Spatiotemporal Distributions of Bacterioplankton Communities in the Qiantang River(Hangzhou Section),China

The spatial and temporal distribution of bacterioplankton communities plays a vital role in understanding the ecological dynamics and health of aquatic ecosystems.In this study,we conducted a comprehensive investigation of the bacterioplankton communities in the Qiantang River(Hangzhou section).Water samples were collected quarterly from seven sites over a one-year period.Physical and chemical parameters,including dissolved oxygen(DO),water temperature(WT),chemical oxygen demand(COD),nitrite(NO_(2)^(-)),active phosphate(PO_(4)^(3-))and other indices were determined.In this study,theαdiversity,βdiversity and abundance differences of bacterial communities were investigated using 16S rRNA high-throughput sequencing analysis.The spatial and temporal distribution characteristics and main driving factors of the bacterioplankton community structure and diversity were discussed.The results showed that a total of 57 phyla were detected in the bacterioplankton community,among which Proteobacteria and Actinomycetes were the two dominant groups with the highest relative abundance.The results of PCoA based on Bray-Curtis distance showed that the sampling season had a slightly greater effect on the changes in bacterioplankton community structure in the Qiantang River.Mantel and partial Mantel test showed that environmental variables(Mantel r=0.6739,P<0.0001;partial Mantel r=0.507,P=0.0001)were more important than geographical distance(Mantel r=0.5322,P<0.001;partial Mantel r=0.1563,P=0.001).The distance attenuation model showed that there was significant distance attenuation in all four seasons,and the maximum limit of bacterial community diffusion was found in spring.RDA analysis showed that nine environmental factors,including COD,WT and DO,significantly affected community distribution(P<0.05).This study provides valuable insights into the spatial and temporal distribution characteristics of bacterioplankton communities,shedding light on their ecological roles in the Qiantang River.The information obtained can guide future research on the interactions between bacterioplankton and their environment,enabling the development of effective conservation strategies and sustainable management practices for aquatic ecosystems.

Spatial-temporal dynamics of bacterioplankton communities in the breeding area of large yellow croaker Larimichthys crocea in Sansha Bay,China

As an important spawning ground for large yellow croaker Larimichthys crocea,Sansha Bay,South China Sea has been a research hotspot.However,studies on the influence of the bacterioplankton community and assessments of its seasonal succession of bacterioplankton in different sea areas in Sansha Bay are still limited.To address the issue,we use 16S rRNA gene amplicon sequencing and functional prediction to investigate the spatial-temporal dynamics of the bacterioplankton community in three distinct areas,i.e.,Breeding Area(BA),Yantian Harbor(YH),and Bay Margin(BM)of Sansha Bay.Results show that the structure of the bacterioplankton community in Sansha Bay had a significant seasonal succession.Moreover,the representative zero-radius Operation Taxon Units in different seasons were significantly different among the three selected sea areas.Specifically,during the breeding season,bacterioplankton communities in BA were characterized by compound-degrading bacteria,such as Rhodococcus and Owenweeksia,while in YH and BM,animal parasites or symbionts such as Vibrio and Arcobacter were dominant.Furthermore,the redundancy analysis and Spearman correlation analysis further explained that water temperature,dissolved oxygen,and ammonia nitrogen were the main environmental factors responsible for the difference.In addition,the bioindicator functions screened by Functional Annotation of Prokaryotic Taxa and random forest machine learning mainly relied on compound degradation,nitrite oxidation,and photoheterotrophy.The compound-degradationcorresponded bacterioplankton genera such as Rhodococcus had relatively higher abundance in BM,while Nitrospina corresponding to nitrite oxidation tended to be abundant in YH and BA.Based on the spatial and temporal variation in the composition and function of bacterioplankton,our findings provide a basis for understanding the theory of bacterioplankton community structure in the inner-bay habitat of the large yellow croaker in Sansha Bay.

