Temporal Patterns in Glycolate-Utilizing Bacterial Community Composition Correlate with Phytoplankton Population Dynamics in Humic Lakes

Previous observations of correlated community dynamics between phytoplankton and bacteria in lakes indicate that phytoplankton populations may influence bacterial community structure. To investigate the possibility that bacterial use of phytoplankton exudates contributes to observed patterns of community change, we characterized the diversity and dynamics of heterotrophic bacterioplankton with genetic potential to use glycolate, a photorespiration-specific exudate, in five lakes over a 15-week period. Culture-independent approaches were used to track different bacterial phylotypes represented by DNA sequence variation in the functional gene glycolate oxidase subunit D (glcD). glcD gene sequences from freshwater bacteria exhibited broad phylogenetic diversity, including sequences representing the Alpha-, Beta-, and Gammaproteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Verrucomicrobia. The majority of glcD gene sequences were betaproteobacterial, with 48% of the sequences clustering with the glcD gene from the cosmopolitan freshwater species Polynucleobacter necessarius. Terminal restriction fragment length polymorphism fingerprinting of the glcD gene revealed changes in glycolate-utilizing assemblages over time. An average of 39% of within-lake temporal variation in glycolate-utilizing assemblages across five lakes was explained by phytoplankton community composition and dynamics. The interaction between phytoplankton populations and the environment explained an additional 17% of variation on average. These observations offer new insight into the diversity and temporal dynamics of freshwater bacteria with genetic potential to use glycolate and support the hypothesis that algal exudates influence the structure of bacterial communities.     

Can Humic Water Discharge Counteract Eutrophication in Coastal Waters?

A common and established view is that increased inputs of nutrients to the sea, for example via river flooding, will cause eutrophication and phytoplankton blooms in coastal areas. We here show that this concept may be questioned in certain scenarios. Climate change has been predicted to cause increased inflow of freshwater to coastal areas in northern Europe. River waters in these areas are often brown from the presence of high concentrations of allochthonous dissolved organic carbon (humic carbon), in addition to nitrogen and phosphorus. In this study we investigated whether increased inputs of humic carbon can change the structure and production of the pelagic food web in the recipient seawater. In a mesocosm experiment unfiltered seawater from the northern Baltic Sea was fertilized with inorganic nutrients and humic carbon (CNP), and only with inorganic nutrients (NP). The system responded differently to the humic carbon addition. In NP treatments bacterial, phytoplankton and zooplankton production increased and the systems turned net autotrophic, whereas the CNP-treatment only bacterial and zooplankton production increased driving the system to net heterotrophy. The size-structure of the food web showed large variations in the different treatments. In the enriched NP treatments the phytoplankton community was dominated by filamentous >20 µm algae, while in the CNP treatments the phytoplankton was dominated by picocyanobacteria <5 µm. Our results suggest that climate change scenarios, resulting in increased humic-rich river inflow, may counteract eutrophication in coastal waters, leading to a promotion of the microbial food web and other heterotrophic organisms, driving the recipient coastal waters to net-heterotrophy.     

Effects of nutrients and dissolved organic matter on the response of phytoplankton to ultraviolet radiation: experimental comparison in spring versus summer

The effects of nutrients and dissolved organic matter (DOM) on the response of phytoplankton community structure to ultraviolet radiation (UVR) was studied using natural phytoplankton assemblages from Lake Giles (Northeastern Pennsylvania), a temperate, oligotrophic, highly UVR-transparent lake. Microcosm experiments were conducted in 1-l bags in the spring and summer. A factorial design was used, with two UVR treatments (ambient and reduced), two nutrient treatments (control with no nutrients added, and nitrogen and phosphorus addition together), and two DOM treatments (control of 1 mg l⁻¹ and doubled). In April, UVR affected the overall phytoplankton community structure, causing a shift in the dominant species. Significant interactive effects of UVR × nutrients and UVR × DOM were found on total phytoplankton biovolumes. In July, all taxa responded positively to the N + P addition, and were affected differentially by the UVR treatments. The initial communities varied in April and July, but Synura sp. and Chroomonas sp. were present in both seasons. Synura sp. responded positively to the addition of DOM in April and the reduction of UVR in July. Chroomonas sp. responded positively to the reduction of UVR in April and the addition of nutrients in July. The differential sensitivity of these two species suggests that changing environmental factors between spring and summer promoted differences in the relative importance of UVR in changing phytoplankton community structure. Handling editor: Luigi Naselli-Flores     

