A phylogenetic approach identifies patterns of beta diversity and floristic subregions of the Qinghai-Tibet Plateau

Patterns of taxonomic and phylogenetic beta diversity and their relationships with environmental correlates can help reveal the origin and evolutionary history of regional biota.The Qinghai-Tibet Plateau(QTP)harbors an exceptionally diverse flora,however,a phylogenetic perspective has rarely been used to investigate its beta diversity and floristic regions.In this study,we used a phylogenetic approach to identify patterns of beta diversity and quantitatively delimit floristic regions on the Qinghai-Tibet Plateau.We also examined the relationships between multifaceted beta diversity,geographical distance,and climatic difference,and evaluated the relative importance of various factors(i.e.,climate,topography and history)in shaping patterns of beta diversity.Sørensen dissimilarity indices indicated that patterns of species turnover among sites dominated the QTP.We also found that patterns of both taxonomic and phylogenetic beta diversity were significantly related to geographical distance and climatic difference.The environmental factors that contributed most to these patterns of beta diversity include annual precipitation,mean annual temperature,climatic gradients and climatic instability.Hierarchical dendrograms of dissimilarity and non-metric multidimensional scaling ordination based on phylogenetic beta diversity data identified ten floristic subregions in the QTP.Our results suggest that the contemporary environment and historical climate changes have filtered species composition among sites and eventually determined beta diversity patterns of plants in the QTP.

Patterns and drivers of avian taxonomic and phylogenetic beta diversity in China vary across geographical backgrounds and dispersal abilities

Geographical background and dispersal ability may strongly influence assemblage dissimilarity;however,these aspects have generally been overlooked in previous large-scale beta diversity studies.Here,we examined whether the patterns and drivers of taxonomic beta diversity(TBD)and phylogenetic beta diversity(PBD)of breeding birds in China vary across(1)regions on both sides of the Hu Line,which demarcates China’s topographical,climatic,economic,and social patterns,and(2)species with different dispersal ability.TBD and PBD were calculated and partitioned into turnover and nestedness components using a moving window approach.Variables representing climate,habitat heterogeneity,and habitat quality were employed to evaluate the effects of environmental filtering.Spatial distance was considered to assess the impact of dispersal limitation.Variance partitioning analysis was applied to assess the relative roles of these variables.In general,the values of TBD and PBD were high in mountainous areas and were largely determined by environmental filtering.However,different dominant environmental filters on either side of the Hu Line led to divergent beta diversity patterns.Specifically,climate-driven species turnover and habitat heterogeneity-related species nestedness dominated the regions east and west of the line,respectively.Additionally,bird species with stronger dispersal ability were more susceptible to environmental filtering,resulting in more homogeneous assemblages.Our results indicated that regions with distinctive geographical backgrounds may present different ecological factors that lead to divergent assemblage dissimilarity patterns,and dispersal ability determines the response of assemblages to these ecological factors.Identifying a single universal explanation for the observed pattern without considering these aspects may lead to simplistic or incomplete conclusions.Consequently,a comprehensive understanding of large-scale beta diversity patterns and effective planning of conservation strategies necessitate the consideration of both geographical background and species dispersal ability.

Diversity and Phylogenetic Analysis of Lactic Acid in Forage of Xinjiang Uigur Autonomous Region