Community composition,co-occurrence,and environmental drivers of bacterioplankton community in surface and 50-m water layers in the subarctic North Pacific

The Western Subarctic Gyre(WSG)is one of the two gyre-systems in the subarctic North Pacific known for high nutrient and low-chlorophyll waters.However,the bacterioplankton in marine water of this area,either in terms of the taxonomic composition or functional structure,remains relatively unexplored.A total of 22 sampling sites from two water layers(surface water,SW and 50-m layer water,FW)were collected in this area.The physiochemical parameters of waters,Synechococcus,and bacterial density,as well as the bacterioplankton community composition and distribution pattern,were analyzed.The nutrient concentrations of DIN,DIP,and DSi,Chl-a concentration,and the average abundance of heterobacteria in FW were higher than those in SW.However,temperature and the average abundance of Synechococcus and pico-eukaryotes were higher in SW.A total of 3269 OTUs were assigned,and 2123OTUs were commonly shared;moreover,similar alpha diversity patterns were observed in both SW and FW.The bacterioplankton community showed significantly obvious correlation with salinity,DIP,DIN,and Chl a in both SW and FW.Proteobacteria,Cyanobacteria,Bacteroidota,Actinobacteriota,and Firmicutes were the main phyla while Synechococcus_CC9902,Psychrobacter,and Sulfitobacter were the dominant genera in each sampling site.Most correlations that happened between the OTUs in the cooccurrence network were positive and inter-module.Higher edges and graph density were found in SW,indicating that more correlations occurred,and the community was more complex in SW.This study provided novel knowledge on the bacterioplankton community structure and the correlation characteristics in WSG.

Spatial and temporal dynamics of phytoplankton and bacterioplankton biomass in Sanya Bay, northern South China Sea

The composition of phytoplankton and the dynamics of phytoplankton and bacterioplankton biomass （PB and BB, respectively） of Sanya Bay, South China Sea, were determined. A total of 168 species （67 genera） phytoplankton were identified, including BaciUariophyta （diatom, 128 species）, Pyrrophyta （35 species）, Cyanophyta （3 species）, and Chrysophyta （2 species）. Annual average zbundance of phytoplankton was 1.2 × 107 cells/m^3, with the highest abundance in autumn, and the lowest in summer. Annual average diversity index （H＇） and evenness （J） values were 3.96 and 0.70, respectively. Average chlorophyll-a was 2.5 mg/m^3, and the average PB was 124 mg C/m^3, with the highest value in autumn. Surface PB was higher than the bottom, except for summer. Annual mean bacterioplankton abundance and BB were 6.9 × 10^1l cells/m^3 and 13.8 mg C/m^3, respectively. The highest BB was found in summer, followed by winter, spring, and autumn. Surface BB was higher than bottom all year round. The spatial distribution patterns of PB and BB were very similar with the highest biomass in the estuary, and decreased seaward, primarily due to the terrestrial input from the Sanya River and influx of oceanic water. The main factor influencing PB and BB was dissolved inorganic nitrogen （DIN）. Other factors such as temperature, which is above 22℃ throughout the year, had a negligible impact. The correlation between BB and PB was significant （P 〈 0.01）. The annual average ratio of BB/PB was 0.12 （0.06-0.15）. Phytoplankton primary production was one of the most important factors in controlling the distribution of bacterioplankton.

Factors dominating bacterioplankton abundance and production in the Nordic seas and the Chukchi Sea in summer 2012

Abundance and production of bacterioplankton were measured in the Nordic seas and Chukchi Sea during the 5th Chinese Arctic Research Expedition in summer 2012. The results showed that average bacterial abundances ranged from 3.31×10^11 cells/m^3 to 2.25× 10^11 cells/m^3, and average bacterial productions （calculated by carbon） were 0.46 mg/（m^3·d） and 0.54 mg/（m^3·d） in the Nordic seas and Chukchi Sea, respectively. T-test result showed that bacterial abundances were significantly different between the Nordic seas and Chukchi Sea, however, no significant difference was observed regarding bacterial productions. Based on the slope of lg bacterial biomass versus lg bacterial production, bacterial communities in the Nordic seas and Chukchi Sea were moderately dominated by bottom-up control. Both Pearson correlation analysis and multivariable linear regression indicated that temperature had significant positive correlation with bacterial abundance in the Chukchi Sea, while no correlations with productions in both areas. Meanwhile, Chl a had positive correlations with both bacterial abundance and production in these two regions. As the temperature and Chl a keep changing in the future, we suggest that both bacterial abundance and production been hanced in the Chukchi Sea but weaken in the Nordic seas, though the enhancement will not be dramatic as a result of higher pressure of predation and viral lysis.

