Anaerobic Photosynthetic Bacteria Research Articles

Molecular and carbon isotopic evidence of pigments indicating a dynamic oceanic chemocline 1.4 billion years ago in northern China

The redox state of the marine photic zone is crucial to the evolution of life, which is further linked to the degree of oxygenation of the atmosphere and ocean systems. Hydrocarbon molecular fossils (biomarkers) and isotopic fingerprints of anoxygenic photoautotrophs can provide direct evidence for seawater redox conditions within the photic zone. In this study, we identified a series of 2,3,6-trimethyl aryl isoprenoids (2,3,6-TMAI) from low-maturity sedimentary organic matter in the Xiamaling Formation (XML), deposited 1.4 billion years ago in the Xiahuayuan area of northern China. The δ13C values of C18 and C19 TMAI ranged from −19.8‰ to −21.3‰. These 13C-enriched values indicate their origin in anaerobic photosynthetic green sulfur bacteria (GSB). The episodic enrichments of 2,3,6-TMAI in the XML Formation suggest dynamic marine geochemistry. Specifically, low concentrations of 2,3,6-TMAI at the bottom of the studied profile reflect an oxygenated deposition environment (unit 4), where the organic matter was almost all decomposed in the oxic water column during deposition, while the gradually increasing 2,3,6-TMAI concentrations from the middle to the upper XML reflects alteration of oceanic redox condition from an oxygen minimum zone (OMZ) in unit 3 through periods of euxinia during the deposition of units 2 and 1. The absence of co-variation between total organic carbon (TOC) and enriched 13C values indicates that anoxygenic photoautotroph activities might have contributed little to sedimentary organic matter burial in the Mesoproterozoic XML sediments.

Photoluminescence and afterglow tuning in ultra-broadband near-infrared Mg3Y2Ge3O12:Cr3+ phosphor via cation substitution

Broadband near-infrared (NIR) long-persistent phosphors with adjustable optical property have been urgently demanded for practical applications in bio-imaging and plant cultivation. Herein, Cr3+ doped Mg3Y2Ge3O12 garnet phosphors with ultra-broadband NIR emissions (600−1200 nm) peaked at 776 nm were prepared via a high-temperature solid-state reaction method, and the cation sites for Cr3+ were well identified and assigned based on the Rietveld refinement and time-resolved emission spectra (TRES). Under the excitation at 436 nm, wide-range modulations in intensity, wavelength (763−834 nm) and bandwidth (143−227 nm) of 4T2→4A2 (4F) transition were achieved via Zn2+/Ca2+ substitution, which completely covers the maximum absorption ranges (715−1050 nm) of bacteriochlorophyll from anaerobic photosynthetic bacteria (PSB). According to the classic Tanabe-Sugano theory, the crystal field parameters around different Cr3+ centers were calculated to explain the spectral tailoring effect. Meanwhile, the afterglow duration was greatly improved from 2 min to 66 and 240 min after co-doping Zn2+/Ca2+, and the trap distribution and mechanism was elaborately explored via thermos-luminescence (TL) experiments. Above results provide an effective strategy for designing NIR-emitting phosphors with desired optical and afterglow performance, which well meets the light requirements of diverse applications especially in plant growth.

Improvement of random coefficient differential models of growth of anaerobic photosynthetic bacteria by combining Bayesian inference and gPC

The time evolution of microorganisms, such as bacteria, is of great interest in biology. In the article by D. Stanescu et al. [Electronic Transactions on Numerical Analysis, 34, 44–58 (2009)], a logistic model was proposed to model the growth of anaerobic photosynthetic bacteria. In the laboratory experiment, actual data for two species of bacteria were considered: Rhodobacter capsulatus and Chlorobium vibrioforme. In this paper, we suggest a new nonlinear model by assuming that the population growth rate is not proportional to the size of the bacteria population, but to the number of interactions between the microorganisms, and by taking into account the beginning of the death phase in the kinetic curve. Stanescu et al. evaluated the effect of randomness into the model coefficients by using generalized polynomial chaos (gPC) expansions, by setting arbitrary distributions without taking into account the likelihood of the data. By contrast, we utilize a Bayesian inverse approach for parameter estimation to obtain reliable posterior distributions for the random input coefficients in both the logistic and our new model. Since our new model does not possess an explicit solution, we use gPC expansions to construct the Bayesian model and to accelerate the Markov chain Monte Carlo algorithm for the Bayesian inference.

