Showing papers by "Leibniz Association published in 2006"

Reconstructing the early evolution of Fungi using a six-gene phylogeny

Abstract: The ancestors of fungi are believed to be simple aquatic forms with flagellated spores, similar to members of the extant phylum Chytridiomycota (chytrids). Current classifications assume that chytrids form an early-diverging clade within the kingdom Fungi and imply a single loss of the spore flagellum, leading to the diversification of terrestrial fungi. Here we develop phylogenetic hypotheses for Fungi using data from six gene regions and nearly 200 species. Our results indicate that there may have been at least four independent losses of the flagellum in the kingdom Fungi. These losses of swimming spores coincided with the evolution of new mechanisms of spore dispersal, such as aerial dispersal in mycelial groups and polar tube eversion in the microsporidia (unicellular forms that lack mitochondria). The enigmatic microsporidia seem to be derived from an endoparasitic chytrid ancestor similar to Rozella allomycis, on the earliest diverging branch of the fungal phylogenetic tree.

Documented and Potential Biological Impacts of Recreational Fishing: Insights for Management and Conservation

Abstract: While the impacts of high exploitation on fish populations and aquatic ecosystems are well-documented for commercial fishing, particularly in the marine environment, the potential biological impacts of angling received less attention. This paper discusses angling patterns within a framework of basic ecological and evolutionary literature and examines potential biological impacts of angling by focusing on study results associated with high exploitation rates and pronounced selective exploitation. The impacts range from impacts occurring directly on the exploited species (truncation of the natural age and size structure, depensatory mechanisms, loss of genetic variability, evolutionary changes), to those that occur on the aquatic ecosystem (changes in trophic cascades, trait-mediated effects). As a third category, impacts related to the angling activity per se are distinguished (habitat modifications, wildlife disturbance, nutrient inputs, loss of fishing gear). Although the main threats to fish often are l...

Three‐dimensional modelling and inversion of dc resistivity data incorporating topography – II. Inversion

Abstract: SUMMARY We present a novel technique for the determination of resistivity structures associated with arbitrary surface topography. The approach represents a triple-grid inversion technique that is based on unstructured tetrahedral meshes and finite-element forward calculation. The three grids are characterized as follows: A relatively coarse parameter grid defines the elements whose resistivities are to be determined. On the secondary field grid the forward calculations in each inversion step are carried out using a secondary potential (SP) approach. The primary fields are provided by a one-time simulation on the highly refined primary field grid at the beginning of the inversion process. We use a Gauss‐Newton method with inexact line search to fit the data within error bounds. A global regularization scheme using special smoothness constraints is applied. The regularization parameter compromising data misfit and model roughness is determined by an L-curve method and finally evaluated by the discrepancy principle. To solve the inverse subproblem efficiently, a least-squares solver is presented. We apply our technique to synthetic data from a burial mound to demonstrate its effectiveness. A resolution-dependent parametrization helps to keep the inverse problem small to cope with memory limitations of today’s standard PCs. Furthermore, the SP calculation reduces the computation time significantly. This is a crucial issue since the forward calculation is generally very time consuming. Thus, the approach can be applied to large-scale 3-D problems as encountered in practice, which is finally proved on field data. As a by-product of the primary potential calculation we obtain a quantification of the topography effect and the corresponding geometric factors. The latter are used for calculation of apparent resistivities to prevent the reconstruction process from topography induced artefacts.

VANTED: A system for advanced data analysis and visualization in the context of biological networks

Abstract: Background Recent advances with high-throughput methods in life-science research have increased the need for automatized data analysis and visual exploration techniques. Sophisticated bioinformatics tools are essential to deduct biologically meaningful interpretations from the large amount of experimental data, and help to understand biological processes.

Antiinflammatory effects of dexamethasone are partly dependent on induction of dual specificity phosphatase 1.