[Objective] The aim was to conduct preliminary investigation and diversity analysis of lactic acid bacteria resources in forage from Turpan of Xinjiang. [Method] The lactic acid bacteria in the three kinds of forage ingredients in Xinjiang were isolated by using plate separation method and screened by MRS＋CaCO3 solid medium. Morphological, physiological and biochemical identification and 16S rDNA gene sequence analysis were carried out to the isolated eighty strains of lactic acid bacteria, to explore its taxonomic status. [Result] Twenty strains of lactic acid bacteria were obtained from alfalfa, forty-one from wheat, and nineteen from corn. The physiological and biochemical identification and 16S rDNA gene sequence analysis results showed that the eighty strains of lactic acid bacteria belonged to two genera, namely, Lactobacillus, Enterococcus; 7 species, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus paracasei, Entercoccus faecium, Entercoccus durans, Lactobacillus plantarum, Entercoccus hirae. Lactobacillus casei and Entercoccus faecium were ubiquitous in the three kinds of forage ingredients. Besides these two lactic acid bacteria, there were Lactobacillus rhamnosus, Lactobacillus paracasei, Lactobacillus plantarum in wheat, Lactobacillus plantarum, Lactobacillus paracasei, Entercoccus hirae, Entercoccus durans in alfalfa, Lactobacillus plantarum, Entercoccus durans in corn. [Conclusion] There is a big diversity of lactic acid bacteria in different forage from Turpan of Xinjiang, in which Lactobacillus casei, Entercoccus faecium are the key bacteria for forage fermentation.

Diversity patterns and phylogenetic structure of vascular plants along elevational gradients in a mountain ecosystem, South Korea

Recently, a phylogenetic diversity and community structure analysis as complementary to species-centric approaches in biodiversity studies provides new insights into the processes of community assembly. In this study, we analyzed species and phylogenetic diversity and community structures for woody and herbaceous plants along two elevational transects on Mt. Baekhwa, South Korea. The species richness and phylogenetic diversity of woody plants showed monotonic declining patterns with increasing elevation along all transects, whereas herbaceous plants showed different patterns, such as no relationship and a reversed unimodal pattern, between the study transects. The main drivers of these patterns were climate and habitat variables for woody and herbaceous plants, respectively. In addition, the phylogenetic community structure primarily showed phylogenetic clustering regulated by deterministic processes, especially environmental filtering, such as climate or habitat factors, along the two transects, although herbaceous plants along a transect depicted phylogenetic randomness as a result of a neutral process. Our findings suggest that deterministic and neutral processes may simultaneously control the community structures along small-scale elevational gradients such as local transects, although the deterministic process may be the predominant type.

Global patterns of taxonomic and phylogenetic diversity of flowering plants: Biodiversity hotspots and coldspots

Species diversity of angiosperms(flowering plants) varies greatly among regions.Geographic patterns of variation in species diversity are shaped by the interplay of ecological and evolutionary processes.Here,using a comprehensive data set for regional angiosperm floras across the world,we show geographic patterns of taxonomic(species) diversity,phylogenetic diversity,phylogenetic dispersion,and phylogenetic deviation(i.e.,phylogenetic diversity after accounting for taxonomic diversity) across the world.Phylogenetic diversity is strongly and positively correlated with taxonomic diversity;as a result,geographic patterns of taxonomic and phylogenetic diversity across the world are highly similar.Areas with high taxonomic and phylogenetic diversity are located in tropical regions whereas areas with low taxonomic and phylogenetic diversity are located in temperate regions,particularly in Eurasia and North America,and in northern Africa.Similarly,phylogenetic dispersion is,in general,higher in tropical regions and lower in temperate regions.However,the geographic pattern of phylogenetic deviation differs substantially from those of taxonomic and phylogenetic diversity and phylogenetic dispersion.As a result,hotspots and coldspots of angiosperm diversity identified based on taxonomic and phylogenetic diversity and phylogenetic dispersion are incongruent with those identified based on phylogenetic deviations.Each of these metrics may be considered when selecting areas to be protected for their biodiversity.

How do altitude and soil properties influence the taxonomic and phylogenetic structure and diversity of Brazilian páramo vegetation?