Enhancement of COD, ammonia, phosphate and sulfide simultaneous removal by the anaerobic photosynthetic bacterium of Ectothiorhodospira magna in batch and sequencing batch culture.

An anaerobic photosynthetic bacterium, with chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total phosphorus (TP) and sulfide (S2-) simultaneous removal ability, strain SU6, was isolated and identified as belonging to Ectothiorhodospira magna. Its removal efficiencies were simultaneously evaluated in batch culture and influenced in sequencing batch culture. The maximum COD, NH3-N, TP and S2- removal rates of 93.04%, 86.70%, 37.55% and 99.99% were obtained in batch culture with an initial pH 8.0 at 35 °C after 72 h. The simultaneous removal efficiency was enhanced in sequencing batch culture, and 789.27 mg/L COD, 68.91 mg/L NH3-N, 70.20 mg/L S2- and 5.26 mg/L TP were removed by the end of the last cycle within 24 h. This was the first time of reporting contaminants' simultaneous removal by a pure-cultured photosynthetic bacterium. The experimental results demonstrate that E. magna can efficiently serve as a good candidate in anaerobic wastewater contaminants' simultaneous removal, and maybe as another model anaerobic photosynthetic microorganism for water purification investigations.

Cupriavidus necator H16 Uses Flavocytochrome c Sulfide Dehydrogenase To Oxidize Self-Produced and Added Sulfide.

Production of sulfide (H2S, HS-, and S2-) by heterotrophic bacteria during aerobic growth is a common phenomenon. Some bacteria with sulfide:quinone oxidoreductase (SQR) and persulfide dioxygenase (PDO) can oxidize self-produced sulfide to sulfite and thiosulfate, but other bacteria without these enzymes release sulfide into the medium, from which H2S can volatilize into the gas phase. Here, we report that Cupriavidus necator H16, with the fccA and fccB genes encoding flavocytochrome c sulfide dehydrogenases (FCSDs), also oxidized self-produced H2S. A mutant in which fccA and fccB were deleted accumulated and released H2S. When fccA and fccB were expressed in Pseudomonas aeruginosa strain Pa3K with deletions of its sqr and pdo genes, the recombinant rapidly oxidized sulfide to sulfane sulfur. When PDO was also cloned into the recombinant, the recombinant with both FCSD and PDO oxidized sulfide to sulfite and thiosulfate. Thus, the proposed pathway is similar to the pathway catalyzed by SQR and PDO, in which FCSD oxidizes sulfide to polysulfide, polysulfide spontaneously reacts with reduced glutathione (GSH) to produce glutathione persulfide (GSSH), and PDO oxidizes GSSH to sulfite, which chemically reacts with polysulfide to produce thiosulfate. About 20.6% of sequenced bacterial genomes contain SQR, and only 3.9% contain FCSD. This is not a surprise, since SQR is more efficient in conserving energy because it passes electrons from sulfide oxidation into the electron transport chain at the quinone level, while FCSD passes electrons to cytochrome c The transport of electrons from the latter to O2 conserves less energy. FCSDs are grouped into three subgroups, well conserved at the taxonomic level. Thus, our data show the diversity in sulfide oxidation by heterotrophic bacteria.IMPORTANCE Heterotrophic bacteria with SQR and PDO can oxidize self-produced sulfide and do not release H2S into the gas phase. C. necator H16 has FCSD but not SQR, and it does not release H2S. We confirmed that the bacterium used FCSD for the oxidation of self-produced sulfide. The bacterium also oxidized added sulfide. The common presence of SQRs, FCSDs, and PDOs in heterotrophic bacteria suggests the significant role of heterotrophic bacteria in sulfide oxidation, participating in sulfur biogeochemical cycling. Further, FCSDs have been identified in anaerobic photosynthetic bacteria and chemolithotrophic bacteria, but their physiological roles are unknown. We showed that heterotrophic bacteria use FCSDs to oxidize self-produced sulfide and extraneous sulfide, and they may be used for H2S bioremediation.

