An approach to analyzing spatial patterns of planktonic ciliate communities for monitoring water quality in Jiaozhou Bay, northern China

Spatial patterns of planktonic ciliate communities for assessment of marine environmental status were studied from June 2007 to May 2008 in Jiaozhou Bay, Qingdao, northern China. Ciliate communities were sampled biweekly at five sampling sites with a spatial gradient of environmental stress. Multivariate/univariate analyses demonstrated that: (1) the planktonic ciliate community structures represented significant differences among the five sites; (2) spatial patterns of the ciliate communities were significantly correlated with environmental variables, especially the nutrients nitrate nitrogen (NO₃-N) and soluble reactive phosphates (SRP); (3) five dominant species (e.g., Rimostrombidium veniliae, Strombidium capitatum, Mesodinium pupula and Strombidinopsis acutum) were significantly correlated with nitrogen and/or SRP; and (4) both species richness and species diversity indices were correlated with NO₃-N and salinity. These results suggest that planktonic ciliated protozoa might be used as a robust bioindicator of marine water quality.

Euxinic freshwater hypolimnia promote bacterial endemicity in continental areas

Bacteria and archaea represent the vast majority of biodiversity on Earth. The ways that dynamic ecological and evolutionary processes interact in the microbial world are, however, poorly known. Here, we have explored community patterns of planktonic freshwater bacteria inhabiting stratified lakes with oxic/anoxic interfaces and euxinic (anoxic and sulfurous) water masses. The interface separates a well-oxygenated upper water mass (epilimnion) from a lower anoxic water compartment (hypolimnion). We assessed whether or not the vertical zonation of lakes promoted endemism in deeper layers by analyzing bacterial 16S rRNA gene sequences from the water column of worldwide distributed stratified lakes and applying a community ecology approach. Community similarity based on the phylogenetic relatedness showed that bacterial assemblages from the same water layer were more similar across lakes than to communities from different layer within lakes and that anoxic hypolimnia presented greater β-diversity than oxic epilimnia. Higher β-diversity values are attributable to low dispersal and small connectivity between community patches. In addition, surface waters had significant spatial but non-significant environmental components controlling phylogenetic β-diversity patterns, respectively. Conversely, the bottom layers were significantly correlated with environment but not with geographic distance. Thus, we observed different ecological mechanisms simultaneously acting on the same water body. Overall, bacterial endemicity is probably more common than previously thought, particularly in isolated and environmentally heterogeneous freshwater habitats. We argue for a microbial diversity conservation perspective still lacking in the global and local biodiversity preservation policies.

[Structure of planktonic ammonia-oxidizing community in the waters near the Three Gorges Dam of the Yangtze River]

OBJECTIVE

Investigation of ammonia-oxidizing microorganisms (AOM) in natural environments is of great importance to understand global nitrogen cycling. However, little is known about the effects of dam constructions on the AOM community. We studied the diversity of the free-living and particle-attached AOM populations in the waters behind and in front of the Three Gorges Dam of the Yangtze River, and analyzed the possible correlation between the observed difference in the two fractions of AOM with the environmental parameters.

METHODS

Two sampling locations near the Three Gorges Dam were selected: one behind and the other in front of the dam. Physicochemical profiles of waters at each location were measured, and the biomass in the waters was collected by filtration. The diversity of AOM in the collected samples was investigated by using an integrated approach including reverse transcription and clone library construction.

RESULTS

The turbidity, dissolved oxygen, and redox potential of the water in front of the dam were higher than those behind the dam. The AOM population behind and in front of the dam was dominated by ammonia-oxidizing archaea, whereas the ammonia-oxidizing bacteria were not detected. The distribution of free-living and particle-attached AOA behind and in front of the dam was different: the particle-attached AOA behind the dam was more diverse than that in front of the dam, whereas the free-living AOA showed the opposite tendency; the difference between the fractions of AOA behind the dam was apparently higher than that in front of the dam.

CONCLUSION

The dominant AOA population did not show significant variation in the waters behind and in front of the dam, whereas the altered water dynamics resulted from the TGD construction may change the distribution of free-living and particle-attached AOA fractions in the waters behind and in front of the dam.

