PHYSIOLOGICAL CHARACTERISTICS OF SPIRULINA PLATENSIS (CYANOBACTERIA) CULTURED AT ULTRAHIGH CELL DENSITIES¹

Abstract

Photosynthetic activity and growth physiology of Spirulina platensis (Nordstedt) Geitler cultures maintained at ultrahigh cell densities (i.e. above 100 mg chlorophyll‐L−1) in a newly designed photobioreactor were investigated. Nitrogen (NaNO3) in standard Zarouk medium was characterized as a major nutrient‐limiting factor in such cultures. The effect of ultrahigh cell density on photoinhibition of photosynthesis, as reflected by chlorophyll fluorescence and photosynthetic oxygen evolution, was studied: elevating the population density may arrest photoinhibition induced by high photon flux density, as well as low temperature. The relationship between incident irradiance and oxygen production rate was linear in situ for cultures at the optimal cell density, indicating that light limitation rather than light saturation or photoinhibition is the dominant condition outdoors in cultures of ultrahigh cell densities. In contrast with other reports, the extent of biomass loss at night due mainly to dark respiration was found to be relatively small when cell density was optimal, exerting only a minor effect on overall net productivity. Measurements of oxygen consumption at night revealed low rates of respiration, which may be explained by the low value of the volumetric mass transfer coefficient (KLa) of oxygen. Hence, reduced oxygen tension may play a role in preventing full expression of the respiratory potential in ultrahigh cell density cultures in which photoadaptive strategy may explain cell composition. Ultrahigh cell densities optimized with respect to the intensity of the light source, the length of the light path, and the extent of stirring represent the key for obtaining high output rates of cell mass and some natural products.

Repeated batch cultivation of the microalga Spirulina platensis

“…light is prevented from reaching all the cells, q.v. Vonshak et al 1982;Gitelson et al 1996;Qiang et al 1996). The use of that blend concentration and of that renewal rate allowed the biomass concentrations to vary between 0.25 and 0.50 g l )1 .…”

Effect of light intensity on the correlation between cell mass concentration and optical density in high density culture of a filamentous microorganism

“…Microalgae undergo significant physiological and chemical changes in response to variations in light, temperature, nutrient availability, and cell density [8][9][10][11][12][13]. However, there have been few researches on the effect of light intensity on OD and cell morphology as reported in this work.…”

Photosynthetic efficiency of Chlorella sorokiniana in a turbulently mixed short light‐path photobioreactor

“…Faster mixing of dense Spirulina ( Arthrospira ) cultures in short light‐path (SLP) panel photobioreactors, for example, can increase the biomass productivity at high light intensities 5, 6. Under such conditions, these cyanobacteria are only shortly exposed to oversaturating light intensities at the bioreactor surface before traveling to darker regions of the photobioreactor, and it was hypothesized that this light regime leads to higher photosynthetic efficiencies by preventing oversaturation and inducing light integration 7.…”

“…In flat panel photobioreactors, mixing is provided by aeration and enhanced by increasing the airflow. To create turbulence, 2.8–4.2 L min −1 of air per liter reactor volume must be provided 5, 6, 8. However, to be able to accurately measure photosynthetic activity through the on‐line monitoring of oxygen production rates (OPRs) and carbon dioxide consumption rates (CURs), the airflow needs to be lower to have larger differences in O 2 and CO 2 mass fractions in the ingoing and outgoing gas.…”