Abstract: Glucocorticoids (GCs), which are used in the treatment of immune-mediated inflammatory diseases, inhibit the expression of many inflammatory mediators. They can also induce the expression of dual specificity phosphatase 1 (DUSP1; otherwise known as mitogen-activated protein kinase [MAPK] phosphatase 1), which dephosphorylates and inactivates MAPKs. We investigated the role of DUSP1 in the antiinflammatory action of the GC dexamethasone (Dex). Dex-mediated inhibition of c-Jun N-terminal kinase and p38 MAPK was abrogated in DUSP1−/− mouse macrophages. Dex-mediated suppression of several proinflammatory genes (including tumor necrosis factor, cyclooxygenase 2, and interleukin 1α and 1β) was impaired in DUSP1−/− mouse macrophages, whereas other proinflammatory genes were inhibited by Dex in a DUSP1-independent manner. In vivo antiinflammatory effects of Dex on zymosan-induced inflammation were impaired in DUSP1−/− mice. Therefore, the expression of DUSP1 is required for the inhibition of proinflammatory signaling pathways by Dex in mouse macrophages. Furthermore, DUSP1 contributes to the antiinflammatory effects of Dex in vitro and in vivo.

The akuB(KU80) mutant deficient for nonhomologous end joining is a powerful tool for analyzing pathogenicity in Aspergillus fumigatus.

Abstract: To increase the frequency of homologous recombination, we inactivated the KU80 homologue in Aspergillus fumigatus (named akuBKU80). Homologous integration reached about 80% for both calcineurin A (calA) and polyketide synthase pksP (alb1) genes in the akuBKU80 mutant to 3 and 5%, respectively, when using a wild-type A. fumigatus strain. Deletion of akuBKU80 had no influence on pathogenicity in a low-dose murine infection model.

Species-specific responses of calcifying algae to changing seawater carbonate chemistry

Abstract: Uptake of half of the fossil fuel CO2 into the ocean causes gradual seawater acidification. This has been shown to slow down calcification of major calcifying groups, such as corals, foraminifera, and coccolithophores. Here we show that two of the most productive marine calcifying species, the coccolithophores Coccolithus pelagicus and Calcidiscus leptoporus, do not follow the CO2-related calcification response previously found. In batch culture experiments, particulate inorganic carbon (PIC) of C. leptoporus changes with increasing CO2 concentration in a nonlinear relationship. A PIC optimum curve is obtained, with a maximum value at present-day surface ocean pCO2 levels (∼360 ppm CO2). With particulate organic carbon (POC) remaining constant over the range of CO2 concentrations, the PIC/POC ratio also shows an optimum curve. In the C. pelagicus cultures, neither PIC nor POC changes significantly over the CO2 range tested, yielding a stable PIC/POC ratio. Since growth rate in both species did not change with pCO2, POC and PIC production show the same pattern as POC and PIC. The two investigated species respond differently to changes in the seawater carbonate chemistry, highlighting the need to consider species-specific effects when evaluating whole ecosystem responses. Changes of calcification rate (PIC production) were highly correlated to changes in coccolith morphology. Since our experimental results suggest altered coccolith morphology (at least in the case of C. leptoporus) in the geological past, coccoliths originating from sedimentary records of periods with different CO2 levels were analyzed. Analysis of sediment samples was performed on six cores obtained from locations well above the lysocline and covering a range of latitudes throughout the Atlantic Ocean. Scanning electron micrograph analysis of coccolith morphologies did not reveal any evidence for significant numbers of incomplete or malformed coccoliths of C. pelagicus and C. leptoporus in last glacial maximum and Holocene sediments. The discrepancy between experimental and geological results might be explained by adaptation to changing carbonate chemistry.

XPS investigation of Mn valence in lanthanum manganite thin films under variation of oxygen content

Abstract: The question whether $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3}$ accepts doping with tetravalent cations such as cerium and thus allows the preparation of electron-doped mixed-valent lanthanum manganites has been discussed controversially so far. Against the background of this problem, we present a comparative x-ray photoemission (XPS) study of epitaxial ${\mathrm{La}}_{0.7}{\mathrm{Ce}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LCeMO) and ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LCMO) thin films. We focus on the exchange splitting of the Mn $3s$ core level peak, which is a direct indicator of the Mn valence and allows us to quantify the Mn valence in the outermost $3\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ of the films. We demonstrate that, depending on the oxygen content, the Mn valence can be tuned between a mixed ${\mathrm{Mn}}^{3+∕4+}$ state and a mixed ${\mathrm{Mn}}^{2+∕3+}$ state in both the LCeMO and the LCMO film. The oxygen content was varied by heating in ultrahigh vacuum for deoxygenation and in an oxygen atmosphere for reoxidation. In the LCeMO film, the deoxygenation not only changes the Mn valence, but also the Ce valence is driven from the $4+$ towards the $3+$ state.

