissolved carbon dioxide (CO₂(aq)) and bicarbonate ion (HCO₃^-) are
essential inorganic carbon forms required for autotrophic algal growth, but few
studies have been systematically conducted on the impact of inorganic carbon on
algal growth.  In this respect, the
growth kinetics of Chlorella vulgaris
was previously investigated dependent on the total inorganic carbon
concentration (i.e., CO₂(aq) and HCO₃^-)  As a result, it was observed that the growth
kinetics was increased when the total inorganic carbon concentration was
increased in the culture medium.

Under many nutrient limiting conditions,
lipids are accumulated as a means of storage when energy (i.e. light) and
carbon (i.e. CO₂ for autotrophic growth) sources are available.  However, many of these nutrients are
essential for photosynthesis responsible for metabolic flux generation into
lipids formation.  These
nutrient-deficient conditions decrease biomass growth rate, and offset the
benefit of lipid accumulation.  The
growth of algal biomass such as Chlorella vulgaris is dependent on bicarbonate ion concentrations
available in the culture medium.  Bicarbonate
ion also plays a critical role as a catalyst in the first step of fatty acids
biosynthesis for the synthesis of malonyl-CoA. 
In this study, a change in total lipids content has been investigated
using the Nile red stain method when the total inorganic carbon concentration
in culture medium is increased.  This is
expected to provide fundamental understanding of the utilization of bicarbonate
ions for the design and operation of bioreactors.

Key
words:  Chlorella vulgaris, total inorganic carbon, nitrogen deficiency,
lipid content.