Resonant plankton patchiness induced by large-scale turbulent flow

Here we study how large-scale variability of oceanic plankton is affected by mesoscale turbulence in a spatially heterogeneous environment. We consider a phytoplankton-zooplankton (PZ) ecosystem model, with different types of zooplankton grazing functions, coupled to a turbulent flow described by the two-dimensional Navier-Stokes equations, representing large-scale horizontal transport in the ocean. We characterize the system using a dimensionless parameter, γ=T(B)/T(F), which is the ratio of the ecosystem biological time scale T(B) and the flow time scale T(F). Through numerical simulations, we examine how the PZ system depends on the time-scale ratio γ and find that the variance of both species changes significantly, with maximum phytoplankton variability at intermediate mixing rates. Through an analysis of the linearized population dynamics, we find an analytical solution based on the forced harmonic oscillator, which explains the behavior of the ecosystem, where there is resonance between the advection and the ecosystem predator-prey dynamics when the forcing time scales match the ecosystem time scales. We also examine the dependence of the power spectra on γ and find that the resonance behavior leads to different spectral slopes for phytoplankton and zooplankton, in agreement with observations.

Analysis of biostimulated microbial communities from two field experiments reveals temporal and spatial differences in proteome profiles

Stimulated by an acetate-amendment field experiment conducted in 2007, anaerobic microbial populations in the aquifer at the Rifle Integrated Field Research Challenge site in Colorado reduced mobile U(VI) to insoluble U(IV). During this experiment, planktonic biomass was sampled at various time points to quantitatively evaluate proteomes. In 2008, an acetate-amended field experiment was again conducted in a similar manner to the 2007 experiment. As there was no comprehensive metagenome sequence available for use in proteomics analysis, we systematically evaluated 12 different organism genome sequences to generate sets of aggregate genomes, or "pseudo-metagenomes", for supplying relative quantitative peptide and protein identifications. Proteomics results support previous observations of the dominance of Geobacteraceae during biostimulation using acetate as sole electron donor, and revealed a shift from an early stage of iron reduction to a late stage of iron reduction. Additionally, a shift from iron reduction to sulfate reduction was indicated by changes in the contribution of proteome information contributed by different organism genome sequences within the aggregate set. In addition, the comparison of proteome measurements made between the 2007 field experiment and 2008 field experiment revealed differences in proteome profiles. These differences may be the result of alterations in abundance and population structure within the planktonic biomass samples collected for analysis.

Coastal bacterioplankton community diversity along a latitudinal gradient in Latin America by means of V6 tag pyrosequencing

The bacterioplankton diversity of coastal waters along a latitudinal gradient between Puerto Rico and Argentina was analyzed using a total of 134,197 high-quality sequences from the V6 hypervariable region of the small-subunit ribosomal RNA gene (16S rRNA) (mean length of 60 nt). Most of the OTUs were identified into Proteobacteria, Bacteriodetes, Cyanobacteria, and Actinobacteria, corresponding to approx. 80% of the total number of sequences. The number of OTUs corresponding to species varied between 937 and 1946 in the seven locations. Proteobacteria appeared at high frequency in the seven locations. An enrichment of Cyanobacteria was observed in Puerto Rico, whereas an enrichment of Bacteroidetes was detected in the Argentinian shelf and Uruguayan coastal lagoons. The highest number of sequences of Actinobacteria and Acidobacteria were obtained in the Amazon estuary mouth. The rarefaction curves and Good coverage estimator for species diversity suggested a significant coverage, with values ranging between 92 and 97% for Good coverage. Conserved taxa corresponded to aprox. 52% of all sequences. This study suggests that human-contaminated environments may influence bacterioplankton diversity.

