Effects of agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum

Abstract

The effect of mechanical agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum was investigated in aerated continuous cultures with and without the added shear protectant Pluronic F68. Damage to cells was quantified through a decrease in the steady state concentration of the biomass in the photobioreactor. For a given aeration rate, the steady state biomass concentration rose with increasing rate of mechanical agitation until an upper limit on agitation speed was reached. This maximum tolerable agitation speed depended on the microalgal species. Further increase in agitation speed caused a decline in the steady state concentration of the biomass. An impeller tip speed of >1.56 m s(-1) damaged P. tricornutum in aerated culture. In contrast, the damage threshold tip speed for P. cruentum was between 2.45 and 2.89 m s(-1). Mechanical agitation was not the direct cause of cell damage. Damage occurred because of the rupture of small gas bubbles at the surface of the culture, but mechanical agitation was instrumental in generating the bubbles that ultimately damaged the cells. Pluronic F68 protected the cells against damage and increased the steady state concentration of the biomass relative to operation without the additive. The protective effect of Pluronic was concentration-dependent over the concentration range of 0.01-0.10% w/v.

A microfluidic perfusion platform for cultivation and screening study of motile microalgal cells

“…Chlamydomonas cells (CC-124) were harvested from a fresh culture and suspended in TAP with 0.2% Pluronic F-68. 16 The media were supplemented with 0.2% of Pluronic F-68 to reduce the adhesion of cells to the chamber wall of microfluidic chip. The operation of the chip was performed in a similar way to the cultivation of cells.…”

Effect of agitation speed on the morphology ofAspergillus nigerHFD5A-1 hyphae and its pectinase production in submerged fermentation

“…The rate of the agitation speed could influenced the extent of mixing in the shake flasks system and affected the nutrient availability as well [4] . Agitation speed has been affected many enzymes activities in different strains of bacteria and fungi [5,6] as well as microalgae [7] . Agitation provides adequate mixing, mass, heat transfer and also improving dissolved oxygen in the culture medium.…”

Dependency of Microalgal Production on Biomass and the Relationship to Yield and Bioreactor Scale-up for Biofuels: a Statistical Analysis of 60+ Years of Algal Bioreactor Data

“…This differential motion reduces the boundary layer around the cell and effectively increases the diffusion flux to the cell. The most common means of creating motions in cultures is by cell sinking [233,234] and by mechanical mixing [235,236].…”

“…Production has been shown to vary with high-light conditions. Increased mixing of increasingly concentrated cultures also enhances production [158,163,236], presumably by increasing the exposure time of the cells to the light regime. Previous to this, Laws et al [48] increased production in a raceway pond using turbulent eddy shedding to create highfrequency fluid motions, thereby exposing cells to high-light fluctuations.…”