Dynamics modeling of hydrogen production by sulfur-deprived Chlamydomonas reinhardtii culture in tubular photobioreactor

A heterogeneous hydrogen production system induced by light attenuation across the culture in a photobioreactor and the boundary conditions is studied by solving the advective-diffusive reaction equation (ADRE) used to describe the system. A uniform light intensity is prescribed on the cylindrical surface of the tubular bioreactor and attenuated by Chlamydomonas reinhardtii culture toward the center. The rate constants and the kinetics orders of the S-system based kinetics equations were determined by correlating with the available experimentally measured data. The photobioreactor was operated for 200 h and the dynamics behavior of O₂ evolution and H₂ production were analyzed. The effects of different initial chlorophyll concentrations and quantities of sulfur re-added to the sulfur deprived culture on H₂ production were studied. The results demonstrate that H₂ production decreases with the light attenuation along radial direction. The overall H₂ production increases with the initial cell concentration and the amount of re-added sulfur, respectively, within the simulated range. The modeled results indicate that optimal combination of the culture parameters under the given light intensity and the mixing condition may exist for high H₂ production.     

Flocculation of wall-deficient cells of Chlamydomonas reinhardtii mutant cw15 by calcium and methanol

Flocculation is a common and inexpensive method for harvesting algae from solution. After nitrogen starvation, it was shown that 83 ± 3% of the wall-deficient cells of the cw 15 mutant of Chlamydomonas reinhardtii flocculated from 12 mL samples within 15 min after the addition of 15 mM calcium chloride at pH 8.4. Only 24 ± 2% of the wildtype strain flocculated under these conditions, thus demonstrating how a simple mutation might facilitate process design. The data suggested that algae grown in waters with similar calcium concentrations (e.g. certain wastewaters) might be harvested through simple pH adjustment. It was also discovered that the addition of small amounts (<5% v/v) of methanol could significantly reduce the calcium needed to achieve flocculation. Within 15 min after addition of 12 mM calcium chloride and 4.6% (v/v) methanol, 83 ± 4% of cw15 cells flocculated. Methanol is fully recoverable by distillation, and its use might enable flocculation without further water salinization when media calcium concentrations fall short of 15 mM. It was further shown that substrates for and/or products of cellular growth affected flocculation adversely. Nearly 81% of cells flocculated from fresh medium compared to only 54% in spent medium.     

Repeated production of hydrogen by sulfate re-addition in sulfur deprived culture of Chlamydomonas reinhardtii

Biological hydrogen production by the green alga, Chlamydomonas reinhardtii can be induced in conditions of sulfur deprivation. In this study, we investigated the repeated and enhanced hydrogen production afforded by the re-addition of sulfate with monitoring of pH and concentration of chlorophyll and sulfate. Without adjustment of the pH, the optimal concentration of re-added sulfate was 30 μM for the hydrogen production. By the re-addition of 30 μM of sulfate and the adjustment of the pH during 4 cycles of repeated production, we obtained the maximum amount of 789 ml H₂ l⁻¹ culture, which is 3.4 times higher than that of one batch production without adjustment of pH, 236 ml H₂ l⁻¹ culture. This means that the enhancement of the hydrogen production can be achieved by the careful control of the sulfate re-addition and pH adjustment in the sulfur deprived culture.     

Lipidomic profiling and discovery of lipid biomarkers in snow alga Chlamydomonas nivalis under salt stress

The snow alga Chlamydomonas nivalis is a typical microalgal species that can adapt and resist to natural habitats in the polar region and similar extreme environments. In response to various stress conditions, the change of lipid profile in cell membrane systems is known to play a vital role in cell survival and reproduction. In the present work, to elucidate the involvement of intracellular lipids in the molecular mechanism of cell response and adaptation to salt stress, C. nivalis was cultured and treated with different sodium chloride (NaCl) concentrations in different time courses. The ultra performance liquid chromatography/quadrupole‐TOF‐MS (UPLC/Q‐TOF‐MS)‐based approach was developed for lipidomic profiling followed by multivariate statistical analysis including partial least squares discriminant analysis and orthogonal projection on latent structure discriminant analysis for data classification and potential biomarkers selection. Seven types and 35 kinds of polar lipid molecules were selected and identified as biomarkers, including monogalactosyldiacylglycerol, digalactosyldiacylglycerol, l, 2‐diacylglyceryl‐3‐O‐4′‐(N,N,N‐trimethyl)‐homoserine, phosphatidylglycerol, sulfoquinovosyl‐diacylglycerol, phosphatidylethanolamine, and phosphatidylinositiol. Their functions in relation to the regulation of cell membrane stability, signal transduction and photosynthesis efficiency under salt stress are also discussed in this paper. This is the first study using UPLC/Q‐TOF‐MS‐based lipidomic profiling with multivariate statistical analysis for lipid biomarkers discovery from microalgae in response to stress conditions.     