[Effects of sediment resuspension on bacterioplankton community composition]

To determine the response of bacterioplankton community to sediment resuspension we set up two different intensities of the sediment resuspension in experimental microcosms. We employed the terminal restriction fragment length polymorphism (T-RFLP), denaturing gradient gel electrophoresis (DGGE) methods to characterize the bacterial community structure. The result demonstrated that the species richness of the bacterioplankton in the treatment with sediment resuspension was higher than that in the controls without sediment resuspension. The bacterioplankton species richness and community diversity in the treatment with weak sediment resuspension (WR) was higher than that with strong sediment resuspension (SR). The relationship between bacterioplankton and environmental factors were investigated using canonical correspondence analysis (CCA) and redundancy analysis (RDA). The CCA and RDA results showed that there was a high degree of correlation between bacterioplankton community composition with Cladocera and particulate phosphorus (PP). It indicates that the sediment resuspension of shallow lakes has a significant effect on the species richness and diversity of bacterioplankton. We speculate the main reason is the dynamics of zooplankton community structure and the function of nutrient concentration influenced by the sediment resuspension.

Substrate utilization profiles of bacterial strains in plankton from the River Warnow, a humic and eutrophic river in north Germany

Bacteria are very important degraders of organic substances in aquatic environments. Despite their influential role in the carbon (and many other element) cycle(s), the specific genetic identity of active bacteria is mostly unknown, although contributing phylogenetic groups had been investigated. Moreover, the degree to which phenotypic potential (i. e., utilization of environmentally relevant carbon substrates) is related to the genomic identity of bacteria or bacterial groups is unclear. The present study compared the genomic fingerprints of 27 bacterial isolates from the humic River Warnow with their ability to utilize 14 environmentally relevant substrates. Acetate was the only substrate utilized by all bacterial strains. Only 60% of the strains respired glucose, but this substrate always stimulated the highest bacterial activity (respiration and growth). Two isolates, both closely related to the same Pseudomonas sp., also had very similar substrate utilization patterns. However, similar substrate utilization profiles commonly belonged to genetically different strains (e.g., the substrate profile of Janthinobacterium lividum OW6/RT-3 and Flavobacterium sp. OW3/15-5 differed by only three substrates). Substrate consumption was sometimes totally different for genetically related isolates. Thus, the genomic profiles of bacterial strains were not congruent with their different substrate utilization profiles. Additionally, changes in pre-incubation conditions strongly influenced substrate utilization. Therefore, it is problematic to infer substrate utilization and especially microbial dissolved organic matter transformation in aquatic systems from bacterial molecular taxonomy.

[Fouling: terminology and definitions]

Current classification of principal ecological groups of hydrobionts is an eclectic one as it confuses two fundamentals, one dealing with organismic ecomorphology and another with water body's topology. This leads to difficulties in determination of interrelations between benthos and fouling communities. The littoral fouling communities cannot be considered as an independent ecological group of the same rank as plankton or benthos because it lacks a unique species composition. The fouling is always a derivate of the benthos, so it could be defined as a community formed by benthic organisms during succession on a solid substrate more or less remote from the water body's bottom. All peculiarities of the fouling communities distinguishing them from similar benthic communities are determined by topology and other properties of the substrate, by relatively short period of the latter's exposition and by hydrological conditions under which the fouling is developing. There is continual transitions between benthic and fouling communities both in space (along gradients of abiotic environmental factors) and in time (along successional series). Such a continuum becomes most frequently broken due to both significant remoteness of the substrate, on which a fouling develops, from the bottom and permanent extreme factors disturbing or retarding fouling communities development. Thus, littoral foulings are just benthos being formed under specific conditions. At the same time, oceanic foulings are connected both evolutionary and ecologically with littoral foulings and benthos.

Genetic diversity of eukaryotic plankton assemblages in Eastern Tibetan Lakes differing by their salinity and altitude