Altitude and environmental variables such as edaphic properties are considered determinants of species distribution and community composition in mountain ecosystems.Here,we aimed to outline the effects of distinct mountain peaks,altitude and soil properties on community composition,species density,phylogenetic structure and diversity of angiosperm páramo communities from the Serra do Brigadeiro State Park,Minas Gerais,southeastern Brazil.For that,we identified all angiosperm species found in 300 plots(1 m×1 m)from three mountain peaks,measured soil depth and analyzed soil fertility and texture in each plot.To reduce the number of soil variables and species composition,we computed principal coordinates based on soil properties and principal coordinates based on species-plot matrix for each plot.Furthermore,we computed the standard effect sizes of the mean phylogenetic pairwise distance and the mean nearest phylogenetic taxon distance for each plot to investigate differences in the degree of relatedness among coexisting species.We compared differences in response variables between peaks and modelled them in function of altitude and principle components of soil properties using mixed effect models.Species density and phylogenetic diversity differed between peaks,but,contrary to the previous findings,no relationships between species richness or phylogenetic diversity and altitude or soil properties were found,indicating that further investigations are necessary to understand the altitude-biodiversity relationship in Brazilian páramo vegetation.Community composition differed between peaks and depended on altitude,soil properties and interactions between them,indicating that upward shifting of bioclimatic conditions due to climate changes may alter communities of this ecosystem.Phylogenetic structure differed between peaks and was influenced by altitude and soil properties.As phylogenetic clustering increased with altitude,eventual upward movements of species in Brazilian páramo vegetation due to climate change may alter community composition and the degree of relatedness among coexisting species,increasing the risk of species from higher altitudes to disappear.Therefore,conservation priorities arise for higher landscape portions,where these high altitude species may find refuges.

Amphibian Species Contribute Similarly to Taxonomic, but not Functional and Phylogenetic Diversity: Inferences from Amphibian Biodiversity on Emei Mountain

Understanding the relationships between species, communities, and biodiversity are important challenges in conservation ecology. Current biodiversity conservation activities usually focus on species that are rare, endemic, distinctive, or at risk of extinction. However, empirical studies of whether such species contribute more to aspects of biodiversity than common species are still relatively rare. The aim of the present study was to assess the contribution of individual amphibian species to different facets of biodiversity, and to test whether species of conservation interest contribute more to taxonomic, functional, and phylogenetic diversity than do species without special conservation status. To answer these questions, 19 000 simulated random communities with a gradient of species richness were created by shuffling the regional pool of species inhabiting Emei Mountain. Differences of diversity values were then computed before and after removing individual species in these random communities. Our results indicated that although individual species contributed similarly to taxonomic diversity, their contribution to functional and phylogenetic diversity was more idiosyncratic. This was primarily driven by the diverse functional attributes of species and the differences in phylogenetic relationships among species. Additionally, species of conservation interest did not show a significantly higher contribution to any facet of biodiversity. Our results support the claims that the usefulness of metrics based only on species richness is limited. Instead, assemblages that include species with functional and phylogenetic diversity should be protected to maintain biodiversity.

Phylogenetic diversity of eastern Asia-eastern North America disjunct plants is mainly associated with divergence time

The underlying causes of biodiversity disparities among geographic regions have long been a fundamental theme in ecology and evolution.However,the patterns of phylogenetic diversity(PD) and phylogenetic beta diversity(PBD) of congeners that are disjunctly distributed between eastern Asia-eastern North America(EA-ENA disjuncts) and their associated factors remain unknown.Here we investigated the standardized effect size of PD(SES-PD),PBD,and potentially associated factors in 11natural mixed forest sites(five in EA and six in ENA) where abundant EA-ENA disjuncts occur.We found that the disjuncts in ENA possessed higher SES-PD than those in EA at the continental scale(1.96vs-1.12),even though the number of disjunct species in ENA is much lower than in EA(128 vs 263).SESPD of the EA-ENA disjuncts tended to decrease with increasing latitude in 11 sites.The latitudinal diversity gradient of SES-PD was stronger in EA sites than in ENA sites.Based on the unweighted unique fraction metric(UniFrac) distance and the phylogenetic community dissimilarity,PBD showed that the two northern sites in EA were more similar to the six-site ENA group than to the remaining southern EA sites.Based on the standardized effect size of mean pairwise distances(SES-MPD),nine of eleven studied sites showed a neutral community structure(-1.96 ≤SES-MPD ≤1.96).Both Pearson’s r and structural equation modeling suggested that SES-PD of the EA-ENA disjuncts was mostly associated with mean divergence time.Moreover,SES-PD of the EA-ENA disjuncts was positively correlated with temperaturerelated climatic factors,although negatively correlated with mean diversification rate and community structure.By applying approaches from phylogenetics and community ecology,our work sheds light on historical patterns of the EA-ENA disjunction and paves the way for further research.

