Bacterial community composition in an Arctic phytoplankton mesocosm bloom: the impact of silicate and glucose

In order to study interactions between microorganisms at different nutrient conditions in an arctic environment, a mesocosm experiment was performed in Kongsfjorden, Svalbard (79°N). A phytoplankton bloom was initiated by daily additions of mineral nutrients (ammonium and phosphate) to all mesocosm units. The addition of silicate and glucose, forming a factorial design (+Si/+C, +Si/−C, −Si/+C, −Si/−C), was intended to produce different types of growth rate limitation for the bacterial community. We here focus on the response in bacterial community composition to different nutrient situations. Phytoplankton, bacteria and viruses were enumerated by flow cytometry, while denaturing gradient gel electrophoresis (DGGE) was used to track changes in the bacterial community composition. Our results showed that both glucose and silicate addition affected the bacterial community composition, with the largest effect from glucose. The initial increase in bacterial abundance was most pronounced in the glucose units. After silicate addition, highest bacterial abundance was observed in the silicate treatments where mineral nutrient competition by diatoms was expected to be highest. The major effect of glucose was expressed by the significant separation of the +C and the −C samples at the end of the experiment, while silicate addition resulted in a more stable bacterial community structure. In the unit, given both silicate and glucose, the diatoms were totally outcompeted by the bacterial community. The competitive success of the heterotrophic bacteria in C-replete situations allows the conclusion that the bacteria were not more negatively affected by low temperatures than phytoplankton.     

Bacterial community composition of a wastewater treatment system reliant on N2 fixation

The temporal stability and change of the dominant phylogenetic groups of the domain bacteria were studied in a model plant-based industrial wastewater treatment system showing high levels of organic carbon removal supported by high levels of N₂ fixation. Community profiles were obtained through terminal restriction fragment length polymorphism analysis and cloning of 16S rRNA amplicons followed by sequencing. Bacterial community profiles showed that ten common terminal restriction fragments made up approximately 50% of the measured bacterial community. As much as 42% of the measured bacterial community could be monitored by using quantitative PCR and primers that targeted three dominant operational taxonomic units. Despite changes in wastewater composition and dissolved oxygen levels, the bacterial community composition appeared stable and was dominated by α-Proteobacteria and β-Proteobacteria, with a lesser amount of the highly diverse bacterial phylum Bacteroidetes. A short period of considerable change in the bacterial community composition did not appear to affect treatment performance indicating functional redundancy in this treatment system.     

Relative contribution of bacterial and photosynthetic production to metazooplankton as carbon sources

Percentages of label transfer (PLT) from bacteria and autotrophsto metazooplankton during 4 h were determined in parallel usingdissolved organic and inorganic¹³C tracers, respectively, inin situ batch incubations, to estimate the relative contributionof each production to the metazooplankton food requirement.The batch incubation for each pathway was done eight times,respectively, during 20 days in a mesocosm where continuousspecies succession of organisms was observed. The PLT in thetwo pathways, dependent on metazooplankton abundance and speciescomposition rather than changes in the activities of producers(bacteria or autotrophs), showed a similar tendency of changeand were of a similar magnitude: mean 1.0% (0.09–2.7%)in the photosynthetic pathway and 0.5% (0.22–1.5%) inthe bacterial pathway. This finding suggests that metazooplanktonare supported by entire microbial food webs including both thebacterial and photosynthetic pathways.     

