Knock-Down of the IFR1 Protein Perturbs the Homeostasis of Reactive Electrophile Species and Boosts Photosynthetic Hydrogen Production in <i>Chlamydomonas reinhardtii</i>

Venkanna D, Südfeld C, Baier T, et al. Knock-Down of the IFR1 Protein Perturbs the Homeostasis of Reactive Electrophile Species and Boosts Photosynthetic Hydrogen Production in &lt;i&gt;Chlamydomonas reinhardtii&lt;/i&gt;. Frontiers in Plant Science. 2017;8: 1347.The protein superfamily of short-chain dehydrogenases/reductases (SDR), including members of the atypical type (aSDR), covers a huge range of catalyzed reactions and in vivo substrates. This superfamily also comprises isoflavone reductase-like (IRL) proteins, which are aSDRs highly homologous to isoflavone reductases from leguminous plants. The molecular function of IRLs in non-leguminous plants and green microalgae has not been identified as yet, but several lines of evidence point at their implication in reactive oxygen species homeostasis. The Chlamydomonas reinhardtii IRL protein IFR1 was identified in a previous study, analyzing the transcriptomic changes occurring during the acclimation to sulfur deprivation and anaerobiosis, a condition that triggers photobiological hydrogen production in this microalgae. Accumulation of the cytosolic IFR1 protein is induced by sulfur limitation as well as by the exposure of C. reinhardtii cells to reactive electrophile species (RES) such as reactive carbonyls. The latter has not been described for IRL proteins before. Over-accumulation of IFR1 in the singlet oxygen response 1 (sor1) mutant together with the presence of an electrophile response element, known to be required for SOR1-dependent gene activation as a response to RES, in the promoter of IFR1, indicate that IFR1 expression is controlled by the SOR1-dependent pathway. An implication of IFR1 into RES homeostasis, is further implied by a knock-down of IFR1, which results in a diminished tolerance toward RES. Intriguingly, IFR1 knock-down has a positive effect on photosystem II (PSII) stability under sulfur-deprived conditions used to trigger photobiological hydrogen production, by reducing PSII-dependent oxygen evolution, in C. reinhardtii. Reduced PSII photoinhibition in IFR1 knock-down strains prolongs the hydrogen production phase resulting in an almost doubled final hydrogen yield compared to the parental strain. Finally, IFR1 knock-down could be successfully used to further increase hydrogen yields of the high hydrogen-producing mutant stm6, demonstrating that IFR1 is a promising target for genetic engineering approaches aiming at an increased hydrogen production capacity of C. reinhardtii cells

Microalgae growth and oxygen production on different textile fabrics

Microalgae can be used for diverse applications in research and industry. Several microalgae grow adhering to surfaces that are usually two-dimensional. A third dimension could increase the amount of microalgae adhering to a given area and can be offered by textile fabrics. Here we report on the microalgae Chlorella vulgaris and Scenedesmus spec. growing on different knitted fabrics under defined light and under office light conditions. Our results show a significant influence of illumination on both algal species and a smaller impact of the chosen medium, while all knitted fabrics under examination were found well suited as substrates. The numbers of alga cells per petri dish were higher on textile fabrics than in pure water or medium by a factor of ~ 4–20, respectively

Development of biocompatible sol-gel methods for microalgae entrapment

Homburg SV. Development of biocompatible sol-gel methods for microalgae entrapment. Bielefeld: Universität Bielefeld; 2019

Silica Hydrogels as Entrapment Material for Microalgae

Homburg SV, Patel A. Silica Hydrogels as Entrapment Material for Microalgae. Polymers. 2022;14(7): 1391.Despite being a promising feedstock for food, feed, chemicals, and biofuels, microalgal production processes are still uneconomical due to slow growth rates, costly media, problematic downstreaming processes, and rather low cell densities. Immobilization via entrapment constitutes a promising tool to overcome these drawbacks of microalgal production and enables continuous processes with protection against shear forces and contaminations. In contrast to biopolymer gels, inorganic silica hydrogels are highly transparent and chemically, mechanically, thermally, and biologically stable. Since the first report on entrapment of living cells in silica hydrogels in 1989, efforts were made to increase the biocompatibility by omitting organic solvents during hydrolysis, removing toxic by-products, and replacing detrimental mineral acids or bases for pH adjustment. Furthermore, methods were developed to decrease the stiffness in order to enable proliferation of entrapped cells. This review aims to provide an overview of studied entrapment methods in silica hydrogels, specifically for rather sensitive microalgae

The project COMBINE - Co-cultivation of microalgae and bacteria

Homburg SV, Patel A. The project COMBINE - Co-cultivation of microalgae and bacteria. In: Special Issue: ProcessNet‐Jahrestagung und 33. DECHEMA‐Jahrestagung der Biotechnologen 2018. Chemie Ingenieur Technik. Vol 90. Wiley; 2018: 1183-1183