Phylogenetic diversity of bacteria associated with the marine sponge Agelas robusta from South China Sea

It is well known that marine sponges harbor large numbers of bacteria,some of which have been proved to be sponge-specific.The diversity of bacteria in marine sponges distributed along the coast of South China Sea has been previously studied but that of bacteria in sponges inhabiting the open sea has been rarely investigated.In this report,the diversity of bacteria associated with the marine sponge Agelas robusta from a remote coral reef in the South China Sea was documented employing 16S rDNA library construction,amplified ribosomal DNA restriction analysis（ARDRA） and phylogenetic analysis.A total of 32 phylotypes were finally categorized in nine phyla including Cyanobacteria,Proteobacteria,Chloroflexi,Firmicutes,Actinobacteria,Acidobacteria,Planctomycetes,Bacteroidetes and Gemmatimonadetes.The dominant phylum was Proteobacteria whereas the dominant genus was Synechococcus in Cyanobacteria.Some spongespecific bacteria were also found in the bacteria population,but the proportion（5 OTUs/32 OTUs） was much lower than other sponges.This study reveals the phylogenetic diversity of bacteria in A.robusta and confirms the presence of some sponge-specific bacteria in the South China Sea.Understanding the diversity of sponge-associated bacteria in China assists to exploit the bacteria resources for biotechnology.

Genetic diversity and phylogenetic relationships between and within wild Pistacia species populations and implications for its conservation

Although cultivation and utilization of Pistacia are fully exploited, the evolutionary history of the Pistacia genus and the relationships among the species and accessions is still not well understood. The aim of this study was to analyze random amplified polymorphic DNA（RAPD） in a total of 50 accessions of wild pistachio species, which included five populations Pistacia vera, Pistacia khinjuk,Pistacia atlantica, Pistacia mutica, and Pistacia eurycarpa.High levels of genetic diversity were detected within wild pistachio accessions, as revealed by using the unweighted pair-group method with arithmetic averaging and supported via analysis of molecular variance. The objectives of this investigation were to estimate marker indices, polymorphic information contents（PICs）, and genetic similarities（GS）for RAPD markers; assess the genetic diversity of Pistacia species, using GS estimated from RAPD fingerprints and molecular characterization; and facilitate the use of markers in inter-specific introgression and cultivar improvement.Out of the 149 polymerase chain reaction fragments that were scored, 146（97.98 %） were polymorphic. Genetic similarities ranged from 0.3 to 0.86 %, marker indices ranged from 2.98 to 17.74 %, and PICs ranged from 0.80 to0.99 %. Our results provided great molecular identification of all assayed genotypes, which have shown that there is large quantity of genetic diversity among the pistachio accessions. This finding might render striking information in breeding management strategies for genetic conservation and cultivar development.

