Response Of Microbial Community Structure Research Articles

Interactive effects of soil warming, throughfall reduction, and root exclusion on soil microbial community and residues in warm-temperate oak forests

Soil microbes are both drivers and contributors of soil organic C (SOC) dynamics. However, information on how the multiple co-occurring environmental changes affecting microbial community and residues is unclear. Here, we measured phospholipid fatty acids and amino sugars (ASs) to explore how soil microbial community and residues changed under soil warming, throughfall reduction, root exclusion and their interactions in a natural deciduous broad-leaved oak forest. Soil warming significantly increased the Gram-positive to Gram-negative bacteria (G+/G−) ratio, and its interaction with root exclusion significantly reduced fungi-to-bacteria (F/B) ratio but stimulated the contributions of ASs to SOC (AS/SOC). Throughfall reduction also marginally increased G+/G− and AS/SOC, and suppressed F/B ratio. However, no interactive effects of soil warming and throughfall reduction on soil microbial community and residues were observed. Light fraction organic C and inorganic nitrogen were the key drivers in regulating the variation in the microbial community structure, and SOC was the controlling factor of microbial residue accumulations. Hence, soil C quality instead of water dominates the responses of microbial community structure and residues contribution to SOC to soil warming. Our results highlight the importance of soil substrate quality when predicting the terrestrial climate-C feedback.

Responses of microbial community structure in turbot (Scophthalmus maximus) larval intestine to the regulation of probiotic introduced through live feed.

Various bacteria that adhere to the gut are important for the health of fish. Regulating the microbial community in a desirable direction may be beneficial in aquaculture for preventing and controlling the diseases caused by pathogenic microbes. In this study, we investigated the changes in the microflora in the intestinal tracts of turbot (Scophthalmus maximus) larvae after introducing a probiotic (Bacillus amyloliquefaciens) after the first feed. B. amyloliquefaciens was added as part of a nutrient enrichment system in live feed (Branchionus plicatilis or Artemia sinica), so it passed into the intestinal tracts of the newly hatched turbot larvae. The turbot larvae were fed on live feed containing B. amyloliquefaciens in the experimental group, whereas live feed without the probiotic was provided to larvae in the control group. The total bacterial genomic DNA in the larval guts was extracted and sequenced with an Illumina HiSeq PE250 system. According to the sequencing results, the abundances of microbial species and the microflora diversity were lower in the intestines in the experimental group than the control. Throughout development, the microflora structure in the intestines was mainly constructed before the first feed and the composition of the dominant operational taxonomic units (OTUs) was stable, where the abundances of OTU8, OTU124, OTU150, OTU107, and OTU17 were always high. Compared with the control, the structures of the microflora in the intestines were similar on different days during the development and the growth of larvae in the experimental group. However, the similarity of the microflora structure between different treatments was low on the same day. Furthermore, the mean proportion of common OTUs was only 74.7% in different treatments on each day, which indicates that the introduction of B. amyloliquefaciens in the live feed changed the microflora structure in the intestine. During the early development stage (days 3–30), the average abundance of Pseudomonas was reduced by 0.8% whereas that of Lactococcus increased by 3.5% in the experimental group. Pseudomonas spp. are considered potentially pathogenic bacteria but there is no direct evidence for the pathogenicity of Lactococcus in turbot. Moreover, several Lactococcus species are regarded as probiotics in aquaculture. Therefore, the use of B. amyloliquefaciens could be beneficial for optimizing the microbial community structure in the intestines of turbot larvae, which may explain the probiotic effect of B. amyloliquefaciens. This study provides a theoretical basis for the biological regulation of the microflora structure in the intestinal tract during turbot breeding.

Chelator-assisted phytoextraction of arsenic, cadmium and lead by Pteris vittata L. and soil microbial community structure response

