Comparison of Bacterioneuston and Bacterioplankton Dynamics during a Phytoplankton Bloom in a Fjord Mesocosm

The bacterioneuston is the community of Bacteria present in surface microlayers, the thin surface film that forms the interface between aquatic environments and the atmosphere. In this study we compared bacterial cell abundances and bacterial community structures of the bacterioneuston and the bacterioplankton (from the subsurface water column) during a phytoplankton bloom mesocosm experiment. Bacterial cell abundance, determined by flow cytometry, followed a typical bacterioplankton response to a phytoplankton bloom, with Synechococcus and high-nucleic acid content (HNA) bacterial cell numbers initially falling, probably due to selective protist grazing. Subsequently HNA and low-nucleic acid content bacterial cells increased in abundance, but Synechococcus cells did not. There was no significant difference between bacterioneuston and bacterioplankton cell abundances during the experiment. Conversely, distinct and consistent differences between the bacterioneuston and the bacterioplankton community structures were observed. This was monitored simultaneously by Bacteria 16S rRNA gene terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis. The conserved patterns of community structure observed in all of the mesocosms indicate that the bacterioneuston is distinctive and nonrandom.Determining and understanding both spatial and temporal patterns in bacterioplankton community structure are a core aim of marine microbial ecology (15). Distributions of bacterioplankton over space and time can be correlated to environmental parameters, and subsequent links can therefore be made to ecosystem function. A broad range of spatial studies made on macro- (34), meso- (20), and microscales (27) have shown clear patterns in distribution of the bacterioplankton.The sea surface microlayer is part of the air-sea interface and is generally considered to be the top 1 mm or less of the ocean (26). Surface microlayers have a fundamental role in regulating transport processes between the ocean and the atmosphere (26) and are often referred to as the neuston (28, 31). For more than 25 years it has been hypothesized that the sea surface microlayer is a hydrated gelatinous layer (40) that contains surface-active organic compounds such as carbohydrates, proteins, lipids, and humic substances in relatively high concentrations (17, 45, 48). Recently, gel-like transparent expolymer particles (TEP) have been shown to be enriched in the surface microlayer, supporting the concept of a gelatinous interfacial layer (46).Bacteria present in surface microlayers or the neuston are regarded as the bacterioneuston. There are relatively few studies which have directly compared the community structure of the bacterioneuston with that of the cognate subsurface (bacterioplankton) in the marine environment. Analysis of Bacteria 16S rRNA gene clone libraries constructed using DNA isolated from surface microlayer and subsurface water (<1 m) samples from the North Sea revealed that the bacterioneuston was dominated by two operational taxonomic units which accounted for 81% of clones analyzed (13). Community structure profiling using denaturing gradient gel electrophoresis (DGGE) of the bacterioneuston at three sites around Oahu Island in the Pacific Ocean showed that the bacterioneuston forms consistent and distinct community structures. Conversely, the archaeal community structure of the same samples using Archaea 16S rRNA gene DGGE analysis did not show the same surface microlayer-specific response, indicating that bacteria and archaea respond to their environment in fundamentally different ways in the neuston (7).Other studies have, however, reported no consistent differences between the bacterioneuston and the bacterioplankton. Samples collected from two separate sites in the Mediterranean Sea were analyzed using single-strand conformation polymorphism of Bacteria 16S rRNA genes (1). The authors did not report any significant differences between the surface microlayer and subsurface samples using this community profiling method.Nonmarine studies of the bacterioneuston and Archaea communities in estuarine (10) and freshwater (5, 19) environments have also shown distinct microbial community structures present in the surface microlayer compared to those in subsurface water ≤1 m below.Recurring phytoplankton blooms are a key feature of coastal waters and strongly influence bacterioplankton community structure and succession (4, 14, 38). Phytoplankton blooms stimulate the bacterioplankton by the release of dissolved organic matter (22) or affect bacterioplankton negatively by direct competition for resources (6). Bacterioplankton community structure may also be influenced by grazing flagellates or viral lysis (47).Mesocosm experiments have been used to study plankton ecology for many decades (33). Mesocosms facilitate study of the effects of key environmental parameters, such as temperature, on plankton communities and allow the succession of natural plankton communities that resemble those found in the marine environment (11). The enclosed water mass means that experiments can be designed which manipulate physicochemical parameters to observe biological effects. Furthermore, with replicated mesocosms, the data collected can be analyzed with statistics rigorously. In this study we monitored the dynamics of the bacterioneuston and the bacterioplankton in mesocosms of fjord surface water during an artificially induced phytoplankton bloom and compared bacterial abundances and bacterial community structures in the surface microlayer and subsurface water.     