Rapid Detection and Quantification of Triacylglycerol by HPLC–ELSD in Chlamydomonas reinhardtii and Chlorella Strains

Triacylglycerol (TAG) analysis and quantification are commonly performed by first obtaining a purified TAG fraction from a total neutral lipid extract using thin-layer chromatography (TLC), and then analyzing the fatty acid composition of the purified TAG fraction by gas chromatography (GC). This process is time-consuming, labor intensive and is not suitable for analysis of small sample sizes or large numbers. A rapid and efficient method for monitoring oil accumulation in algae using high performance liquid chromatography for separation of all lipid classes combined with detection by evaporative light scattering (HPLC–ELSD) was developed and compared to the conventional TLC/GC method. TAG accumulation in two Chlamydomonas reinhardtii (21 gr and CC503) and three Chlorella strains (UTEX 1230, CS01 and UTEX 2229) grown under conditions of nitrogen depletion was measured. The TAG levels were found to be 3–6 % DW (Chlamydomonas strains) and 7–12 % DW (Chlorella strains) respectively by both HPLC–ELSD and TLC/GC methods. HPLC–ELSD resolved the major lipid classes such as carotenoids, TAG, diacylglycerol (DAG), free fatty acids, phospholipids, and galactolipids in a 15-min run. Quantitation of TAG content was based on comparison to calibration curves of trihexadecanoin (16:0 TAG) and trioctadecadienoin (18:2 TAG) and showed linearity from 0.2 to 10 μg. Algal TAG levels >0.5 μg/g DW were detectable by this method. Furthermore TAG content in Chlorella kessleri UTEX 2229 could be detected. TAG as well as DAG and TAG content were estimated at 1.6 % DW by HPLC–ELSD, while it was undetectable by TLC/GC method.     

The microalgae derived hydrogen process in compact photobioreactors

This paper investigates the feasibility of a microalgae derived hydrogen process at a pilot scale. For that, a general transient mathematical model for managing microalgae derived hydrogen production, with temperature dependence of the cultivation medium is developed. The tool allows for the determination of the resulting whole system temperature, and mass fractions distribution. The simplified physical model combines principles of classical thermodynamics, mass, species and heat transfer, resulting in a system of differential equations which are discretized in space using a three-dimensional cell-centered finite volume scheme, namely a volume element model (VEM). A Michaelis–Menten type expression is proposed for modeling the rate of H₂ production with dependence on O₂ inhibition. Tridimensional simulations are performed in order to determine the mass fractions distributions inside a compact photobioreactor (PBR), under different operating conditions. A relatively coarse mesh was used (6048 volume elements) to obtain converged results for a large compact PBR computational domain (2 m × 5 m × 8 m). The largest computational time required for obtaining results was 560 s, i.e., less than 10 min. The numerical results for microalgal growth are validated by direct comparison to experimental measurements. Hydrogen production simulations are conducted to demonstrate PBR intermittent operation (aerobic and anaerobic stages) feasibility and adequate species evolution trends in an indirect biophotolysis approach. Therefore, after experimental validation for a particular H₂ production system, it is reasonable to state that the model could be used as an efficient tool for PBR systems thermal design, control and optimization for maximum H₂ production.     

Light-Dependent Nitrate Removal Capacity of Green Microalgae

In the present study, Chlamydomonas sp. MACC-216 was used to investigate total nitrate removal in TAP medium with sodium nitrate as the sole nitrogen source under several light conditions made up of permuted combinations of three light colors (referred to as blue, red, and white light) and three light intensities (50 µmol m⁻² s⁻¹, 100 µmol m⁻² s⁻¹, and 250 µmol m⁻² s⁻¹). It was observed that nitrate removal efficiency is influenced by light color as well as light intensity. Additionally, Chlamydomonas sp. MACC-216 was cultivated in synthetic wastewater under four light conditions, namely, Blue 250, Blue 125 + Red 125, Red 250, and White 250, where it showed the highest nitrate removal efficiency and nitrate reductase activity under the Blue 125 + Red 125 light condition. To observe the impact of light color on the nitrate removal capacity of Chlamydomonas sp. MACC-216, the expression of five genes participating in nitrate transport and reduction (NRT1, NRT2.1, NRT2.2, NIA, and MCP) was also analyzed; these genes showed the highest expression under the Blue 125 + Red 125 light condition. Based on the above-mentioned findings, the blue + red light combination emerged as a promising light combination for nitrate removal. Hence, our study suggests the importance of the blue + red light combination together with high light intensity, as the optimal light condition for nitrate removal from synthetic wastewater in comparison to other monochromatic lights with high light intensity.     

Central Apparatus,the Molecular Kickstarter of Ciliary and Flagellar Nanomachines

Motile cilia and homologous organelles, the flagella, are an early evolutionarily invention, enabling primitive eukaryotic cells to survive and reproduce. In animals, cilia have undergone functional and structural speciation giving raise to typical motile cilia, motile nodal cilia, and sensory immotile cilia. In contrast to other cilia types, typical motile cilia are able to beat in complex, two-phase movements. Moreover, they contain many additional structures, including central apparatus, composed of two single microtubules connected by a bridge-like structure and assembling numerous complexes called projections. A growing body of evidence supports the important role of the central apparatus in the generation and regulation of the motile cilia movement. Here we review data concerning the central apparatus structure, protein composition, and the significance of its components in ciliary beating regulation.