Growth and lipid synthesis promotion in mixotrophic Neochloris oleoabundans (Chlorophyta) cultivated with glucose

Abstract

In the recent years, the studies concerning the cultivation of Neochloris oleoabundans for biofuel purposes have increased, in relation to its capability to accumulate lipids when grown under nutrient starvation. Unfortunately, this cultivation mode does not allow to reach high biomass densities, which are required to improve the feasibility of the process. Increasing knowledge of the microalgal physiology is necessary to obtain new useful information for the improvement of culture performance in the perspective of large-scale cultivation. In this work, the mixotrophic cultivation of N. oleoabundans in a brackish medium added with different glucose concentrations has been tested under shaking, with the aim of stimulating growth alongside lipid accumulation inside cells. Cell morphology, glucose consumption, photosynthetic pigment content and photosynthetic efficiency were also investigated. Among all tested glucose concentrations (0-30 g L(-1)), it was observed that 2.5 g L(-1) was the optimal concentration, allowing to obtain the best compromise between glucose supplement, biomass production and lipid accumulation. Growth was highly enhanced in mixotrophic cultures, linked to the release of cells from sporocysts. A unique feature characterising mixotrophy in N. oleoabundans was the promotion of the maximum quantum yield of Photosystem II. Moreover, when mixotrophic cells entered the stationary phase, high lipid accumulation was induced. This study shows that the addition of glucose to N. oleoabundans remarkably increases the production of biomass enriched in lipids and represents an advancement for the cultivation of this microalga for applied purposes.

Use of lanthanides to alleviate the effects of metal ion-deficiency in Desmodesmus quadricauda (Sphaeropleales, Chlorophyta)

“…Physiological stress by nutrient limitation was specifically measured not only by declines in cellular growth and reproduction, but also in terms of photosynthetic parameters. PAM fluorometry has been shown to be an effective method to study stress (see Komenda, 1998 ; Mallick and Mohn, 2003 ; White et al, 2011 ; Figueroa et al, 2013 ; Giovanardi et al, 2014 ), and in this work, demonstrated a significant decrease in F v / F m , rETR max , E k , and α in comparison with standard conditions (Table 5 , Figures 3 , 4 ). For comparison, values of F v / F m expressed for different species of the genus Desmodesmus under different standard nutrient media ranged from 0.60 to 0.74 (see Komenda, 1998 ; Koblížek et al, 2001 ; Karsten et al, 2007 ; Hu et al, 2013 ; Samorí et al, 2013 ).…”

“…Aliquots (2 mL) of samples were harvested from the photobioreactors in pre-weighed tubes by centrifugation. The supernatant was discarded and pellets were dried at 105°C until they reached a constant weight (Giovanardi et al, 2014 ).…”

“…Pulse amplitude modulated (PAM) fluorometry is a valuable tool to detect physiological stress and to measure photosynthetic efficiency (Baker, 2008 ; White et al, 2011 ; Giovanardi et al, 2014 ). Photosystem II (PSII) is very sensitive to changes in the environment, and under unfavorable or stressful environmental conditions, such as strong light, high concentrations of salt, or low or high temperatures, the activity of PSII declines rapidly (measured as changes in the maximal quantum yield of PSII photochemistry, F v / F m ), so this parameter is often one of the earliest and most sensitive indicators of physiological stress (Figueroa et al, 2003 ; Hou and Hou, 2013 ).…”

“…Photosystem II (PSII) is very sensitive to changes in the environment, and under unfavorable or stressful environmental conditions, such as strong light, high concentrations of salt, or low or high temperatures, the activity of PSII declines rapidly (measured as changes in the maximal quantum yield of PSII photochemistry, F v / F m ), so this parameter is often one of the earliest and most sensitive indicators of physiological stress (Figueroa et al, 2003 ; Hou and Hou, 2013 ). Phytoplankton, growing under non-stressed conditions, normally presents relatively constant values of F v / F m in ranges from 0.6 to 0.7; a decrease in these values is interpreted as a stress condition (White et al, 2011 ; Samorí et al, 2013 ; Giovanardi et al, 2014 ).…”

Combining glucose and sodium acetate improves the growth of Neochloris oleoabundans under mixotrophic conditions

“…The effects of carbon supplementation were also studied by Giovanardi et al ( 2014 ), who observed that a lower concentration of glucose (2.5 g L −1 ) was optimal for boosting the cell density and lipid accumulation in the biomass of N. oleoabundans UTEX#1185. These authors also concluded that the growth of this microalga was limited when the glucose concentration was greater than 10.0 g L −1 .…”