Optimization of CO2 Supply for the Intensive Cultivation of Chlorella sorokiniana IPPAS C-1 in the Laboratory and Pilot-Scale Flat-Panel Photobioreactors.

Microalgae are increasingly being used for capturing carbon dioxide and converting it into valuable metabolites and biologically active compounds on an industrial scale. The efficient production of microalgae biomass requires the optimization of resources, including CO2. Here, we estimated the productivity of Chlorella sorokiniana IPPAS C-1 depending on CO2 concentrations and the ventilation coefficient of the gas-air mixture (GAM) in flat-panel photobioreactors (FP-PBRs) at laboratory (5 L) and pilot (18 L) scales. For the laboratory scale, the PBRs operated at 900 µmol quanta m-2 s-1 and 35.5 ± 0.5 °C; the optimal CO2 flow rate was estimated at 3 mL CO2 per 1 L of suspension per minute, which corresponds to 1.5% CO2 in the GAM and an aeration rate of 0.2 vvm. These parameters, being scaled up within the pilot PBRs, resulted in a high specific growth rate (µ ≈ 0.1 h-1) and high specific productivity (Psp ≈ 1 g dw L-1 d-1). The principles of increasing the efficiency of the intensive cultivation of C. sorokiniana IPPAS C-1 are discussed. These principles are relevant for the development of technological regimes for the industrial production of Chlorella in flat-panel PBRs of various sizes.

Cultivation of Chlorella sorokiniana IPPAS C-1 in Flat-Panel Photobioreactors: From a Laboratory to a Pilot Scale.

Flat-panel photobioreactors are effective systems for microalgae cultivation. This paper presents the growth characteristics of the microalgae Chlorella sorokiniana IPPAS C-1 as a result of three-stage scale-up cultivation in a specially designed cultivation system. First, C. sorokiniana was grown aseptically in 250 mL glass vessels; then, it was diluted and inoculated into a 5-liter flat-panel horizontal photobioreactor; and, at the last stage, the culture was diluted and inoculated into a 70-liter flat-panel vertical photobioreactor. In the presented cycle, the cultured biomass increased by 326 times in 13 days (from 0.6 to 195.6 g dw), with a final biomass concentration of 2.8 g dw L-1. The modes of semi-continuous cultivation were considered. The biomass harvest and dilution of the suspension were carried out either every day or every 3-4 days. For C. sorokiniana IPPAS C-1, a conversion coefficient of optical density values to dry biomass (g L-1) was refined through a factor of 0.33. The key parameters of the photobioreactors tested in this work are discussed.

Highly active extracellular α-class carbonic anhydrase of Cyanothece sp. ATCC 51142.

Here, for the first time, we report the presence of highly active extracellular carbonic anhydrase (CA) of α-class in cyanobacterial cells. The enzyme activity was confirmed both in vivo in intact cells and in vitro, using the recombinant protein. CA activity in intact cells of Cyanothece sp. ATCC 51142 reached ∼0.6 Wilbur-Anderson units (WAU) per 1 mg of total cell protein, and it was inhibited by a specific CAs inhibitor, ethoxyzolamide. The genes cce_4328 (ecaA) and cce_0871 (ecaB), encoding two potential extracellular CAs of Cyanothece have been cloned, and the corresponding proteins EcaA and EcaB, representing CAs of α- and ß-class, respectively, have been heterologously expressed in Escherichia coli. High specific activity (∼1.1 × 104 WAU per 1 mg of target protein) was detected for the recombinant EcaA only. The presence of EcaA in the outer cellular layers of Cyanothece was confirmed by immunological analysis with antibodies raised against the recombinant protein. The absence of redox regulation of EcaA activity indicates that this protein does not possess a disulfide bond essential for some α-class CAs. The content and activity of EcaA in a fraction of periplasmic proteins was higher in Cyanothece cells grown at ambient concentration of CO2 (0.04%) compared to those grown at an elevated CO2 concentration (1.7%). At the same time, the level of ecaA gene mRNA varied insignificantly in response to changes in CO2 supply. Our results indicate that EcaA is responsible for CA activity of intact Cyanothece cells and point to its possible physiological role under low-CO2 conditions.

Hydrogen Peroxide Participates in Perception and Transduction of Cold Stress Signal in Synechocystis.

The double mutant ΔkatG/tpx of cyanobacterium Synechocystis sp. strain PCC 6803, defective in the anti-oxidative enzymes catalase (KatG) and thioredoxin peroxidase (Tpx), is unable to grow in the presence of exogenous H2O2. The ΔkatG/tpx mutant is shown to be extremely sensitive to very low concentrations of H2O2, especially when intensified with cold stress. Analysis of gene expression in both wild-type and ΔkatG/tpx mutant cells treated by combined cold/oxidative stress revealed that H2O2 participates in regulation of expression of cold-responsive genes, affecting either signal perception or transduction. The central role of a transmembrane stress-sensing histidine kinase Hik33 in the cold/oxidative signal transduction pathway is discussed.

Draft Genome Sequences of Two Thermotolerant Cyanobacterial Strains Isolated from Hot Springs.

We report here two draft cyanobacterial genome sequences, those of Cyanobacterium aponinum IPPAS B-1201, isolated from a hot spring in the Turgen Gorge (Kazakhstan), and the uncharacterized cyanobacterium IPPAS B-1203, isolated from a hot spring in Karlovy Vary (Czech Republic). These two strains were deposited at the Collection of Microalgae (IPPAS) of the Timiryazev Institute of Plant Physiology.