Regulation of bacterioplankton production and biomass in an oligotrophic cleanvater lake--the importance of the phytoplankton community

Estimations of bacterioplankton production and biomass werecarried out in enclosure experiments during two consecutiveyears (1989 and 1990) in oligotrophic clearwater Lake Njupfatet.The lake was limed in November 1989, and the experiments werecarried out both in 1989 (unlimed) and in 1990 (limed). Bags(3001) were manipulated with inorganic phosphorus and nitrogen,organic carbon, and metazoan zooplankton abundance. Both years,bacterial production was stimulated by inorganic nutrients aloneand in combination with organic carbon. However, the increasein bacterial production when inorganic nutrients were addedalone was much stronger in 1990 than in 1989. In 1989. bacterialproduction increased strongly only when inorganic nutrientsand organic carbon were added together. The phytoplankton communitywas dominated by the cyanobacterium Merismopedia tenuis-simaduring 1989, and the phytoplankton biomass increased only slightlywhen receiving inorganic nutrients. In 1990, when the lake hadbeen limed. M.tenuissima had completely disappeared and thephytoplankton community, dominated by Chrysophyceae and Chlorophyceae,responded strongly to additions of inorganic nutrients. Theincreased phytoplankton productivity in 1990 may have resultedin increased release of organic carbon, and this in turn thatthe carbon limitation of bacterioplankton production decreasedfrom 1989 to 1990. Zooplankton had a positive effect on bacterioplanktonproduction in 1989, but no effect in 1990. The loss of bacterialbiomass approximated 60% of the bacterial production in 1989,while in 1990 it almost equalled the bacterioplankton production.     

Phosphorus chemistry and bacterial community composition interact in brackish sediments receiving agricultural discharges

Background

External nutrient discharges have caused eutrophication in many estuaries and coastal seas such as the Baltic Sea. The sedimented nutrients can affect bacterial communities which, in turn, are widely believed to contribute to release of nutrients such as phosphorus from the sediment.

Methods

We investigated relationships between bacterial communities and chemical forms of phosphorus as well as elements involved in its cycling in brackish sediments using up-to-date multivariate statistical methods. Bacterial community composition was determined by terminal restriction fragment length polymorphism and cloning of the 16S rRNA gene.

Results and Conclusions

The bacterial community composition differed along gradients of nutrients, especially of different phosphorus forms, from the estuary receiving agricultural phosphorus loading to the open sea. This suggests that the chemical composition of sediment phosphorus, which has been affected by riverine phosphorus loading, influenced on bacterial communities. Chemical and spatial parameters explained 25% and 11% of the variation in bacterial communities. Deltaproteobacteria, presumptively sulphate and sulphur/iron reducing, were strongly associated to chemical parameters, also when spatial autocorrelation was taken into account. Sulphate reducers correlated positively with labile organic phosphorus and total nitrogen in the open sea sediments. Sulphur/iron reducers and sulphate reducers linked to iron reduction correlated positively with aluminium- and iron-bound phosphorus, and total iron in the estuary. The sulphate and sulphur/iron reducing bacteria can thus have an important role both in the mineralization and mobilization of nutrients from sediment.

Significance

Novelty in our study is that relationships between bacterial community composition and different phosphorus forms, instead of total phosphorus, were investigated. Total phosphorus does not necessarily bring out interactions between bacteria and phosphorus chemistry since proportions of easily usable mobile (reactive) phosphorus and immobile phosphorus forms in different sediments can vary. Our study suggested possible feedbacks between different forms of phosphorus and bacterial community composition.     

