Effects of Sodium Bicarbonate on Biomass and Carbohydrate Production in Synechococcus PCC 7002

Abstract

Microalgae and cyanobacteria have attracted much attention for developing new biofuels production technologies. In particular, cyanobacteria seem to be promising in view of third generation bioethanol production. The most used source of inorganic carbon for algal cultivation is concentrated CO2 in air. However the use of this source can account of up to 50% of the biomass production costs. Bicarbonate salts, supplied to the culture medium, may be a valid alternative as source of inorganic carbon for photosynthetic microorganisms able to capture, use and recovery carbon from this substrate. In this study Synechocococcus PCC 7002 was used in order to test the capability of this strain to exploit bicarbonate and to elucidate the effect of such a carbon source on carbohydrates production. Batch experiments were carried out, using automatic control of pH and temperature (set to 8.5 and 28 °C, respectively). The concentrations of sodiumbicarbonate used were 5.5, 11, 22, 44 and 88 g L-1. The cyanobacteria was able to grow in all concentrationsof bicarbonate presenting high potential for production of biomass, with DCW 6 g L-1 in 44 and 88 g L-1 and productivity as high as 1.12 g L-1 day-1. An accumulation of carbohydrates was observed up to a maximum of 25% using 88 g L-1 of sodium bicarbonate, however this value was reached under nitrogen starvation in the stationary growth phase, when the carbon source was still limiting, because all the bicarbonate ion was completely consumed in all experiments.