Eukaryotic plankton assemblages in 11 high-mountain lakes located at altitudes of 2,817 to 5,134 m and over a total area of ca. one million square kilometers on the Eastern Tibet Plateau, spanning a salinity gradient from 0.2 (freshwater) to 187.1 g l(-1) (hypersaline), were investigated by cultivation independent methods. Two 18S rRNA gene-based fingerprint approaches, i.e., the terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis (DGGE) with subsequent band sequencing were applied. Samples of the same lake type (e.g., freshwater) generally shared more of the same bands or T-RFs than samples of different types (e.g., freshwater versus saline). However, a certain number of bands or T-RFs among the samples within each lake were distinct, indicating the potential presence of significant genetic diversity within each lake. PCA indicated that the most significant environmental gradient among the investigated lakes was salinity. The observed molecular profiles could be further explained (17-24%) by ion percentage of chloride, carbonate and bicarbonate, and sulfate, which were also covaried with change of altitude and latitude. Sequence analysis of selected major DGGE bands revealed many sequences (largely protist) that are not related to any known cultures but to uncultured eukaryotic picoplankton and unidentified eukaryotes. One fourth of the retrieved sequences showed < or =97% similarity to the closest sequences in the GenBank. Sequences related to well-known heterotrophic nanoflagellates were not retrieved from the DGGE gels. Several groups of eukaryotic plankton, which were found worldwide and detected in low land lakes, were also detected in habitats located above 4,400 m, suggesting a cosmopolitan distribution of these phylotypes. Collectively, our study suggests that there was a high beta-diversity of eukaryotic plankton assemblages in the investigated Tibetan lakes shaped by multiple geographic and environmental factors.

Bacterial succession within an ephemeral hypereutrophic Mojave Desert playa Lake

Ephemerally wet playas are conspicuous features of arid landscapes worldwide; however, they have not been well studied as habitats for microorganisms. We tracked the geochemistry and microbial community in Silver Lake playa, California, over one flooding/desiccation cycle following the unusually wet winter of 2004-2005. Over the course of the study, total dissolved solids increased by approximately 10-fold and pH increased by nearly one unit. As the lake contracted and temperatures increased over the summer, a moderately dense planktonic population of approximately 1x10(6) cells ml(-1) of culturable heterotrophs was replaced by a dense population of more than 1x10(9) cells ml(-1), which appears to be the highest concentration of culturable planktonic heterotrophs reported in any natural aquatic ecosystem. This correlated with a dramatic depletion of nitrate as well as changes in the microbial community, as assessed by small subunit ribosomal RNA gene sequencing of bacterial isolates and uncultivated clones. Isolates from the early-phase flooded playa were primarily Actinobacteria, Firmicutes, and Bacteroidetes, yet clone libraries were dominated by Betaproteobacteria and yet uncultivated Actinobacteria. Isolates from the late-flooded phase ecosystem were predominantly Proteobacteria, particularly alkalitolerant isolates of Rhodobaca, Porphyrobacter, Hydrogenophaga, Alishwenella, and relatives of Thauera; however, clone libraries were composed almost entirely of Synechococcus (Cyanobacteria). A sample taken after the playa surface was completely desiccated contained diverse culturable Actinobacteria typically isolated from soils. In total, 205 isolates and 166 clones represented 82 and 44 species-level groups, respectively, including a wide diversity of Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, Gemmatimonadetes, Acidobacteria, and Cyanobacteria.

Laser damage to marine plankton and its application to checking biofouling and invasion by aquatic species: a laboratory study

In this laboratory study, the ability of low-power pulsed laser irradiation to kill planktonic organisms in a flowing water system was examined, thus, to test the possibility of using this technique as a water treatment strategy to reduce biofouling growth in condenser tubes of power plants and to reduce bioinvasion via the ballast water of ships. Two flow rates (4.6 and 9.0 l h(-1)) were tested on three planktonic organisms: two marine centric diatoms viz. Skeletonema costatum and Chaetoceros gracilis and a dinoflagellate, Heterocapsa circularisquama. A low-power pulsed laser irradiation at 532 nm with a fluence of 0.1 J cm(-2) from a frequency-doubled Nd:YAG laser was used as the irradiation source. The laser irradiation resulted in a heavy mortality of the test cells. The mortality observed was >90% for S. costatum and H. circularisqama and >70% for C. gracilis. The results suggest that laser irradiation has the potential to act as a water treatment strategy to reduce biofouling of condenser tubes in power plants as well as to reduce species invasion via the ballast water of ships.