Diverse responses of pqqC- and phoD-harbouring bacterial communities to variation in soil properties of Moso bamboo forests

Phosphate-mobilizing bacteria (PMB) play a critical role in the regulation of phosphorus availability in the soil. The microbial genes pqqC and phoD encode pyrroloquinoline quinone synthase and bacterial alkaline phosphatase, respectively, which regulate inorganic and organic phosphorus mobilization, and are therefore used as PMB markers. We examined the effects of soil properties in three Moso bamboo forest sites on the PMB communities that were profiled using high-throughput sequencing. We observed differentiated responses of pqqC- and phoD-harbouring PMB communities to various soil conditions. There was significant variation among the sites in the diversity and structure of the phoD-harbouring community, which correlated with variation in phosphorus levels and non-capillary porosity; soil organic carbon and soil water content also affected the structure of the phoD-harbouring community. However, no significant difference in the diversity of pqqC-harbouring community was observed among different sites, while the structure of the pqqC-harbouring bacteria community was affected by soil organic carbon and soil total nitrogen, but not soil phosphorus levels. Overall, changes in soil conditions affected the phoD-harbouring community more than the pqqC-harbouring community. These findings provide a new insight to explore the effects of soil conditions on microbial communities that solubilize inorganic phosphate and mineralize organic phosphate.     

小麦-甘薯轮作长期增施有机肥对碱性土壤固氮菌群落结构及多样性的影响

生物固氮为农业生态系统提供天然的氮素来源,探究长期增施有机肥对土壤固氮菌群落的影响,为合理增施有机肥和维持土壤固氮微生物群落多样性提供科学依据。选取小麦-甘薯轮作中连续37a不施肥对照(CK)、单施化肥(NPK)、化肥+有机肥(NPKM)处理的甘薯季碱性土壤样品为研究对象。采用Illumina MiSeq高通量测序技术,研究土壤固氮菌群落的组成、多样性及其与土壤特性的关系。结果表明:与对照和单施化肥相比,长期增施有机肥降低土壤固氮菌群落丰富度和多样性,且丰富度与土壤pH显著正相关,与有机碳、全氮和有效养分(硝态氮、有效磷和速效钾)显著负相关。主坐标分析表明长期施肥显著改变土壤固氮菌群落结构,与对照相比,增施有机肥比单施化肥对固氮菌群落结构的影响更大。冗余分析表明土壤有机碳和速效钾是影响固氮菌群落结构改变最主要的因素。长期增施有机肥显著降低变形菌门、蓝藻菌门、Beta-变形菌和固氮弧菌属的相对丰度,显著增加硝化螺旋菌门、酸杆菌门和硝化螺菌属的相对丰度,这与土壤pH、有机碳和有效养分显著相关。因此,在碱性土壤上长期增施有机肥对固氮菌群落结构的改变更大,对群落多样性的抑制作用更强。     

The effect of increased nitrogen load on phytoplankton in a phosphorus‐limited lake

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Increased freshwater discharge shifts the trophic balance in the coastal zone of the northern Baltic Sea

Increased precipitation is one projected outcome of climate change that may enhance the discharge of freshwater to the coastal zone. The resulting lower salinity, and associated discharge of both nutrients and dissolved organic carbon, may influence food web functioning. The scope of this study was to determine the net outcome of increased freshwater discharge on the balance between auto‐ and heterotrophic processes in the coastal zone. By using long‐term ecological time series data covering 13 years, we show that increased river discharge suppresses phytoplankton biomass production and shifts the carbon flow towards microbial heterotrophy. A 76% increase in freshwater discharge resulted in a 2.2 times higher ratio of bacterio‐ to phytoplankton production (P_b:P_p). The level of P_b:P_p is a function of riverine total organic carbon supply to the coastal zone. This is mainly due to the negative effect of freshwater and total organic carbon discharge on phytoplankton growth, despite a concomitant increase in discharge of nitrogen and phosphorus. With a time lag of 2 years the bacterial production recovered after an initial decline, further synergistically elevating the microbial heterotrophy. Current climate change projections suggesting increased precipitation may therefore lead to increased microbial heterotrophy, thereby decreasing the transfer efficiency of biomass to higher trophic levels. This prognosis would suggest reduced fish production and lower sedimentation rates of phytoplankton, a factor of detriment to benthic fauna. Our findings show that discharge of freshwater and total organic carbon significantly contributes to the balance of coastal processes at large spatial and temporal scales, and that model's would be greatly augmented by the inclusion of these environmental drivers as regulators of coastal productivity.     