Phylogenetic diversity and specificity of bacteria associated with Microcystis aeruginosa and other cyanobacteria

Interactions between bacteria and cyanobacteria have been suggested to have a potential to influence harmful algal bloom dynamics; however, little information on these interactions has been reported. In this study, the bacterial communities associated with five strains of Microcystis aeruginosa, three species of other Microcystis spp., and four representative species of non-Microcystis cyanobacteria were compared. Bacterial 16S rDNA fragments were amplified and separated by denaturing gradient gel electrophoresis （DGGE） followed by DNA sequence analysis. The similarities among bacterial communities associated with these cyanobacteria were compared to the digitized DGGE profiles using the cluster analyses. The bacterial community structure of all cyanobacterial cultures differed. Cluster analysis showed that the similarity values among M. aeruginosa cultures were higher than those of other cyanobacterial cultures. Sequence analysis of DGGE fragments indicated the presence of bacteria including, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Bacteroidetes and Actinobacteria in the cyanobacterial cultures. Members of the Sphingomonadales were the prevalent group among the Microcystis-associated bacteria. The results provided further evidence for species-specific associations between cyanoabcteria and heterotrophic bacteria, which are useful for understanding interactions between Microcystis and their associated bacteria.

Geographic patterns of taxonomic and phylogenetic β-diversity of angiosperm genera in regional floras across the world

Beta diversity(β-diversity)is the scalar between local(α)and regional(γ)diversity.Understanding geographic patterns ofβ-diversity is central to ecology,biogeography,and conservation biology.A full understanding of the origin and maintenance of geographic patterns ofβ-diversity requires exploring both taxonomic and phylogeneticβ-diversity,as well as their respective turnover and nestedness components,and exploring phylogenetic p-diversity at different evolutionary depths.In this study,we explore and map geographic patterns ofβ-diversity for angiosperm genera in regional floras across the world.We examine both taxonomic and phylogeneticβ-diversity and their constituent components,and both tip-weighted and basal-weighted phylogeneticβ-diversity,and relate them to latitude.On the one hand,our study found that the global distribution ofβ-diversity is highly heterogeneous.This is the case for both taxonomic and phylogeneticβ-diversity,and for both tip-weighted and basal-weighted phylogeneticβ-diversity.On the other hand,our study found that there are highly consistent geographic patterns among different metrics ofβ-diversity.In most cases,metrics ofβ-diversity are negatively associated with latitude,particularly in the Northern Hemisphere.Different metrics of taxonomicβ-diversity are strongly and positively correlated with their counterparts of phylogeneticβ-diversity.

Genetic diversity and phylogenetic analysis of EG95 sequences of Echinococcus granulosus:Implications for EG95 vaccine application

Objective:To analyse the genetic variability of EG95 sequences and provide guidance for EG95 vaccine application against Echinococcus granulosus(E. granulosus). Methods:We analysed EG95 polymorphism by collecting total 97 different E. granulosus isolates from 12 different host species that originated from 10 different countries. Multiple sequence alignments and the homology were performed by Lasergene 1(DNASTAR Inc.,Madison,WI),and the phylogenetic analysis was performed by using MEGA5.1(CEMI,Tempe,AZ,USA). In addition,linear and conformational epitopes were analysed,including secondary structure,NXT/S glycosylation,fibronectin type ecoⅢ(Fnndary Ⅲ) domain and glycosylphosphatidylinositol anchor signal(GPIanchor). The s structure was predicted by PSIPRED method. Results:Our results indicated that most isolates overall shared 72.6-100% identity in EG95 gene sequence with the published standard EG95 sequence,X90928. However,EG95 gene indeed has polymorphism in different isolates. Phylogenetic analysis showed that different isolates could be divided into three subgroups. Subgroup 1 contained 87 isolates while Subgroup 2 and Subgroup 3 consisted of 3 and 7 isolates,respectively. Four sequences cloned from oncosphere shared a high identity with the parental sequence of the current vaccine,X90928,and they belonged to Subgroup 1. However,in comparison to X90928,several amino acid mutations occurred in most isolates besides oncosphere,which potentially altered the immunodominant linear epitopes,glycosylation sites and secondary structures in EG95 genes. All these variations might change their previous antigenicity and thereby affecting the efficacy of current EG95 vaccine. Conclusions:This study reveals the genetic variability of EG95 sequences in different E. granulosus isolates,and proposed that more vaccination trials would be needed to test the effectiveness of current EG95 vaccine against distinct isolates in different countries.