Using biodegradable chelators to assist in phytoextraction may be an effective approach to enhance the heavy-metal remediation efficiencies of plants. A pot experiment was conducted to investigate the effects of ethylenediamine disuccinic acid (EDDS), citric acid (CA), and oxalic acid (OA) on the growth of the arsenic (As) hyperaccumulator Pteris vittata L., its arsenic (As), cadmium (Cd), and lead (Pb) uptake and accumulation, and soil microbial responses in multi-metal(loid)-contaminated soil. The addition of 2.5-mmol kg−1 OA (OA-2.5) produced 26.7 and 14.9% more rhizoid and shoot biomass, respectively compared with the control, while EDDS and CA treatments significantly inhibited plant growth. The As accumulation in plants after the OA-2.5 treatment increased by 44.2% and the Cd and Pb accumulation in plants after a 1-mmol kg−1 EDDS treatment increased by 24.5 and 19.6%, respectively. Soil urease enzyme activities in OA-2.5 treatment were significantly greater than those in the control and other chelator treatments (p < 0.05). A PCR–denatured gradient gel electrophoresis analysis revealed that with the addition of EDDS, CA and OA enhanced soil microbial diversity. It was concluded that the addition of OA-2.5 was suitable for facilitating phytoremediation of soil As and did not have negative effects on the microbial community.

Response of microbial community structure to the hydrochemical evolution during riverbank filtration: a case study in Shenyang, China

Microorganisms are widely involved in the transformation process of physical and chemical properties in the geological and hydrogeological environment. Active participation of microorganisms is important features of the biogeochemical reactions during groundwater exploiting along the riverbank filtration. Hydrodynamic condition has a direct or indirect difference control of the biological effectiveness, chemical activity and mobility of the pollution components, which can affect biogeochemical process. In different biogeochemistry, there will be some exclusive functional bacteria, which is of great significance to understand the biogeochemical mechanism of river water infiltration. This study confirms that there are two main different flow paths from river to the center of the depression cone due to different hydrodynamic conditions and spatial characteristics and scaling effects of redox zonation during riverbank filtration. In different flow paths, the microbial abundance shows obvious spatial heterogeneity. The microbial abundance and species similarity degree of the riverbed and deep flow path sediments has significant correlation. There is a significant correlation between the dominant bacteria and the environmental factors in different hydrodynamic conditions on a spatial scale. This study is the first to reveal the response of microbial community structure to water chemical evolution during riparian filtration. Due to significant positive correlation between the Fe/Mn and As, it brings the potential danger for drinking water.

Mixed-surfactant-enhanced phytoremediation of PAHs in soil: Bioavailability of PAHs and responses of microbial community structure

The present study was conducted to explore the mechanisms of surfactant-enhanced phytoremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs), focusing on the bioavailability of PAHs and microbial diversity. We investigated the remediation efficiencies of phenanthrene and pyrene after the addition of mixed surfactants (sodium dodecyl benzene sulfonate (SDBS) and Tween 80) of different ratios (1:1, 1:2, and 2:1) at the concentration of 100 mg/kg to soils cultured with ryegrass (Lolium multiflorum L.). The fractions of phenanthrene and pyrene were determined using a sequential extraction method, and the microbial diversity was evaluated using 16S rRNA gene high-throughput sequencing. The results showed that mixed surfactants could enhance the remediation efficiencies of PAHs, and mainly occurred in the initial 21 days. Mixed surfactants at the ratio of 1:1 (HM1) showed the best remediation efficiency in enhancing the dissipation of pyrene in 21 days. Mixed surfactants showed little effects on the removal of phenanthrene. In general, HM1 significantly decreased the bioavailable, bound and residual fractions of pyrene; additionally, higher abundances of PAH-degradation bacteria and degradation-related genes were observed. Pearson correlation analysis among PAH degraders, degradation-related genes and bioavailable fraction of PAHs was performed. Our results indicated that mixed surfactants could promote the transformation of pyrene from the bound and residual fractions to bioavailable fractions and enhance the abundances of PAH degradation bacteria and PAH degradation-related genes, thereby enhancing the degradation of pyrene.

Response of microbial community structure and metabolic profile to shifts of inlet VOCs in a gas-phase biofilter

The effects of inlet VOCs (Volatile Organic Compounds) shifts on microbial community structure in a biofiltration system were investigated. A lab-scale biofilter was set up to treat eight VOCs sequentially. Short declines in removal efficiency appeared after VOCs shifts and then later recovered. The number of OTUs in the biofilter declined from 690 to 312 over time. At the phylum level, Actinobacteria and Proteobacteria remained dominant throughout the operation for all VOCs, with their combined abundance ranging from 60 to 90%. The abundances of Planctomycetes and Thermi increased significantly to 20% and 5%, respectively, with the intake of non-aromatic hydrocarbons. At the genus level, Rhodococcus was present in the highest abundance (≥ 10%) throughout the experiment, indicating its wide degradability. Some potential degraders were also found; namely, Thauera and Pseudomonas, which increased in abundance to 19% and 12% during treatment with ethyl acetate and toluene, respectively. Moreover, the microbial metabolic activity declined gradually with time, and the metabolic profile of the toluene-treating community differed significantly from those of other communities.

