Tomáš Brányik

Microalgae—novel highly efficient starch producers

The freshwater alga Chlorella, a highly productive source of starch, might substitute for starch‐rich terrestrial plants in bioethanol production. The cultivation conditions necessary for maximizing starch content in Chlorella biomass, generated in outdoor scale‐up solar photobioreactors, are described. The most important factor that can affect the rate of starch synthesis, and its accumulation, is mean illumination resulting from a combination of biomass concentration and incident light intensity. While 8.5% DW of starch was attained at a mean light intensity of 215 µmol/(m2 s1), 40% of DW was synthesized at a mean light intensity 330 µmol/(m2 s1). Another important factor is the phase of the cell cycle. The content of starch was highest (45% of DW) prior to cell division, but during the course of division, its cellular level rapidly decreased to about 13% of DW in cells grown in light, or to about 4% in those kept in the dark during the division phase. To produce biomass with high starch content, it is necessary to suppress cell division events, but not to disturb synthesis of starch in the chloroplast. The addition of cycloheximide (1 mg/L), a specific inhibitor of cytoplasmic protein synthesis, and the effect of element limitation (nitrogen, sulfur, phosphorus) were tested. The majority of the experiments were carried out in laboratory‐scale photobioreactors, where culture treatments increased starch content to up to about 60% of DW in the case of cycloheximide inhibition or sulfur limitation. When the cells were limited by phosphorus or nitrogen supply, the cellular starch content increased to 55% or 38% of DW, respectively, however, after about 20 h, growth of the cultures stopped producing starch, and the content of starch again decreased. Sulfur limited and cycloheximide‐treated cells maintained a high content of starch (60% of DW) for up to 2 days. Sulfur limitation, the most appropriate treatment for scaled‐up culture of starch‐enriched biomass, was carried out in an outdoor pilot‐scale experiment. After 120 h of growth in complete mineral medium, during which time the starch content reached around 18% of DW, sulfur limitation increased the starch content to 50% of DW. Biotechnol. Bioeng. 2011; 108:766–776.

Adhesion of Chlorella vulgaris to solid surfaces, as mediated by physicochemical interactions

Although adhesion of bacteria and yeast have been extensively studied by a wide range of experimental and theoretical approaches, significantly less attention has been focused on microalgae adhesion to solid materials. This work is focused on physicochemical aspects of microalgae adhesion. The results are based on experimental characterization of surface properties of both microalgae and solids by contact angle and zeta potential measurements. These data are used in modeling the surface interactions (thermodynamic and colloidal models) resulting in quantitative prediction of the interaction intensities. Finally, the model predictions are compared with experimental adhesion tests of microalgae onto model solids in order to identify the physicochemical forces governing the microalgae–solid interaction. The model solids were prepared in order to cover a wide range of properties (hydrophobicity and surface charge). The results revealed that, in low ionic strength environment, the adhesion was influenced mostly by electrostatic attraction/repulsion between surfaces, while with increasing ionic strength grew the importance of apolar (hydrophobic) interactions. The impact of solid surface properties on the degree of colonization by microlagae was statistically more significant than the influence of medium composition on cell surface of Chlorella vulgaris.

Repetitive inductions of bioluminescence of Pseudomonas putida TVA8 immobilised by adsorption on optical fibre

Physico-chemical models of the interactions of cells with solid surfaces, which use contact angles and zeta potentials, indicated more facile adsorption of cells of Pseudomonas putida TVA8 on the quartz surface after its treatment with 3-aminopropyltriethoxysilane (APTES). A whole-cell optical fibre sensor of toluene was prepared by the adsorption of P. putida TVA8, bacteria producing light in contact with toluene on the wider end of APTES- treated quartz tapered optical fibre. The results of the measurements of luminescence from both sides of the layer of adsorbed cells were compared. Over the 135 days trial, the fibre biosensor was repetitively induced with toluene solution (26.5 mg L−1) 68 times. The intensities of bioluminescence gradually decreased due to release of the adsorbed cells and they were only temporarily restored by the addition of nutrients. The intensities of bioluminescence induced with contaminated ground water were lower than in the mineral medium (MSM) with the same content of toluene.

Magnetically modified microalgae and their applications

Abstract The majority of algal cells can interact with a wide range of nano- and microparticles. Upon interaction the modified cells usually maintain their viability and the presence of foreign material on their surfaces or in protoplasm can provide additional functionalities. Magnetic modification and labeling of microalgal biomass ensures a wide spectrum of biotechnological, bioanalytical and environmental applications. Different aspects of microalgal cell magnetic modification are covered in the review, followed by successful applications of magnetic algae. Modified cells can be employed during their harvesting and removal, applied in toxicity microscreening devices and also as efficient adsorbents of different types of xenobiotics.

Erratum to: Selective bioaccumulation of rubidium by microalgae from industrial wastewater containing rubidium and lithium

Bioaccumulation of rubidium (Rb+) and lithium (Li+) from alkaline wastewater containing 480 mg L−1 Rb+ and 540 mg L−1 Li+, a by-product of zinnwaldite processing, was studied at laboratory scale using growing freshwater microalgae (Chlorella vulgaris, Desmodesmus quadricauda and Scenedesmus obliquus). Bioaccumulation of Li+ was very low, while the bioaccumulation of Rb+ was significant by all tested strains. The best result was found for C. vulgaris, which accumulated 54% of the original amount of rubidium in growth media (48 mg L−1) within 4 days. In addition, the wastewater did not affect the growth rate of C. vulgaris. The effect of potassiun (K+) concentration on total bioaccumulation of alkali metal ions and its selectivity by C. vulgaris was also tested. The highest K+ concetration (334 mg L−1) resulted in bioaccumulation of 4.3 mg Rb+ per gram of biomass with Rb+:Li+ uptake ratio of 26.9. By decreasing the K+ concetration in medium (56 mg L−1), the total bioaccumulation improved (4.70 Li+ per gram of biomass, 5.93 Rb+ per gram of biomass) but at the cost of lower selectivity (Rb+:Li+ uptake ratio 1.3). These findings have a potential of practical utilization, as both Rb+ and Li+can be recovered from biomass by incineration and subsequent chemical separation.

EFFECT OF XANTHOHUMOL ON BREWING YEAST CELLS

Xanthohumol, a prenylated chalcone from hops and beer, is a phenolic compound that has received considerable attention in recent years. This compound has a range of interesting biological properties that may have therapeutic utility: anti-inflammatory, antioxidant, antilipoperoxidative activities as well as antiangiogenic, antiproliferative and apoptotic effects, mainly assessed in vitro studies that reasonably suggest a potential chemopreventive activity. Phenomenon how xanthohumol affects brewing yeast’s metabolism, yeast viability and vitality were studied during the production of a xanthohumol enriched beer (10 mg/L xanthohumol). The results showed that yeast viability was slightly decreased by xanthohumol, but on the other hand yeast vitality in the xanthohumol enriched brewing trials was slightly better. The content of higher alcohols and esters was similar to the control in all the xanthohumol enriched brewing trials. In laboratory scale experiment about effect of xanthohumol on brewing yeast growing was done. No effect of xanthohumol on yeast growth was detected. Due to the fact that yeast viability was slightly decreased by xanthohumol, experiment with zymolyase was done. Yeast cells cultivated with xanthohumol are significantly more sensitive to zymolyase treatment.