Phylogenetic diversity of ribulose-1, 5-bisphosphate carboxylase/oxygenase large subunit genes of bacterioplankton in the East China Sea

Phylogenetic diversity of Form I and Form II ribulose1, 5-bisphosphate carboxylase/oxygenase (RubisCO) largesubunit (rbcL) genes in the inshore and offshore areas of the East China Sea were investigated. Two new primer setswere designed for amplifying partial sequences of rbcL genes from Proteobacteria. Four rbcL gene clone libraries wereconstructed by amplification and cloning of approximately 640~800 bp sequences of bacterioplankton populations.The method of screening library by denaturing gradient gel electrophoresis (DGGE) was introduced. The resultsshow that the diversity of Form I is higher in offshore waters with higher salinity and lower productivity, while thatof Form II is higher at the inshore station where salinity is lower and productivity is higher. Several clusters ofsequences obtained are deeply rooted and show low similarity (60%~78%) to the known rbcL in existing databases.The degree of diversity of rbcL genes is directly related to environmental variables, including temperature, salinity,pH, dissolved oxygen, etc. These results indicate that rbcL gene can be used as an effective indicator for geneticdiversity and population variability of bacterioplankton with the ability of carbon dioxide fixation in the sea.

Functional trait and community phylogenetic analyses reveal environmental filtering as the major determinant of assembly of tropical forest tree communities in the Western Ghats biodiversity hotspot in India

Background: Improved understanding of the processes shaping the assembly of tropical tree communities is crucial for gaining insights into the evolution of forest communities and biological diversity. The climate is thought to be the first order determinant of abundance and distribution patterns of tree species with contrasting traits such as evergreen and deciduous leaf phenology. However, the relative role of neutral, and niche-based processes in the evolution of these patterns remain poorly understood.Methods: Here, we perform an integrated analysis of the data on tree species abundance, functional traits and community phylogeny from a network of 96 forest plots, each 1 ha in size, distributed along a broad environmental gradient in the central Western Ghats, India. Then, we determine the relative importance of various process in assembly and structuring of tropical forest communities with evergreen and deciduous leaf phenology.Results: The deciduous leaf phenological trait has repeatedly evolved among multiple distantly related lineages. Tree communities in dry deciduous forests were phylogenetically clustered and showed a low range and variance of functional traits related to light harvesting, reproduction, and growth suggesting niche-based processes such as environmental filtering play a vital role in the assembly of tree communities in these forests. The external factors such as human-mediated disturbance also significantly, but to a lesser extent, influences the species and phylogenetic turnover.Conclusions: These findings revealed that the environmental filtering plays a significant role in assembly of tree communities in the biologically diverse tropical forests in the Western Ghats biodiversity hotspot.

Current patterns of plant diversity and phylogenetic structure on the Kunlun Mountains

Large-scale patterns of biodiversity and the underlying mechanisms that regulate these patterns are central topics in biogeography and macroecology.The Qinghai-Tibet Plateau serves as a natural laboratory for studying these issues.However,most previous studies have focused on the entire Qinghai-Tibet Plateau,leaving independent physical geographic subunits in the region less well understood.We studied the current plant diversity of the Kunlun Mountains,an independent physical geographic subunit located in northwestern China on the northern edge of the Qinghai-Tibet Plateau.We integrated measures of species distribution,geological history,and phylogeography,and analyzed the taxonomic richness,phylogenetic diversity,and community phylogenetic structure of the current plant diversity in the area.The distribution patterns of 1911 seed plants showed that species were distributed mainly in the eastern regions of the Kunlun Mountains.The taxonomic richness,phylogenetic diversity,and genera richness showed that the eastern regions of the Kunlun Mountains should be the priority area of biodiversity conservation,particularly the southeastern regions.The proportion of Chinese endemic species inhabiting the Kunlun Mountains and their floristic similarity may indicate that the current patterns of species diversity were favored via species colonization.The Hengduan Mountains,a biodiversity hotspot,is likely the largest source of species colonization of the Kunlun Mountains after the Quaternary.The net relatedness index indicated that 20 of the 28 communities examined were phylo-genetically dispersed,while the remaining communities were phylogenetically clustered.The nearest taxon index indicated that 27 of the 28 communities were phylogenetically clustered.These results suggest that species colonization and habitat filtering may have contributed to the current plant diversity of the Kunlun Mountains via ecological and evolutionary processes,and habitat filtering may play an important role in this ecological process.