Hydrogen containing fuel gas generation from organic wastes using photon activated magnesium metal catalyst

Experimental studies have been carried out to find the combined effect of visible light and magnesium (Mg0)-metal powder on anaerobic photosynthetic bacteria present in slurry of cowdung and various kinds of organic wastes. The chemical combination of all the above factors helps in producing high quality fuel gas under anaerobic condition. In the fluidized bed reaction, bacteria have been allowed to undergo biophysical and biochemical reactions in the presence of Mg0-metal powder under the continuous flow of photons. The source of photons in the biological media is an artificial light (100 W tungsten bulbs) used at 38 °C. Mg0-metal powder has been added to the slurry to catalyze the biochemical process in presence of light energy. The population rate of bacteria and composition of fuel gas have been estimated under the action of visible photons in presence and absence of induced Mg0-atoms. The fuel gas composition has been measured by Gas-Chromatography and its calorific value measured by flame temperature. Metagenome analysis of consensus ‘V3’-region of 16S rRNA gene amplicons and entire downstream analysis have shown increased bacterial population of Clostridia, Bacteroidia and γ-proteobacteria in presence of Mg0-atom. Mg0-atom has been observed to activate hydG, mgtE and corA genes of the bacterial community.

Relación entre la producción primaria y bacteriana pelágicas en dos lagunas húmicas vegetadas

In this study, we show that depth-integrated pelagic primary production (PP) can exceed bacterioplankton production (BP) in vegetated humic shallow lakes, giving as a result an autotrophic water column, despite light restrictions and availability of organic carbon for lake bacteria. Intuitively, these conditions should favor the development of a heterotrophic water column. Instead, during our survey, BP represented between 1.3 to 5% of PP most of the time. Only once, during late summer, BP was ~71% of PP. Although we cannot conclude about the mechanisms behind the observed results, previous surveys and experimentation in the wetland allow us to hypothesize that autotrophic conditions were favored by: i) the shallow nature of the lakes, which compensates for light attenuation by organic matter when integrating production in the water column, ii) the presence of anaerobic anoxygenic photosynthetic bacteria below the macrophyte cover, and iii) high predation rates on bacterioplankton by heterotrophic flagellates below the floating plants.

Orientations of Iron-Sulfur Clusters FA and FB in the Homodimeric Type-I Photosynthetic Reaction Center of Heliobacterium modesticaldum.

Orientations of the FA and FB iron-sulfur (FeS) clusters in a structure-unknown type-I homodimeric heriobacterial reaction center (hRC) were studied in oriented membranes of the thermophilic anaerobic photosynthetic bacterium Heliobacterium modesticaldum by electron paramagnetic resonance (EPR), and compared with those in heterodimeric photosystem I (PS I). The Rieske-type FeS center in the cytochrome b/c complex showed a well-oriented EPR signal. Illumination at 14 K induced an FB(-) signal with g-axes of gz = 2.066, gy = 1.937, and gx = 1.890, tilted at angles of 60°, 60°, and 45°, respectively, with respect to the membrane normal. Chemical reduction with dithionite produced an additional signal of FA(-), which magnetically interacted with FB(-), with gz = 2.046, gy = 1.942, and gx = 1.911 at 30°, 60°, and 90°, respectively. The angles and redox properties of FA(-) and FB(-) in hRC resemble those of FB(-) and FA(-), respectively, in PS I. Therefore, FA and FB in hRC, named after their g-value similarities, seem to be located like FB and FA, not like FA and FB, respectively, in PS I. The reducing side of hRC could resemble those in PS I, if the names of FA and FB are interchanged with each other.

Carbon roadmap from syngas to polyhydroxyalkanoates in Rhodospirillum rubrum.