Comparison of Bacterioplankton Communities in Three Heavily Polluted Streams in China

Objective To compare the bacterioplankton communities in streams exposed to pollution of different types. Methods The bacterioplankton communities in three selected heavily polluted streams were investigated by using terminal‐restriction fragment length polymorphism （T‐RFLP） analysis in combination with 16S rRNA gene clone library analysis. Results Both T‐RFLP and 16S rRNA gene clone library revealed a great difference in bacterioplankton community composition in the different streams. Conclusion This work might provide some new insights into bioremediation of heavily polluted streams.

Spatiotemporal pattern of bacterioplankton in Donghu Lake

Bacterioplankton play key roles in the biogeochemical cycle and in organic contaminant degradation. The species richness and abundance of bacterial subgroups are generally distinct from each other, and this is attributed to their different functions in aquatic ecosystems. The spatiotemporal variations of eight phylogenetic subgroups （Actinobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Planctomycetes, alpha-, beta-, and gamma-Proteobacteria） derived from Donghu Lake were investigated using PCR-DGGE fingerprinting, to explore their responses to environmental factors. Results indicate that Actinobacteria and beta-Proteobacteria were the two largest bacterial subgroups detected. These two groups and Bacteroidetes showed clear seasonal patterns in composition of the operational taxonomic unit. Results also suggest that the bacterioplankton subgroups in Donghu Lake were significantly correlated with different environmental factors. In brief, the total nitrogen was one of the major factors regulating all the bacterioplankton except for Actinobacteria. However, total phosphorus, another important eutrophication factor, contributed to the two largest bacterial groups （Actinobacteria and beta-Proteobacteria）, as well as to the Cyanobacteria and Firmicutes. Therefore, the responses of bacterioplankton subgroups to environmental factors were different, and this should be attributed to the differences in the fimctions of different groups.

Bacterioplankton production in dilution zone of the Changjiang (Yangtze) Estuary

The bacterioplankton production and bacterioplankton abundance were surveyed in dilution zone of the Changjiang Estuary and a mesocosm experimental device for enriched phosphate experiment and oil contaminated experiment was placed in the waters nearby Luhua Island during October 1997 and May 1998. The results showed that the average bacterioplankton production in spring was higher than that in autumn, the production at the surface water was higher than that at the bottom in the surveyed area; the higher values appeared in the middle of the area. The results from mesocosm experiment with adding phosphate and oil contaminated showed that the bacterioplankton production increased rising trend day by day during the experiment period.

Contrasting patterns of free-living bacterioplankton diversity in macrophyte-dominated versus phytoplankton blooming regimes in Dianchi Lake,a shallow lake in China

Freshwater shallow lakes typically exhibit two alternative stable states under certain nutrient loadings:macrophyte-dominated and phytoplankton-dominated water regimes.An ecosystem regime shift from macrophytes to phytoplankton blooming typically reduces the number of species of invertebrates and fishes and results in the homogenization of communities in freshwater lakes.We investigated how microbial biodiversity has responded to a shift of the ecosystem regime in Dianchi Lake,which was previously fully covered with submerged macrophytes but currently harbors both ecological states.We observed marked divergence in the diversity and community composition of bacterioplankton between the two regimes.Although species richness,estimated as the number of operational taxonomic units and phylogenetic diversity(PD),was higher in the phytoplankton dominated ecosystem after this shift,the dissimilarity of bacterioplankton community across space decreased.This decrease in beta diversity was accompanied by loss of planktonic bacteria unique to the macrophyte-dominated ecosystem.Mantel tests between bacterioplankton community distances and Euclidian distance of environmental parameters indicated that this reduced bacterial community differentiation primarily reflected the loss of environmental niches,particularly in the macrophyte regime.The loss of this small-scale heterogeneity in bacterial communities should be considered when assessing long-term biodiversity changes in response to ecosystem regime conversions in freshwater lakes.

Terrestrial dissolved organic carbon consumption by heterotrophic bacterioplankton in the Huanghe River estuary during water and sediment regulation