水稻种子的细菌含量和群落结构及其影响因素分析

【目的】种子是植物微生物群代际传递的重要途径，但种子携带的微生物群落尚缺乏系统的研究。本研究以水稻种子为模型，定量分析种子的细菌含量、测定种子的细菌群落结构、探究地域与品种对细菌含量及群落结构的影响和鉴定水稻种子的核心菌群。【方法】选取18个水稻品种，每个品种分别来自中国海南和天津2个地域，共36组样本。每组样本包含5或10个DNA样本，每个DNA样本由3粒种子提取的总DNA构成。使用细菌特异性16S rDNA介导的荧光定量PCR技术测定种子的细菌含量，并分析影响因素；使用16S rDNA扩增子测序技术测定种子的细菌群落结构，并用生物信息学方法分析了影响因素和核心菌群。【结果】本研究测定了1 080粒水稻种子的细菌含量，发现经过表面除菌的水稻种子内部存在共栖细菌，平均每克种子的细菌含量为1.53×10⁶。水稻品种对种子的细菌含量有显著影响，而地域无影响。测定180个扩增子文库的细菌群落结构，发现水稻种子的菌群与水稻植株有相似之处，均以变形菌门为主要的细菌门类；地域对水稻种子的细菌群落结构有重要影响，不同地域的水稻种子在主坐标分析(principal co-ordinate analysis, PCoA)中有明显分离；而粳稻和籼稻之间无显著差异。还发现水稻种子存在核心菌群，且相对丰度高达总菌群的85.56%。【结论】本研究系统地揭示了水稻种子的细菌含量、群落结构及其影响因素，为利用种传微生物促进水稻健康提供了数据和方法支持。     

Structure and grazing impact of the mesozooplankton community during late summer 1994 near South Georgia, Antarctica

Mesozooplankton abundance, community structure and grazing impact were determined during late austral summer (February/March) 1994 at eight oceanic stations near South Georgia using samples collected with a Bongo and WP-2 nets in the upper 200-m and 100-m layer, respectively. The zooplankton abundance was generally dominated by copepodite stages C3–C5 of six copepod species: Rhincalanus gigas, Calanus simillimus, Calanoides acutus, Metridia spp., Clausocalanus laticeps and Ctenocalanus vanus. Most copepods had large lipid sacs. All copepods accounted for 41–98% of total zooplankton abundance. Juvenile euphausiids were the second most important component contributing between 1 and 20% of total abundance. Pteropods, mainly Limacina inflata, were important members of the pelagic community at two sites, accounting for 44 and 53% of total abundance. Average mesozooplankton biomass in the upper 200 m was 8.0 g dry weight m⁻², ranging from 4.3 to 11.5 g dry weight m⁻². With the exception of Calanussimillimus, gut pigment contents and feeding activity of copepod species were low, suggesting that some species, after having stored large lipid reserves, had probably started undergoing developmental arrest. Daily mesozooplankton grazing impact, measured using in situ gut fluorescence techniques and in vitro incubations, varied widely from <1 to 8% (mean 3.5%) of phytoplankton standing stock, and from 5 to 102% (mean 36%) of primary production. The highest grazing impact was found northeast of the island co-incident with the lowest phytoplankton biomass and primary production levels. Received: 30 October 1996 / Accepted: 23 February 1997     

Altering the balance between bacterial production and protistan bacterivory triggers shifts in freshwater bacterial community composition

Bacterivorous protists are known to induce changes in bacterial community composition (BCC). We hypothesized that changes in BCC could be related quantitatively to a measure of grazing: the ratio of bacterial mortality to growth rate. To test this hypothesis, we analyzed time-course changes in BCC, protistan grazing rate, and bacterial production from 3 in situ studies conducted in a freshwater reservoir and three laboratory studies. In the field experiments, samples were manipulated to yield different levels of protistan bacterivory and incubated in dialysis bags. Laboratory investigations were continuous cultivation studies in which different bacterivorous protists were added to bacterial communities. BCC was assessed using 4–6 different rRNA-targeted oligonucleotide probes for community analysis. Change in BCC (Δ BCC) was estimated as the sum of changes in the proportions of the two phylogenetic groups that showed the largest shifts. Analysis of a set of 22 estimates of shifts in the ratio of grazing to production rate over periods of 48–72 h and Δ BCC showed that Δ BCC was positively and tightly correlated (r ² = 0.784) with shifts in the ratio of grazing mortality to cell production. While the nature of a shift in BCC is unpredictable, the magnitude of the change can be related to changes in the balance between bacterial production and protistan grazing. This revised version was published online in August 2006 with corrections to the Cover Date.     