The gasification of organic waste materials to synthesis gas (syngas), followed by microbial fermentation, provides a significant resource for generating bioproducts such as polyhydroxyalkanoates (PHA). The anaerobic photosynthetic bacterium, Rhodospirillum rubrum, is an organism particularly attractive for the bioconversion of syngas into PHAs. In this study, a quantitative physiological analysis of R. rubrum was carried out by implementing GC-MS and HPLC techniques to unravel the metabolic pathway operating during syngas fermentation that leads to PHA production. Further, detailed investigations of the central carbon metabolites using (13) C-labelled substrate showed significant CO2 assimilation (of 40%) into cell material and PHA from syngas carbon fraction. By a combination of quantitative gene expression and enzyme activity analyses, the main role of carboxylases from the central carbon metabolism in CO2 assimilation was shown, where the Calvin-Benson-Bassham cycle (CBB) played a minor role. This knowledge sheds light about the biochemical pathways that contribute to synthesis of PHA during syngas fermentation being valuable information to further optimize the fermentation process.

Exergy analysis of biohydrogen production from various carbon sources via anaerobic photosynthetic bacteria (Rhodospirillum rubrum)

In this study, exergy analysis of batch biohydrogen production through WGS (water–gas shift) reaction using an anaerobic photosynthetic bacteria Rhodospirillum rubrum was carried out for the first time. Various carbon sources including formate, acetate, malate, glucose, fructose, and sucrose were applied to support microbial growth in the presence of CO-rich syngas. The microorganisms utilized carbon monoxide and produced molecular hydrogen concurrently. The process was analyzed based on both conventional exergy and eco-exergy concepts for determining the exergetic parameters i.e., exergy destruction and exergy efficiency. Unlike the exergy efficiency, the exergy destruction based on the eco-exergy concept was remarkably lower than what obtained via the conventional exergy theory. Minimum normalized exergy destruction values of 189.67 and 181.40 kJ/kJ H2 were achieved for acetate as substrate using the exergy and eco-exergy approaches, respectively. In better words, acetate was identified as the most appropriate carbon source for biohydrogen production from the exergy point of view. Finally, the findings of this study confirmed that exergy analysis could be employed as an adaptable framework to determine and compare the renewability of biological hydrogen production using different routes in order to decide on the most suitable approach and conditions.

Photodynamic Combined with Magnetic Field Applications for Viability Activation of Anaerobic Photosynthetic Bacteria

This paper reports the influence of light exposure (photodynamic) and magnetic field application on viability activation of anaerobic photosynthetic bacteria (rhodobacter sphaeroides). For photosynthetic process, the rhodobacter sphaeroides have bacteriochlorophyll and carotenoid as major and accessory pigments, respectively. A customized equipment was developed for investigating the effect of light and magnetic field applications on the growth of the bacterial colonies. It was consisted of three main parts, namely a sample holder, an array of light emitting diode (LED) as light source and Helmholtz coils as magnetic field source. The systems of this equipment were controlled by a microntroller of AVR ATMega-8535. Prior to the application in vitro, all LEDs were calibrated, both their intensity and wavelength. After the treatments, all bacteria substances were grown in photosynthetic media (PMS) for 48 hours followed by calculating the number bacterial colonies growth using a total plate count (TPC) method and Quebec colony counter. It was found that the growths of bacterial colonies were influenced by both light intensity and wavelength of LED array. At the same intensities, the wavelength of 430 nm showed highest effect on the growth of bacterial colonies. In addition, upon application of the optimum light combined with magnetic field, the highest growth of bacterial colonies was achieved more than 110% when the optimized light source of energy dose was 204 J/cm2 and magnetic field was 1.8 mT.

Purification and biochemical characterization of the ATP synthase from Heliobacterium modesticaldum

Heliobacterium modesticaldum is an anaerobic photosynthetic bacterium that grows optimally at pH 6–7 and 52°C and is the only phototrophic member of the Firmicutes phylum family (gram-positive bacteria with low GC content). The ATP synthase of H. modesticaldum was isolated and characterized at the biochemical and biophysical levels. The isolated holoenzyme exhibited the subunit patterns of F-type ATP synthases containing a 5-subunit hydrophilic F1 subcomplex and a 3-subunit hydrophobic F0 subcomplex. ATP hydrolysis by the isolated HF1F0 ATP synthase was successfully detected after pretreatment with different detergents by an in-gel ATPase activity assay, which showed that the highest activity was detected in the presence of mild detergents such as LDAO; moreover, high catalytic activity in the gel was already detected after the initial incubation period of 0.5h. In contrast, HF1F0 showed extremely low ATPase activity in harsher detergents such as TODC. The isolated fully functional enzyme will form the basis for future structural studies.