Effects of selected root exudate components on soil bacterial communities

Low-molecular-weight organic compounds in root exudates play a key role in plant-microorganism interactions by influencing the structure and function of soil microbial communities. Model exudate solutions, based on organic acids (OAs) (quinic, lactic, maleic acids) and sugars (glucose, sucrose, fructose), previously identified in the rhizosphere of Pinus radiata, were applied to soil microcosms. Root exudate compound solutions stimulated soil dehydrogenase activity and the addition of OAs increased soil pH. The structure of active bacterial communities, based on reverse-transcribed 16S rRNA gene PCR, was assessed by denaturing gradient gel electrophoresis and PhyloChip microarrays. Bacterial taxon richness was greater in all treatments than that in control soil, with a wide range of taxa (88-1043) responding positively to exudate solutions and fewer (<24) responding negatively. OAs caused significantly greater increases than sugars in the detectable richness of the soil bacterial community and larger shifts of dominant taxa. The greater response of bacteria to OAs may be due to the higher amounts of added carbon, solubilization of soil organic matter or shifts in soil pH. Our results indicate that OAs play a significant role in shaping soil bacterial communities and this may therefore have a significant impact on plant growth.     

Influence of nutrient availability on phytoplankton growth and community structure in the Port Adelaide River,Australia: [2pt] bioassay assessment of potential nutrient limitation

We investigated the influence of nutrient availability, specifically nitrogen, phosphorus and silicon on growth and community structure of phytoplankton from the Port Adelaide River estuary, South Australia. Two bioassay experiments were conducted. The first, Nutrich1, involved addition of nutrients in vitro to samples of the natural phytoplankton community from a single location in the upper estuary. The second, Nutrich2, involved nutrient addition and incubation of water from five locations in the estuary following inoculation with a `standardised' phytoplankton assemblage derived from laboratory cultures. In Nutrich1, enrichment with silicon led to greatly enhanced phytoplankton biomass due to increased growth of diatoms. Addition of nitrogen or phosphorus had little effect on phytoplankton growth. In Nutrich2, addition of nitrogen resulted in enhanced growth of phytoplankton in water collected from near the mouth the estuary, but there were no differences in growth among nutrient treatments for the remaining locations. Comparison of phytoplankton growth rate among locations revealed a trend of decreasing growth in moving towards the mouth of the estuary. This trend was unaffected by enrichment with nitrate, phosphate or silicate. We suggest that spatial variation in growth potential within the Port Adelaide River estuary may relate to variation in the concentration of nitrogen as ammonium.     

Nutrient limitation in detritus-based microcosms in Sarracenia purpurea

Most prior work on the role of top-down and bottom-up effects in aquatic communities has ignored the significant detrital component that occurs in natural systems. We investigated the effects of specific nutrients (carbon, phosphorus, and nitrogen), as well as a top predator (the mosquito Wyeomyia smithii), on the structure of the detritivore community found in the water-filled leaves of the pitcher plant Sarracenia purpurea. The concentrations of three nutrients and the presence of the predators were manipulated in a factorial design, while the response of the remaining community was quantified. Bacterial growth was found to be strongly carbon-limited and somewhat less limited by phosphorus and there was an interaction between the effects of the two nutrients. Neither carbon or phosphorus addition affected protozoan or rotifer abundance, and nitrogen had only a minor effect. The presence of the predator, however, significantly reduced the abundance of the four numerically dominant bacteriovores. There were no interactions between top-down and bottom-up effects; the strong direct reciprocal effects between adjacent trophic levels seem to be greatly attenuated as they are propagated farther up or down the food chain.     

Importance of phytoplankton carbon to heterotrophic bacteria in the Ohio,Cumberland, and Tennessee rivers,USA

The flux of carbon and nutrients through aquatic systems is largely dependent upon interactions between autotrophic and heterotrophic processes. As a means of assessing the relative importance of autotrophy and heterotrophy in large rivers, we compared phytoplankton production, heterotrophic bacterial production and community respiration in three regulated rivers of the Midwestern USA. Samples were collected monthly (March to December 1999) from impoundments of the Ohio (McAlpine Pool), Cumberland (Lake Barkley), and Tennessee (Kentucky Lake) Rivers. Bacterial production was tightly coupled to phytoplankton production at each site (r ² = 0.63–0.85). Ratios of phytoplankton production to bacterial production ranged from <1 to 15 in the Tennessee and Cumberland Rivers and 2 to 90 in the Ohio River. The ratio of primary production to community respiration (P:R) ranged from 0.03 to 2.76 across all sites, with average P:R values lower in the Ohio River (0.14) than the Tennessee River (0.39) and the Cumberland River (1.10). P:R values above unity (P > R) were observed only in the Tennessee and Cumberland Rivers during seasonal (April–July) spikes in primary production. We estimate that 3, 6, and 20% of annual bacterial carbon requirements were met by exudates from in situ phytoplankton in the Ohio River, Tennessee River, and Cumberland River, respectively. Our findings indicate that heterotrophic bacteria were largely dependant upon allochthonous carbon. Autochthonous sources provided supplemental organic matter (up to 40% of bacterial carbon demand) during summer low flow. Handling editor: J. Padisak     