Taxonomic composition of Lake Baikal bacterioneuston communities

The taxonomic composition of microbial communities of Lake Baikal surface microlayer was studied by pyrosequencing of the 16S rDNA amplicons. Statistically reliable differences were found between bacterioneuston of the shallow and deep-water stations. The shallow station community was characterized by higher diversity than the deep-water one. While bacterioneuston communities were shown to be less diverse than the water column communities, their diversity was comparable to that of other biofilm associations. Microbial communities of Lake Baikal surface microlayer were shown to be similar to those of the water column in the composition of predominant phyla, while differing considerably at the genus level. Bacterioneuston of Lake Baikal was comparable to microbial communities of the surface microlayer of other freshwater basins, although it was characterized by high abundance of the Alphaproteobacteria and Verrucomicrobia. High abundance of photoheterotrophs compared to the water column communities of other freshwater basins was another distinctive feature of Lake Baikal bacterioneuston. Our results showed the Lake Baikal surface microlayer to be a specific microbial community with low species diversity and relatively high abundance of photoheterotrophic microorganisms.     

Structures of bacterial communities on the surface of <Emphasis Type="Italic">Ulva prolifera</Emphasis> and in seawaters in an <Emphasis Type="Italic">Ulva</Emphasis> blooming region in Jiaozhou Bay,China

Bacterial community structure on the surface of Ulva prolifera thalli and in seawater in an Ulva blooming region in Jiaozhou Bay was investigated by methods of denaturing gradient gel electrophoresis and 16S rDNA clone libraries. Statistical analysis on the clone libraries indicated that bacterial community structure presented no significant differences between two algal samples. Thallus-surface bacterial communities identified by 16S rDNA clone library were dominated by Alteromonadales, Flavobacteriales, and Rhodobacterales. Sequences affiliated with Gammaproteobacteria, Alphaproteobacteria and CFB were detected in all the four seawater samples. However, their different distribution frequencies among the four samples and the presence of some specific bacterial clusters in some samples indicated changes in the bacterial community composition over the course of the bloom. The dominant bacterial clades changed from Alteromonadales and Rickettsiales in A-SW, to Flavobacteriales and Alteromonadales in B-SW, to Alteromonadales and Campylobacterales in C-SW, and to Rickettsiales, Rhodobacterales and Flavobacteriales in D-SW. Some specific dominant bacterial assemblages were present in some seawater samples, such as Campylobacterales in C-SW and Actinobacteria in D-SW. Our results give an insight into the changes in the bacterial community composition in seawater in blooming region during the course of macroalgal Ulva bloom.     

Bacterioneuston community structure in the southern Baltic sea and its dependence on meteorological conditions

The bacterial community in the sea surface microlayer (SML) (bacterioneuston) is exposed to unique physicochemical properties and stronger meteorological influences than the bacterial community in the underlying water (ULW) (bacterioplankton). Despite extensive research, however, the structuring factors of the bacterioneuston remain enigmatic. The aim of this study was to examine the effect of meteorological conditions on bacterioneuston and bacterioplankton community structures and to identify distinct, abundant, active bacterioneuston members. Nineteen bacterial assemblages from the SML and ULW of the southern Baltic Sea, sampled from 2006 to 2008, were compared. Single-strand conformation polymorphism (SSCP) fingerprints were analyzed to distinguish total (based on the 16S rRNA gene) and active (based on 16S rRNA) as well as nonattached and particle-attached bacterial assemblages. The nonattached communities of the SML and ULW were very similar overall (similarity: 47 to 99%; mean: 88%). As an exception, during low wind speeds and high radiation levels, the active bacterioneuston community increasingly differed from the active bacterioplankton community. In contrast, the particle-attached assemblages in the two compartments were generally less similar (similarity: 8 to 98%; mean: 62%), with a strong variability in the active communities that was solely related to wind speed. Both nonattached and particle-attached active members of the bacterioneuston, which were found exclusively in the SML, were related to environmental clones belonging to the Cyanobacteria, Bacteroidetes, and Alpha-, Beta-, and Gammaproteobacteria originally found in diverse habitats, but especially in water columns. These results suggest that bacterioneuston communities are strongly influenced by the ULW but that specific meteorological conditions favor the development of distinctive populations in the air-water interface.     

