Jeffrey J. Cosgrove

Applying Pulse Amplitude Modulation (PAM) fluorometry to microalgae suspensions: stirring potentially impacts fluorescence

The use of microalgae suspensions in PAM-fluorometers such as the Water-PAM (Walz GmbH, Germany) presents the problem of maintaining a homogeneous sample. The Water-PAM is marketed with an optional accessory for stirring the sample within the cuvette while in the emitter–detector (ED) unit. This stirring device can help to prevent cells from settling out of suspension over the time-course of chlorophyll-a fluorescence measurements. The ED unit was found to provide a vertically heterogeneous light environment and, therefore, cells within a single sample can exist in different quenched states. Enhancing cell movement by stirring was found to substantially influence measured fluorescence yield while performing induction curve and rapid light curve analyses. This is likely to result from relatively unquenched cells outside the main light-path moving into a higher light region and thus emitting disproportionately more fluorescence than quenched cells. Samples containing cells with high sinking rates or motile species may encounter similar (but reduced) problems. This effect can be mitigated by: (a) reducing analysis time to minimise the distance cells can sink/swim during the measurement procedure and avoiding the necessity of stirring; (b) limiting the proportion of sample outside the light path by minimising sample volume or; (c) by activating the stirrer only for short periods between saturation pulses and allowing enough time after stirring for quenching to stabilise before activation of the saturation pulse. Alternatively, modifications to the instrument providing a vertical dimension to the LED-array could resolve the issue by providing a more homogeneous light environment for the sample.

Chlorophyll Fluorescence Terminology: An Introduction

The terminology used to describe the various components of variable chlorophyll fluorescence has evolved as our understanding of variable chlorophyll fluorescence has increased. For the newcomer to in vivo chlorophyll a (chl-a) fluorescence studies one of the most confusing aspects can be the large number of terms and notations used, many of which often refer to the same parameter. Several proposals to standardise fluorescence notation, most notably by van Kooten and Snel (1990) and Maxwell and Johnson (2000), have reduced the extent of this variation in more recent publications, but some variation still occurs (Baker and Oxborough 2004). Furthermore, in recent years the notation used necessarily has become more complex as new instruments have allowed researchers to apply several techniques within a single study. On such occasions it is essential that notation also distinguishes between techniques (e.g. single turnover vs. multiple turnover) or method (e.g. steady-state light curve vs. non-steady-state light curve).

Sustainable cultivation of microalgae by an insulated glazed glass plate photobioreactor

Microalgae growth in closed photobioreactors is greatly inhibited by elevated temperatures caused mainly by the infra‐red portion of light. Current passive evaporative cooling systems for temperature control in outdoor photobioreactors are neither economical nor sustainable. Here we built a novel flat plate photobioreactor with its illumination surface customized with insulated glazing units (IGP). The IGP design enabled transmission of more than 50% of visible light while blocking 90% of ultraviolet and infrared radiations. The growth and productivity of Nannochloropsis sp. (MUR 267) in the IGP was compared against conventional flat plate photobioreactors subjected to the full spectrum (HLP) and also externally modified spectrum (CLP) of halogen lights. High temperature (up to 42°C) resulted in no growth in the HLP. Biomass productivities of Nannochloropsis sp. grown in the CLP was significantly higher than the IGP due to higher light transmission and lower temperature profiles recorded in the CLP. Lipid content of Nannochloropsis was highest in the CLP (60.23%) while protein was highest in the IGP (42.43%). All photosynthesis parameters were negatively affected in the HLP. The IGPs ability to remove infrared (heat) makes this newly developed photobioreactor a promising and sustainable cultivation system for mass algal production especially for high value products.