The effects of copper on the photosynthetic response of Phaeocystis cordata

Abstract

We investigated the effects of limiting (1.96 × 10(-9) mol l(-1) total Cu, corresponding to pCu 14.8; where pCu = -log [Cu(2+)]) and toxic Cu concentrations up to 8.0 × 10(-5) mol l(-1) total Cu (equivalent to pCu 9.5) on growth rates and photosynthetic activity of exponentially grown Phaeocystis cordata, using batch and semi-continuous cultures. With pulse amplitude modulated (PAM) fluorometry, we determined the photochemical response of P. cordata to the various Cu levels, and showed contrasting results for the batch and semi-continuous cultures. Although maximum photosystem II (PSII) quantum yield (Φ(M)) was optimal and constant in the semi-continuous P. cordata, the batch cultures showed a significant decrease in Φ(M) with culture age (0-72 h). The EC50 for the batch cultures was higher (2.0 × 10(-10) mol l(-1), pCu9.7), than that for the semi-continuous cultures (6.3 × 10(-11) mol l(-1), pCu10.2). The semi-continuous cultures exhibited a systematic and linear decrease in Φ(M) as Cu levels increased (for [Cu(2+)] < 1.0 × 10(-12) mol l(-1), pCu12.0), however, no effect of high Cu was observed on their operational PSII quantum yield (Φ'(M)). Similarly, semi-continuous cultures exhibited a significant decrease in Φ(M), but not in Φ'(M), because of low-Cu levels. Thus, Cu toxicity and Cu limitation damage the PSII reaction centers, but not the processes downstream of PSII. Quenching mechanisms (NPQ and Q (n)) were lower under high Cu relative to the controls, suggesting that toxic Cu impairs photo-protective mechanisms. PAM fluorometry is a sensitive tool for detecting minor physiological variations. However, culturing techniques (batch vs. semi-continuous) and sampling time might account for literature discrepancies on the effects of Cu on PSII. Semi-continuous culturing might be the most adequate technique to investigate Cu effects on PSII photochemistry.

Effects of cadmium and nitrogen on lipid composition of Chlorella vulgaris (Trebouxiophyceae, Chlorophyta)

“…Daily monitoring was performed by measuring optical density at 684 nm using a HACH DR 5000 (HACH, Loveland, Colorado, USA) spectrophotometer. Based on equations (1 and 2 below) described in Lombardi & Maldonado (2011) specific growth rates ( ) were obtained.…”

Growth and biochemical composition of Chlorella vulgaris in different growth media

“…Harrison and Berges (2005) proposed that three main experimental categories, culture maintenance, algal biomass yield and physiological/growth experiments are a good way to search for ideal production conditions. Growth rates give a general index of algal health status and physiological condition in the cultures, since it reflects algal metabolism, as a response to all of its cellular cycles (Lombardi and Maldonado 2011). From this rationale, it is clear that batch cultures can offer adequate growth conditions for microalgae only during a short period of time, after which cell metabolism begins to collapse and photosynthesis is reduced (Lombardi and Maldonado 2011).…”

Biochemical Composition of Chlorella Sorokiniana Grown in a Novel Design of Hybrid Photobioreactor

“…Therefore, initial cell density of 180 L culture was 105 cells mL -1 . The choice of 106 cells mL -1 maximum inoculum density was based on the results of Lombardi and Maldonado [6] that showed that 106 cells mL -1 is the maximum density permitted for high photosynthetic efficiency, a measurement microalgae health status. Thus, healthy beginning of the 180 L cultures was guaranteed by carefully controlling the inoculum density and cells' physiological conditions…”

“…During microalgal growth in batch cultures, chemical and physical variations in cell surroundings can affect photosynthetic efficiency [6] and βbiochemical composition [3,7,8] argued that such effects can be expected because cell division decreases and carbon is allocated to lipids and carbohydrates, so these molecules are increased at the expense of proteins.…”

“…Open ponds are also predisposed to culture contamination. Continuous or semi-continuous systems applied to closed photobioreactors for algal culture is one of the best methods to maintain cultures close to their maximum growth rate, hence under healthy physiological conditions [6]. Continuous cultures have the advantage of producing algae of more predictable quality (biochemical composition) and keeping cells under healthy conditions for longer periods than batch or fed-batch systems.…”