Examination of a freshwater surface microlayer for diel changes in the bacterioneuston

The surface microlayer of a small freshwater pond was sampled every 6–8 hours on four occasions (April, July, September, and November) to examine changes in total and respiring bacterioneuston for diel cycles and comparing them to similar measurements of the bacterioplankton. Dissolved organic carbon (DOC), dissolved reactive phosphorous (DRP) and ammonia nitrogen (NH₃-N) were also measured. Both the mean numbers and enrichments of the two bacterial parameters in the surface microlayer samples showed seasonal differences, but in general, no significant difference (P > 0.05, ANOVA) in the mean numbers of total and respiring bacterioneuston were observed over diel periods except in November. The converse was true for the bacterioplankton. The presence of a visually thick surface film contributed to the results. The mean numbers of bacterioneuston and their enrichments were not correlated to any of the physical/chemical parameters measured.     

The UV responses of bacterioneuston and bacterioplankton isolates depend on the physiological condition and involve a metabolic shift

Bacteria from the surface microlayer (bacterioneuston) and underlying waters (bacterioplankton) were isolated upon exposure to UV-B radiation, and their individual UV sensitivity in terms of CFU numbers, activity (leucine and thymidine incorporation), sole-carbon source use profiles, repair potential (light-dependent and independent), and photoadaptation potential, under different physiological conditions, was compared. Colony counts were 11.5-16.2% more reduced by UV-B exposure in bacterioplankton isolates (P?相似文献   

The role of transparent exopolymer particles (TEP) in the increase in apparent particle stickiness ({alpha}) during the decline of a diatom bloom

The termination of diatom spring blooms in temperate watershas been connected with the formation and subsequent rapid sedimentationof aggregates. According to coagulation theory, the rate ofaggregate formation depends on the probability of particle collisionand on the efficiency with which two particles adhere once theyhave collided (stickiness). During this study, the variationin particle stickiness was determined over the decline of adiatom bloom using the Couette Chamber assay with low shear(G = 0.86 s^–1). A mixed diatom population, dominated bySkeletonema costatum, was sampled during the spring bloom inthe Baltic Sea and incubated in the laboratory for 18 days.Measurements of diatom species composition, transparent exopolymerparticles (TEP) and bulk particle abundance, as well as chemicaland biological variables, were conducted in order to revealthe determinants of coagulation efficiency. The investigationshowed that an increase in TEP concentration relative to conventionalparticles at the decline of the bloom significantly enhancedapparent coagulation efficiencies. High proportions of TEP ledto apparent values of stickiness >1, which indicates thatcollision rates can be substantially underestimated when thestickiness parameter     

Microbial Biogeography along an Estuarine Salinity Gradient: Combined Influences of Bacterial Growth and Residence Time

Shifts in bacterioplankton community composition along the salinity gradient of the Parker River estuary and Plum Island Sound, in northeastern Massachusetts, were related to residence time and bacterial community doubling time in spring, summer, and fall seasons. Bacterial community composition was characterized with denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S ribosomal DNA. Average community doubling time was calculated from bacterial production ([¹⁴C]leucine incorporation) and bacterial abundance (direct counts). Freshwater and marine populations advected into the estuary represented a large fraction of the bacterioplankton community in all seasons. However, a unique estuarine community formed at intermediate salinities in summer and fall, when average doubling time was much shorter than water residence time, but not in spring, when doubling time was similar to residence time. Sequencing of DNA in DGGE bands demonstrated that most bands represented single phylotypes and that matching bands from different samples represented identical phylotypes. Most river and coastal ocean bacterioplankton were members of common freshwater and marine phylogenetic clusters within the phyla Proteobacteria, Bacteroidetes, and Actinobacteria. Estuarine bacterioplankton also belonged to these phyla but were related to clones and isolates from several different environments, including marine water columns, freshwater sediments, and soil.     

Seasonal dynamics of bacterioplankton community structure in a eutrophic lake as determined by 5S rRNA analysis.