Eutrophic waters, algal bloom and fish kill in fish farming areas in Bolinao, Pangasinan, Philippines

The coastal waters of Bolinao, Pangasinan, Philippines experienced environmental changes over a 10-year period (1995-2005), the most significant effect of which was the major fish kill event in 2002 that coincided with the first reported Philippine bloom of a dinoflagellate Prorocentrum minimum. Days before the bloom, dissolved oxygen was < 2.0 mg/l in the waters that were stratified. These conditions may be linked to the uncontrolled proliferation of fish pens and cages to more than double the allowable limit of 544 units for Bolinao waters. Mariculture activities release organic matter from unconsumed feed and fecal material that accumulate in the water and sediments. In over 10 years, water quality conditions have become eutrophic with ammonia increasing by 56%, nitrite by 35%, nitrate by 90%, and phosphate by 67%. The addition of more fish pens and cages placed additional stress to this poorly flushed, shallow area that affected water quality due to changes in the water residence time.

Dilution-to-extinction culturing of psychrotolerant planktonic bacteria from permanently ice-covered lakes in the McMurdo Dry Valleys, Antarctica

Lakes in the McMurdo Dry Valleys of Antarctica are characterized by a permanent ice cover and little or no anthropogenic influence. Although bacterial cultures have been obtained from these habitats, recent culture-independent studies indicate that the most abundant microbes in these systems are not yet cultivated. By using dilution-to-extinction cultivation methods with sterilized and nutrient-amended lake water as media, we isolated 148 chemotrophic psychrotolerant bacterial cultures from fresh surface water of Lake Fryxell and the east lobe of Lake Bonney and the hypersaline, suboxic bottom water from the west lobes of Lake Bonney. Screening of the 16S ribosomal ribonucleic acid (rRNA) genes of the cultures by restriction fragment length polymorphism (RFLP) yielded 57 putatively pure psychrotolerant, slow growing cultures grouped into 18 clusters. The sequencing of 16S rRNA genes of randomly selected representatives of each RFLP cluster revealed that the corresponding isolates belong to the Alphaproteobacteria (six RFLP patterns), Betaproteobacteria (six RFLP patterns), Bacteroidetes (four RFLP patterns), and Actinobacteria (two RFLP patterns). Phylogenetic analysis of the sequences showed that the vast majority of the isolates were not closely related to previously described species. Thirteen of 18 RFLP patterns shared a 16S ribosomal deoxyribonucleic acid sequence similarity of 97% or less with the closest described species, and four isolates had a sequence similarity of 93% or less with the nearest described species. Phylogenetic analysis showed that these sequences were representatives of deeply branching organisms in the respective phylum. A comparison of the isolates with 16S rRNA clone libraries prepared from the same environments showed substantial overlap, indicating that dilution-to-extinction culturing in natural lake water media can help isolate some of the most abundant organisms in these perennially ice-covered lakes.

[Genetic diversity of eukarytic microplankton in different areas of Lake Taihu]

The methods of DGGE and cloning/sequencing were used to study the diversity and community structures of small planktons (0.8 - 20 microm) in different areas of Lake Taihu. DGGE indicated that there were markly various fingerprints in different areas and the diversities were higher in areas with low trophic status than those with relatively high trophic status. There were 23, 24 DGGE bands in East Taihu and Gonghu Bay, respectively (Shannon index were 3.135 and 3.178) and 18 bands in both Meiliang Bay and Wuli Bay (Both shannon index were 2.890). The result of cloning/sequencing indicated that there was a high diversity of small planktons in Lake Taihu and most of them phototrophic flagellate, heterotrophic flagellate, ciliate and fungi. There were various community structures in the three different clone libraries. In Meilang Bay, 28.6% OTUs(operational taxonomic unit)belonged to heterotrophic flagellate, followed by Cryptophyta (22.9%) and Chrysophyta (14.3%). In Central Lake, 25.7% OTUs belonged to Chrysophyta, followed by heterotrophic flagellate (20.0%) and Cryptophyta (14.3 %). In East Taihu, ciliates were the dominant group and only a few heterotrophic flagellates (40.9%) were detected. In addition, fungi were relatively abundant (12.2%) in this area.

