|Other Abstract||The cultivation of Nostoc sphaeroides Kützing and N. commune Vauch, the two important economic cyanbacterial strains, were studied on a pilot scale. In this study, the whole process of the cultivation of Nostoc sphaeroides and N. commune was studied. At the same time, the variation of the structure on the colonies of N. sphaeroides, the physiological characteristics on different layers of the colonies and the effect of inoculum density on the growth were investigated. Main results were as follows:
N. sphaeroides and N. commune was cultured indoors and outdoors using raceway-shape culture ponds. The culture volume of media was up to 5 m3 indoors. The maximum biomass productivity was about 297.4 Kg (Fw) per month and the average productivity was 180.9 Kg (Fw) per month. The culture temperature higher than 35 0C acutely reduced the biomass productivith considerably. When the culture was proformed outdoors using raceway-shape culture ponds, the productivity of N. sphaeroides and N. commune was up to 445.2 and 269.2 g•m-2•d-1 (Fw), respectively. The productivity of N. commune was positively correlated with the inoculum density when initial density was below 9 Kg/m2. As far as N. sphaeroides was concerned, the breakage of larger colonies led to the decrease in the biomass productivity. The chlorophyll a content (on the basis of fresh weight) of different size colonies of decreased significantly with increasing the colony diameter. On the contrary, RWC and total soluble carbohydrates increased with increasing colony diameter. At the same time the content of was correlated with the diameter.
The structure of the colonies of N. sphaeroides was affected by the diameter, light intensity and temperature. With increasing in the colony diameter, the structure of macrocolonies also underwent systematic changes. The cross section of the colonies appeared dense pots, rings, with or without central core, then the central core region was in aged colonies. Finally the colonies broke and release filaments into the enviroment. For instance, macrocolonies of ca. 1mm diameter were fully filled with long trichomes, which were entangled homogeneously and enwrapped by sheaths. In contrast, the filaments in larger macrocolonies showed a more differential pattern. The filaments occurred in the peripheral region of the macrocolony were usually over 500 μm long and were densely packed in an orderly fashion, whereas the filaments in the core region were shorter than 100 μm and distributed unevenly in a more loosen pattern. Furthermore the filaments of the peripheral region showed higher photosynthesic activities, while those of core region showed higher content of Chl a and phycobiliprotein. The temperature and light intensity also affected the structure of colonies.
During the cultivation of N. sphaeroides outdoors using glass vessels, the biomass productivity, the contents of total soluble carbohydrates and Chl a, the ratio of Dw/Fw had different variational trendency under the conditions of one, two or no layers of black nylon webs to cover. Usually the productivity covered by no web was highest, and up to 5.354±1.055 g•L-1 •d-1 (Fw) [14.925±2.940 g•m-2 •d-1 (Dw)]. During the whole culture experiment, the average productivity was 1.569±0.003 g•L-1•d-1 (Fw), which is far more than the productivity by using the raceway-shape culture ponds.
In batch culture, the inoculum density influenced the growth, the increase of the colonies diameter and the bursting on the colonies of Nostoc sphaeroides. Maintained at 25 0C and under continuous illumination of 200 μ·mol·m-2·s-1, the lower the inoculum density, the higher the increase in diameter. When the inoculum density was 50 g·L-1 (Fw), the content of Chl a was the highest, and the bursting was the lowest.|