Improvement of cultivation medium for enhanced production of coenzyme Q10 by photosynthetic Rhodospirillum rubrum

Coenzyme Q10 (CoQ10), a potent antioxidative dietary supplement, was produced by submerged fermentation using an anaerobic photosynthetic bacteria Rhodospirillum rubrum ATCC 25852 instead of chemical synthesis or solvent extraction. Five nutritional factors, including malic acid, yeast extract, (NH 4) 2SO 4, MgSO 4·7H 2O, and ferric citrate, were optimized for CoQ10 production using response surface methodology (RSM) in static test tube cultures. The optimal medium for CoQ10 production were (g/l): malic acid, 2.5; yeast extract, 1.29; (NH 4) 2SO 4, 1.34; MgSO 4·7H 2O, 0.20; 0.90 g/l K 2HPO 4, 0.90; KH 2PO 4, 0.60; ferric citrate, 0.08; and EDTA, 0.02. The highest yield of CoQ10 was 9.76 mg/l, in agreement with the RSM predicted yield (9.63 mg/l). The yield of CoQ10 in a 3-l fermentor was higher than that achieved in the static culture and reached 10.81 mg/l, which could be attributed to the constant agitation (400 rpm) that enhanced cell–substrate contact throughout the fermentation. The optimal medium compositions acquired in the present study provide a solid foundation for further improvement and optimization of fermentation processes that can be suitable for industrial-scale production of CoQ10.

Roles of Thioredoxins in the Obligate Anaerobic Green Sulfur Photosynthetic Bacterium Chlorobaculum tepidum

Thioredoxin is a small ubiquitous protein that is involved in the dithiol-disulfide exchange reaction, by way of two cysteine residues located on the molecule surface. In order to elucidate the role of thioredoxin in Chlorobaculum tepidum, an anaerobic green sulfur bacterium that uses various inorganic sulfur compounds and H(2)S as electron donors under strict anaerobic conditions for growth, we applied the thioredoxin affinity chromatography method (Motohashi et al., 2001). In this study, 37 cytoplasmic proteins were captured as thioredoxin target candidates, including proteins involved in sulfur assimilation. Furthermore, six of the candidate proteins were members of the reductive tricarboxylic acid cycle (pyruvate orthophosphate dikinase, pyruvate flavodoxin/ferredoxin oxidoreductase, alpha-oxoglutarate synthase, citrate lyase, citrate synthase, malate dehydrogenase). The redox sensitivity of three enzymes was then examined: citrate lyase, citrate synthase, and malate dehydrogenase, using their recombinant proteins. Based on the information relating to the target proteins, the significance of thioredoxin as a reductant for the metabolic pathway in the anaerobic photosynthetic bacteria is discussed.

Biohydrogen production in a continuous stirred tank bioreactor from synthesis gas by anaerobic photosynthetic bacterium: Rhodopirillum rubrum

Hydrogen may be considered a potential fuel for the future since it is carbon-free and oxidized to water as a combustion product. Bioconversion of synthesis gas (syngas) to hydrogen was demonstrated in continuous stirred tank bioreactor (CSTBR) utilizing acetate as a carbon source. An anaerobic photosynthetic bacterium, Rhodospirillum rubrum catalyzed water-gas shift reaction which was applied for the bioconversion of syngas to hydrogen. The continuous fermentation of syngas in the bioreactor was continuously operated at various gas flow rates and agitation speeds, for the period of two months. The gas flow rates were varied from 5 to 14 ml/min. The agitation speeds were increasingly altered in the range of 150–500 rpm. The pH and temperature of the bioreactor was set at 6.5 and 30 °C. The liquid flow rate was kept constant at 0.65 ml/min for the duration of 60 days. The inlet acetate concentration was fed at 4 g/l into the bioreactor. The hydrogen production rate and yield were 16 ± 1.1 mmol g −1 cell h −1 and 87 ± 2.4% at fixed agitation speed of 500 rpm and syngas flow rate of 14 ml/min, respectively. The mass transfer coefficient ( K L a) at this condition was approximately 72.8 h −1. This new approach, using a biocatalyst was considered as an alternative method of conventional Fischer-Tropsch synthetic reactions, which were able to convert syngas into hydrogen.