Seasonal variation of particulate organic carbon, dissolved organic carbon and the contribution of microbial communities to the live particulate organic carbon in a shallow near-bottom ecosystem at the Northwestern Mediterranean Sea

Microbial planktonic communities (i.e. bacteria and protozoa), phytoplankton, dissolved organic carbon (DOC) and particulate organic carbon (POC) were seasonally examined at Medes Islands (Northwestern Mediterranean) to assess their variation in abundance and composition throughout the year in a near-bottom littoral ecosystem. From October 1995 to November 1996, samples were collected between two and six times per month at 0.5 m above the bottom. Mean DOC and POC values throughout the year were 2560 180 (SE) and 387 ± 35 g C l^-1, respectively. All year, detrital organic carbon (detrital=total POC - live carbon) represented the main POC fraction, and mean live carbon was 24 ± 9 g C l^-1. Winter and spring had maximum values of POC, and spring and summer had maximum values of DOC. Heterotrophic bacteria, with a mean abundance of 5.16 ± 0.08 x 10⁵ cells ml^-1, were the main contributor to live carbon (26 ± 7%). During winter, heterotrophic bacterial biomass decreased 40% due to a decrease in mean biovolume per cell. Synechococcus sp. and Prochlorococcus sp. abundance were 2.24 ± 0.09 x 10⁴ and 1.05 ± 0.07 x 10⁴ cells ml^-1, respectively. However, while Synechococcus sp. were present all year, Prochlorococcus sp. were not observed from April to July. Mean phytoplankton (i.e. diatoms and dinoflagellates) abundance was 2.06 ± 0.40 x 10⁴ cells l^-1 with biomass at a maximum during the winter months, the period with the lowest temperature and the highest nutrient concentration. The size composition of live carbon showed two clearly distinct periods: from December to March, live carbon was dominated in biomass by microplankton, while from April to November, pico- and nanoplankton cells were dominant. Overall, the dynamics of the near-bottom planktonic communities was characterized by a low biomass of heterotrophic and autotrophic bacteria, phytoplankton and ciliates in contrast to previous water column studies. This pattern and the high temporal heterogeneity of the different planktonic communities are discussed in relation to the physical and chemical characteristics of the environment, as well as to the potential role that benthic communities may be exerting in the control of the near-bottom planktonic communities.      

不同树叶凋落物对人参土壤理化性质及微生物群落结构的影响

树种选择是林下山参护育成败的关键,研究树叶凋落物对人参土壤养分、微生物群落结构组成的影响,旨在为林下山参护育选择适宜林地及农田栽参土壤改良提供科学依据和理论指导。通过盆栽试验,研究添加5.0 g色木槭Acer mono.Maxim.var.mono(A)、赤松Pinus densiflora Sieb.et Zucc.(B)、胡桃楸Juglans mandshurica Maxim.(C)、紫椴Tilia amurensis Rupr.(D)、蒙古栎Quercus mongolica Fisch.ex Ledeb.(E)树叶凋落物到土壤中,种植人参(Panax ginseng C.A.meyer)后研究土壤理化性质以及微生物群落结构的变化。结果表明:添加不同树叶处理后人参土壤性质发生改变,土壤p H值显著高于对照土壤5.91(P0.05),土壤全氮、速效氮磷、微生物碳氮在所有树叶处理中显著增加(P0.05),而土壤容重、速效钾和C/N在添加树叶处理中降低。18个土壤样品基因组,经16S和ITS1测序分别得到6064和1900个OUTs。其中细菌涵盖了42门、117纲、170目、213科、225属,真菌涵盖了24门、98纲、196目、330科、435属。不同树叶处理人参土壤细菌和真菌地位发生改变,细菌Proteobacteria是树叶分解的关键微生物,添加树叶后其多样性显著高于对照(P0.05)。而细菌Bacteroidetes和真菌Basidiomycota可能是区别阔叶林和针叶林树种的关键微生物,针叶林中含量显著低于阔叶林(P0.05),而真菌Ascomycota是针叶林分解的关键微生物。进一步从不同分类水平上得到特定树叶凋落物的特异细菌和真菌。典型相关分析(CDA)表明细菌Bacteroidetes、Chloroflexi、Actinobacteria及真菌Basidiomycota、Zygomycota、Chytridiomycota及Ascomycota的位置及多样性的改变均与土壤因子SMBN、TN、AP、SOC、AK、C/N、p H有关。综上所述,添加不同树叶后不仅提高土壤微生物量碳氮、改善土壤理化性质,同时改变微生物群落结构组成,不同树叶处理土壤理化性质不同导致人参土壤微生物组成的差异,本结果对于林下参选地和农田栽参土壤微生物改良具有理论指导作用。     