PageMan: an interactive ontology tool to generate, display, and annotate overview graphs for profiling experiments.

Abstract: Microarray technology has become a widely accepted and standardized tool in biology. The first microarray data analysis programs were developed to support pair-wise comparison. However, as microarray experiments have become more routine, large scale experiments have become more common, which investigate multiple time points or sets of mutants or transgenics. To extract biological information from such high-throughput expression data, it is necessary to develop efficient analytical platforms, which combine manually curated gene ontologies with efficient visualization and navigation tools. Currently, most tools focus on a few limited biological aspects, rather than offering a holistic, integrated analysis. Here we introduce PageMan, a multiplatform, user-friendly, and stand-alone software tool that annotates, investigates, and condenses high-throughput microarray data in the context of functional ontologies. It includes a GUI tool to transform different ontologies into a suitable format, enabling the user to compare and choose between different ontologies. It is equipped with several statistical modules for data analysis, including over-representation analysis and Wilcoxon statistical testing. Results are exported in a graphical format for direct use, or for further editing in graphics programs. PageMan provides a fast overview of single treatments, allows genome-level responses to be compared across several microarray experiments covering, for example, stress responses at multiple time points. This aids in searching for trait-specific changes in pathways using mutants or transgenics, analyzing development time-courses, and comparison between species. In a case study, we analyze the results of publicly available microarrays of multiple cold stress experiments using PageMan, and compare the results to a previously published meta-analysis. PageMan offers a complete user's guide, a web-based over-representation analysis as well as a tutorial, and is freely available at http://mapman.mpimp-golm.mpg.de/pageman/ . PageMan allows multiple microarray experiments to be efficiently condensed into a single page graphical display. The flexible interface allows data to be quickly and easily visualized, facilitating comparisons within experiments and to published experiments, thus enabling researchers to gain a rapid overview of the biological responses in the experiments.

Recent history of artificial outcrossing facilitates whole-genome association mapping in elite inbred crop varieties

Abstract: Genomewide association studies depend on the extent of linkage disequilibrium (LD), the number and distribution of markers, and the underlying structure in populations under study. Outbreeding species generally exhibit limited LD, and consequently, a very large number of markers are required for effective whole-genome association genetic scans. In contrast, several of the world's major food crops are self-fertilizing inbreeding species with narrow genetic bases and theoretically extensive LD. Together these are predicted to result in a combination of low resolution and a high frequency of spurious associations in LD-based studies. However, inbred elite plant varieties represent a unique human-induced pseudooutbreeding population that has been subjected to strong selection for advantageous alleles. By assaying 1,524 genomewide SNPs we demonstrate that, after accounting for population substructure, the level of LD exhibited in elite northwest European barley, a typical inbred cereal crop, can be effectively exploited to map traits by using whole-genome association scans with several hundred to thousands of biallelic SNPs.

Connections between atmospheric sulphuric acid and new particle formation during QUEST III–IV campaigns in Heidelberg and Hyytiälä

Abstract: This study investigates the connections between atmospheric sulphuric acid and new particle formation dur- ing QUEST III and BACCI/QUEST IV campaigns. The campaigns have been conducted in Heidelberg (2004) and Hyyti¨ al¨ a (2005), the first representing a polluted site sur- rounded by deciduous forest, and the second a rural site in a boreal forest environment. We have studied the role of sul- phuric acid in particle formation and growth by determin- ing 1) the power-law dependencies between sulphuric acid ((H2SO4)), and particle concentrations (N3 6) or formation rates at 1 nm and 3 nm (J1 and J3); 2) the time delays be- tween (H2SO4) and N3 6 or J3, and the growth rates for 1- 3 nm particles; 3) the empirical nucleation coefficients A and K in relations J1=A(H2SO4) and J1=K(H2SO4) 2 , respec- tively; 4) theoretical predictions for J1 and J3 for the days when no significant particle formation is observed, based on the observed sulphuric acid concentrations and conden- sation sinks. In both environments, N3 6 or J3 and (H2SO4) were linked via a power-law relation with exponents typi- cally ranging from 1 to 2. The result suggests that the clus- ter activation theory and kinetic nucleation have the potential to explain the observed particle formation. However, some differences between the sites existed: The nucleation coeffi- cients were about an order of magnitude greater in Heidel- berg than in Hyyti¨¨ conditions. The time lags between J3 and (H2SO4) were consistently lower than the corresponding