Nearly 20%–50% of the annual terrestrial dissolved organic carbon(DOC)from the Huanghe(Yellow)River was transported to the estuary during the 5-14d of water and sediment regulation.The concentration of DOC increased sharply during the period of water and sediment regulation,which may promote the terrestrial DOC consumption by heterotrophic bacterioplankton.Water and sediment regulation provides an ideal condition for the study of terrestrial DOC consumption by heterotrophic bacterioplankton when terrestrial DOC increases sharply in rainy season,which may help to seek the fates of terrestrial DOC in the estuaries and coasts.In this study,the concentration and stable isotope of DOC,the biomass,growth,and respiration of heterotrophic bacterioplankton were determined.By the study,we found both average percent contribution of terrestrial DOC to the DOC pool and Contribution of terrestrial DOC to the carbon composition of heterotrophic bacterioplankton decreased as distance from the river mouth increased off shore,which was deceased from(39.2±4.0)%,(37.5±4.3)%to(30.3±3.9)%,(28.2±3.9)%respectively.255-484μg C/(L·d)terrestrial DOC was consumed by heterotrophic bacterioplankton.And 29%-45%terrestrial DOC consumed by heterotrophic bacterioplankton releasing as CO2 by respiration.Comparing with tropical estuary,terrestrial DOC consumed by heterotrophic bacterioplankton was lower in temperate estuary(this study).Temperature may limit the consumption of terrestrial DOC by heterotrophic bacterioplankton.

The ecological risks of hydrogen peroxide as a cyanocide:its effect on the community structure of bacterioplankton

Microcystis blooms are an environmental and ecological concern that has received a serious attention. Hydrogen peroxide(H_2O_2) is an environment-friendly cyanocide that is commonly used to control Microcystis blooms. While the ecological safety of H_2O_2 has been previously studied, its influence on bacterioplankton has not been investigated to date. In this study, we used mesocosm experiments to determine the influence of H_2O_2 on the dynamic changes of the community structure of bacterioplankton. By using deep-sequencing and metagenomics strategy we determined the community structures of phytoplankton and bacterioplankton assemblages that were dominated by M icrocystis at a highly eutrophic Dianchi Lake, China. The results showed that M icrocystis was more sensitive to H_2O_2 than other eukaryotic algae. More interestingly, application of H_2O_2 changed the community structure of bacterioplankton, evidenced by the emergence of F irmicutes as the dominant species in place of B acteroidetes and Proteobacteria. The H_2O_2 treatment resulted in the community of bacterioplankton that was primarily dominated by E xiguobacterium and Planomicrobium. Our results show that the abundance changed and the bacterioplankton diversity did not recover even after the concentration of H_2O_2 reached to the background level. Thus, the response of bacterioplankton must be considered when assessing the ecological risks of using H_2O_2 to control Microcystis blooms, because bacterioplankton is the key player that forms the basis of food web of aquatic environment.

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.

The effect of cylindrospermopsin on the bacterioplankton community:a microcosm experiment on water from Dishui Lake,Shanghai,China

Eutrophication and climate warming have intensified the global expansion of invasive cyanobacteria such as Cylindrospermopsis spp.and Chrysosporum spp.Cylindrospermopsin(CYN)produced by species of the latter two genera may harm phytoplankton,zooplankton,and fishes.However,effects of CYN on the bacterioplankton community have not been studied.Based on high-throughput sequencing,we explored the effect of CYN on the structure and function of the bacterioplankton community by adding pure CYN to in-situ water collected from a brackish coastal shallow lake:Dishui Lake,China.We found that most bacterioplankton taxa had a certain tolerance potential to CYN,but that high concentrations of CYN(40μg/L)caused a significant decrease in microbial abundance and functional groups.Of the dominant phyla,Actinobacteria had the strongest tolerance to CYN.Network analysis indicated that CYN caused shifts in the community structure of the bacterioplankton,reducing community stability and structural complexity.High CYN concentrations also reduced the correlation between the different bacterioplankton groups,and the abundances of some bacterial taxa associated with the denitrification function and the process of carbon transfer in the microbial food web were inhibited.Our study provide s new insight into the response of the bacterioplankton communities to harmful algal toxins produced by cyanobacteria.

The Effects of Ocean Acidity and Elevated Temperature on Bacterioplankton Community Structure and Metabolism