Changes in Bacterioplankton Composition under Different Phytoplankton Regimens

The results of empirical studies have revealed links between phytoplankton and bacterioplankton, such as the frequent correlation between chlorophyll a and bulk bacterial abundance and production. Nevertheless, little is known about possible links at the level of specific taxonomic groups. To investigate this issue, seawater microcosm experiments were performed in the northwestern Mediterranean Sea. Turbulence was used as a noninvasive means to induce phytoplankton blooms dominated by different algae. Microcosms exposed to turbulence became dominated by diatoms, while small phytoflagellates gained importance under still conditions. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments showed that changes in phytoplankton community composition were followed by shifts in bacterioplankton community composition, both as changes in the presence or absence of distinct bacterial phylotypes and as differences in the relative abundance of ubiquitous phylotypes. Sequencing of DGGE bands showed that four Roseobacter phylotypes were present in all microcosms. The microcosms with a higher proportion of phytoflagellates were characterized by four phylotypes of the Bacteroidetes phylum: two affiliated with the family Cryomorphaceae and two with the family Flavobacteriaceae. Two other Flavobacteriaceae phylotypes were characteristic of the diatom-dominated microcosms, together with one Alphaproteobacteria phylotype (Roseobacter) and one Gammaproteobacteria phylotype (Methylophaga). Phylogenetic analyses of published Bacteroidetes 16S rRNA gene sequences confirmed that members of the Flavobacteriaceae are remarkably responsive to phytoplankton blooms, indicating these bacteria could be particularly important in the processing of organic matter during such events. Our data suggest that quantitative and qualitative differences in phytoplankton species composition may lead to pronounced differences in bacterioplankton species composition.     

Dominance of Endozoicomonas bacteria throughout coral bleaching and mortality suggests structural inflexibility of the Pocillopora verrucosa microbiome

The importance of Symbiodinium algal endosymbionts and a diverse suite of bacteria for coral holobiont health and functioning are widely acknowledged. Yet, we know surprisingly little about microbial community dynamics and the stability of host‐microbe associations under adverse environmental conditions. To gain insight into the stability of coral host‐microbe associations and holobiont structure, we assessed changes in the community structure of Symbiodinium and bacteria associated with the coral Pocillopora verrucosa under excess organic nutrient conditions. Pocillopora‐associated microbial communities were monitored over 14 days in two independent experiments. We assessed the effect of excess dissolved organic nitrogen (DON) and excess dissolved organic carbon (DOC). Exposure to excess nutrients rapidly affected coral health, resulting in two distinct stress phenotypes: coral bleaching under excess DOC and severe tissue sloughing (>90% tissue loss resulting in host mortality) under excess DON. These phenotypes were accompanied by structural changes in the Symbiodinium community. In contrast, the associated bacterial community remained remarkably stable and was dominated by two Endozoicomonas phylotypes, comprising on average 90% of 16S rRNA gene sequences. This dominance of Endozoicomonas even under conditions of coral bleaching and mortality suggests the bacterial community of P. verrucosa may be rather inflexible and thereby unable to respond or acclimatize to rapid changes in the environment, contrary to what was previously observed in other corals. In this light, our results suggest that coral holobionts might occupy structural landscapes ranging from a highly flexible to a rather inflexible composition with consequences for their ability to respond to environmental change.     