Diversity and distribution of photosynthetic bacteria in the Black Sea

Abstract Using an infrared fast-repetition-rate (IRFRR) fluorometer, we measured bacteriochlorophyll a (BChl a) fluorescence kinetics to examine the spatial pattern of the distribution of aerobic and anaerobic photosynthetic bacteria in the Black Sea in June 2001. Aerobic photosynthetic bacteria containing BChl a were distributed together with chlorophyll-containing phytoplankton in the upper, aerobic portion of the water column, confirming their exclusive requirement for oxygen. The BChl a to chlorophyll a ratio averaged 10−2 within the euphotic zone. Seven strains of aerobic photosynthetic bacteria were isolated and partially characterized. They belong to two subgroups closely related to Erythrobacter and Roseobacter genera. Green sulfur photosynthetic bacteria were detected in the central part of the basin, at the boundary between suboxic and anoxic (hydrogen sulfide) zone. However, the population of green sulfur bacteria was extremely small, and confined to a very narrow density layer deep in the water column.

A Survey on Various Carbon Sources for Biological Hydrogen Production via the Water-Gas Reaction Using a Photosynthetic Bacterium (Rhodospirillum rubrum)

Growth model of anaerobic photosynthetic bacteria on various carbon sources for fermentative hydrogen production growth from synthesis gas was investigated. It was found that the rate of utilization of carbon monoxide (CO) by Rhodospirillum rubrum on acetate was growth related. A biologically based water-gas shift reaction was catalyzed by the specific bacterium at ambient temperature to convert the gaseous substrate, CO to carbon dioxide, while simultaneously convert water to a useful product, molecular hydrogen. Experiments were conducted to measure the specific CO uptake and hydrogen production rates. Also, effect of initial organic substrate concentration was investigated. The microorganism was grown on formate, acetate, malate, glucose, fructose, and sucrose. The modified Teissier and Contois equations were further developed for the growth model based on existing theory and experimental data. It was also found that the improvement in the yield of hydrogen production using acetate as a suitable substrate for R. rubrum, resulted in 0.87 mmole H 2 /mmole CO. The obtained hydrogen yield of R. rubrum on acetate was 87% of stoichiometric conversion. The main objective of this research was to demonstrate that the biological hydrogen production may efficiently be implemented as an alternative energy for fossil fuel replacement in the future.

Records of environmental and climatic changes during the late Holocene from Svalbard: palaeolimnology of Kongressvatnet