Community structure of bacterioplankton was studied during the major growth season for phytoplankton (April to October) in the epilimnion of a temperate eutrophic lake (Lake Plusssee, northern Germany) by using comparative 5S rRNA analysis. Estimates of the relative abundances of single taxonomic groups were made on the basis of the amounts of single 5S rRNA bands obtained after high-resolution electrophoresis of RNA directly from the bacterioplankton. Full-sequence analysis of single environmental 5S rRNAs enabled the identification of single taxonomic groups of bacteria. Comparison of partial 5S rRNA sequences allowed the detection of changes of single taxa over time. Overall, the whole bacterioplankton community showed two to eight abundant (>4% of the total 5S rRNA) taxa. A distinctive seasonal succession was observed in the taxonomic structure of this pelagic community. A rather-stable community structure, with seven to eight different taxonomic units, was observed beginning in April during the spring phytoplankton bloom. A strong reduction in this diversity occurred at the beginning of the clear-water phase (early May), when only two to four abundant taxa were observed, with one taxon dominating (up to 72% of the total 5S rRNA). The community structure during summer stagnation (June and July) was characterized by frequent changes of different dominating taxa. During late summer, a dinoflagellate bloom (Ceratium hirudinella) occurred, with Comamonas acidovorans (beta-subclass of the class Proteobacteria) becoming the dominant bacterial species (average abundance of 43% of the total 5S rRNA). Finally, the seasonal dynamics of the community structure of bacterioplankton were compared with the abundances of other major groups of the aquatic food web, such as phyto- and zooplankton, revealing that strong grazing pressure by zooplankton can reduce microbial diversity substantially in pelagic environments.     

Diversity in UV sensitivity and recovery potential among bacterioneuston and bacterioplankton isolates

Aims: To assess the variability in UV‐B (280–320 nm) sensitivity of selected bacterial isolates from the surface microlayer and underlying water of the Ria de Aveiro (Portugal) estuary and their ability to recover from previous UV‐induced stress. Methods and Results: Bacterial suspensions were exposed to UV‐B radiation (3·3 W m^?2). Effects on culturability and activity were assessed from colony counts and ³H‐leucine incorporation rates, respectively. Among the tested isolates, wide variability in UV‐B‐induced inhibition of culturability (37·4–99·3%) and activity (36·0–98·0%) was observed. Incubation of UV‐B‐irradiated suspensions under reactivating regimes (UV‐A, 3·65 W m^?2; photosynthetic active radiation, 40 W m^?2; dark) also revealed diversity in the extent of recovery from UV‐B stress. Trends of enhanced resistance of culturability (up to 15·0%) and enhanced recovery in activity (up to 52·0%) were observed in bacterioneuston isolates. Conclusions: Bacterioneuston isolates were less sensitive and recovered more rapidly from UV‐B stress than bacterioplankton isolates, showing enhanced reduction in their metabolism during the irradiation period and decreased culturability during the recovery process compared to bacterioplankton. Significance and Impact of the Study: UV exposure can affect the diversity and activity of microbial communities by selecting UV‐resistant strains and alter their metabolic activity towards protective strategies.     

Bacterioplankton community structure in the Arctic waters as revealed by pyrosequencing of 16S rRNA genes

Fjords and open oceans are two typical marine ecosystems in the Arctic region, where glacial meltwater and sea ice meltwater have great effects on the bacterioplankton community structure during the summer season. This study aimed to determine the differences in bacterioplankton communities between these two ecosystems in the Arctic region. We conducted a detailed census of microbial communities in Kongsfjorden (Spitsbergen) and the Chukchi Borderland using high-throughput pyrosequencing of the 16S rRNA gene. Gammaproteobacteria and Bacteroidetes were the dominant members of the bacterioplankton community in Kongsfjorden. By contrast, the most abundant bacterial groups in the surface seawater samples from the Chukchi Borderland were Alphaproteobacteria and Actinobacteria. Differences in bacterial communities were found between the surface and subsurface waters in the investigation area of the Chukchi Borderland, and significant differences in bacterial community structure were also observed in the subsurface water between the shelf and deep basin areas. These results suggest the effect of hydrogeographic conditions on bacterial communities. Ubiquitous phylotypes found in all the investigated samples belonged to a few bacterial groups that dominate marine bacterioplankton communities. The sequence data suggested that changes in environmental conditions result in abundant rare phylotypes and reduced amounts of other phylotypes.     