By the end of the 21st century, mean sea surface temperatures are expected to increase 4?C, while atmospheric CO2 concentrations are predicted to triple causing seawater to become acidic. These compounding effects will undoubtedly have major consequences for the organisms and processes in the oceans. Bacterioplankton play a vital role in the marine carbon cycle and the oceans’ ability to sequester CO2. We utilized pCO2 perturbation experiments to investigate the effects of ocean acidity and elevated temperature on bacterioplankton community structure and metabolism. Terminal-restriction fragment length polymorphism (T-RFLP) of small subunit ribosomal (SSU) genes revealed that bacterioplankton incubated in lower pH conditions exhibited a reduction of species richness, evenness, and overall diversity, relative to those incubated in ambient pH conditions. Non-metric multidimensional scaling (MDS) of T-RFLP data resulted in clustering by pH suggesting that pH influenced the structure of these communities. Shifts in the dominant members of bacterioplankton communities incubated under different pH were observed in both T-RFLP and SSU clone library analyses. Both ambient and low pH communities were dominated by Gammaproteobacteria and Alphaproteobacteria, although abundance of Alphaproteobacteria increased in communities incubated at lower pH. This was expressed by the gamma to alpha ratio dropping from ~9 to 4, respectively. In general, the representative taxa from these two classes were distinctly different between the treatments, with a few taxa found to be persistent in both treatments. Changes in the structure of bacterioplankton communities coincided with significant changes to their overall metabolism. Bacterial production rates decreased, while bacterial respiration increased under lower pH conditions. This study highlights the ability of bacterioplankton communities to respond to ocean acidification both structurally and metabolically, which may have significant implications for their ecological function in the marine carbon cycle and the ocean’s response to global climate change.

Molecular analyses of bacterioplankton communities with highly abundant Vibrio clades: a case study in Bohai Sea coastal waters

We investigated the bacterioplankton abundance, community composition and the associated Vibrio clades of natural seawater in Bohai Sea coastal waters. Seawater samples (10 L in triplicate) were collected at 0.5, 3, and 5 m depths near the coastal aquaculture zone of the Bohai Sea on May 12, 2016. Real-time PCR and 16S rRNA gene amplicon high-throughput sequencing methods were employed by which 485 operational taxonomic units (OTUs) at a 97% sequence similarity level were generated. Gammaproteobacteria, Alphaproteobacteria, and Bacteroidetes were the most abundant groups, accounting for 49.5%, 23.5%, and 18.9% of the total assemblage, respectively. Obvious variations in Pseudoalteromonas, Vibrio, and Octadecabacter , which were the most abundant genera, could be observed among diff erent samples. Notably, the results of Vibrio -specifi c real-time PCR indicated that Vibrio had extremely high 16S rRNA gene copy numbers. The 16S rRNA gene sequencing results across all the samples also indicated that they occupied a large proportion of the total assemblage. Both the alpha diversity and major bacterioplankton group Pseudoalteromonas had significant correlations with the concentration of PO4^3-. Overall, studies on bacterioplankton communities with highly abundant Vibrio clades can provide interesting insight into the microbial function and health assessment of the Bohai Sea coastal ecosystem.

BACTERIOPLANKTON SECONDARY PRODUCTION ESTIMATES FOR ARTIFICIALLY FERTILIZED SHRIMP POND

Experiments were conducted from June to September, 1995 in a controlled integrated culture pond-enclosure ecosystem.The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton production in situ in a fertilization pond ecosystem.This paper presents a method by which bacterial production was estimated through incubation in situ and measurement of increased bacterial abundance with time. Bacterial growth rates. production and tumover per day during the periods of culture were estimated. The influence of zooplankton grazing, substrate limiting and water temperature on the bacterial growth rates and production were studied also.

Drivers of coastal bacterioplankton community diversity and structure along a nutrient gradient in the East China Sea

Anthropogenic nutrient discharge poses widespread threats to coastal ecosystems and has increased environmental gradients from coast to sea. Bacterioplankton play crucial roles in coastal biogeochemical cycling, and a variety of factors af fect bacterial community diversity and structure. We used 16 S r RNA gene pyrosequencing to investigate the spatial variation in bacterial community composition(BCC) across five sites on a coast-of fshore gradient in the East China Sea. Overall, bacterial alpha-diversity did not diff er across sites, except that richness and phylogenetic diversity were lower in the of fshore sites, and the highest alpha-diversity was found in the most landward site, with Chl-abeing the main factor. BCCs generally clustered into coastal and of fshore groups. Chl-a explained 12.3% of the variation in BCCs, more than that explained by either the physicochemical(5.7%) or spatial(8.5%) variables. Nutrients(particularly nitrate and phosphate), along with phytoplankton abundance, were more important than other physicochemical factors, co-explaining 20.0% of the variation in BCCs. Additionally, a series of discriminant families(primarily affiliated with Gammaproteobacteria and Alphaproteobacteria), whose relative abundances correlated with Chl-a, DIN, and phosphate concentrations, were identified, implying their potential to indicate phytoplankton blooms and nutrient enrichment in this marine ecosystem. This study provides insight into bacterioplankton response patterns along a coast-of fshore gradient, with phytoplankton abundance increasing in the of fshore sites. Time-series sampling across multiple transects should be performed to determine the seasonal and spatial patterns in bacterial diversity and community structure along this gradient.

