Anoxygenic phototrophic bacterial community of Lake Shira (Khakassia)

The anoxygenic phototrophic bacterial community of the brackish meromictic Lake Shira (Khakassia) was investigated in August 2001, July 2002, and February–March 2003. In all the periods of investigation, the prevailing microorganisms were purple sulfur bacteria similar to Lamprocystis purpurea in morphology and pigment composition. Their highest number (3 × 10⁵ cells/ml) was recorded in July 2002 at the depth of 15 m. According to 16S rRNA gene analysis, the strain of purple sulfur bacteria isolated in 2001 and designated ShAm01 exhibited 98.6% similarity to the type strain of Thiocapsa roseopersicina and 97.1–94.4% similarity to the type strains of Tca. pendens, Tca. litoralis, and Tca. rosea. The minor microorganisms of the anoxygenic phototrophic bacterial community within the period of investigation were nonsulfur purple bacteria phylogenetically close to Rhodovulum strictum (98.3% similarity, strain ShRb01), Ahrensia kielensis (of 93.9% similarity, strain ShRb02), Rhodomicrobium vannieli (of 99.7% similarity, strain ShRmc01), and green sulfur bacteria, phylogenetically close to Chlorobium limicola (of 98.7% similarity, strain ShCl03).     

Seasonal changes in the structure of the anoxygenic photosynthetic bacterial community in Lake Shunet,Khakassia

Seasonal studies of the anoxygenic phototrophic bacterial community of the water column of the saline eutrophic meromictic Lake Shunet (Khakassia) were performed in 2002 (June) and 2003 (February–March and August). From the redox zone down, the lake water was of dark green color. Green sulfur bacteria predominated in every season. The maximum number of green sulfur bacteria was 10⁷ cells/ml in summer and 10⁶ cells/ml in winter. A multi-syringe stratification sampler was applied for the study of the fine vertical distribution of phototrophs in August 2003; the sampling was performed every 5 cm. A 5-cm-thick pink-colored water layer inhabited by purple sulfur bacteria was shown to be located above the layer of green bacteria. The species composition and ratio of purple bacterial species depended on the sampling depth and on the season. In summer, the number of purple sulfur bacteria in the layer of pink water was 1.6 × 10⁸ cells/ml. Their number in winter was 3 × 10⁵ cells/ml. In the upper oxygen-containing layer of the chemocline the cells of purple nonsulfur bacteria were detected in summer. The maximum number of nonsulfur purple bacteria, 5 × 10² cells/ml, was recorded in August 2003. According to the results of the phylogenetic analysis of pure cultures of the isolated phototrophic bacteria, which were based on 16S rDNA sequencing, green sulfur bacteria were close to Prosthecochloris vibrioformis, purple sulfur bacteria, to Thiocapsa and Halochromatium species, and purple nonsulfur bacteria, to Rhodovulum euryhalinum and Pinkicyclus mahoneyensis.     

Anoxygenic phototrophic bacteria of the high-altitude meromictic Lake Gek-Gel,Azerbaijan

The anoxygenic phototrophic bacterial community of the high-altitude meromictic Lake Gek-Gel (Azerbaijan) was investigated in September 2003. The highest concentration of bacteriochlorophyll e (48 μg/l) was detected at a depth of 30 m; the peak of bacteriochlorophyll a (4.5 μg/l) occurred at 29 m. Phylogenetic analysis revealed that brown-colored green sulfur bacteria Chlorobium phaeobacteroides predominated in the lake. Nonsulfur purple bacteria phylogenetically close to Blastochloris sulfoviridis were found in insignificant amounts; these organisms have not been previously reported in Lake Gek-Gel.     

