Distinctive Phyllosphere Bacterial Communities in Tropical Trees

Recent work has suggested that in temperate and subtropical trees, leaf surface bacterial communities are distinctive to each individual tree species and dominated by Alpha- and Gammaproteobacteria. In order to understand how general this pattern is, we studied the phyllosphere bacterial community on leaves of six species of tropical trees at a rainforest arboretum in Malaysia. This represents the first detailed study of ‘true’ tropical lowland tree phyllosphere communities. Leaf surface DNA was extracted and pyrosequenced targeting the V1–V3 region of 16S rRNA gene. As was previously found in temperate and subtropical trees, each tree species had a distinctive bacterial community on its leaves, clustering separately from other tree species in an ordination analysis. Bacterial communities in the phyllosphere were unique to plant leaves in that very few operational taxonomic units (0.5%) co-occurred in the surrounding soil environment. A novel and distinctive aspect of tropical phyllosphere communities is that Acidobacteria were one of the most abundant phyla across all samples (on average, 17%), a pattern not previously recognized. Sequences belonging to Acidobacteria were classified into subgroups 1–6 among known 24 subdivisions, and subgroup 1 (84%) was the most abundant group, followed by subgroup 3 (15%). The high abundance of Acidobacteria on leaves of tropical trees indicates that there is a strong relationship between host plants and Acidobacteria in tropical rain forest, which needs to be investigated further. The similarity of phyllosphere bacterial communities amongst the tree species sampled shows a significant tendency to follow host plant phylogeny, with more similar communities on more closely related hosts.     

Distance-Decay Relationships Partially Determine Diversity Patterns of Phyllosphere Bacteria on Tamrix Trees across the Sonoran Desert

Dispersal limitation in phyllosphere communities was measured on the leaf surfaces of salt-excreting Tamarix trees, which offer unique, discrete habitats for microbial assemblages. We employed 16S rRNA gene pyrosequencing to measure bacterial community dissimilarity on leaves of spatially dispersed Tamarix specimens in sites with uniform climatic conditions across the Sonoran Desert in the Southwestern United States. Our analyses revealed diverse bacterial communities with four dominant phyla that exhibited differential effects of environmental and geographic variables. Geographical distance was the most important parameter that affected community composition, particularly that of betaproteobacteria, which displayed a statistically significant, distance-decay relationship.     

Bacterial Succession on the Leaf Surface: A Novel System for Studying Successional Dynamics

Succession is a widely studied process in plant and animal systems, but succession in microbial communities has received relatively little attention despite the ubiquity of microorganisms in natural habitats. One important microbial habitat is the phyllosphere, or leaf surface, which harbors large, diverse populations of bacteria and offers unique opportunities for the study of succession and temporal community assembly patterns. To explore bacterial community successional patterns, we sampled phyllosphere communities on cottonwood (Populus deltoides) trees multiple times across the growing season, from leaf emergence to leaf fall. Bacterial community composition was highly variable throughout the growing season; leaves sampled as little as a week apart were found to harbor significantly different communities, and the temporal variability on a given tree exceeded the variability in community composition between individual trees sampled on a given day. The bacterial communities clearly clustered into early-, mid-, and late-season clusters, with early- and late-season communities being more similar to each other than to the mid-season communities, and these patterns appeared consistent from year to year. Although we observed clear and predictable changes in bacterial community composition during the course of the growing season, changes in phyllosphere bacterial diversity were less predictable. We examined the species–time relationship, a measure of species turnover rate, and found that the relationship was fundamentally similar to that observed in plant and invertebrate communities, just on a shorter time scale. The temporal dynamics we observed suggest that although phyllosphere bacterial communities have high levels of phylogenetic diversity and rapid turnover rates, these communities follow predictable successional patterns from season to season.     

