Impact of phosphorus quota and growth phase on carbon allocation inChlamydomonas reinhardtii: an FTIR microspectroscopy study

Abstract

Batch cultures of Chlamydomonas reinhardtii were used to study carbon allocation in relation to growth phase and phosphorus availability. Cultures were grown at initial phosphorus (PO 4 -P) concentrations of 500 mg l À1 (high-P) and 50 mg l À1 (low-P).Cellular carbon allocation was monitored using Fourier transform infrared (FTIR) microspectroscopy with the ratio of the band intensities at 1736 cm À1 (lipid) and the 1180-950 cm À1 region (carbohydrate) to 1652 cm À1 (amide I) used as an index of changing carbon balance. Cellular phosphorus concentrations (P quota) were measured by energy dispersive X-ray microanalysis (EDXRMA). Both treatments entered stationary phase on day 18. Increased cell counts in the high-P treatment (max. 3.0 Â 10 6 cells ml À1 at stationary phase) led to a rapid decrease in external P availability to <20 mg l À1 during early log phase, with a subsequent decrease in P quota from 0.5% to <0.1% DW. The fall of P quota to <0.1% led to an increase in the lipid/protein ratio (0.13 to 0.23) and carbohydrate/protein ratio (0.37 to 1.57), with ratios increasing further (lipid:protein 1.85; carbohydrate:protein 2.77) in late stationary phase. In the low-P treatment external P concentrations (<20 mg l À1 from day 1) restricted population growth (max. 0.75 Â 10 6 cells ml À1 at stationary phase). P quotas fell to <0.1% in early log phase, with the carbohydrate/protein ratio increasing from 0.15 to 3.7 and remaining high into stationary phase while the lipid/ protein ratio increased from 0.2 to 1.2. In both treatments increasing synthesis of lipid and carbohydrate storage products resulted in an increased cell volume. Transfer of P-deficient cells (late stationary) to fresh media led to a rapid stimulation of growth, a rapid reduction in lipid/protein and carbohydrate/protein ratios, and decreased cell volumes.

Phosphate-induced changes in fatty acid biosynthesis in Chlorella sp. KS-MA2 strain

“…2B). When cell division slows down, there is no requirement for the synthesis of new membrane compounds and instead cells divert fatty acids into TAG (Dean et al, 2008). Our results indicated that fatty acid biosynthesis catalyzed that by KAS1 was highly correlated with Chlorella biomass (Table 2).…”

Changing patterns of carbon allocation in lake phytoplankton: an FTIR analysis

“…Earlier laboratory studies using both bulk analysis (Healey & Hendzel, 1979;Ganff et al, 1986;Kilham et al, 1997) and FTIR techniques (Beardall et al, 2001;Stehfest et al, 2005) have shown that changes in the C/P ratio and the L/P ratio of algal monocultures are indicative of P deficiency. Two studies combining FTIR with X-ray microanalysis on laboratory cultures of Chlamydomonas reinhardtii and Scenedesmus subspicatus Dean et al, 2008a) have shown that, under conditions of P-depletion, Q ph values fell below a critical value of 0.1%, triggering the increases in L/P and C/P ratios. Corresponding studies on P-limited A. flos-aquae (Dean et al, 2008b) revealed Q ph values falling to 0.01%, with a significant increase in the carbohydrate/protein ratio at this Q ph level.…”

“…The technique has recently been used to study physiological changes in microalgae in relation to changes in carbon allocation in laboratory monocultures (Beardall et al, 2001;Giordano et al, 2001;Stehfest et al, 2005;Sigee et al, 2007;Dean et al, 2008aDean et al, , b, 2010. These studies have shown that conditions of nutrient deprivation lead to relative increases in the synthesis of lipids and carbohydrates, resulting in elevated lipid/protein (L/P) and carbohydrate/protein (C/P) ratios.…”

Title: Freshwater phytoplankton responses to global warming

“…On the other hand, N-replete cells showing high metabolic rates are characterized by a higher amount of proteins and ribosomes per cell (50% and 60% more, respectively) (Schmollinger et al, 2014). Analogue responses have been reported under conditions of P-limitation (Dean et al, 2008;Heraud et al, 2008).…”