A complete energy balance from photons to new biomass reveals a light- and nutrient-dependent variability in the metabolic costs of carbon assimilation

Abstract

The energy balance of Phaeodactylum tricornutum cells from photon to biomass have been analysed under nutrient-replete and N-limiting conditions in combination with fluctuating (FL) and non-fluctuating (SL) dynamic light. For this purpose, the amount of photons absorbed has been related to electrons transported by photosystem II, to gas exchange rates, and to the newly formed biomass differentially resolved into carbohydrates, proteins, and lipids measured by means of Fourier transform infrared (FTIR) spectroscopy. Under high nutrient conditions, the quantum efficiency of carbon-related biomass production (Phi(C)) and the metabolic costs of carbon (C) production were found to be strongly controlled by the light climate. Under N-limited conditions, the light climate was less important for the efficieny of primary production. Thus, the largest range of Phi(C) dependent on the nutrient status of the cells was observed under non-fluctuating light conditions which are comparable with stratified conditions in the natural environment. It is evident that N limitation induced pronounced changes in the composition of macromolecular compounds and, thus, influenced the degree of reduction of the biomass as well as the metabolic costs of C production. However, Phi(C) and the metabolic costs are not predictable from the photosynthesis rates. In consequence, the results clearly show that bio-optical methods as well as gas exchange measurements during the light phase can severely mismatch the true energy storage in the biomass especially under high nutrient in combination with non-fluctuating light conditions.

The use of FTIR spectroscopy to assess quantitative changes in the biochemical composition of microalgae

“…For example, the allocation of carbon into the protein pool requires roughly 60% more electrons than its allocation into the carbohydrate pool [38]. Hence, an increased carbohydrate to protein ratio will result in lower energy content of the biomass, as has been shown in P. tricorntum under nitrogen limitation [14] and in C. acidophila under different external pH values [39]. Our present results reveal a changing degree of reduction in algal biomass in a daily course even under constant light and non-limiting nutrient conditions.…”

“…Here we focus on the chemical composition of phytoplankton cells as it is an important indicator of their physiological state, reflecting, for example, the trophic status of an aquatic ecosystem [6][7][8]. It has been shown that nitrogen limitation increases the C/N ratio because reduced synthesis of amino acid and proteins leads to an increasing portion of carbon stored in carbohydrates and/or lipids [9][10][11][12][13][14]. In addition, it is generally agreed that the optimal ratios of macromolecular compounds are species-specific [15][16][17][18].…”

“…A previous study showed that FTIR spectroscopy has the potential to overcome the limitations of biochemical methods [3] and proved to be a sensitive technique to study species-specific changes in the molecular composition of microalgae, even at the single cell level [21]. In Jakob et al [14] a first attempt was made to use FTIR spectroscopy as a quantitative tool. However, the calculations of the macromolecular ratios in the former study have been performed with different equations that are not included in standard spectroscopy software and the results lack a systematic method evaluation.…”

Differential Transcriptional Analysis of the Cyanobacterium Cyanothece sp. Strain ATCC 51142 during Light-Dark and Continuous-Light Growth

“…We therefore determined the glycogen content using an FTIR spectrometer, which permitted careful analysis with small culture volumes. The absorption maxima of the IR spectra can be assigned to different macromolecules (24). The absorption around 1,000 to 1,200 cm Ϫ1 can be assigned to carbohydrates, and an increased absorption at these wave numbers is a result of an accumulation of carbohydrates.…”

Photosynthesis of microalgae in outdoor mass cultures and modelling its effects on biomass productivity for fuels, feeds and chemicals

“…Even under steady state optimal light, an estimated 25% of electrons produced by PSII are lost to alternative electron flows in C. reinhardtii, rather than used for NADP + reduction and this increases under light stress (Wagner et al, 2006, Jakob et al, 2007.…”