Anoxygenic phototrophic bacteria of the Kislo-Sladkoe stratified lake (White Sea,Kandalaksha Bay)

The community of anoxygenic phototrophic bacteria (APB) in the water column of the Kislo-Sladkoe stratified lake recently isolated from the sea (White Sea, Kandalaksha Bay) was investigated in September 2010. The water of the sulfide-rich zone was greenish-brown due to intense development of green sulfur bacteria (GSB). Nine APB strains were isolated from the water samples: three belonging to GSB, five, to purple sulfur bacteria (PSB), and one, to purple nonsulfur bacteria (PNB). GSB predominated in the phototrophic community of the chemocline. Unexpectedly, two morphologically different green-colored GSB strains were found to be phylogenetically identical and related to the brown-colored Chlorobium phaeovibrioides (99% similarity according to the 16S rRNA gene sequencing). Homology to the closest green-colored species (Chlorobium luteolum) was 98%. Two morphologically and physiologically similar PSB strains (TcrPS10 and AmPS10) had rounded cells containing okenone and gas vesicles. According to the 16S rRNA gene sequencing, these strains were most closely related (99%) to two different Thiocapsa species: Tca. marina (containing okenonee and no gas vesicles) and Tca. rosea (containing spirilloxanthin and gas vesicles). The remaining isolates of purple bacteria were similar to the already described APB species.     

The structure of phototrophic communities of soda lakes of the southeastern Transbaikal Region

The structure of benthic phototrophic communities of 24 soda lakes of the southeastern Transbaikal Region was studied. The physicochemical properties of the lakes were determined. The results of enumeration of anoxygenic phototrophic bacteria (APB) belonging to various groups are presented. The influence of salinity on the structure of APB communities was investigated. The APB reaction to environmental conditions was determined. Massive development of phototrophic microorganisms in the form of mats and films was observed in the majority of the investigated lakes. The APB communities were characterized by a wide diversity and evenness of species composition. Purple sulfur bacteria of the families Ectothiorhodospiraceae and Chromatiaceae were predominant. Purple nonsulfur bacteria of the family Rhodobacteraceae, green filamentous bacteria Oscillochloris sp., and heliobacteria were also detected. According to preliminary data, no less than 15 species of APB occur in the studied lakes. Among them, three novel genera and four species have already been described. Identification of other isolates is still in progress. The lakes make an almost continuous series of fresh, brackish, and saline water bodies, varying in their degree of mineralization. It was demonstrated that the structure of APB communities was unaffected by changes in salinity from 5 to 40 g/l. At salt concentrations of lower than 5 g/l, the level of water mineralization became a limiting factor. Experiments with the isolated cultures showed that the APB were obligately dependent on the presence of carbonate ions in the medium. They were haloalkalitolerant or haloalkaliphilic. Thus, they are well adapted to the conditions of soda lakes with a low of moderate mineralization. It was demonstrated that soda lakes of the southeastern Transbaikal Region represent a special type of habitat which harbors a peculiar autochthonous microflora and differs from both highly mineralized soda lakes and shallow saline water bodies of the sea origin.     

Phylogenetic and functional prokaryotic diversity in the Hoito-Gol mesothermal mineral spring (Eastern Sayan Mountains,Buryat Republic)

High-throughput sequencing was used for comparative analysis of microbial communities of the water and mat from the Hoito-Gol mesothermal mineral sulfide spring (Eastern Sayan Mountains, Buryat Republic). Activity of microbial communities was determined. While both spring biotopes were dominated by members of three bacterial phyla—Proteobacteria, Bacteroidetes, and Firmicutes—they differed drastically in the composition of predominant phylotypes (at the genus level). In the water, the organisms widespread in aquatic environments were predominant, mostly aerobic chemoorganotrophs of the genera Acinetobacter, Pedobacter, and Flavobacterium. In the microbial mat, the organisms actively involved in the sulfur cycle predominated, including sulfur-reducing bacteria Sulfurospirillum, sulfate-reducing deltaproteobacteria, sulfuroxidizing chemoautotrophic bacteria, anoxygenic phototrophic bacteria of the phyla Chloroflexi and Chlorobi, as well as purple bacteria belonging to the α-, ß-, and γ-Proteobacteria. Microbial mats of the spring exhibited higher phylogenetic diversity compared to high-temperature mats containing photosynthetic microorganisms.     