Summer season and long-term drought increase the richness of bacteria and fungi in the foliar phyllosphere of Quercus ilex in a mixed Mediterranean forest

We explored the changes in richness, diversity and evenness of epiphytic (on the leaf surface) and endophytic (within leaf tissues) bacteria and fungi in the foliar phyllosphere of Quercus ilex, the dominant tree species of Mediterranean forests. Bacteria and fungi were assessed during ontogenic development of the leaves, from the wet spring to the dry summer season in control plots and in plots subjected to drought conditions mimicking those projected for future decades. Our aim was to monitor succession in microbiota during the colonisation of plant leaves and its response to climate change. Ontogeny and seasonality exerted a strong influence on richness and diversity of the microbial phyllosphere community, which decreased in summer in the whole leaf and increased in summer in the epiphytic phyllosphere. Drought precluded the decrease in whole leaf phyllosphere diversity and increased the rise in the epiphytic phyllosphere. Both whole leaf bacterial and fungal richness decreased with the decrease in physiological activity and productivity of the summer season in control trees. As expected, the richness of epiphytic bacteria and fungi increased in summer after increasing time of colonisation. Under summer dry conditions, there was a positive relationship between TRF (terminal restriction fragments) richness and drought, both for whole leaf and epiphytic phyllosphere, and especially for fungal communities. These results demonstrate that changes in climate are likely to significantly alter microbial abundance and composition of the phyllosphere. Given the diverse functions and large number of phyllospheric microbes, the potential functional implications of such community shifts warrant exploration.     

Microbial and chemical characterization of underwater fresh water springs in the Dead Sea

Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16S rRNA gene and community fingerprinting methods showed that the spring community originates from the Dead Sea sediments and not from the aquifer. Furthermore, it suggested that there is a dense Archaeal community in the shoreline pore water of the lake. Sequences of bacterial sulfate reducers, nitrifiers iron oxidizers and iron reducers were identified as well. Analysis of white and green biofilms suggested that sulfide oxidation through chemolitotrophy and phototrophy is highly significant. Hyperspectral analysis showed a tight association between abundant green sulfur bacteria and cyanobacteria in the green biofilms. Together, our findings show that the Dead Sea floor harbors diverse microbial communities, part of which is not known from other hypersaline environments. Analysis of the water's chemistry shows evidence of microbial activity along the path and suggests that the springs supply nitrogen, phosphorus and organic matter to the microbial communities in the Dead Sea. The underwater springs are a newly recognized water source for the Dead Sea. Their input of microorganisms and nutrients needs to be considered in the assessment of possible impact of dilution events of the lake surface waters, such as those that will occur in the future due to the intended establishment of the Red Sea-Dead Sea water conduit.     

The ecology of the phyllosphere: geographic and phylogenetic variability in the distribution of bacteria on tree leaves

Large populations of bacteria live on leaf surfaces and these phyllosphere bacteria can have important effects on plant health. However, we currently have a limited understanding of bacterial diversity on tree leaves and the inter‐ and intra‐specific variability in phyllosphere community structure. We used a barcoded pyrosequencing technique to characterize the bacterial communities from leaves of 56 tree species in Boulder, Colorado, USA, quantifying the intra‐ and inter‐individual variability in the bacterial communities from 10 of these species. We also examined the geographic variability in phyllosphere communities on Pinus ponderosa from several locations across the globe. Individual tree species harboured high levels of bacterial diversity and there was considerable variability in community composition between trees. The bacterial communities were organized in patterns predictable from the relatedness of the trees as there was significant correspondence between tree phylogeny and bacterial community phylogeny. Inter‐specific variability in bacterial community composition exceeded intra‐specific variability, a pattern that held even across continents where we observed minimal geographic differentiation in the bacterial communities on P. ponderosa needles.     

Experimental evidence of microbial inheritance in plants and transmission routes from seed to phyllosphere and root

While the environment is considered the primary origin of the plant microbiome, the potential role of seeds as a source of transmitting microorganisms has not received much attention. Here we tested the hypothesis that the plant microbiome is partially inherited through vertical transmission. An experimental culturing device was constructed to grow oak seedlings in a microbe-free environment while keeping belowground and aboveground tissues separated. The microbial communities associated with the acorn's embryo and pericarp and the developing seeding's phyllosphere and root systems were analysed using amplicon sequencing of fungal ITS and bacterial 16S rDNA. Results showed that the seed microbiome is diverse and non-randomly distributed within an acorn. The microbial composition of the phyllosphere was diverse and strongly resembled the composition found in the embryo, whereas the roots and pericarp each had a less diverse and distinct microbial community. Our findings demonstrate a high level of microbial diversity and spatial partitioning of the fungal and bacterial community within both seed and seedling, indicating inheritance, niche differentiation and divergent transmission routes for the establishment of root and phyllosphere communities.     