Response of microbial community structure to seasonal fluctuation on soils of Rann of Kachchh, Gujarat, India: Representing microbial dynamics and functional potential

Abstract Study of saline ecosystems often contributes to our perception of extreme environments and diverse functional genes accountable for the biogeochemical cycle of the elements. In this study, metagenomic DNA was extracted from saline desert soil of Rann of Kachchh and analyzed to characterize the structural and functional dynamics of microbial community along with seasonal climatic alterations and changes in soil physicochemical properties. The samples differing in salinity gradient with seasonal fluctuation were collected and subjected to metagenome sequencing on Illumina Miseq platform. Transversely, bacteria were dominant as compare to archaea and three phyla of bacteria namely Proteobacteria, Firmicutes and Bacteroidetes accounted for the preponderance of taxa detected. Upon multivariate statistics, the resident microbial community was astonishingly diverse concealing wide diversity of taxa. The community from domain archaea was found to correlate with higher salt concentration and salinity along with electrical conductivity. The metabolic potential for all the seasons displayed a pathway profile representing carbon, nitrogen, methane and sulfur metabolism. Thus, the current study reveals metagenomic potential and possibility of novel microbial interactions for functioning of ecosystem in Rann of Kachchh.

Cascading influence of inorganic nitrogen sources on DOM production, composition, lability and microbial community structure in the open ocean.

Nitrogen frequently limits oceanic photosynthesis and the availability of inorganic nitrogen sources in the surface oceans is shifting with global change. We evaluated the potential for abrupt increases in inorganic N sources to induce cascading effects on dissolved organic matter (DOM) and microbial communities in the surface ocean. We collected water from 5 m depth in the central North Pacific and amended duplicate 20 liter polycarbonate carboys with nitrate or ammonium, tracking planktonic carbon fixation, DOM production, DOM composition and microbial community structure responses over 1 week relative to controls. Both nitrogen sources stimulated bulk phytoplankton, bacterial and DOM production and enriched Synechococcus and Flavobacteriaceae; ammonium enriched for oligotrophic Actinobacteria OM1 and Gammaproteobacteria KI89A clades while nitrate enriched Gammaproteobacteria SAR86, SAR92 and OM60 clades. DOM resulting from both N enrichments was more labile and stimulated growth of copiotrophic Gammaproteobacteria (Alteromonadaceae and Oceanospirillaceae) and Alphaproteobacteria (Rhodobacteraceae and Hyphomonadaceae) in weeklong dark incubations relative to controls. Our study illustrates how nitrogen pulses may have direct and cascading effects on DOM composition and microbial community dynamics in the open ocean.

Effect of electrode potentials on the microbial community of photo bioelectrochemical systems.

Increasing attention is being paid to the adoption of photoautotrophic microbes in bioelectrochemical systems (BESs) because of the advantages of self-sustainability. Biased potential on the anode was capable of adjusting the performance of non-photo BESs, and the microbial community structure was also changed; however, few studies have been conducted to investigate the effects of potential on microbial community structure in photo-BESs. In this work, the response of microbial community structure to different potentials (i.e., 0, 0.2, 0.4 and 0.6V vs. Ag/AgCl) was characterized with 454 pyrosequencing. Four samples were collected and they generated 42865 16S rDNA sequencing reads with an average length of 429bp. The potential at 0.2V resulted in the highest current density (378.8mAm-2) and showed a strong selection for γ-proteobacteria (30.8% of the sequences). α-Diversity analysis showed that microbial diversity increased with increased potential. Rhodopseudomonas palustris was dominant among known exoelectrogens in the biofilm biased at 0.4V. The results provided an insight into the mechanism of potential regulation on the performance of photo-BESs and changes in microbial community structure.