稻草还田对水稻土固氮基因(nifH)组成结构和多样性的影响

以中国科学院桃源农业生态试验站长期定位施肥试验为平台,选取稻草还田(C)、氮磷钾(NPK)、氮磷钾加稻草还田(NPK+C)和不施肥对照(CK)4个处理,在晚稻的分蘖期、孕穗期和成熟期分别采集土样,利用实时定量PCR(Q-PCR)和末端限制性片段多态性(T-RFLP)等分子生物学方法研究长期稻草还田对水稻土含nifH基因固氮微生物群落丰度、组成和多样性的影响.结果表明：与对照相比,稻草还田和单施化肥处理均显著增加nifH基因的丰度(分蘖期除外),NPK+C处理中含nifH基因的微生物数量最高;nifH基因组成也受到长期施肥的影响,其中CK处理nifH基因组成与各施肥处理明显不同,C与NPK处理间nifH基因组成存在一定差异,而NPK与NPK+C处理间无显著差异.长期施肥不会引起含nifH基因微生物群落多样性的显著改变.可见,稻草还田不仅引起nifH基因群落的组成发生变化,而且导致其数量显著增加,因而可增加土壤的固氮能力.     

Effects of ocean acidification on microbial community composition of, and oxygen fluxes through, biofilms from the Great Barrier Reef

Rising anthropogenic CO(2) emissions acidify the oceans, and cause changes to seawater carbon chemistry. Bacterial biofilm communities reflect environmental disturbances and may rapidly respond to ocean acidification. This study investigates community composition and activity responses to experimental ocean acidification in biofilms from the Australian Great Barrier Reef. Natural biofilms grown on glass slides were exposed for 11 d to four controlled pCO(2) concentrations representing the following scenarios: A) pre-industrial (～300 ppm), B) present-day (～400 ppm), C) mid century (～560 ppm) and D) late century (～1140 ppm). Terminal restriction fragment length polymorphism and clone library analyses of 16S rRNA genes revealed CO(2) -correlated bacterial community shifts between treatments A, B and D. Observed bacterial community shifts were driven by decreases in the relative abundance of Alphaproteobacteria and increases of Flavobacteriales (Bacteroidetes) at increased CO(2) concentrations, indicating pH sensitivity of specific bacterial groups. Elevated pCO(2) (C + D) shifted biofilm algal communities and significantly increased C and N contents, yet O(2) fluxes, measured using in light and dark incubations, remained unchanged. Our findings suggest that bacterial biofilm communities rapidly adapt and reorganize in response to high pCO(2) to maintain activity such as oxygen production.     

Dynamics of a benthic microbial community in a riverine environment subject to hydrological fluctuations (Mulargia River,Italy)

Temporary rivers are characterized by recurrent dry phases, and global warming will stress their hydrology by amplifying extreme events. Microbial degradation and transformation of organic matter (OM) in riverbed sediment are key processes with regard to carbon and nutrient fluxes. In this study, we describe structural and functional changes of benthic microbial communities in a riverine environment subject to hydrological fluctuation. Sampling was carried out in the outlet section of the Mulargia River (Sardinia, Italy) under various water regimes, including one flood event. Overall, sediments were characterized by low bacterial cell abundance (range 0.6–1.8 × 10⁹ cell g⁻¹) as a consequence of their low nutrient and OM concentrations. No major differences were found in the community composition. Alpha-Proteobacteria dominated during the whole year (range 21–30%) followed by Beta-Proteobacteria, Gamma-Proteobacteria, and Cytophaga-Flavobacteria which always contributed <18%. Planctomycetes and Firmicutes were found in smaller amounts (<7%). In spring, when the highest total organic carbon content was also detected (0.42% w/w), both bacterial abundance and C production (BCP, 170 nmol C h⁻¹ g⁻¹) reached relatively high values. During the flood event, an increase in BCP and the highest values of community respiration (CR, 74 nmol C h⁻¹ g⁻¹) were observed. Moreover, most of the extracellular enzyme activities (EEA) changed significantly during the flood. The variation of the water flow itself can explain part of these changes and other factors also come into play. The presence of different patterns of functional parameters could suggest that the quality of the OM could be the major driving force in nutrient flux.     