Comparative transcriptome analysis of toxic metal responses in Arabidopsis thaliana and the Cd2+-hypertolerant facultative metallophyte Arabidopsis halleri

Abstract: Toxic effects of both essential and non-essential heavy metals are well documented in plants. Very little is known, however, about their modes of toxicity, about tolerance mechanisms and the signalling cascades involved in mediating transcriptional responses to toxic metal excess. We analysed transcriptome changes upon Cd2+ and Cu2+ exposure in roots of Arabidopsis thaliana and the Cd(2+)-hypertolerant metallophyte Arabidopsis halleri. Particularly, three categories of genes were identified with the help of this comparative approach: (1) common responses, which might indicate stable and functionally relevant changes conserved across plant species; (2) metallophyte-specific responses as well as transcripts differentially regulated between the two species, representing candidate genes for Cd2+ hypertolerance; and (3) those specifically responsive to Cd2+ and therefore indicative of toxicity mechanisms or potentially involved in signalling cascades. Our data define, for instance, Arabidopsis core responses to Cd2+ and Cu2+. In addition, they suggest that Cd2+ exposure very rapidly results in apparent Zn deficiency, and they show the existence of highly specific Cd2+ responses and distinct signalling cascades. Array results were independently confirmed by real-time quantitative PCR, thereby further validating cross-species transcriptome analysis with oligonucleotide microarrays.

Dissolved humic substances – ecological driving forces from the individual to the ecosystem level?

Abstract: SUMMARY 1. This review focuses on direct and indirect interactions between dissolved humic substances (HS) and freshwater organisms and presents novel opinions and hypotheses on their ecological significance. Despite their abundance in freshwaters, the role of HS is still inadequately understood. These substances have been considered too large to be taken up by freshwater organisms. On the contrary, here we present evidence that dissolved HS are indeed taken up and interact directly and/or indirectly with freshwater organisms. 2. We show that dissolved HS exert a mild chemical stress upon aquatic organisms in many ways; they induce molecular chaperones (stress shock proteins), induce and modulate biotransformation enzymes and modulate (mainly inhibiting) the photosynthetic release of oxygen by freshwater plants. Furthermore, they produce an oxidative stress, which may lead to membrane oxidation. HS modulate the multixenobiotic resistance activity and probably other membrane-bound pumps. This property may lead to the increased bioaccumulation of xenobiotic chemicals. Furthermore, they can modulate the numbers of offspring in a nematode and feminise fish and amphibians. The ecological consequences of this potential remain obscure at present. HS also have the potential to act as chemical attractants (as shown with a nematode). 3. In some macrophytes and algae we show that HS interfere with photosynthesis and growth. For instance, the presence of HS suppresses cyanobacteria more than eukaryotic algae. By applying a quantitative structure activity relationship approach, we show that

Cladocerans versus copepods: the cause of contrasting top–down controls on freshwater and marine phytoplankton

Abstract: Top–down control of phytoplankton by crustacean mesozooplankton is a cornerstone of freshwater ecology. Apparently, trophic cascades are more frequently reported from freshwater than from marine plankton. We argue that this difference is real and mainly caused by biological differences at the zooplankton–phytoplankton link: cladocerans (particularly Daphnia) in the lakes and copepods in the sea. We derive these conclusions from recent literature and a number of own, similarly designed mesocosm experiments conducted in a lake, a brackish water and a marine site. In all experiments, phytoplankton were exposed to gradients of experimentally manipulated densities of zooplankton, including freshwater copepods and cladocerans, and marine copepods and appendicularians. The suggested reasons for the difference between lake and marine trophic cascades are: (1) Both copepods and cladocerans suppress only part of the phytoplankton size spectrum: cladocerans the small and copepods the large phytoplankton. (2) If not controlled by grazing, small phytoplankton may increase their biomass faster than large phytoplankton. (3) Copepods additionally release small phytoplankton from grazing pressure by intermediate consumers (protozoa) and competitors (predation on appendicularian eggs), while cladocerans do not release large phytoplankton from grazing pressure by any functional group. (4) Cladocerans sequester more of the limiting nutrient than copepods, leaving fewer nutrients available for compensatory growth of ungrazed phytoplankton.