Spatial and temporal analysis of estuarine bacterioneuston and bacterioplankton using culture-dependent and culture-independent methodologies

Bacterioneuston may play a key role in water–air exchange of gases and in processing organic matter and pollutants that accumulate at the sea-surface microlayer (SML). However, the phylogenetic diversity of bacterioneuston has been poorly characterized. We analyzed 24 samples each from the SML and underlying water (UW) at three sites in the Ria de Aveiro estuary, Portugal. Cultivation and culture-independent techniques were used to compare bacterioneuston and bacterioplankton. Culturable heterotrophic bacteria were enriched in the SML. The culturable community was dominated by Psychrobacter and Acinetobacter. The presence of high numbers of Psychrobacter was a notable result. Differences were confined to a few genera overrepresented in UW samples (Kocuria, Agrococcus and Vibrio). 16S rDNA DGGE profiles were highly stable in terms of number and position of bands between sampling sites and dates but cluster analysis revealed a slight tendency for grouping according to sampled layer. SML-specific DGGE bands affiliated with Actinobacteria, Cyanobacteria, Gammaproteobacteria and Bacteroidetes. Low similarity between nucleotide sequences of DGGE-bands and previously reported sequences suggest the occurrence of SML-specific populations. Enrichment of SML for Pseudomonas and Aeromonas was questioned and the diversity of both communities was analyzed. Consistent differences between SML and UW aeromonads communities were not identified. In terms of Pseudomonas, a culturable operational taxonomic unit was consistently overrepresented within SML samples. Taken together, our results indicate that the similarity between SML and UW communities depends on spatial and temporal factors.     

The Temporal Scaling of Bacterioplankton Composition: High Turnover and Predictability during Shrimp Cultivation

The spatial distribution of microbial communities has recently been reliably documented in the form of a distance–similarity decay relationship. In contrast, temporal scaling, the pattern defined by the microbial similarity–time relationships (STRs), has received far less attention. As a result, it is unclear whether the spatial and temporal variations of microbial communities share a similar power law. In this study, we applied the 454 pyrosequencing technique to investigate temporal scaling in patterns of bacterioplankton community dynamics during the process of shrimp culture. Our results showed that the similarities decreased significantly (P?=?0.002) with time during the period over which the bacterioplankton community was monitored, with a scaling exponent of w?=?0.400. However, the diversities did not change dramatically. The community dynamics followed a gradual process of succession relative to the parent communities, with greater similarities between samples from consecutive sampling points. In particular, the variations of the bacterial communities from different ponds shared similar successional trajectories, suggesting that bacterial temporal dynamics are predictable to a certain extent. Changes in bacterial community structure were significantly correlated with the combination of Chl a, TN, PO₄ ^3-, and the C/N ratio. In this study, we identified predictable patterns in the temporal dynamics of bacterioplankton community structure, demonstrating that the STR of the bacterial community mirrors the spatial distance–similarity decay model.     

Microbial community of freshwater sponges in Lake Baikal

The microbial community of Baikal sponges has been studied in five species belonging to the genera Swartschewskia, Baicalospongia, and Lubomirskia of the endemic family Lubomirskiidae. The results show that the total numbers of bacteria and bacterioplankton production have an effect on the growth of L. baicalensis body. Bacteria of the genera Pseudomonas, Bacillus, Micrococcus, Sarcina, Flavobacterium, Arthrobacter, and Acinetobacter living in the sponges are representatives of the Baikal bacterioplankton. Actinomycetes of the genera Streptomyces and Micromonospora are a permanent component of the cultivable sponge microbial community. The numbers and enzyme activities of heterotrophic, oligotrophic, and psychrophilic bacteria isolated from different sponge species and from the ambient water in autumn and in winter have been estimated.     