Microbial community structure in anaerobic co-digestion of grass silage and cow manure in a laboratory continuously stirred tank reactor

The impacts of feeding ratio and loading rate on the microbial community during co-digestion of grass silage with cow manure in an anaerobic laboratory continuously stirred tank reactor were investigated by 16S rRNA gene-based fingerprints. The microbial community remained stable when the reactor was fed with cow manure alone and with up to 20% of grass silage in feedstock at an organic loading rate (OLR) of 2 kg VS m⁻³ day⁻¹. Large changes in the bacterial community were observed when the loading ratio of grass was increased to 40%, while there was little change in the archaeal community. During the increase in OLR from 2 to 4 kg VS m⁻³ day⁻¹ the bacterial community structure showed few differences, whereas Archaea was undetectable. Sequencing of the major DGGE bands indicated that the phylum Bacteriodetes predominated in the bacterial community. Two unclassified bacteria with high abundance survived throughout the operation of the reactor.     

Responses of Baltic Sea Ice and Open-Water Natural Bacterial Communities to Salinity Change

To investigate the responses of Baltic Sea wintertime bacterial communities to changing salinity (5 to 26 practical salinity units), an experimental study was conducted. Bacterial communities of Baltic seawater and sea ice from a coastal site in southwest Finland were used in two batch culture experiments run for 17 or 18 days at 0°C. Bacterial abundance, cell volume, and leucine and thymidine incorporation were measured during the experiments. The bacterial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified partial 16S rRNA genes with sequencing of DGGE bands from initial communities and communities of day 10 or 13 of the experiment. The sea ice-derived bacterial community was metabolically more active than the open-water community at the start of the experiment. Ice-derived bacterial communities were able to adapt to salinity change with smaller effects on physiology and community structure, whereas in the open-water bacterial communities, the bacterial cell volume evolution, bacterial abundance, and community structure responses indicated the presence of salinity stress. The closest relatives for all eight partial 16S rRNA gene sequences obtained were either organisms found in polar sea ice and other cold habitats or those found in summertime Baltic seawater. All sequences except one were associated with the α- and γ-proteobacteria or the Cytophaga-Flavobacterium-Bacteroides group. The overall physiological and community structure responses were parallel in ice-derived and open-water bacterial assemblages, which points to a linkage between community structure and physiology. These results support previous assumptions of the role of salinity fluctuation as a major selective factor shaping the sea ice bacterial community structure.     

机场草坪植被调控对土壤细菌群落结构与功能的影响

为了探究植被调控对土壤细菌群落结构和功能的影响,对天津滨海国际机场草地植被进行单一草坪植物建植和高强度刈割,在调控后第3年的春、夏、秋季节取调控区土壤样本,利用16S rRNA基因高通量测序和PICRUSt软件,分析了不同植被调控方式下土壤细菌组成、多样性及季节性变化,预测细菌功能特征。结果表明,各样地共有的优势菌门（相对丰度>5%）有变形菌门（Proteobacteria）、放线菌门（Actinobacteria）、酸杆菌门（Acidobacteria）、芽单胞菌门（Gemmatimonadetes）和绿弯菌门（Chloroflexi）。与对照区相比,刈割调控区土壤放线菌门相对丰度显著增加;单一草坪建植调控区,夏季土壤芽单胞菌门相对丰度显著增加（P<0.05）。刈割调控、高羊茅及黑麦草调控区,土壤细菌门之间相关性较对照分别减弱21.4%、46.4%和67.9%,使细菌网络结构更为简单。夏季和秋季3个调控区土壤细菌群落的Shannon指数和Chao1指数显著高于对照区,而秋季Simpson指数显著低于对照区（P<0.05）。KEGG代谢途径差异分析可知,刈割调控、高羊茅和黑麦草调控区,土壤细菌分别有25、24和23个代谢通路的功能基因丰度显著低于对照区,主要体现在聚糖的生物合成与代谢、细胞运动、细胞生长与死亡、核苷酸代谢等通路上。可见,机场植被调控改变了土壤细菌群落的组成,简化了细菌网络结构,代谢功能也明显下降。     