Response of microbial community structure to pre-acclimation strategies in microbial fuel cells for domestic wastewater treatment

Microbial community structures and performance of air-cathode microbial fuel cells (MFCs) inoculated with activated sludge from domestic wastewater were investigated to evaluate the effects of three substrate pre-acclimation strategies: 1, serial pre-acclimation with acetate and glucose before supplying domestic wastewater; 2, one step pre-acclimation with acetate before supplying domestic wastewater; and 3, direct supply of domestic wastewater without any pre-acclimation. Strategy 1 showed much higher current generation (1.4mA) and Coulombic efficiency (33.5%) than strategies 2 (0.7mA and 9.4%) and 3 (0.9mA and 10.3%). Pyrosequencing showed that microbial communities were significantly affected by pre-acclimation strategy. Although Proteobacteria was the dominant phylum with all strategies, Actinobacteria was abundant when MFCs were pre-acclimated with glucose after acetate. Not only anode-respiring bacteria (ARB) in the genus Geobacter but also non-ARB belonging to the family Anaerolinaceae seemed to play important roles in air-cathode MFCs to produce electricity from domestic wastewater.

Response of microbial community structure and function to short-term biochar amendment in an intensively managed bamboo (Phyllostachys praecox) plantation soil: Effect of particle size and addition rate

Biochar incorporated into soil has been known to affect soil nutrient availability and act as a habitat for microorganisms, both of which could be related to its particle size. However, little is known about the effect of particle size on soil microbial community structure and function. To investigate short-term soil microbial responses to biochar addition having varying particle sizes and addition rates, we established a laboratory incubation study. Biochar produced via pyrolysis of bamboo was ground into three particle sizes (diameter size<0.05mm (fine), 0.05–1.0mm (medium) and 1.0–2.0mm (coarse)) and amended at rates of 0% (control), 3% and 9% (w/w) in an intensively managed bamboo (Phyllostachys praecox) plantation soil. The results showed that the fine particle biochar resulted in significantly higher soil pH, electrical conductivity (EC), available potassium (K) concentrations than the medium and coarse particle sizes. The fine-sized biochar also induced significantly higher total microbial phospholipid fatty acids (PLFAs) concentrations by 60.28% and 88.94% than the medium and coarse particles regardless of addition rate, respectively. Redundancy analysis suggested that the microbial community structures were largely dependent of particle size, and that improved soil properties were key factors shaping them. The cumulative CO2 emissions from biochar-amended soils were 2–56% lower than the control and sharply decreased with increasing addition rates and particle sizes. Activities of α-glucosidase, β-glucosidase, β-xylosidase, N-acetyl-β-glucosaminidase, peroxidase and dehydrogenase decreased by ranging from 7% to 47% in biochar-amended soils over the control, indicating that biochar addition reduced enzyme activities involved carbon cycling capacity. Our results suggest that biochar addition can affect microbial population abundances, community structure and enzyme activities, that these effects are particle size and rate dependent. The fine particle biochar may additionally produce a better habitat for microorganisms compared to the other particle sizes.

Grassland to woodland transitions: Dynamic response of microbial community structure and carbon use patterns

AbstractWoodland encroachment into grasslands is a globally pervasive phenomenon attributed to land use change, fire suppression, and climate change. This vegetation shift impacts ecosystem services such as ground water allocation, carbon (C) and nutrient status of soils, aboveground and belowground biodiversity, and soil structure. We hypothesized that woodland encroachment would alter microbial community structure and function and would be related to patterns in soil C accumulation. To address this hypothesis, we measured the composition and δ13C values of soil microbial phospholipids (PLFAs) along successional chronosequences from C4‐dominated grasslands to C3‐dominated woodlands (small discrete clusters and larger groves) spanning up to 134 years. Woodland development increased microbial biomass, soil C and nitrogen (N) concentrations, and altered microbial community composition. The relative abundance of gram‐negative bacteria (cy19:0) increased linearly with stand age, consistent with decreases in soil pH and/or greater rhizosphere development and corresponding increases in C inputs. δ13C values of all PLFAs decreased with time following woody encroachment, indicating assimilation of woodland C sources. Among the microbial groups, fungi and actinobacteria in woodland soils selectively assimilated grassland C to a greater extent than its contribution to bulk soil. Between the two woodland types, microbes in the groves incorporated relatively more of the relict C4‐C than those in the clusters, potentially due to differences in below ground plant C allocation and organo‐mineral association. Changes in plant productivity and C accessibility (rather than C chemistry) dictated microbial C utilization in this system in response to shrub encroachment.