Fish-mediated changes in bacterioplankton community composition: an in situ mesocosm experiment

We characterized variations in bacterioplankton community composition(BCC) in mesocosms subject to three different treatments. Two groups contained fish(group one: Cyprinus carpio; group two: Hypophthalmichthys molitrix); and group three, the untreated mesocosm, was the control. Samples were taken seven times over a 49-d period, and BCC was analyzed by PCR-denaturing gradient gel electrophoresis(DGGE) and real-time quantitative PCR(q PCR). Results revealed that introduction of C. carpio and H. molitrix had a remarkable impact on the composition of bacterioplankton communities, and the BCC was significantly diff erent between each treatment. Sequencing of DGGE bands revealed that the bacterioplankton community in the different treatment groups was consistent at a taxonomic level, but differed in its abundance. H. molitrix promoted the richness of Alphaproteobacteria and Actinobacteria, while more bands affiliated to Cyanobacteria were detected in C. carpio mesocosms. The redundancy analysis(RDA) result demonstrated that the BCC was closely related to the bottom-up(total phosphorus, chlorophyll a, phytoplankton biomass) and top-down forces(biomass of copepods and cladocera) in C. carpio and control mesocosms, respectively. We found no evidence for top-down regulation of BCC by zooplankton in H. molitrix mesocosms, while grazing by protozoa(heterotrophic nanoflagellates, ciliates) became the major way to regulate BCC. Total bacterioplankton abundances were significantly higher in C. carpio mesocosms because of high nutrient concentration and suspended solids. Our study provided insights into the relationship between fish and bacterioplankton at species level, leading to a deep understanding of the function of the microbial loop and the aquatic ecosystem.

The Relationship between Salinity and Bacterioplankton in Three Relic Coastal Ponds (Macchiatonda Wetland, Italy)

The great environmental importance of wetlands is linked to the high biodiversity of flora and fauna they support, so that the international Ramsar Convention focused on these areas and highlighted the need to preserve them. The bacterial communities that thrive in these ecosystems play a key role in regulating the local biogeochemical processes and yet their distribution, abundance and dynamics are poorly known. This work is aimed to study the bacterial assemblages over a year long, to contribute to the understanding of the natural processes occurring in wetlands at variable salinity. The knowledge of bacterial groups, species or assemblages can provide a useful bioindicator for conservation and restoration efforts. Macchiatonda Natural Reserve (Santa Severa, Rome, Italy) is a relic ecosystem, once found along the entire Tyrrhenian coast. This wetland encompasses three coastal ponds with different salinity, where both peculiar vegetation and highly diverse migratory and resident avifauna can be found. This ancient system has been scarcely investigated and nothing is known about its microbial community. The molecular metagenomic analyses performed to investigate the salinity/bacterioplankton relationship, highlighted differences in the bacterial structure, between ponds and seasons. Analogous trends in SSCP profiles, Shannon Index, and bacterial composition (16S) were observed in the two saltier ponds, whereas the entire set of results was different for the less salty one. The species diversity in the three ponds varied according the salinity gradient, with the maximum diversity corresponding to a salt concentration range between 20 and 30. At higher and lower salinity, the microbial diversity lowers, according to the “Intermediate Disturbance Hypothesis”.

Distribution of biomass of heterotrophic bacterioplankton in the Bohai Sea

Distribution, variation and impact factors of biomass of bacterioplankton from April to May 1999 in Bohai Sea were studied in DAPI method with epifluorescence microscopy. The biomass in surface waters showed a small day-night variation, varying from 0.13 to 2.51 μg/dm 3 with an average of 0.84 μg/dm 3 . The bio- mass in bottom waters showed, however, a large variation, changing from 0.15 to 4.18 μg/dm 3 with an average of 1.36 μg/dm 3 . The peak values occurred at 5 and 11 a.m. The bottom water biomass showed a significant correla- tion with particulate organic carbon (r=0.639, P<0.05). Heterotrophic bacterioplankton biomass was high in nearshore waters and low in offshore areas with a high biomass zone around Huanghe (Yellow) River mouth, showing the same distribution of nutrients. In vertical distribution, heterotrophic bacteria biomass in bottom wa- ters was higher than that in surface water.