Seasonal Changes in the Structure of the Anoxygenic Phototrophic Bacterial Community in Lake Mogilnoe,a Relict Lake on Kil'din Island in the Barents Sea

An anaerobic phototrophic bacterial community in Lake Mogilnoe, a relict lake on Kil'din Island in the Barents Sea, was studied in June 1999 and September 2001. Irrespective of the season, the upper layer of the anaerobic zone of this lake had a specific species composition of sulfur phototrophic bacteria, which were dominated by the brown-colored green sulfur bacterium Chlorobium phaeovibrioides. The maximum number of sulfur phototrophic bacteria was observed in June 1999 at a depth of 9 m, which corresponded to a concentration of bacteriochlorophyll (Bchl) e equal to 4.6 mg/l. In September 2001, the maximum concentration of this pigment (3.4 mg/l) was found at a depth of 10 m. In both seasons, the concentration of Bchl a did not exceed 3 μg/l. Purple sulfur bacteria were low in number, which can be explained by their poor adaptation to the hydrochemical and optical conditions of the Lake Mogilnoe water. In June 1999, the water contained a considerable number of Pelodictyon phaeum microcolonies and Prosthecochloris phaeoasteroides cell chains, which was not the case in September 2001. A 16S rDNA-based phylogenetic analysis of pure cultures of phototrophic bacteria isolated from the lake water confirmed that the bacterial community is dominated by Chl. phaeovibrioides and showed the presence of three minor species, Thiocystis gelatinosa, Thiocapsa sp., and Thiorhodococcus sp., the last of which is specific to Lake Mogilnoe.     

Sulphur metabolism in Thiorhodaceae. III. Storage and turnover of thiosulphate sulphur inThiocapsa floridana andChromatium species

Thiocapsa floridana strain 1711 andChromatium strains 1211 and 1611 utilize sulphide, thiosulphate, and elementary sulphur as electron donors for growth; sulphite can be used only byChromatium strain 1611. In contrast to the other strains, thiosulphate utilization inChromatium strain 1211 is inducible and not constitutive: thiosulphate is consumed only after an induction period of about 20 hours. The turnover rate of different sulphur compounds is controlled by the CO₂ fixation rate. Using differently labeled³⁵S thiosulphates in short term experiments in a special stirred cuvette, it was shown that the maximum amount of stored intracellular sulphur depends on the strain as well as on the experimental conditions like pH and thiosulphate concentration. WhileChromatium strain 1211 showed a maximum storage of only 10% from sulphane-labeled thiosulphate at pH 6.7, and of 25.7% at pH 6.2,Thiocapsa floridana accumulated 75–90% of the radioactivity into the cells at pH 6.7. While in theChromatium strains the labeling of the cells remained at a constant level until all thiosulphate was consumed, inThiocapsa floridana a defined peak of radioactivity storage was obtained, followed by a steady but 3–4 times slower rate of excretion. With sulphonelabeled thiosulphate no significant accumulation of radioactivity occurred in the cells. During dark-incubation ofThiocapsa floridana (free of intracellular sulphur) in phosphate buffer, pH 6.5, with thiosulphate a production of sulphide could be measured while sulphite was not detected; no sulphide was produced by disrupted cells under the same conditions. The results obtained withThiocapsa floridana strongly support the concept of an initial cleavage of thiosulphate. The present observations do not allow a decision concerning the enzymatic mechanism of the cleavage itself.     