Impact of 17alpha-ethinylestradiol on the plankton in freshwater microcosms--I: response of zooplankton and abiotic variables

We investigated effects of 17alpha-ethinylestradiol (EE) in vertebrate free 230 L still water microcosms. Zooplankton composition and physico-chemical variables were observed during 4 weeks of pre-application, 6 weeks of dosing via controlled release, and a 12 weeks post-treatment period. In the treated microcosms, time-weighted averages of EE concentration ranged between 7 and 220 ng/L during the dosing period, with concentration maxima up to 724 ng/L. EE exposure resulted in a decrease of species numbers and diversity (Shannon-Wiener, Simpson). Abundances of cladocerans, copepods, and, less unambiguously, rotifers declined. Strongest affected groups were the offspring of cladocerans and copepods and, on species level, the cladoceran species Daphnia longispina and Chydorus sphaericus as well as the rotifer species Keratella quadrata and Polyarthra sp. EE apparently affected the phosphate cycle as indicated by increased phosphate concentrations in the water. During post-treatment period, the treated microcosms recovered, but especially the highest treated microcosms did not fully re-approximate to the controls. Whereas EE affected cladocerans and copepods directly, shifts of rotifers may (partly) be caused indirectly, e.g. by competition with crustaceae. Although not providing an absolute proof, the traits of direct and indirect effects on different taxonomic groups and larval stages as well as the time course of the effects indicate that effects primarily resulted from endocrine activity of EE.

Plankton community composition in the Three Gorges Reservoir Region revealed by PCR-dGGE and its relationships with environmental factors

To explore the relationships between community composition and the environment in a reservoir ecosystem, plankton communities from the Three Gorges Reservoir Region were studied by PCR-denaturing gradient gel electrophoresis fingerprinting. Bacterial and eukaryotic operational taxonomic units (OTUs), generated by DGGE analysis of the PCR-amplified 16S and 18S rRNA genes, were used as surrogates for the dominant "biodiversity units". OTU composition among the sites was heterogeneous; 46.7% of the total bacterial OTUs (45) and 64.1% of the eukaryotic OTUs (39) were identified in less than half of the sampling sites. Unweighted pair group method with arithmetic averages (UPGMA) clustering of the OTUs suggested that the plankton communities in the Xiangxi River sites were not always significantly different from those from the Yangtze River sites, despite clear differences in their environmental characterizations. Canonical correspondence analysis (CCA) was applied to further investigate the relationships between OTU composition and the environmental factors. The first two CCA ordination axes suggested that the bacterial community composition was primarily correlated with the variables of NO(3-)-N, dissolved oxygen (DO), and SiO3(2-)-Si, whereas, the eukaryotic community was mainly correlated with the concentrations of DO, PO4(3-)-P, and SiO3(2-)-Si.

The native bacterioplankton community in the central baltic sea is influenced by freshwater bacterial species

The Baltic Sea is one of the largest brackish environments on Earth. Despite extensive knowledge about food web interactions and pelagic ecosystem functioning, information about the bacterial community composition in the Baltic Sea is scarce. We hypothesized that due to the eutrophic low-salinity environment and the long water residence time (>5 years), the bacterioplankton community from the Baltic proper shows a native "brackish" composition influenced by both freshwater and marine phylotypes. The bacterial community composition in surface water (3-m depth) was examined at a single station throughout a full year. Denaturing gradient gel electrophoresis (DGGE) showed that the community composition changed over the year. Further, it indicated that at the four extensive samplings (16S rRNA gene clone libraries and bacterial isolates from low- and high-nutrient agar plates and seawater cultures), different bacterial assemblages associated with different environmental conditions were present. Overall, the sequencing of 26 DGGE bands, 160 clones, 209 plate isolates, and 9 dilution culture isolates showed that the bacterial assemblage in surface waters of the central Baltic Sea was dominated by Bacteroidetes but exhibited a pronounced influence of typical freshwater phylogenetic groups within Actinobacteria, Verrucomicrobia, and Betaproteobacteria and a lack of typical marine taxa. This first comprehensive analysis of bacterial community composition in the central Baltic Sea points to the existence of an autochthonous estuarine community uniquely adapted to the environmental conditions prevailing in this brackish environment.