Responses of microbial community structure to land-use conversion and fertilization in southern China

A short-term experiment was carried out in southern China to investigate the effects of land-use conversion from rice paddies to vegetable fields and fertilization on soil microbial community structure by analyzing soil phospholipid fatty acid (PLFA) profiles. A split-plot design with four replicates was adopted, in which land use (paddy and vegetable field) was the first-level treatment and fertilization (conventional fertilization and no fertilization) was nested as the second level. Our results showed that both land-use conversion and fertilization had significant effects on microbial community structure. After 2 years of land-use conversion, the total amount of PLFAs were 3.54 and 2.97 nmol g−1 for fertilized (V–F) and unfertilized (V–NF) vegetable fields, respectively, and 3.19 and 2.32 nmol g−1 for fertilized (R–F) and unfertilized (R–NF) rice paddies, respectively. Soil fungal PLFAs were 1.04 and 0.87 nmol g−1 for V–F and V–NF, respectively, which were significantly increased by 13.9 and 11.4 times compared with those of R–F and R–NF, respectively. The ratio of fungal to bacterial PLFAs significantly increased in vegetable fields compared with rice paddies. No significant differences were found in the total, bacterial, and actinomycetic PLFAs between vegetable fields and rice paddies. The application of fertilizer significantly increased the amount of total PLFAs and bacterial PLFAs. With land-use conversion and fertilization, soil physicochemical properties also changed, and microbial community structure showed a significant relationship with soil water content, NH4+-N, and pH, which explained the land-use conversion and fertilization effects on soil microbial community composition.

闽江河口区淡水和半咸水潮汐沼泽土壤产甲烷菌多样性研究

Methane is one of the main greenhouse gases and plays an important role in global climate change. Wetlands are the main source of global methane emission. Microbial communities inhabiting anoxic habitats such as freshwater wetlands and marine sediment are important for biological carbon cycling. Methanogenesis is the final step of degradation of organic substrates and mediated by methanogenic archaea. Rising sea levels and excessive water withdrawals upstream are making previously freshwater wetlands saline. Plant community responses to change in the freshwater-saline gradient have been well studied in the estuarine wetlands; however,microbial community structure response to salinity gradient remains relatively unexplored,including the methanogens in tidal marsh soil along salinity gradient in subtropical estuary are poorly characterized.It is essential to investigate the influence of salinity on the community structure of methanogen in tidalmarshes. With the development of molecular biological techniques,molecular methods independent of culture techniques has vastly improved the potential to describe microbial diversity. Methyl-coenzyme M reductase is a critical enzyme in methanogenesis and the mcrA gene is a favorable functional gene and widely used to detect methanogens in soils of wetlands.Here,we determined the diversity of methanogen communities using molecular technique targeting the mcrA gene and restriction fragment length polymorphism( RFLP) from the soil of the tidal freshwater and brackish Cyperus malaccensis marshes in the Min River estuary,southeast China. The community structure of methanogen in the tidal C. malaccensis marshes changed with salinity. Values of Shannon-Weiner index of methanogen from the soil of tidal freshwater C.malaccensis marshes are 2.81 and 2.65 in the Xiayangzhou and Tajiaozhou wetlands,and 2.33 and 2.27 in the soil of tidal brackish C. malaccensis marshes in the Bianfuzhou and Shanyutan wetlands. The diversity of methanogen communities from the tidal C. malaccensis marshes decreased with increasing salinity in the Min River estuary. Phylogenetic analysis revealed that the communities of methanogens in the C. malaccensis marshes were mainly divided into three groups which were Methanomicrobiales,Methanosarcinales and Methanobacteriales. The freshwater C. malaccensis marshes were mainly dominated by Methanoregula,Methanosarcina and Methanobacterium. However,the brackish C. malaccensis marshes only dominated by Methanoregula. We conclude that methanogen diversity in estuarine tidal marshes is shaped by salinity conditions,suggesting an influence of impending sea level rise.