Marine bacterial community structure resilience to changes in protist predation under phytoplankton bloom conditions

To test whether protist grazing selectively affects the composition of aquatic bacterial communities, we combined high-throughput sequencing to determine bacterial community composition with analyses of grazing rates, protist and bacterial abundances and bacterial cell sizes and physiological states in a mesocosm experiment in which nutrients were added to stimulate a phytoplankton bloom. A large variability was observed in the abundances of bacteria (from 0.7 to 2.4 × 10⁶ cells per ml), heterotrophic nanoflagellates (from 0.063 to 2.7 × 10⁴ cells per ml) and ciliates (from 100 to 3000 cells per l) during the experiment (∼3-, 45- and 30-fold, respectively), as well as in bulk grazing rates (from 1 to 13 × 10⁶ bacteria per ml per day) and bacterial production (from 3 to 379 μg per C l per day) (1 and 2 orders of magnitude, respectively). However, these strong changes in predation pressure did not induce comparable responses in bacterial community composition, indicating that bacterial community structure was resilient to changes in protist predation pressure. Overall, our results indicate that peaks in protist predation (at least those associated with phytoplankton blooms) do not necessarily trigger substantial changes in the composition of coastal marine bacterioplankton communities.     

Small-scale spatial heterogeneity of arbuscular mycorrhizal fungal abundance and community composition in a wetland plant community

Although it has become increasingly clear that arbuscular mycorrhizal fungi (AMF) play important roles in population, community, and ecosystem ecology, there is limited information on the spatial structure of the community composition of AMF in the field. We assessed small-scale spatial variation in the abundance and molecular diversity of AMF in a calcareous fen, where strong underlying environmental gradients such as depth to water table may influence AMF. Throughout an intensively sampled 2 × 2 m plot, we assessed AMF inoculum potential at a depth of 0–6 and 6–12 cm and molecular diversity of the AMF community using terminal restriction fragment length polymorphism of 18S rDNA. Inoculum potential was only significantly spatially autocorrelated at a depth of 6–12 cm and was significantly positively correlated with depth to water table at both depths. Molecular diversity of the AMF community was highly variable within the plot, ranging from 2–14 terminal restriction fragments (T-RFs) per core, but the number of T-RFs did not relate to water table or plant species richness. Plant community composition was spatially autocorrelated at small scales, but AMF community composition showed no significant spatial autocorrelation. Saturated soils of calcareous fens contain many infective AMF propagules and the abundance and diversity of AMF inoculum is patchy over small spatial scales. An erratum to this article can be found at     

大亚湾浮游植物群落特征

于2002年冬、春、夏和秋季对大亚湾浮游植物进行采样调查,分析了浮游植物的种类组成、丰度、优势种、多样性及群落结构的季节变化特征和平面分布特征。并讨论了浮游植物与营养盐、水温及环流等环境因子之间的关系。2002年大亚湾浮游植物共鉴定出48属114种(包括变型和变种),丰度范围在5.79×104~5.37×106cells/m3之间,平均值为1.14×106cells/m3。其中硅藻共37属84种,其种数和细胞丰度都占绝对优势,平均丰度为1.08×106cells/m3,其次为甲藻,9属23种,平均丰度为9.91×104cells/m3。此外还鉴定出蓝藻和金藻。大亚湾浮游植物丰度变化呈单一周期型,春夏季高,秋冬季节低。虽然硅藻的丰度占优势,但秋季硅藻丰度降低(占总丰度75.8%)使甲藻和蓝藻所占比例上升。研究得出春夏季大亚湾浮游植物主要以沿岸暖水性种类为主,秋季和冬季除沿岸暖水种之外,广布种和大洋种也较多,尤其在冬季后者占优势。大亚湾浮游植物优势种类多,不同季节既有交叉又有演替。与以往调查资料相比,部分优势种发生变化,优势程度顺序和细胞丰度发生了一定改变,个体较大的细胞丰度优势逐渐增加。另外,受季风、潮流、地理位置及人类活动影响,大亚湾浮游植物丰度和群落结构有一定的季节和平面分布特征。大亚湾浮游植物的多样性在夏季偏低,尤其在大亚湾核电站和大鹏澳养殖区附近表现明显。大亚湾浮游植物的丰度、种数、优势种演替及群落结构等其它群落特征与营养盐尤其是氮、磷和N/P、水温、环流等环境因子密切相关。     