[DNA fingerprinting structure of plankton community and its relations to environmental physical-chemical factors in Donghu Lake]

By the method of RAPD fingerprinting, this paper studied the DNA fingerprinting structure of plankton community and its relations to the main environmental physical-chemical factors at five sites in Donghu Lake. From the screened 9 random primers, a total of 210 observable bands with a length of 150-2 000 bp were amplified, 93.3% of which were polymorphic. At the five sites, the average number of amplified bands was 42, with the maximum (53) at site IV and the minimum (35) at site V. The PO4(3-)-P and TP contents were the highest at site I, NH4(+)-N, TN and NO2(-)-N contents were the highest at site V, while the values of all test physical-chemical parameters were the lowest at site IV. No obvious differences in COD, alkalinity, rigidity, and calcium content were observed among the study sites. Similarity clustering analysis showed that the DNA fingerprinting of plankton community based on RAPD marker could cluster the five sites into two groups, i. e., sites I, II and III could be clustered into one group, while sites IV and V could be clustered into another group, which was consistent with the clustering analysis based on the main environmental physical-chemical factors. In conclusion, there was a close relation between the DNA fingerprinting structure of plankton community and the main environmental physical-chemical factors in Donghu Lake.

[Characteristic of combined floating bed ecosystem for water purification under dynamic condition]

A new type of ecological floating bed was developed that combined hydrophyte, aquatic animal and biofilm. The dynamic pilot study on purification characteristic and mechanism of the floating bed for eutrophic was carried out. Result shows that the removal efficiencies of TN, TP and COD(Mn), are 53.8%, 86.0% and 35.4% respectively under the water exchange period of 7 days. Main purification role is played by artificial medium and aquatic macrophyte in pollutants removal, but the Corbicula fluminea introduced to food chain of combined floating bed enhances the purification effect through the ways as follows: improving the resolvability, ammonification and biodegradability of particulate organic matters, meliorating the substrate supply condition for absorption of plant and degradation of microorganism attached on artificial medium, hastening the growth and activity of microorganism.

Respiratory succession and community succession of bacterioplankton in seasonally anoxic estuarine waters

Anoxia occurs in bottom waters of stratified estuaries when respiratory consumption of oxygen, primarily by bacteria, outpaces atmospheric and photosynthetic reoxygenation. Once water becomes anoxic, bacterioplankton must change their metabolism to some form of anaerobic respiration. Analysis of redox chemistry in water samples spanning the oxycline of Chesapeake Bay during the summer of 2004 suggested that there was a succession of respiratory metabolism following the loss of oxygen. Bacterial community doubling time, calculated from bacterial abundance (direct counts) and production (anaerobic leucine incorporation), ranged from 0.36 to 0.75 day and was always much shorter than estimates of the time that the bottom water was anoxic (18 to 44 days), indicating that there was adequate time for bacterial community composition to shift in response to changing redox conditions. However, community composition (as determined by PCR-denaturing gradient gel electrophoresis analysis of 16S rRNA genes) in anoxic waters was very similar to that in surface waters in June when nitrate respiration was apparent in the water column and only partially shifted away from the composition of the surface community after nitrate was depleted. Anoxic water communities did not change dramatically until August, when sulfate respiration appeared to dominate. Surface water populations that remained dominant in anoxic waters were Synechococcus sp., Gammaproteobacteria in the SAR86 clade, and Alphaproteobacteria relatives of Pelagibacter ubique, including a putative estuarine-specific Pelagibacter cluster. Populations that developed in anoxic water were most similar (<92% similarity) to uncultivated Firmicutes, uncultivated Bacteroidetes, Gammaproteobacteria in the genus Thioalcalovibrio, and the uncultivated SAR406 cluster. These results indicate that typical estuarine bacterioplankton switch to anaerobic metabolism under anoxic conditions but are ultimately replaced by different organisms under sulfidic conditions.