Life‐history traits of lake plankton species may govern their phenological response to climate warming

Abstract: A prominent response of temperate aquatic ecosystems to climate warming is changes in phenology – advancements or delays in annually reoccurring events in an organism's life cycle. The exact seasonal timing of warming, in conjunction with species-specific life-history events such as emergence from resting stages, timing of spawning, generation times, or stage-specific prey requirements, may determine the nature of a species' response. We demonstrate that recent climate-induced shifts in the phenology of lake phytoplankton and zooplankton species in a temperate eutrophic lake (Muggelsee, Germany) differed according to differences in their characteristic life cycles. Fast-growing plankton in spring (diatoms, Daphnia) showed significant and synchronous forward movements by about 1 month, induced by concurrent earlier ice break-up dates (diatoms) and higher spring water temperature (Daphnia). No such synchrony was observed for slow-growing summer zooplankton species with longer and more complex life cycles (copepods, larvae of the mussel Dreissena polymorpha). Although coexisting, the summer plankton responded species specifically to seasonal warming trends, depending on whether the timing of warming matched their individual thermal requirements at decisive developmental stages such as emergence from diapause (copepods), or spawning (Dreissena). Others did not change their phenology significantly, but nevertheless, increased in abundances. We show that the detailed seasonal pattern of warming influences the response of phyto- and zooplankton species to climate change, and point to the diverse nature of responses for species exhibiting complex life-history traits.

454 sequencing put to the test using the complex genome of barley

Abstract: During the past decade, Sanger sequencing has been used to completely sequence hundreds of microbial and a few higher eukaryote genomes. In recent years, a number of alternative technologies became available, among them adaptations of the pyrosequencing procedure (i.e. "454 sequencing"), promising a ~100-fold increase in throughput over Sanger technology – an advancement which is needed to make large and complex genomes more amenable to full genome sequencing at affordable costs. Although several studies have demonstrated its potential usefulness for sequencing small and compact microbial genomes, it was unclear how the new technology would perform in large and highly repetitive genomes such as those of wheat or barley. To study its performance in complex genomes, we used 454 technology to sequence four barley Bacterial Artificial Chromosome (BAC) clones and compared the results to those from ABI-Sanger sequencing. All gene containing regions were covered efficiently and at high quality with 454 sequencing whereas repetitive sequences were more problematic with 454 sequencing than with ABI-Sanger sequencing. 454 sequencing provided a much more even coverage of the BAC clones than ABI-Sanger sequencing, resulting in almost complete assembly of all genic sequences even at only 9 to 10-fold coverage. To obtain highly advanced working draft sequences for the BACs, we developed a strategy to assemble large parts of the BAC sequences by combining comparative genomics, detailed repeat analysis and use of low-quality reads from 454 sequencing. Additionally, we describe an approach of including small numbers of ABI-Sanger sequences to produce hybrid assemblies to partly compensate the short read length of 454 sequences. Our data indicate that 454 pyrosequencing allows rapid and cost-effective sequencing of the gene-containing portions of large and complex genomes and that its combination with ABI-Sanger sequencing and targeted sequence analysis can result in large regions of high-quality finished genomic sequences.

Drilling to gabbro in intact ocean crust

Abstract: Sampling an intact sequence of oceanic crust through lavas, dikes, and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid-ocean ridges, but it has been an elusive goal of scientific ocean drilling for decades. Recent drilling in the eastern Pacific Ocean in Hole 1256D reached gabbro within seismic layer 2, 1157 meters into crust formed at a superfast spreading rate. The gabbros are the crystallized melt lenses that formed beneath a mid-ocean ridge. The depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid-ocean ridges: Melt lenses occur at shallower depths at faster spreading rates. The gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas, precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by Hole 1256D.