Study on Nutrient Removal Performance and Biological Community Structure in Hybrid Biofilm Reactor

To investigate nutrient removal and biological community structure in wastewater treatment system under different ratio of C/N/P, hybrid biofilm reactor (HBR) and sequencing batch reactor (SBR) in lab scale were set up. Results showed that both HBR and SBR achieved the best removal efficiency of nitrogen and phosphorus when C/N/P=100/6.25/1. With the rise of C/N/P from 50/6.25/1 to 100/6.25/1, the removal efficiencies of NH3-N were greater than 93% in three phases of both reactors; the efficiencies of TN were increased from 65% to 79% in SBR while these values at HBR were from 73% to 86%; the efficiencies of TP were increased from 42% to 93% in SBR while these values at HBR were from 32% to 93%. Microbial community structure response to different C/N/P was determined by PCR-DGGE technology. Similarity coefficient was lowest and denitrifying phosphate accumulating bacteria became dominant bacteria in SBR when C/N/P was 100/6.25/1. There were many functional bacteria in HBR, such as bacteria for removing nutrients (Uncultured BacteroidetesFJ828150), bacteria for removing organic (Uncultured Saprospiraceae) bacteria for removing nitrogen (Ferribacterium sp.), and nitrifying bacteria (Uncultured Nitrospira sp.) which became dominant bacteria. Because of microbial diversity index of biofilm was up to 3.3, similarity coefficient was as low as 43.4%.

Litter Supply as a Driver of Microbial Activity and Community Structure on Decomposing Leaves: a Test in Experimental Streams

Succession of newly created landscapes induces profound changes in plant litter supplied to streams. Grasses dominate inputs into open-land streams, whereas tree litter is predominant in forested streams. We set out to elucidate whether the activity and structure of microbial communities on decomposing leaves are determined by litter quality (i.e., grass or tree leaves colonized) or whether changes during riparian succession affecting litter standing stocks on the stream bed play an overriding role. We used 15 outdoor experimental streams to simulate changes in litter supplies reflecting five stages of riparian succession: (i) a biofilm stage with no litter, (ii) an open-land stage characterized by grass litter inputs, (iii) a transitional stage with a mix of grass and tree litter, (iv) an early forested stage with tree litter, and (v) an advanced forested stage with 2.5 times the amount of tree litter. Microbial activities on tree (Betula pendula) and grass (Calamagrostis epigejos) litter were unaffected by either the quantity or type of litter supplied to the experimental streams (i.e., litter standing stock) but differed between the two litter types. This was in stark contrast with bacterial and fungal community structure, which markedly differed on grass and tree litter and, to a lesser extent, also among streams receiving different litter inputs. These patterns reveal distinct responses of microbial community structure and activity to the bulk litter available in streams but consistent responses to the litter type colonized.

Response of microbial community structure to microbial plugging in a mesothermic petroleum reservoir in China

Microbial plugging, a microbial enhancement of oil recovery (MEOR) technique, has been applied in a candidate oil reservoir of Daqing Oil Field (China). The goal of this study is to monitor the survival of injected bacteria and reveal the response of microbial communities in field trial of microbial plugging through injection of selected microbial culture broth and nutrients. Culture-dependent enrichment and culture-independent 16S rDNA clone library methods were used. The results show that it was easy to activate targeted biopolymer-producing bacteria in a laboratory environment, and it was difficult for injected exogenous bacteria to survive. In addition, microbial communities in the oil reservoir also changed before and after the field trial. However, microbial communities, activated by fermentative medium for biopolymer-producing bacteria, appeared to show greater differences in the laboratory than in the natural reservoir. It was concluded that microbial populations monitoring was important to MEOR; results of response of microbial communities could provide a guide for the future field trials.

Response of microbial community structure to natural and accelerated hydrarch successions in the boreal wetlands in northern Hokkaido, Japan

We estimated the effect of invading Sasa vegetation and accelerated terrestrialization on the microbial community structure in Sarobetsu-genya wetland (SGW) and Nakanominedaira wetland (NW) (original vegetation, Sphagnum). All examined peat-pore water samples were acidic. Electrical conductivity significantly differed between SGW and NW. Nonmetric multidimensional scaling (NMDS) and analysis of similarity based on denaturing gradient gel electrophoresis (DGGE) band patterns revealed differences in the bacterial community structure between the Sasa and Sphagnum vegetations at a depth of 10 cm in NW. In contrast, the bacterial NMDS profiles at all depths differed between the 2 wetlands rather than between the 2 vegetations. The archaeal community structure significantly differed between the wetlands at depths of 30 and 50 cm. The bacterial diversity index derived from the DGGE profiles significantly differed between the wetlands at all depths. The archaeal diversity index significantly differed between the wetlands at a depth of 50 cm. Sasa invasion affected the microbial community structure in the rhizosphere, up to a depth of 10 cm; this effect differed with the terrestrialization speed. These results suggest that in peat bogs subjected to artificially accelerated terrestrialization, the microbial community changes before the occurrence of the natural hydrarch ecological succession involving ground vegetation.