Phylogenetic diversity of dinoflagellates in polar regions

Because of the limitations of sampling and seasonal study in polar regions, knowledge of dinoflagellate diversity, distribution and ecology are limited. Dinoflagellates have been incidentally reported from polar regions during some seasons and some populations have been reported as components of microalgae. Surveys of molecular diversity link the genotype of dinoflagellates from polar regions with environmental adaptation. In this study, 37 positive clones of dinoflagellates collected from different sites were used for genotype analysis, providing new insights into the biodiversity and distribution of these species based on 18S rRNA sequencing. Diverse genotypes were recorded for the summer season in Kongsfjorden （high Arctic） whilst a single novel genotype of dinoflagellate was recorded from winter samples from the Antarctic Ocean. Data from ice cores suggests that this single dinoflagellate genotype was adapted to extreme cold and clone library screening found that it was occasionally the only microbial eukaryotic genotype found in winter ice cores. The findings of this study could improve our understanding of the diverse dinoflagellate genotypes occurring in these perennially cold microbial ecosystems.

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.

Morphological and phylogenetic diversity of magnetotactic bacteria and multicellular magnetotactic prokaryotes from a mangrove ecosystem in the Sanya River,South China

Magnetotactic bacteria(MTB)are morphologically and phylogenetically diverse prokaryotes commonly able to produce magnetic nanocrystals within intracellular membrane-bound organelles(i.e.,magnetosomes)and to swim along geomagnetic field lines.We studied the diversity of MTB in the samples collected from a mangrove area in the Sanya River,Hainan,South China,using microscopic and microbial phylogenetic methods.Results of microanalysis and observation in microscopy and energy dispersive X-ray spectroscopy(EDXS)reveal a highly morphological diversity of MTB including unicellular cocci,vibrios,rod-shaped bacteria,and three morphotypes of multicellular magnetotactic prokaryotes(MMPs).In addition,analysis of the 16S rRNA gene showed that these MTB were clustered into 16 operational taxonomic units affi liated to the Alpha-,Delta-,and Gamma-proteobacteria classes within the Proteobacteria phylum.Meanwhile,by using the coupled fluorescence and transmission electron microscopy analysis,rodshaped bacteria,vibrio,and cocci were phylogenetically and structurally identified at the single-cell level.This study demonstrated highly diverse MTB communities in the mangrove ecosystem and provide a new insight into the overall diversity of MTB.

Phylogenetic diversity of TypeⅠpolyketide synthase genes from sediments of Ardley Island in Antarctica

The diversity of modular polyketide synthase （PKS） genes in sediments of Ardley Island in Antarctica, was studied by restriction fragment length polymorphism （RFLP） analysis. Phylogenetic analysis of 14 amino acid （AA） sequences indicates that the identified ketosynthase （KS） domains were clustered with those from diverse bacterial groups, including Cyanobacteria, γ-Proteobacteria, Actinobacteria, Firmicutes, and some unidentified microorganisms from marine sponge, bryozoan and other environmental samples. The obtained KS domains showed 43%–81% similarity at the AA level to reference sequences in GenBank. Six identified KS domains showed diverse sequences of the motif （VQTACSTS） that was used to identify the hybrid PKS/nonribosomal peptide synthetase （NRPS） enzyme complex, and formed a new branch. These results reveal a high diversity and novelty of PKS genes in antarctic sediments.