Silica Hydrogels as Entrapment Material for Microalgae

Despite being a promising feedstock for food, feed, chemicals, and biofuels, microalgal production processes are still uneconomical due to slow growth rates, costly media, problematic downstreaming processes, and rather low cell densities. Immobilization via entrapment constitutes a promising tool to overcome these drawbacks of microalgal production and enables continuous processes with protection against shear forces and contaminations. In contrast to biopolymer gels, inorganic silica hydrogels are highly transparent and chemically, mechanically, thermally, and biologically stable. Since the first report on entrapment of living cells in silica hydrogels in 1989, efforts were made to increase the biocompatibility by omitting organic solvents during hydrolysis, removing toxic by-products, and replacing detrimental mineral acids or bases for pH adjustment. Furthermore, methods were developed to decrease the stiffness in order to enable proliferation of entrapped cells. This review aims to provide an overview of studied entrapment methods in silica hydrogels, specifically for rather sensitive microalgae

Atomic Force Microscopy (AFM) on Biopolymers and Hydrogels for Biotechnological Applications—Possibilities and Limits

Joshi J, Homburg SV, Ehrmann A. Atomic Force Microscopy (AFM) on Biopolymers and Hydrogels for Biotechnological Applications—Possibilities and Limits. Polymers. 2022;14(6): 1267.Atomic force microscopy (AFM) is one of the microscopic techniques with the highest lateral resolution. It can usually be applied in air or even in liquids, enabling the investigation of a broader range of samples than scanning electron microscopy (SEM), which is mostly performed in vacuum. Since it works by following the sample surface based on the force between the scanning tip and the sample, interactions have to be taken into account, making the AFM of irregular samples complicated, but on the other hand it allows measurements of more physical parameters than pure topography. This is especially important for biopolymers and hydrogels used in tissue engineering and other biotechnological applications, where elastic properties, surface charges and other parameters influence mammalian cell adhesion and growth as well as many other effects. This review gives an overview of AFM modes relevant for the investigations of biopolymers and hydrogels and shows several examples of recent applications, focusing on the polysaccharides chitosan, alginate, carrageenan and different hydrogels, but depicting also a broader spectrum of materials on which different AFM measurements are reported in the literature

Entrapment of Green Algae in Novel Silica Gels

Homburg SV, Kruse O, Patel A. Entrapment of Green Algae in Novel Silica Gels. In: Special Issue: ProcessNet‐Jahrestagung und 32. DECHEMA‐Jahrestagung der Biotechnologen 2016. Chemie Ingenieur Technik. Vol 88. Wiley; 2016: 1243-1244

Growth and photosynthetic activity of Chlamydomonas reinhardtii entrapped in lens-shaped silica hydrogels.

Homburg SV, Kruse O, Patel A. Growth and photosynthetic activity of Chlamydomonas reinhardtii entrapped in lens-shaped silica hydrogels. Journal of biotechnology. 2019;302(302):58-66.Entrapment of microalgae in silica hydrogels enables the application as biocatalysts in continuous production of secreted products. Despite a mitigation of substrate and product diffusion limitations by lens-shaped particles, there are no reports on light supply and limitation. This study investigated the impact of hydrogel structure, particle size and biomass loading on the behaviour of the microalga Chlamydomonas reinhardtii entrapped in lens-shaped silica particles. Entrapment in tetraethyl orthosilicate and tetra(n-propylamino)silane based hydrogels reduced the growth rate by 30% and 23%, respectively. In contrast, cells entrapped in sodium silicate based hydrogels displayed a growth rate similar to free cells and cells entrapped in calcium alginate (1.13 d-1), indicating a suitable biocompatibility. Reduction of lens height by 26% maintained the growth rate in silica hydrogel. A fourfold increase in biomass loading reduced the growth rate by 20% and elevated the yield coefficient by 211%, indicating the impact of biomass loading on light and nutrient supply on photosynthetic growth. Finally, hydrogen production was observed by entrapped cells. The results of this work will pave the way for robust biocatalytic processes where photosynthetically active cells are protected against harmful mechanical and biological influences. Copyright © 2019. Published by Elsevier B.V

Atomic Force Microscopy (AFM) on Biopolymers and Hydrogels for Biotechnological Applications&mdash;Possibilities and Limits

Atomic force microscopy (AFM) is one of the microscopic techniques with the highest lateral resolution. It can usually be applied in air or even in liquids, enabling the investigation of a broader range of samples than scanning electron microscopy (SEM), which is mostly performed in vacuum. Since it works by following the sample surface based on the force between the scanning tip and the sample, interactions have to be taken into account, making the AFM of irregular samples complicated, but on the other hand it allows measurements of more physical parameters than pure topography. This is especially important for biopolymers and hydrogels used in tissue engineering and other biotechnological applications, where elastic properties, surface charges and other parameters influence mammalian cell adhesion and growth as well as many other effects. This review gives an overview of AFM modes relevant for the investigations of biopolymers and hydrogels and shows several examples of recent applications, focusing on the polysaccharides chitosan, alginate, carrageenan and different hydrogels, but depicting also a broader spectrum of materials on which different AFM measurements are reported in the literature