Nitrogen removal performance and microbial community structure dynamics response to carbon nitrogen ratio in a compact suspended carrier biofilm reactor

A compact suspended carrier biofilm reactor (SCBR) was developed for simultaneous nitrification and denitrification (SND) in a single reactor and the performance of nutrient removal was investigated. Microbial community structure response to different ratio of carbon to nitrogen (C/N) was determined by denaturing gel gradient electrophoresis (DGGE) profiles of 16S rDNA V3 region and amoA gene amplifications. In addition, the population dynamics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were estimated by fluorescence in situ hybridization (FISH) with 16S rDNA-targeted oligonucleotide probes. Results showed that the compact SCBR was efficient in nutrient removal with COD Cr removal efficiency over 90% and SND efficiency ( E SND) about 83.3%. The diversity of microbial community structure was positively correlated with C/N ratio, while the three communities of amoA gene were relativity homogenous. The population of nitrifiers was in inverse proportions to C/N ratio with the average fraction of AOB and NOB to all bacteria 5.4, 4.8, 3.1% and 4.6, 3.5, 2.7% respectively as C/N ratio changing from 3:1, 5:1 to 10:1. Therefore we could reach a conclusion that the compact SCBR was practical to treat municipal wastewater and the shift of microbial community monitored by molecular technologies could offer guidance to the process optimization in engineering.

Response of microbial community structure to environmental forcing in the Arabian Sea

The effect of environmental forcing on microbial community structure was investigated in the Arabian Sea during four seasonal cruises during 1995: late Northeast Monsoon (January); Spring Intermonsoon (March–April); late Southwest Monsoon (August–September); and early Northeast Monsoon (December). The distributions of picoplankton populations—heterotrophic bacteria (HBac), Prochlorococcus ( Pro), Synechococcus spp. ( Syn) and picoeucaryotic algae (Peuc)—were determined by flow cytometric analysis. Seasonal variations in abundance maxima, vertical profiles, integrated abundance (0–200 m), and estimated carbon biomass were contrasted along two transects from the coast of Oman to 1500 km offshore. HBac were numerically dominant in surface waters in all regions (1–3×10 6 cells ml -1), with higher maximum abundances in coastal waters than at offshore stations. Conversely, Pro were most abundant at the oligotrophic offshore stations, and 100-fold lower, or absent, at coastal stations, except during the Spring Intermonsoon when abundances were extremely high along the entire southern transect. Syn abundances were highly variable, with no consistent trend between coastal and offshore stations. This variability may be explained by the prevalence of mesoscale eddies, but also could be due to overlapping distributions of multiple Syn populations distinguished by pigment type. Syn with a low phycourobilin (PUB) to phycoerythrobilin (PEB) ratio pigment type were more abundant at coastal stations, whereas Syn with a high PUB : PEB ratio increased in abundance offshore. Average depth profiles for Pro, Syn, and HBac displayed uniform abundance in the surface mixed layer, with a rapid decrease below the surface mixed layer depth; however, during the Spring Intermonsoon most profiles had a peak at the base of the surface mixed layer. Distributions of Peuc typically displayed a subsurface maximum near the base of the surface mixed layer, except during the SW Monsoon when abundance peaked near the surface. This report is the first to describe the seasonal and spatial variation in microbial community structure in the Arabian Sea over a complete monsoon cycle. Overall, the eucaryotic component was more important at coastal stations, and the procaryotic components were predominant at offshore stations. Pro abundance was restricted to warm oligotrophic waters and was inversely related to surface nitrate concentrations; thus, an increase in the % Pro as a fraction of total procaryote abundance was also indicative of oligotrophic conditions. The effects of SW Monsoonal forcing on microbial community structure resulted in an increase of Peuc, but this response was limited to coastal stations. Pro and Syn remained dominant at offshore stations.