Inheritance and QTL mapping of resistance to gummy stem blight in cucumber stem

Gummy stem blight (GSB), a common disease of all major cucurbits, is caused by the fungus Didymella bryoniae. It results in serious losses in fruit production, which in cucumber can be up to 80% or more. Because the severity of the disease varies from season to season and also because of the harm to the environment caused by using pesticides to control the disease, the best method for overcoming GSB in cucumber is to develop more resistant cultivars by molecular breeding. There are no reports on molecular markers for use in breeding GSB resistance and no studies on chromosomal mapping of resistance. In this paper, a set of 160 F₉ recombinant inbred lines (RILs) were derived from the cross between the wild-type GSB-resistant cucumber accession PI 183967 and the cultivated GSB-susceptible accession 931. A total of 2112 pairs of SSR primers were used to study the inheritance of GSB resistance and to detect quantitative trait loci (QTLs) conferring resistance in the cucumber stem. Genetic analysis indicated that resistance to GSB in PI 183967 was quantitative and mainly governed by three pairs of additive epistatic major genes. Five QTLs, gsb-s1.1, gsb-s2.1, gsb-s6.1, gsb-s6.2, and gsb-s6.3, for resistance to GSB in cucumber stems were detected. The loci gsb-s1.1 and gsb-s2.1 with phenotypic variations of 8.7 and 6.7% were mapped to chromosomes (Chr.) 1 and 2, respectively. The loci gsb-s6.1, gsb-s6.2, and gsb-s6.3 were linked on Chr.6. Locus gsb-s6.2 accounted for the highest phenotypic variation of 22.7% and was flanked by markers SSR04083 and SSR02940 with genetic distances of 5.0 and 1.8 cM, respectively. There were 117 candidate genes predicted between SSR04083 and SSR02940, of which 14 were related to disease resistance.     

Insight into the molecular mechanism of the sulfur oxidation process by reverse sulfite reductase (rSiR) from sulfur oxidizer <Emphasis Type="Italic">Allochromatium vinosum</Emphasis>

Sulfur metabolism is one of the oldest known biochemical processes. Chemotrophic or phototrophic proteobacteria, through the dissimilatory pathway, use sulfate, sulfide, sulfite, thiosulfate or elementary sulfur by either reductive or oxidative mechanisms. During anoxygenic photosynthesis, anaerobic sulfur oxidizer Allochromatium vinosum forms sulfur globules that are further oxidized by dsr operon. One of the key redox enzymes in reductive or oxidative sulfur metabolic pathways is the DsrAB protein complex. However, there are practically no reports to elucidate the molecular mechanism of the sulfur oxidation process by the DsrAB protein complex from sulfur oxidizer Allochromatium vinosum. In the present context, we tried to analyze the structural details of the DsrAB protein complex from sulfur oxidizer Allochromatium vinosum by molecular dynamics simulations. The molecular dynamics simulation results revealed the various types of molecular interactions between DsrA and DsrB proteins during the formation of DsrAB protein complex. We, for the first time, predicted the mode of binding interactions between the co-factor and DsrAB protein complex from Allochromatium vinosum. We also compared the binding interfaces of DsrAB from sulfur oxidizer Allochromatium vinosum and sulfate reducer Desulfovibrio vulgaris. This study is the first to provide a comparative aspect of binding modes of sulfur oxidizer Allochromatium vinosum and sulfate reducer Desulfovibrio vulgaris.     

Phylogenetic Diversity of the Sulfur Cycle Bacteria in the Bottom Sediments of the Chersonesus Bay