Biogeography of bacterioplankton in lakes and streams of an Arctic tundra catchment

Bacterioplankton community composition was compared across 10 lakes and 14 streams within the catchment of Toolik Lake, a tundra lake in Arctic Alaska, during seven surveys conducted over three years using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified rDNA. Bacterioplankton communities in streams draining tundra were very different than those in streams draining lakes. Communities in streams draining lakes were similar to communities in lakes. In a connected series of lakes and streams, the stream communities changed with distance from the upstream lake and with changes in water chemistry, suggesting inoculation and dilution with bacteria from soil waters or hyporheic zones. In the same system, lakes shared similar bacterioplankton communities (78% similar) that shifted gradually down the catchment. In contrast, unconnected lakes contained somewhat different communities (67% similar). We found evidence that dispersal influences bacterioplankton communities via advection and dilution (mass effects) in streams, and via inoculation and subsequent growth in lakes. The spatial pattern of bacterioplankton community composition was strongly influenced by interactions among soil water, stream, and lake environments. Our results reveal large differences in lake-specific and stream-specific bacterial community composition over restricted spatial scales (<10 km) and suggest that geographic distance and connectivity influence the distribution of bacterioplankton communities across a landscape.

Planktonic dinoflagellates of the northern Levantine Basin, northeastern Mediterranean Sea

In the present study, a checklist of planktonic dinoflagellates was prepared from studies conducted on the northeastern Mediterranean coast of Turkey and by evaluating previously conducted studies. The sampling areas included Iskenderun Bay, the coast near Karataş at the west end of the Bay, and Babadillimani Bight, situated at the west of Mersin Bay, and its surroundings. The data of the present study derives from over 90 locations visited between 1994 and 2004. A total of 174 taxa were reported. Ceratium (57 taxa) and Protoperidinium (28 taxa) were the most species-rich genera. The most common taxa were Ceratium kofoidii, Ceratium trichoceros, Ceratium tripos var. atlanticum, Protoperidinium divergens, Protoperidinium steinii, Ceratocorys horrida, Goniodoma acuminatum and Gonyaulax polygramma. Toxic species such as Dinophysis caudata, Dinophysis tripos were reported, and Scrippsiella trochoidea and Prorocentrum micans, which are known as red tide species elsewhere, were also common. The number of species is similar to those along other coasts of the Levantine Basin. However, some species were observed that had not previously been reported for the Levantine Basin, which can be attributed to the fact that the number of studies conducted in the region has increased and that new species may have entered the environment.

Bacterioplankton assemblages transforming dissolved organic compounds in coastal seawater

To characterize bacterioplankton functional assemblages that transform specific components of the coastal seawater dissolved organic carbon (DOC) pool, bromodeoxyuridine (BrdU) was used to label the bacterioplankton cells that were active following addition of single-DOC model compounds: two organic osmolytes [dimethylsulfoniopropionate (DMSP) and glycine betaine (GlyB)] and two aromatic monomers [para-hydroxybenzoic acid (pHBA) and vanillic acid (VanA)]. Bacterial populations were analysed based on in situ fluorescent immunodetection of BrdU incorporation followed by fluorescence-activated cell sorting (FACS). Sorted cells were then characterized by 16S rDNA-based analysis. Populations with high BrdU incorporation level (HI) developed within 8 h of introduction of 100 nM model compound. Terminal restriction fragment length polymorphisms (T-RFLP) analysis indicated that the HI populations in all four amendments were composed of bacteria from the same major taxa (phylum and subphylum levels), but the relative abundance of each differed. High-resolution clone libraries (each containing approximately 200 clones) showed that the HI populations in the GlyB and VanA amendments consisted of both metabolic generalists and specialists within the alpha-Proteobacteria (mainly members of the Roseobacter clade), beta-Proteobacteria and gamma-Proteobacteria (mainly members of Altermonadaceae, Chromatiaceae, Oceanospirillaceae and Pseudomonadaceae). The presence of members of OM60/241, OM185, SAR11, SAR86 and SAR116 in the HI populations indicated that members of these groups can assimilate the model DOC compounds, providing some of the first glimpses into heterotrophy by members of these poorly understood environmental clusters.