Short-term variations in the abundance and cell volume of bacterioplankton in an artificial tropical lake

Circadian and spatial fluctuations in bacterioplankton abundance and cell volume were examined, for the first time, in the Municipal Lake located in the down town area of Yaoundé (Capital of Cameroon, Central Africa, ca 3° 52′ N, 11° 31′ E). Bacterial cell volumes (range, 0.05 to 0.2 μm3) were consistent with those reported for other aquatic systems while bacterial densities (0.8 to 2 × 108 cells ml-1) were among the highest values reported in pelagic systems. These variables and chlorophyll a and dissolved oxygen concentrations within a single depth-zone varied from 13 to 61%, while water temperature fluctuated only from 2 to 6%. Spatial fluctuations of physical-chemical and biological variables were generally higher during the day-time than during the night-time. A significant diel variation was provided for bacterial cell volume in the surface waters where synchronized cell division was occurring during the night. The measured bacterial abundances in this study were 4 to 17 fold higher than values known from other lakes of similar trophic status, and both cell abundance and volume were not correlated with chlorophyll. We conclude that this was due to the dependence of bacterial populations to different sources of allochthonous substrates, including untreated sewage from the major influents of the lake, resuspension of benthic material, and substrate releasing from macrophytes which are prevalent in the littoral zone of the lake. This revised version was published online in September 2006 with corrections to the Cover Date.     

Secondary productivity (3H-Leucine and 3H-Thymidine incorporation), abundance and biomass of the epiphytic bacteria attached to detritus of Typha domingensis pers. in a tropical coastal lagoon

Senescent, naturally dried leaves of Typha domingensis were incubated inthe littoral region of a coastal lagoon and epiphytic bacterial volume,abundance, biomass and secondary productivity were measured during 127 daysof decomposition. The peak of cell abundance was registered at t =127 days when expressed per leaf surface area (10.07×10⁷cells cm^-2; 7.26 µgC cm^-2), and at t= 26 days when expressed per biofilm dry mass (38.10 ×10⁷ cells (mgDM biofilm)^-1, 30.52 µgC(mgDM biofilm)^-1). The highest values of bacterial biovolumesand lower turnover time were usually obtained in the beginning of thecolonization. Leu:Tdr ratios were also higher in the beginning of thecolonization, when bacterial community presented unbalanced metabolism.Consequently, the highest discrepancies between the bacterial secondaryproduction estimated by leu and Tdr incorporation were observed in the first2 days of decomposition. On average, the bacterial secondary productivityestimated by leu incorporation was 2.1 times higher than the valuesestimated by Tdr incorporation when the empirical factor for Tdr wasobtained from the relationship between Tdr and biomass increment. Thisdifference increased to 4.2 when the empirical factor was obtained from therelationship between Tdr and cell numbers increment. An average of bothmethods (0.0037 to 0.1397 µgC cm^-2 h^-1)produced results that fall within the range reported in the literature forepiphytic bacteria of freshwater ecosystems.     