A mesocosm study of Phaeocystis globosa (Prymnesiophyceae) population dynamics: II. Significance for the microbial community

The impact of Phaeocystis globosa population decline on the microbial community was studied during a mesocosm experiment, with irradiance regime and inorganic N:P ratios (4, 16, and 44) as controlling factors. Heterotrophic bacterial activity was closely related to enhanced (viral) lysis rates of P. globosa cells and disintegration of the colonies. Up to 85% of the bacterial C demand could be supplied by P. globosa-specific cellular C release. The bacterial populations with high DNA content became dominant (>70% of total). The bacterial community showed a rapid shift in composition to take advantage of the changing conditions during the demise of the P. globosa bloom. Members of the Alphaproteobacteria and the Bacteroidetes group emerged directly upon bloom decay. Multidimensional scaling analysis in conjunction with DGGE fingerprinting implied that clustering was more related to the availability of organic carbon (the collapse of the P. gobosa bloom) than to the nature of the phytoplankton growth-controlling nutrient. Reduced irradiance delayed the development of the P. globosa population and subsequently changes in the bacterial community composition. Disintegration of P. globosa colonies resulted in the formation of transparent exopolymeric particles (TEP) and aggregates, more so under P-depletion than under N-deficient conditions. The colonial matrix transformed into big aggregates under P-depleted conditions but remained largely as ghost colonies under N-depleted conditions. In the mesocosm with initial nitrogen and phosphorus supplied in the Redfield ratio, features intermediate to conditions with either N- or P-depletion were observed. It was hypothesized that TEP affected microbial population dynamics directly through bacterial colonization and indirectly through scavenging of predators and viruses.     

Production characteristics of bacteria and phytoplankton in the Sea of Okhotsk and Bering Sea during spring–summer

Production parameters for bacterioplankton were assessed during the spring–summer period in the western parts of the Sea of Okhotsk and the Bering Sea, as well as in northwestern Pacific Ocean. The lowest values of bacterial production were observed in early June during the spring phytoplankton bloom (0.08 mg C day^–1 m^–3), while the maximum values (up to 55 mg C day^–1 m^–3) occurred in late July?early August, 1.5 to 2 months after the bloom. The concentration of dissolved organic matter, the substrate for bacterioplankton, was assessed using satellite data. The ratio between bacterial and primary production in the surface samples varied from 0.5% at the peak of phytoplankton bloom to 180% at the peak of bacterioplankton development.     

Seasonal dynamics of prokaryotes and their associations with diatoms in the Southern Ocean as revealed by an autonomous sampler

The Southern Ocean remains one of the least explored marine environments. The investigation of temporal microbial dynamics has thus far been hampered by the limited access to this remote ocean. We present here high-resolution seasonal observations of the prokaryotic community composition during phytoplankton blooms induced by natural iron fertilization. A total of 18 seawater samples were collected by a moored remote autonomous sampler over 4 months at 5–11 day intervals in offshore surface waters (central Kerguelen Plateau). Illumina sequencing of the 16S rRNA gene revealed that among the most abundant amplicon sequence variants, SAR92 and Aurantivirga were the first bloom responders, Pseudomonadaceae, Nitrincolaceae and Polaribacter had successive peaks during the spring bloom decline, and Amylibacter increased in relative abundance later in the season. SAR11 and SUP05 were abundant prior to and after the blooms. Using network analysis, we identified two groups of diatoms representative of the spring and summer bloom that had opposite correlation patterns with prokaryotic taxa. Our study provides the first seasonal picture of microbial community dynamics in the open Southern Ocean and thereby offers biological insights to the cycling of carbon and iron, and to an important puzzling issue that is the modest nitrate decrease associated to iron fertilization.     

Bacterioplankton communities in a high-altitude freshwater wetland

Microbial communities play a crucial role in various biogeochemical processes in aquatic ecosystems. However, existing knowledge on microbial communities in the waters of wetlands is still very scant. The objective of the present study was to investigate the bacterioplankton community in the Luoshijiang Wetland, a high-altitude freshwater wetland in the Yunnan-Kweichow Plateau. Water samples were collected from different sites. The bacterioplankton community was characterized using 16S rRNA gene clone library analysis. A spatial variation of the diversity and composition of the bacterioplankton community was observed. Verrucomicrobia and Proteobacteria were the most abundant components. Proteobacteria might play an important role in water self-purification, but the significance of Verrucomicrobia remained unclear. Moreover, Pearson’s correlation analysis showed that Actinobacteria and Gemmatimonadetes were positively correlated with nitrite nitrogen in waters, while Alphaproteobacteria with dissolved phosphorous.