Bacterial Community Assemblages Associated with the Phyllosphere,Dermosphere, and Rhizosphere of Tree Species of the Atlantic Forest are Host Taxon Dependent

Bacterial communities associated with tree canopies have been shown to be specific to their plant hosts, suggesting that plant species-specific traits may drive the selection of microbial species that comprise their microbiomes. To further examine the degree to which the plant taxa drive the assemblage of bacterial communities in specific plant microenvironments, we evaluated bacterial community structures associated with the phyllosphere, dermosphere, and rhizosphere of seven tree species representing three orders, four families and four genera of plants from a pristine Dense Ombrophilous Atlantic forest in Brazil, using a combination of PCR-DGGE of 16S rRNA genes and clone library sequencing. Results indicated that each plant species selected for distinct bacterial communities in the phyllosphere, dermosphere, and rhizosphere, and that the bacterial community structures are significantly related to the plant taxa, at the species, family, and order levels. Further characterization of the bacterial communities of the phyllosphere and dermosphere of the tree species showed that they were inhabited predominantly by species of Gammaproteobacteria, mostly related to Pseudomonas. In contrast, the rhizosphere bacterial communities showed greater species richness and evenness, and higher frequencies of Alphaproteobacteria and Acidobacteria Gp1. With individual tree species each selecting for their specific microbiomes, these findings greatly increase our estimates of the bacterial species richness in tropical forests and provoke questions concerning the ecological functions of the microbial communities that exist on different plant parts.     

Sulfate-reducing prokaryotic communities in two deep hypersaline anoxic basins in the Eastern Mediterranean deep sea

In the Eastern Mediterranean Sea, deep hypersaline anoxic basins (DHABs) and deep-sea sediment contain anoxic environments where sulfate reduction is an important microbial metabolic process. The objective of this study was to characterize the sulfate-reducing community in the brine and interface of the DHABs L'Atalante and Urania based on a phylogenetic analysis of the dissimilatory sulfite reductase gene (dsrA). Results demonstrated that the sulfate-reducing community was diverse, except for the sulfidogenic brine of the Urania basin. The similarity of the dsrA sequences between different environments was very low demonstrating that each environment had a unique sulfate-reducing community. Sequences had 67.6-93.3% similarity to dsrA sequences from GenBank database and were mostly related to the delta-proteobacteria. Each environment was dominated by a different family within the delta-proteobacteria except for the Urania interface, which was dominated by sequences related to the Gram-positive Peptococcaceae. We conclude that sulfate-reducing communities inhabiting the L'Atalante and Urania basins are highly diverse with low similarities to each other and contain a sulfate-reducing species composition that is very different from sulfate-reducing species compositions in previously studied ecosystems.     

Seasonal and spatial diversity of microbial communities in marine sediments of the South China Sea

This study was conducted to characterize the diversity of microbial communities in marine sediments of the South China Sea by means of 16S rRNA gene clone libraries. The results revealed that the sediment samples collected in summer harboured a more diverse microbial community than that collected in winter, Deltaproteobacteria dominated 16S rRNA gene clone libraries from both seasons, followed by Gammaproteobacteria, Acidobacteria, Nitrospirae, Planctomycetes, Firmicutes. Archaea phylotypes were also found. The majority of clone sequences shared greatest similarity to uncultured organisms, mainly from hydrothermal sediments and cold seep sediments. In addition, the sedimentary microbial communities in the coastal sea appears to be much more diverse than that of the open sea. A spatial pattern in the sediment samples was observed that the sediment samples collected from the coastal sea and the open sea clustered separately, a novel microbial community dominated the open sea. The data indicate that changes in environmental conditions are accompanied by significant variations in diversity of microbial communities at the South China Sea.     