The Black Sea is the largest meromictic basin, in the bottom sediments of which a powerful biogenic process of sulfide production occurs. The goal of the present work was to obtain data on phylogenetic diversity of the sulfur cycle microorganisms (sulfate-reducing and sulfur-oxidizing bacteria) in the Black Sea coastal gas-saturated bottom sediments. The samples were collected in the Chersonesus (Blue) Bay near Sevastopol from whitish bacterial mats of sulfurettes, and from the upper layer of the nearby seabed. Using DNA isolated from the native samples and obtained enrichment cultures, PCR analysis was performed with oligonucleotide primers specific to the fragments of the 16S rRNA genes of the main subgroups of sulfatereducing bacteria (SRB) and to the fragments of the dsrB gene (both reductive and oxidative types), encoding the β-subunit of dissimilatory (bi)sulfite reductase, the key enzyme in the sulfur cycle, inherent in both sulfate- reducing and sulfur-oxidizing microorganisms. The presence of 16S rRNA gene fragments specific to the genera Desulfobacterium, Desulfobacter, Desulfococcus–Desulfonema–Desulfosarcina, and Desulfovibrio–Desulfomicrobium was detected in the DNA samples isolated from coastal bottom bacterial mats. Usage of denaturing gradient gel electrophoresis (DGGE) with subsequent sequencing of reamplified dsrB gene fragments revealed that according to deduced amino acid sequences encoded by the dsrB gene (reductive type), SRB from the coastal gas-saturated bottom sediments of the Black Sea had the highest homology (92?99%) with the dsrB gene of cultured SRB belonging to the genera Desulfovibrio, Desulfatitalea, Desulfobacter, and Desulfobacterium, as well as with uncultured SRB strains from various marine habitats, such as bottom sediments of the Northern and Japanese seas. Deduced amino acid sequences encoded by the oxidative dsrB gene had the highest homology (90?99%) with the relevant sequences of the genera Thiocapsa, Thiobaca, Thioflavicoccus, and Thiorhodococcus.     

Phylogenetic in situ/ex situ analysis of a sulfur mat microbial community from a thermal sulfide spring in the north Caucasus

A phylogenetic in situ/ex situ analysis of a sulfur mat formed by colorless filamentous sulfur bacteria in a thermal sulfide spring (northern spur of the main Caucasian ridge) was carried out. Nine phylotypes were revealed in the mat. Thiothrix sp. and Sphaerotilus sp. were the dominant phylotypes (66.3% and 26.3%, respectively). The 16S rRNA gene nucleotide sequence of Sphaerotilus sp. phylotype from the clone library was identical to the sequences of the seven Sphaerotilus strains isolated from the same source. A very high degree of similarity of Sphaerotilus strains revealed by ERIC-PCR fingerprints indicated little or no population diversity of this species in the mat. Thiothrix phylotype from the clone library and two Thiothrix strains isolated from the same mat sample differed in one to three nucleotides of 16S rRNA genes; this is an indication of this organism’s population variability in the mat. 16S rRNA genes of the strains and clones of Thiothrix sp. exhibited the highest similarity (ca. 99%) with Thiothrix unzii; the strains and clones of Sphaerotilus had 99% similarity with the type species Sphaerotilus natans (the only species of this genus) and therefore can be assigned to this species. The minor seven components belong to the phylotypes from the Proteobacteria (3%), as well as the Chlorobia, Cyanobacteria, Clostridia, and Bacteroidetes phylogenetic groups, each of them constituting not more than 1%. Intracellular accumulation of elemental sulfur by Sphaerotilus similar to other filamentous sulfur bacteria was demonstrated for the first time (both in the population of the sulfur spring and in cultures with sulfide). Although mass growth of Sphaerotilus and Thiothrix is typical of bacterial populations of anthropogenic ecosystems (the activated sludge of treatment facilities), stable communities of these bacteria have not been previously found in the sulfur mats or “threads” of natural sulfide springs.     

Living off the Sun: chlorophylls,bacteriochlorophylls and rhodopsins

Pigments absorbing 350–1,050 nm radiation have had an important role on the Earth for at least 3.5 billion years. The ion pumping rhodopsins absorb blue and green photons using retinal and pump ions across cell membranes. Bacteriochlorophylls (BChl), absorbing in the violet/blue and near infra red (NIR), power anoxygenic photosynthesis, with one photoreaction centre; and chlorophylls (Chl), absorbing in the violet/blue and red (occasionally NIR) power oxygenic photosynthesis, with two photoreaction centres. The accessory (bacterio)chlorophylls add to the spectral range (bandwidth) of photon absorption, e.g., in algae living at depth in clear oceanic water and in algae and photosynthetic (PS) bacteria in microbial mats. Organism size, via the package effect, determines the photon absorption benefit of the costs of synthesis of the pigment–protein complexes. There are unresolved issues as to the evolution of Chls vs. BChls and the role of violet/blue and NIR radiation in PS bacteria.     