A multi-core, multidisciplinary palaeolimnological study of the partially varved sediment of a deep, meromictic, arctic lake, Kongressvatnet (Svalbard, Western Spitsbergen), provides a record of environmental and climatic changes during last ca. 1800 years. The chronology of sedimentation was established using several dating techniques (137Cs, 210Pb, varve counts, palaeomagnetic correlation). A multiproxy record of palaeolimnological variability was compiled based on sedimentation rates, magnetic properties, varve thickness, organic matter, geochemistry, pigments from algal and photosynthetic bacteria, mineralogy and biological assemblages (diatoms, Cladocera). The major features recognised in our master core K99-3 include a shift in sediment source and supply (magnetic measurements, geochemistry) probably caused by glaciological changes in the catchment around 38–32 cm core depth (AD 700–820). Additional environmental changes are inferred at 20–18, 8–4.5 and 3–2 cm (AD ca. 1160–1255; 1715–1880; 1940–1963, respectively). During the past ca. 120 years a prominent sedimentological change from brownish-grey, partly laminated silt-clay (varves) to black organic-rich deposits was observed. From AD 1350 to AD1880 the sediment is comprised of a continuous sequence of varves, whereas the earlier sediments are mostly homogeneous with only a few short intercalated laminated sections between AD 860 and 1350. Sedimentation and accumulation rates increased during the last 30 years (modern warming). Pigment concentrations are very low in the lower ca. 32 cm of the core (AD 820) probably because of the high turbidity high energy environment. The high sulphur content in the uppermost 32 cm of sediment has given rise to two horizontally stratified populations of sulphur anaerobic photosynthetic bacteria, as inferred from their specific carotenoids. These bacteria populations are much more abundant during the Little Ice Age (LIA) than during warmer periods (e.g., during the Medieval Warm Period and 20th century). Diatoms are lacking from the core base up to 18 cm (ca. AD 1255); at this level, species indicative of mesotrophic water are present, whereas from 17 cm to the top of the core, oligotrophic taxa such as Staurosira construens/S. pinnata complex dominate, indicating extended ice coverage and more oligotrophic waters during the LIA. The concentration of Cladocera subfossil remains (dominated by Chydorus) are relatively high in the deepest sections (54–32 cm), whereas the upper 32 cm are characterized by a very low concentration of remains, possibly because of the strongly anoxic conditions, and in this upper sediment section rotifer resting eggs become prevalent. We interpret these changes as responses to climate forcing through its impact on glacial melt water, lake ice cover duration and mainly redox conditions in deep water. The observed changes suggest that at least some of our recorded changes may parallel the Greenland Ice core, although our study added more details about the inferred climatic changes. Further aspects are discussed, such as catchment processes, glacial activity, duration of the Medieval Warm Period, the Little Ice Age, local human activity, and limnology.

Hydrogen Production from Synthesis Gas Using the Photosynthetic Bacterium Rhodospirillum rubrum

Production of biological hydrogen by anaerobic photosynthetic bacteria, specifically Rhodospirillum rubrum, from synthesis gas was successfully conducted at ambient temperature and pressure. The influence of initial acetate concentration as the substrate for microbial growth was investigated in a batch system. Series of experiments were conducted using serum bottles as bioreactor. The agitation rate and light intensity were adjusted at 200 rpm and 1,000 lux, respectively. The concentration of acetate as carbon source was varied from 0.5 to 3.0 g/I. It was observed that the increase in concentration of the carbon source from 2.5 to 3 g/l resulted in the decrease both in the growth of the microorganism and in hydrogen production rate. Experimental results showed that the optimum acetate concentration would be from 1 to 2 g/I. The resulting data also showed that in 1-2 g/I acetate, highest hydrogen formation and cell concentration were obtained. Additional acetate in the initial culture medium inhibited the growth of R. rubrum. An inverse relationship between acetate concentration and initial cell growth was observed. This article presents a method to calculate the mass transfer coefficient for gaseous substrates and the process parameters involved in a gas and liquid fermentation system. The procedure had been defined by experimental data for the bioconversion of CO to C02' while H20 is converted into hydrogen. Hence, a biologically-based water-gas shift reaction provided an attractive alternative improvement for renewable resources to achieve higher hydrogen production. Keywords: Anaerobic bacteria, batch culture, coefficient, CO uptake rate, mass transfer, photobiological hydrogen, and Rhodospirillum rubrum.

In vivo carotenoid triplet formation in response to excess light: a supramolecular photoprotection mechanism revisited

Carotenoids have been known for their photoprotective role for about 50 years. However, despite many advances in laser flash photolysis, no photodynamic studies have been so far performed on whole cells to determine the harmful threshold of light. In the present work, we investigate the coupling between energy conversion and energy deactivation, in isolated complexes of RC-LH1 and LH2 increasingly integrated systems up to intact cells of the purple anaerobic photosynthetic bacterium Rubrivivax gelatinosus. A continuous light similar to the mean daily sun irradiance on the surface of the earth is found to saturate the in vivo electron transfer turnover and to give rise to carotenoid triplet formation. This accounts for the widespread use of carotenoids among phototrophic prokaryotes and emphasizes their essential protective role in the natural environment.