Effects of transgenic fructan-producing potatoes on the community structure of rhizosphere and phyllosphere bacteria

The rhizosphere and phyllosphere microbial communities of transgenic potatoes producing fructan were studied in comparison with isogenic controls and conventional varieties in a field release experiment over a period of 3 years. Population densities and 16S rRNA gene-based terminal restriction fragment length polymorphism (T-RFLP) analysis of the rhizosphere bacterial community only displayed the influence of annual and seasonal effects and the influence of field heterogeneity. In contrast, the T-RFLP analysis of the phyllosphere bacteria revealed in two of the 3 years significant differences in the community structure between the transgenic lines producing inulin and the other variants. This effect was studied in more detail through the analysis of bacterial isolates and a 16S rRNA gene clone library obtained from a transgenic line and the control. Both methods revealed a lower genetic diversity in the transgenic line and changes in the abundance of several bacterial groups. The isolates of the transgenic line were dominated by Bacilli, whereas most of the control isolates represented Actinobacteria. The clones were dominated by Proteobacteria, with main differences between both variants in Deltaproteobacteria, Bacilli and Bacteroidetes. However, all in all, the impact of the transgenic lines did not exceed the natural variability of the phyllosphere community structure on potato plants.     

Exploring Biodiversity in the Bacterial Community of the Mediterranean Phyllosphere and its Relationship with Airborne Bacteria

We studied the structure and diversity of the phyllosphere bacterial community of a Mediterranean ecosystem, in summer, the most stressful season in this environment. To this aim, we selected nine dominant perennial species, namely Arbutus unedo, Cistus incanus, Lavandula stoechas, Myrtus communis, Phillyrea latifolia, Pistacia lentiscus, Quercus coccifera (woody), Calamintha nepeta, and Melissa officinalis (herbaceous). We also examined the extent to which airborne bacteria resemble the epiphytic ones. Genotype composition of the leaf and airborne bacteria was analysed by using denaturing gradient gel electrophoresis profiling of a 16S rDNA gene fragment; 75 bands were cloned and sequenced corresponding to 28 taxa. Of these, two were found both in the air and the phyllosphere, eight only in the air, and the remaining 18 only in the phyllosphere. Only four taxa were found on leaves of all nine plant species. Cluster analysis showed highest similarity for the five evergreen sclerophyllous species. Aromatic plants were not grouped all together: the representatives of Lamiaceae, bearing both glandular and non-glandular trichomes, formed a separate group, whereas the aromatic and evergreen sclerophyllous M. communis was grouped with the other species of the same habit. The epiphytic communities that were the richest in bacterial taxa were those of C. nepeta and M. officinalis (Lamiaceae). Our results highlight the remarkable presence of lactic acid bacteria in the phyllosphere under the harsh conditions of the Mediterranean summer, the profound dissimilarity in the structure of bacterial communities in phyllosphere and air, and the remarkable differences of leaf microbial communities on neighbouring plants subjected to similar microbial inocula; they also point to the importance of the leaf glandular trichome in determining colonization patterns.     

Microbiota associated with Mollitrichosiphum aphids (Hemiptera: Aphididae: Greenideinae): diversity,host species specificity and phylosymbiosis

Symbiotic association is universal in nature, and an array of symbionts play a crucial part in host life history. Aphids and their diverse symbionts have become a good model system to study insect-symbiont interactions. Previous symbiotic diversity surveys have mainly focused on a few aphid clades, and the relative importance of different factors regulating microbial community structure is not well understood. In this study, we collected 65 colonies representing eight species of the aphid genus Mollitrichosiphum from different regions and plants in southern China and Nepal and characterized their microbial compositions using Illumina sequencing of the V3 − V4 hypervariable region of the 16S rRNA gene. We evaluated how microbiota varied across aphid species, geography and host plants and the correlation between microbial community structure and host aphid phylogeny. Heritable symbionts dominated the microbiota associated with Mollitrichosiphum, and multiple infections of secondary symbionts were prevalent. Ordination analyses and statistical tests highlighted the contribution of aphid species in shaping the structures of bacterial, symbiont and secondary symbiont communities. Moreover, we observed a significant correlation between Mollitrichosiphum aphid phylogeny and microbial community composition, providing evidence for a pattern of phylosymbiosis between natural aphid populations and their microbial associates.     