Characterization of the prokaryotic diversity through a stratigraphic permafrost core profile from the Qinghai-Tibet Plateau

Permafrost on the Qinghai-Tibet Plateau is one of the most sensitive regions to climate warming, thus characterizing its microbial diversity and community composition may be important for understanding their potential responses to climate changes. Here, we investigated the prokaryotic diversity in a 10-m-long permafrost core from the Qinghai-Tibet Plateau by restriction fragment length polymorphism analysis targeting the 16S rRNA gene. We detected 191 and 17 bacterial and archaeal phylotypes representing 14 and 2 distinct phyla, respectively. Proteobacteria was the dominant bacterial phylum, while archaeal communities were characterized by a preponderance of Thaumarchaeota. Some of prokaryotic phylotypes were closely related to characterized species involved in carbon and nitrogen cycles, including nitrogen fixation, methane oxidation and nitrification. However, the majority of the phylotypes were only distantly related to known taxa at order or species level, suggesting the potential of novel diversity. Additionally, both bacterial α diversity and community composition changed significantly with sampling depth, where these communities mainly distributed according to core horizons. Arthrobacter-related phylotypes presented at high relative abundance in two active layer soils, while the deeper permafrost soils were dominated by Psychrobacter-related clones. Changes in bacterial community composition were correlated with most measured soil variables, such as carbon and nitrogen contents, pH, and conductivity.     

Molecular Characterization of the Total Bacteria and Dissimilatory Arsenate-Reducing Bacteria in Core Sediments of the Jianghan Plain,Central China

Arsenic contamination in groundwater has been reported in the Jianghan Plain of China since 2005, yet little is known about the microbial communities involved in As mobilization in this area, especially the dissimilatory arsenate-reducing bacteria (DARB) communities. Here, we conducted a cultivation-independent investigation on core sediments collected from a region with arsenic-contaminated groundwater in the Jianghan Plain to reveal the total bacteria and DARB community structures. Highly diverse As-resistant bacteria communities were found from sediment samples via high-throughput sequencing of 16S rRNA genes. Notably, we identified 27 unique arrA gene (encoding the alpha subunit of dissimilatory arsenate reductase) phylotypes, none of which was related to any previously described arrA gene sequence. This suggests a novel and unique DARB community in the sediments of the Jianghan Plain and expands our knowledge about the distribution and diversity of this group of bacteria in natural environments. Moreover, RDA and CCA demonstrated that total bacterial communities and specific functional groups are controlled by different environmental factors. Specifically, sediment pH, NH₄⁺, total nitrogen, total Fe, total organic carbon and total phosphorus were the key factors driving total bacterial community compositions, while As significantly shaped DARB community structures. This report is the first to describe DARB communities and their correlation with environmental factors in Jianghan Plain sediments, which could give us clues about the origin of the arsenic contamination of groundwater in this region.     

再生水补水对河道底泥细菌群落结构的影响

以北京市永定河麻峪湿地再生水补水口附近河道底泥为研究对象,应用末端限制性片段长度多态性(Terminal Restriction Fragment Length Polymorphism,T-RFLP)技术探究再生水补水口附近底泥细菌群落结构的空间差异特征以及环境因子所产生的影响,并借助典范对应分析(Canonical Correspondence Analysis,CCA)方法分析麻峪湿地底泥细菌群落结构空间差异特征的形成原因。分析结果表明:河道底泥微生物群落对再生水的净化主要发生在距补水口1200m的范围内,随着再生水与上游来水径向混合净化渐变过程,在补水口2000m处河道底泥微生物群落结构与河道再生水补水口上游趋于相似。基于样点聚类结果的群落结构多样性分析表明随着再生水净化过程的实现微生物综合多样性指数呈现下降的趋势,从均匀度指数的变化趋势看,再生水补水口具有最高均匀度指数,补水口下游1200米处由于非优势菌群所占相对丰度最低以及偶见菌群缺失,导致群落结构比较单一、群落多样性和均匀度指数都最低。CCA方面分析结果表明再生水补水口上游细菌群落与因累积效应形成的重金属有密切关系,补水口出口底泥细菌群落则主要受到总磷和总有机碳的影响较大,而再生水补水与上游来水汇水径向渐变过程可能与氨氮净化具密切关系。研究区的主要优势菌种为假单胞菌属、贪食菌属和芽孢杆菌属,是与再生水中有机碳、氮降解具有密切关系的菌属。