Prokaryotic diversity in a Tunisian hypersaline lake,Chott El Jerid

Prokaryotic diversity was investigated in a Tunisian salt lake, Chott El Jerid, by quantitative real-time PCR, denaturing gradient gel electrophoresis (DGGE) fingerprinting methods targeting the 16S rRNA gene and culture-dependent methods. Two different samples S1-10 and S2-10 were taken from under the salt crust of Chott El Jerid in the dry season. DGGE analysis revealed that bacterial sequences were related to Firmicutes, Proteobacteria, unclassified bacteria, and Deinococcus-Thermus phyla. Anaerobic fermentative and sulfate-reducing bacteria were also detected in this ecosystem. Within the domain archaea, all sequences were affiliated to Euryarchaeota phylum. Quantitative real-time PCR showed that 16S rRNA gene copy numbers of bacteria was 5 × 10⁶ DNA copies g^?1 whereas archaea varied between 5 × 10⁵ and 10⁶ DNA copies g^?1 in these samples. Eight anaerobic halophilic fermentative bacterial strains were isolated and affiliated with the species Halanaerobium alcaliphilum, Halanaerobium saccharolyticum, and Sporohalobacter salinus. These data showed an abundant and diverse microbial community detected in the hypersaline thalassohaline environment of Chott El Jerid.     

<Superscript>15</Superscript>N photo-CIDNP MAS NMR analysis of reaction centers of <Emphasis Type="Italic">Chloracidobacterium thermophilum</Emphasis>

Photochemically induced dynamic nuclear polarization (photo-CIDNP) has been observed in the homodimeric, type-1 photochemical reaction centers (RCs) of the acidobacterium, Chloracidobacterium (Cab.) thermophilum, by ¹⁵N magic-angle spinning (MAS) solid-state NMR under continuous white-light illumination. Three light-induced emissive (negative) signals are detected. In the RCs of Cab. thermophilum, three types of (bacterio)chlorophylls have previously been identified: bacteriochlorophyll a (BChl a), chlorophyll a (Chl a), and Zn-bacteriochlorophyll a′ (Zn-BChl a′) (Tsukatani et al. in J Biol Chem 287:5720–5732, 2012). Based upon experimental and quantum chemical ¹⁵N NMR data, we assign the observed signals to a Chl a cofactor. We exclude Zn-BChl because of its measured spectroscopic properties. We conclude that Chl a is the primary electron acceptor, which implies that the primary donor is most likely Zn-BChl a′. Chl a and 8¹-OH Chl a have been shown to be the primary electron acceptors in green sulfur bacteria and heliobacteria, respectively, and thus a Chl a molecule serves this role in all known homodimeric type-1 RCs.     

Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors

The reduction kinetics of the photo-oxidized primary electron donor P₇₀₀ in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P₇₀₀, secondary quinone acceptor A₁, iron-sulfur clusters and external electron donor and acceptors – methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl₂NQ) and oxygen. PS I complexes containing various quinones in the A₁-binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl₂NQ) as well as F _X-core complexes, depleted of terminal iron–sulfur F _A/F _B clusters, were studied. The acceleration of charge recombination in F _X-core complexes by PhQ/PQ substitution indicates that backward ET from the iron–sulfur clusters involves quinone in the A₁-binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P₇₀₀ ⁺ reduction with the kinetic model. The free energy gap ΔG ₀ between F _X and F _A/F _B clusters was estimated as ?130 meV. The driving force of ET from A₁ to F _X was determined as ?50 and ?220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A_1A-site, this reaction was found to be endergonic (ΔG ₀?=?+75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis–Menten kinetics. The second-order rate constants of ET from F _A/F _B, F _X and Cl₂NQ in the A₁-site of PS I to external acceptors were estimated. The side production of superoxide radical in the A₁-site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.     