Genotypic variation in Norway spruce correlates to fungal communities in vegetative buds

The taxonomically diverse phyllosphere fungi inhabit leaves of plants. Thus, apart from the fungi's dispersal capacities and environmental factors, the assembly of the phyllosphere community associated with a given host plant depends on factors encoded by the host's genome. The host genetic factors and their influence on the assembly of phyllosphere communities under natural conditions are poorly understood, especially in trees. Recent work indicates that Norway spruce (Picea abies) vegetative buds harbour active fungal communities, but these are hitherto largely uncharacterized. This study combines internal transcribed spacer sequencing of the fungal communities associated with dormant vegetative buds with a genome‐wide association study (GWAS) in 478 unrelated Norway spruce trees. The aim was to detect host loci associated with variation in the fungal communities across the population, and to identify loci correlating with the presence of specific, latent, pathogens. The fungal communities were dominated by known Norway spruce phyllosphere endophytes and pathogens. We identified six quantitative trait loci (QTLs) associated with the relative abundance of the dominating taxa (i.e., top 1% most abundant taxa). Three additional QTLs associated with colonization by the spruce needle cast pathogen Lirula macrospora or the cherry spruce rust (Thekopsora areolata) in asymptomatic tissues were detected. The identification of the nine QTLs shows that the genetic variation in Norway spruce influences the fungal community in dormant buds and that mechanisms underlying the assembly of the communities and the colonization of latent pathogens in trees may be uncovered by combining molecular identification of fungi with GWAS.     

Seed Dispersers,Seed Predators,and Browsers Act Synergistically as Biotic Filters in a Mosaic Landscape

In this study, we analize the functional influence of animals on the plants they interact with in a mediterranean mountain. We hypothesise that seed dispersers, seed predators, and browsers can act as biotic filters for plant communities. We analyse the combined effects of mutualistic (seed dispersal) and antagonistic (seed predation, herbivory) animal interactions in a mosaic landscape of Mediterranean mountains, basing our results on observational and experimental field. Most of the dispersed seeds came from tree species, whereas the population of saplings was composed predominantly of zoochorous shrub species. Seed predators preferentially consumed seeds from tree species, whereas seeds from the dominant fleshy-fruited shrubs had a higher probability of escaping these predators. The same pattern was repeated among the different landscape units by browsers, since they browsed selectively and far more intensely on tree-species saplings than on the surrounding shrubs. In synthesis, our work identifies the major biotic processes that appear to be favoring a community dominated by shrubs versus trees because seed dispersers, predators, and herbivores together favored shrub dispersal and establishment versus trees.     

Species abundance distributions and richness estimations in fungal metagenomics--lessons learned from community ecology

Results of diversity and community ecology studies strongly depend on sampling depth. Completely surveyed communities follow log-normal distribution, whereas power law functions best describe incompletely censused communities. It is arguable whether the statistics behind those theories can be applied to voluminous next generation sequencing data in microbiology by treating individual DNA sequences as counts of molecular taxonomic units (MOTUs). This study addresses the suitability of species abundance models in three groups of plant-associated fungal communities - phyllosphere, ectomycorrhizal and arbuscular mycorrhizal fungi. We tested the impact of differential treatment of molecular singletons on observed and estimated species richness and species abundance distribution models. The arbuscular mycorrhizal community of 48 MOTUs was exhaustively sampled and followed log-normal distribution. The ectomycorrhizal (153 MOTUs) and phyllosphere (327 MOTUs) communities significantly differed from log-normal distribution. The fungal phyllosphere community in particular was clearly undersampled. This undersampling bias resulted in strong sensitivity to the exclusion of molecular singletons and other rare MOTUs that may represent technical artefacts. The analysis of abundant (core) and rare (satellite) MOTUs clearly identified two species abundance distributions in the phyllosphere data - a log-normal model for the core group and a log-series model for the satellite group. The prominent log-series distribution of satellite phyllosphere fungi highlighted the ecological significance of an infrequent fungal component in the phyllosphere community.     

Annual and Seasonal Variation in the Phyllosphere Bacterial Community Associated with Leaves of the Southern Magnolia (Magnolia grandiflora)