On the Apparently Striking Disconnect between Motivation and Satisfaction in Recreational Fishing: The Case of Catch Orientation of German Anglers

Abstract: In this study, three distinct segments of German anglers differing with respect to degree of catch orientation as the main fishing motive were identified in a nationwide telephone survey (N = 474). Noncatch aspects of the fishing experience played a major role in the motivations of anglers: about 80% of the sample was classified as anglers with a low, or minimal, catch orientation. Angler satisfaction and its determinants were examined across degrees of catch orientation to improve understanding of the link between angler motivation and satisfaction. Highly catch-oriented anglers were significantly less satisfied with the previous angling season than were minimally catch-oriented anglers. An exclusivity of activity-specific, mainly catch-related, satisfaction components as predictors of overall angling year satisfaction was found in all angler segments, irrespective of catch orientation. Satisfaction was unrelated to actual catch or harvest rates, and no significant differences in catch and harve...

Analysis of molecular diversity, population structure and linkage disequilibrium in a worldwide survey of cultivated barley germplasm (Hordeum vulgare L.).

Abstract: The goal of our study was a systematic survey of the molecular diversity in barley genetic resources. To this end 953 cultivated barley accessions originating from all inhabited continents except Australia were genotyped with 48 SSR markers. Molecular diversity was evaluated with routine statistics (allelic richness, gene diversity, allele frequency, heterozygosity and unique alleles), Principal Coordinate Analysis (PCoA), and analysis of genome-wide linkage disequilibrium. A genotyping database for 953 cultivated barley accessions profiled with 48 SSR markers was established. The PCoA revealed structuring of the barley population with regard to (i) geographical regions and (ii) agronomic traits. Geographic origin contributed most to the observed molecular diversity. Genome-wide linkage disequilibrium (LD) was estimated as squared correlation of allele frequencies (r2). The values of LD for barley were comparable to other plant species (conifers, poplar, maize). The pattern of intrachromosomal LD with distances between the genomic loci ranging from 1 to 150 cM revealed that in barley LD extended up to distances as long as 50 cM with r2 > 0.05, or up to 10 cM with r2 > 0.2. Few loci mapping to different chromosomes showed significant LD with r2 > 0.05. The number of loci in significant LD as well as the pattern of LD were clearly dependent on the population structure. The LD in the homogenous group of 207 European 2-rowed spring barleys compared to the highly structured worldwide barley population was increased in the number of loci pairs with r2 > 0.05 and had higher values of r2, although the percentage of intrachromosomal loci pairs in significant LD based on P 0.80) provided higher LD values as compared to 19 low polymorphic loci (PIC < 0.73) in both structured (all accessions) and non-structured (European 2-rowed spring varieties) barley populations. A global population of cultivated barley accessions was highly structured. Clustering highlighted the accessions with the same geographic origin, as well as accessions possessing similar agronomic characters. LD in barley extended up to 50 cM, and was strongly dependent on the population structure. The data on LD were summarized as a genome-wide LD map for barley.

Diversity and Seasonal Dynamics of Actinobacteria Populations in Four Lakes in Northeastern Germany

Abstract: The phylogenetic diversity and seasonal dynamics of freshwater Actinobacteria populations in four limnologically different lakes of the Mecklenburg-Brandenburg Lake District (northeastern Germany) were investigated. Fluorescence in situ hybridization was used to determine the seasonal abundances and dynamics of total Actinobacteria (probe HGC69a) and the three actinobacterial subclusters acI, acI-A, and acI-B (probes AcI-852, AcI-840-1, and AcI-840-2). Seasonal means of total Actinobacteria abundances in the epilimnia of the lakes varied from 13 to 36%, with maximum values of 30 to 58%, of all DAPI (4',6'-diamidino-2-phenylindole)-stained cells. Around 80% of total Actinobacteria belonged to the acI cluster. The two subclusters acI-A and acI-B accounted for 60 to 91% of the acI cluster and showed seasonal means of 49% (acI-B) and 23% (acI-A) in relation to the acI cluster. Total Actinobacteria and members of the clusters acI and acI-B showed distinct seasonal changes in their absolute abundances, with maxima in late spring and fall/winter. In eight clone libraries constructed from the lakes, a total of 76 actinobacterial 16S rRNA gene sequences were identified from a total of 177 clones. The majority of the Actinobacteria sequences belonged to the acI and acIV cluster. Several new clusters and subclusters were found (acSTL, scB1-4, and acIVA-D). The majority of all obtained 16S rRNA gene sequences are distinct from those of already-cultured freshwater Actinobacteria.