Pelagic community respiration on the continental shelf off Georgia, USA

The South Atlantic Bight (SAB) has been a focus for the study of continental shelf ecosystem respiration during the past two decades. However, two questions concerning respiration in this area have yet to be answered. First, why do previous estimates of respiration in the SAB exceed measured carbon fixation rates by almost an order of magnitude? Second, considering that bacteria are responsible for most of the pelagic community respiration in the SAB, why is respiration almost uniform from the coastline to the shelf break, while bacterial production estimates decrease offshore? This study addresses these critical questions by presenting new pelagic community respiration data that were collected across the entire width of the continental shelf off Georgia, USA from June 2003 to May 2006. The respiration was calculated as in vitro changes of dissolved oxygen and dissolved inorganic carbon concentrations during deck incubations. The measured respiration rates ranged from 0.3(±0.1) to 21.2(±1.4) mmol m^?3 day^?1. They followed a clear seasonal pattern, being lowest over the entire shelf in winter and reaching maxima in summer. Summertime respiration rates were highest on the inner shelf and decreased with distance offshore. Consistent with this trend, bacterial abundance measurements taken during the sampling month of July 2005 followed a pattern of seaward decline. The SAB organic carbon fluxes calculated from the respiration data are close to the estimates for primary production, which resolves a long-standing mystery regarding perceived carbon imbalance in the SAB.     

High-grain diets altered rumen fermentation and epithelial bacterial community and resulted in rumen epithelial injuries of goats

This study evaluated the effects of high-grain diets on the rumen fermentation, epithelial bacterial community, morphology of rumen epithelium, and local inflammation of goats during high-grain feeding. Twelve 8-month-old goats were randomly assigned to two different diets, a hay diet or a high-grain diet (65% grain, HG). At the end of 7 weeks of treatment, samples of rumen content and rumen epithelium were collected. Rumen pH was lower (P < 0.05), but the levels of volatile fatty acids and lipopolysaccharides were higher (P < 0.05) in the HG group than those in the hay group. The principal coordinate analysis indicated that HG diets altered the rumen epithelial bacterial community, with an increase in the proportion of genus Prevotella and a decrease in the relative abundance of the genera Shuttleworthia and Fibrobacteres. PICRUSt analysis suggested that the HG-fed group had a higher (P < 0.05) relative abundance of gene families related to energy metabolism; folding, sorting, and degradation; translation; metabolic diseases; and immune system. Furthermore, HG feeding resulted in the rumen epithelial injury and upregulated (P < 0.05) the gene expressions of IL-1β and IL-6, and the upregulations were closely related to the rumen pH, LPS level, and rumen epithelial bacteria abundance. In conclusion, our results indicated that the alterations in the rumen environment and epithelial bacterial community which were induced by HG feeding may result in the damage and local inflammation in the rumen epithelium, warranting further study of rumen microbial–host interactions in the HG feeding model.     

The impact of temperature change on the activity and community composition of sulfate-reducing bacteria in arctic versus temperate marine sediments

Arctic regions may be particularly sensitive to climate warming and, consequently, rates of carbon mineralization in warming marine sediment may also be affected. Using long-term (24 months) incubation experiments at 0°C, 10°C and 20°C, the temperature response of metabolic activity and community composition of sulfate-reducing bacteria were studied in the permanently cold sediment of north-western Svalbard (Arctic Ocean) and compared with a temperate habitat with seasonally varying temperature (German Bight, North Sea). Short-term ³⁵S-sulfate tracer incubations in a temperature-gradient block (between −3.5°C and +40°C) were used to assess variations in sulfate reduction rates during the course of the experiment. Warming of arctic sediment resulted in a gradual increase of the temperature optima ( T _opt) for sulfate reduction suggesting a positive selection of psychrotolerant/mesophilic sulfate-reducing bacteria (SRB). However, high rates at in situ temperatures compared with maximum rates showed the predominance of psychrophilic SRB even at high incubation temperatures. Changing apparent activation energies ( E _a) showed that increasing temperatures had an initial negative impact on sulfate reduction that was weaker after prolonged incubations, which could imply an acclimatization response rather than a selection process of the SRB community. The microbial community composition was analysed by targeting the 16S ribosomal RNA using catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH). The results showed the decline of specific groups of SRB and confirmed a strong impact of increasing temperatures on the microbial community composition of arctic sediment. Conversely, in seasonally changing sediment sulfate reduction rates and sulfate-reducing bacterial abundance changed little in response to changing temperature.