The phyllosphere contains a diverse bacterial community that can be intimately associated with the host plant; however, few studies have examined how the phyllosphere community changes over time. We sampled replicate leaves from a single magnolia (Magnolia grandiflora) tree in the winter of three consecutive years (2007?C2009) as well as during four seasons of 1?year (2008) and used molecular techniques to examine seasonal and year-to-year variation in bacterial community structure. Multivariate analysis of denaturing gradient gel electrophoresis profiles of 16S rRNA gene fragments revealed minimal leaf to leaf variation and much greater temporal changes, with the summer (August 2008) leaf community being most distinct from the other seasons. This was confirmed by sequencing and analysis of 16S rRNA gene clone libraries generated for each sample date. All phyllosphere communities were dominated by Alphaproteobacteria, with a reduction in the representation of certain Beijerinckiaceae during the summer and a concurrent increase in the Methylobacteriaceae being the most significant seasonal change. Other important components of the magnolia phyllosphere included members of the Bacteroidetes, Acidobacteria, and Actinobacteria, with the latter two lineages also showing differences in their representation in samples collected at different times. While the leaf-associated bacterial community sampled at the same time of year in three separate years showed some similarities, generally these communities were distinct, suggesting that while there are seasonal patterns, these may not be predictable from year to year. These results suggest that seasonal differences do occur in phyllosphere communities and that broad-leafed evergreen trees such as M. grandiflora may present interesting systems to study these changes in the context of changing environmental conditions.     

Genetic variation in a tropical tree species influences the associated epiphytic plant and invertebrate communities in a complex forest ecosystem

Genetic differences among tree species, their hybrids and within tree species are known to influence associated ecological communities and ecosystem processes in areas of limited species diversity. The extent to which this same phenomenon occurs based on genetic variation within a single tree species, in a diverse complex ecosystem such as a tropical forest, is unknown. The level of biodiversity and complexity of the ecosystem may reduce the impact of a single tree species on associated communities. We assessed the influence of within-species genetic variation in the tree Brosimum alicastrum (Moraceae) on associated epiphytic and invertebrate communities in a neotropical rainforest. We found a significant positive association between genetic distance of trees and community difference of the epiphytic plants growing on the tree, the invertebrates living among the leaf litter around the base of the tree, and the invertebrates found on the tree trunk. This means that the more genetically similar trees are host to more similar epiphyte and invertebrate communities. Our work has implications for whole ecosystem conservation management, since maintaining sufficient genetic diversity at the primary producer level will enhance species diversity of other plants and animals.     

Phyllosphere Bacterial Community of Floating Macrophytes in Paddy Soil Environments as Revealed by Illumina High-Throughput Sequencing

The phyllosphere of floating macrophytes in paddy soil ecosystems, a unique habitat, may support large microbial communities but remains largely unknown. We took Wolffia australiana as a representative floating plant and investigated its phyllosphere bacterial community and the underlying driving forces of community modulation in paddy soil ecosystems using Illumina HiSeq 2000 platform-based 16S rRNA gene sequence analysis. The results showed that the phyllosphere of W. australiana harbored considerably rich communities of bacteria, with Proteobacteria and Bacteroidetes as the predominant phyla. The core microbiome in the phyllosphere contained genera such as Acidovorax, Asticcacaulis, Methylibium, and Methylophilus. Complexity of the phyllosphere bacterial communities in terms of class number and α-diversity was reduced compared to those in corresponding water and soil. Furthermore, the bacterial communities exhibited structures significantly different from those in water and soil. These findings and the following redundancy analysis (RDA) suggest that species sorting played an important role in the recruitment of bacterial species in the phyllosphere. The compositional structures of the phyllosphere bacterial communities were modulated predominantly by water physicochemical properties, while the initial soil bacterial communities had limited impact. Taken together, the findings from this study reveal the diversity and uniqueness of the phyllosphere bacterial communities associated with the floating macrophytes in paddy soil environments.     

Comparison of wintertime eukaryotic community from sea ice and open water in the Baltic Sea, based on sequencing of the 18S rRNA gene

The Baltic Sea is one of the world’s largest brackish water basins and is traditionally considered to be species poor. Here, we assessed the diversity of the nano-sized eukaryotic microbial wintertime community, using molecular ecological methods based on sequencing of small-subunit ribosomal RNA gene clone libraries. The results demonstrate that a rich community of small eukaryotes inhabits the Baltic Sea ice and water during winter. The community was dominated by alveolates and stramenopiles. Ciliates and cercozoans were the richest groups present, while in contrast to previous studies, diatoms showed a lower richness than expected. Furthermore, fungi and parasitic Syndiniales were present both in the water and in the sea ice. Some of the organisms in the sea-ice community were active, based on the RNA data, but a number of organisms were inactive or remnants from the freezing process. The results demonstrate that the sea-ice communities in the Baltic Sea are highly diverse and that water and ice of different ages include different protistan assemblages. Our study emphasizes the potential loss in biodiversity through diminishing ice cover as a result of climate change.