Photosynthesis and primary production in Lake Kasumigaura (Japan) monitored monthly since 1981

This study reports the primary production of phytoplankton determined with a ¹³C tracer, and their related variables, in Lake Kasumigaura, a shallow, hyper-eutrophic lake, and the second largest lake in Japan. Measurements were conducted monthly from August 1981 to December 2013 at four stations within the lake. Monitoring was a component of the Lake Kasumigaura Long-term Environmental Monitoring program, conducted by the National Institute for Environmental Studies (NIES) since 1977. The program collects data on water quality, and plankton and benthic communities. Lake Kasumigaura is registered as a core site of the Japan Long-term Ecological Research Network (JaLTER), which is a member of the International Long-term Ecological Research Network (ILTER). This dataset includes daily primary production (Pzd gC m^?2 d^?1) and the six parameters required to calculate Pzd: maximum photosynthesis rate (P _max gC gC^?1 h^?1); light irradiance at the junction of the initial slope (α (gC gC^?1 h^?1) (μmol photon m^?2 s^?1)^?1) and P _max of the photosynthesis vs. irradiance (P vs. E) curve (E _k μmol photon m^?2 s^?1); attenuation coefficient of photosynthetically available radiation (PAR) (K _PAR m^?1); water depth at each sampling station (Z _b , m); dissolved inorganic carbon (DIC mgC L^?1) and particulate organic carbon concentrations (POC gC m^?3); and chlorophyll a amounts (Chl.a μg L^?1). Daily primary production was calculated by obtaining a P vs. E curve over a short-term incubation (approximately 1 h) in a water tank using in situ water temperature in the laboratory, based on the field conditions of the sampling date. The dataset has been used for ecological studies as well as for management studies on water quality and ecosystems. This dataset is unique among the available published papers concerning lakes or primary production in various ecosystems, collected over a long period of time and freely available.     

Endogenous expression of FAD-linked PS1 impairs proliferation,neuronal differentiation and survival of adult hippocampal progenitors

Background

Alzheimer’s disease (AD) is characterized by progressive memory loss and impaired cognitive function. Early-onset familial forms of the disease (FAD) are caused by inheritance of mutant genes encoding presenilin 1 (PS1) variants. We have demonstrated that prion promoter (PrP)-driven expression of human FAD-linked PS1 variants in mice leads to impairments in environmental enrichment (EE)-induced adult hippocampal neural progenitor cell (AHNPC) proliferation and neuronal differentiation, and have provided evidence that accessory cells in the hippocampal niche expressing PS1 variants may modulate AHNPC phenotypes, in vivo. While of significant interest, these latter studies relied on transgenic mice that express human PS1 variant transgenes ubiquitously and at high levels, and the consequences of wild type or mutant PS1 expressed under physiologically relevant levels on EE-mediated AHNPC phenotypes has not yet been tested.

Results

To assess the impact of mutant PS1 on EE-induced AHNPC phenotypes when expressed under physiological levels, we exposed adult mice that constitutively express the PSEN1 M146V mutation driven by the endogenous PSEN1 promoter (PS1 M146V “knock-in” (KI) mice) to standard or EE-housed conditions. We show that in comparison to wild type PS1 mice, AHNPCs in mice carrying homozygous (PS1 ^M146V/M146V ) or heterozygous (PS1 ^M146V/+ ) M146V mutant alleles fail to exhibit EE-induced proliferation and commitment towards neurogenic lineages. More importantly, we report that the survival of newborn progenitors are diminished in PS1 M146V KI mice exposed to EE-conditions compared to respective EE wild type controls.

Conclusions

Our findings reveal that expression at physiological levels achieved by a single PS1 M146V allele is sufficient to impair EE-induced AHNPC proliferation, survival and neuronal differentiation, in vivo. These results and our finding that microglia expressing a single PS1 M146V allele impairs the proliferation of wild type AHNPCs in vitro argue that expression of mutant PS1 in the AHNPC niche impairs AHNPCs phenotypes in a dominant, non-cell autonomous manner.