Evaluation of light energy to H2 energy conversion efficiency in thin films of cyanobacteria and green alga under photoautotrophic conditions

Cyanobacteria and green algae harness solar energy to split water and to fix CO2. Under specific conditions, they are capable of photoproduction of molecular hydrogen (H2). This study compares the light-energy-to-hydrogen-energy conversion efficiency (LHCE) in two heterocystous, N2-fixing cyanobacteria (wild-type Calothrix sp. strain 336/3 and the δhupL mutant of Anabaena sp. strain PCC 7120) and in the sulfur-deprived green alga, Chlamydomonas reinhardtii strain CC-124, after entrapment of the cells in thin Ca2+-alginate films. The experiments, performed under photoautotrophic conditions, showed higher LHCEs in the cyanobacteria as compared to the green alga. The highest efficiency of ca. 2.5% was obtained in films of the entrapped δhupL strain under low light condition (2.9Wm-2). Calothrix sp. 336/3 films produced H2with a maximum efficiency of 0.6% under 2.9Wm-2, while C. reinhardtii films produced H2most efficiently under moderate light (0.14% at 12.1Wm-2). Exposure of the films to light above 16Wm-2led to noticeable oxidative stress in all three strains, which increased with light intensity. The presence of oxidative stress was confirmed by increased (i) degradation of chlorophylls and some structural carotenoids (such as β-carotene), (ii) production of hydroxylated carotenoids (such as zeaxanthin), and (iii) carbonylation of proteins. We conclude that the H2photoproduction efficiency in immobilized algae and cyanobacteria can be further improved by entrapping cultures in immobilization matrices with increased permeability for gases, especially oxygen, while matrices with low porosity produced increased amounts of xanthophylls and other antioxidant compounds.</p

A new approach for sustained and efficient H2 photoproduction by Chlamydomonas reinhardtii

Sustained H2 photoproduction is demonstrated in green algae under a train of strong white light pulses interrupted by longer dark phases. The devised protocol relies on the presence of the [FeFe]-hydrogenase in algal chloroplasts, which is activated within a few seconds after the establishment of anaerobiosis. H2 photoproduction proceeds for up to 3 days with the maximum rate occurring in the first 6 hours

Drought stress-induced upregulation of components involved in ferredoxin-dependent cyclic electron transfer

Linear photosynthetic electron transfer, consisting of both Photosystem (PS) II and PSI, converts light energy into the chemical forms ATP and NADPH, whereas PSI cyclic electron transfer (CET) is exclusively involved in ATP synthesis. In the chloroplasts of higher plants, there are two partially redundant CET routes. The ferredoxin (FD) or ferredoxin-plastoquinone reductase (FQR)-dependent route cycles electrons from PSI to plastoquinone via ferredoxin (FD), while in the NDH-dependent route, NADPH donates electrons to the NDH-complex for reduction of the plastoquinone pool. In the present study, we show that drought stress induces transcriptional and translational upregulation of the PCR5 and PGRL1 genes, which are the only characterized components of the FQR-dependent CET thus far. In contrast, the expression of the NDH-H gene, a representative of the NDH-complex, did not differ between the drought-stressed and the control plants. The overall expression level of the ferredoxin-NADP(+)-oxidoreductase (FNR) genes increased upon drought stress, with a concomitant release of FNR from the thylakoid membrane. Moreover, drought stress accelerated the rate of P700(+) re-reduction, which may indicate induction of CET. Responses of the PSAE, FD and PSAD gene families upon drought stress are also described. (C) 2010 Elsevier GmbH. All rights reserved

Dissecting the Photoprotective Mechanism Encoded by the flv4-2 Operon: a Distinct Contribution of Sll0218 in Photosystem II Stabilization

In Synechocystis sp. PCC 6803, the flv4-2 operon encodes the flavodiiron proteins Flv2 and Flv4 together with a small protein, Sll0218, providing photoprotection for Photosystem II (PSII). Here, the distinct roles of Flv2/Flv4 and Sll0218 were addressed, using a number of flv4-2 operon mutants. In the sll0218 mutant, the presence of Flv2/Flv4 rescued PSII functionality as compared with sll0218-flv2, where neither Sll0218 nor the Flv2/Flv4 heterodimer are expressed. Nevertheless, both the sll0218 and sll0218-flv2 mutants demonstrated deficiency in accumulation of PSII proteins suggesting a role for Sll0218 in PSII stabilization, which was further supported by photoinhibition experiments. Moreover, the accumulation of PSII assembly intermediates occurred in Sll0218-lacking mutants. The YFP-tagged Sll0218 protein localized in a few spots per cell at the external side of the thylakoid membrane, and biochemical membrane fractionation revealed clear enrichment of Sll0218 in the PratA-defined membranes, where the early biogenesis steps of PSII occur. Further, the characteristic antenna uncoupling feature of the flv4-2 operon mutants is shown to be related to PSII destabilization in the absence of Sll0218. It is concluded that the Flv2/Flv4 heterodimer supports PSII functionality, while the Sll0218 protein assists PSII assembly and stabilization, including optimization of light harvesting. This work clarifies and dissects the roles of the flv4-2 operon-encoded proteins, Flv2/Flv4 heterodimer and the elusive Sll0218, in photoprotection of the photosynthetic apparatus in Synechosystis. While Flv2/Flv4 heterodimer is involved in an alternative electron transfer route, the Sll0218 protein is localized to specific cell compartments where photosynthetic complexes are assembled, and it is involved in the stabilization of Photosystem II complexes

Functional redundancy between flavodiiron proteins and NDH-1 in Synechocystis sp. PCC 6803

In oxygenic photosynthetic organisms, excluding angiosperms, flavodiiron proteins (FDPs) catalyze light-dependent reduction of O(2)to H2O. This alleviates electron pressure on the photosynthetic apparatus and protects it from photodamage. InSynechocystissp. PCC 6803, four FDP isoforms function as hetero-oligomers of Flv1 and Flv3 and/or Flv2 and Flv4. An alternative electron transport pathway mediated by the NAD(P)H dehydrogenase-like complex (NDH-1) also contributes to redox hemostasis and the photoprotection of photosynthesis. Four NDH-1 types have been characterized in cyanobacteria: NDH-1(1)and NDH-1(2), which function in respiration; and NDH-1(3)and NDH-1(4), which function in CO(2)uptake. All four types are involved in cyclic electron transport. Along with single FDP mutants ( increment flv1and Delta flv3) and the double NDH-1 mutants ( increment d1d2, which is deficient in NDH-1(1,2)and increment d3d4, which is deficient in NDH-1(3,4)), we studied triple mutants lacking one of Flv1 or Flv3, and NDH-1(1,2)or NDH-1(3,4). We show that the presence of either Flv1/3 or NDH-1(1,2), but not NDH-1(3,4), is indispensable for survival during changes in growth conditions from high CO2/moderate light to low CO2/high light. Our results show functional redundancy between FDPs and NDH-1(1,2)under the studied conditions. We suggest that ferredoxin probably functions as a primary electron donor to both Flv1/3 and NDH-1(1,2), allowing their functions to be dynamically coordinated for efficient oxidation of photosystem I and for photoprotection under variable CO(2)and light availability

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the e'ort toward sustainable advanced functional materials, nanocellu- loses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entan- gled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modi- fiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional proper- ties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, bio- logical sca'olding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected per- spectives toward new directions for sustainable high-tech functional mate- rials science based on nanocelluloses are described. </div

Flavodiiron Proteins in Oxygenic Photosynthetic Organisms: Photoprotection of Photosystem II by Flv2 and Flv4 in Synechocystis sp. PCC 6803

BACKGROUND: Flavodiiron proteins (FDPs) comprise a group of modular enzymes that function in oxygen and nitric oxide detoxification in Bacteria and Archaea. The FDPs in cyanobacteria have an extra domain as compared to major prokaryotic enzymes. The physiological role of cyanobacteria FDPs is mostly unknown. Of the four putative flavodiiron proteins (Flv1-4) in the cyanobacterium Synechocystis sp. PCC 6803, a physiological function in Mehler reaction has been suggested for Flv1 and Flv3. PRINCIPAL FINDINGS: We demonstrate a novel and crucial function for Flv2 and Flv4 in photoprotection of photosystem II (PSII) in Synechocystis. It is shown that the expression of Flv2 and Flv4 is high under air level of CO(2) and negligible at elevated CO(2). Moreover, the rate of accumulation of flv2 and flv4 transcripts upon shift of cells from high to low CO(2) is strongly dependent on light intensity. Characterization of FDP inactivation mutants of Synechocystis revealed a specific decline in PSII centers and impaired translation of the D1 protein in Delta flv2 and Delta flv4 when grown at air level CO(2) whereas at high CO(2) the Flvs were dispensable. Delta flv2 and Delta flv4 were also more susceptible to high light induced inhibition of PSII than WT or Delta flv1 and Delta flv3. SIGNIFICANCE: Analysis of published sequences revealed the presence of cyanobacteria-like FDPs also in some oxygenic photosynthetic eukaryotes like green algae, mosses and lycophytes. Our data provide evidence that Flv2 and Flv4 have an important role in photoprotection of water-splitting PSII against oxidative stress when the cells are acclimated to air level CO(2). It is conceivable that the function of FDPs has changed during evolution from protection against oxygen in anaerobic microbes to protection against reactive oxygen species thus making the sustainable function of oxygen evolving PSII possible. Higher plants lack FDPs and distinctly different mechanisms have evolved for photoprotection of PSII