Monitoring of microbial community structure and succession in the biohydrogen production reactor by denaturing gradient gel electrophoresis (DGGE)

Biohydrogen production has been concerned ex-tremely as a new technology of energy resource pro-duction by many scientists[1—4]. Enhancement of hy-drogen production efficiency and cutting down the operating cost are very important problems, which are the limiting factors for the industrialization of hydro-gen production process. The fermentation hydrogen production technology offers a new method to resolve these difficulties[5—8]. Compared with photosynthetic hydrogen production possesses, f…     

Monitoring of microbial community structure and succession in the biohydrogen production reactor by denaturing gradient gel electrophoresis (DGGE)

To study the structure of microbial communities in the biological hydrogen production reactor and determine the ecological function of hydrogen producing bacteria, anaerobic sludge was obtained from the continuous stirred tank reactor (CSTR) in different periods of time, and the diversity and dynamics of microbial communities were investigated by denaturing gradient gel electrophoresis (DGGE). The results of DGGE demonstrated that an obvious shift of microbial population happened from the beginning of star-up to the 28th day, and the ethanol type fermentation was established. After 28 days the structure of microbial community became stable, and the climax community was formed. Comparative analysis of 16S rDNA sequences from reamplifying and sequencing the prominent bands indicated that the dominant population belonged to low G+C Gram-positive bacteria (Clostridium sp. andEthanologenbacterium sp.), β-proteobacteria (Acidovorax sp.), γ-proteobacteria (Kluyvera sp.), Bacteroides (uncultured bacterium SJA-168), and Spirochaetes (uncultured eubacterium E1-K13), respectively. The hydrogen production rate increased obviously with the increase ofEthanologenbacterium sp.,Clostridium sp. and uncultured Spirochaetes after 21 days, meanwhile the succession of ethanol type fermentation was formed. Throughout the succession the microbial diversity increased however it decreased after 21 days. Some types ofClostridium sp.Acidovorax sp.,Kluyvera sp., and Bacteroides were dominant populations during all periods of time. These special populations were essential for the construction of climax community. Hydrogen production efficiency was dependent on both hydrogen producing bacteria and other populations. It implied that the cometabolism of microbial community played a great role of biohydrogen production in the reactors.     

Microbial community interactions and population dynamics of an algicidal bacterium active against Karenia brevis (Dinophyceae)

The population dynamics of Cytophaga strain 41-DBG2, a bacterium algicidal to the harmful algal bloom (HAB) dinoflagellate Karenia brevis, were investigated in laboratory experiments using fluorescent in-situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE). Following its introduction into non-axenic K. brevis cultures at concentrations of 10³ or 10⁵ bacterial cells per milliliter, 41-DBG2 increased to 10⁶ cells per milliliter before initiation of its algicidal activity. Such threshold concentrations were not achieved when starting algal cell numbers were relatively low (10³ cells per milliliter), suggesting that the growth of this bacterium may require high levels of dissolved organic matter (DOM) excreted by the algae. It remains to be determined whether this threshold concentration is required to trigger an algicidal response by 41-DBG2 or, alternatively, is the point at which the bacterium accumulates to an effective killing concentration. The ambient microbial community associated with these algal cultures, as determined by DGGE profiles, did not change until after K. brevis cells were in the process of lysing, indicating a response to the rapid input of algal-derived organic matter. Resistance to algicidal attack exhibited by several K. brevis clones was found to result from the inhibition of 41-DBG2 growth in the presence of currently unculturable bacteria associated with those clones. These bacteria apparently prevented 41-DBG2 from reaching the threshold concentration required for initiation of algicidal activity. Remarkably, resistance and susceptibility to the algicidal activity of 41-DBG2 could be transferred between K. brevis clones with the exchange of their respective unattached bacterial communities, which included several dominant phylotypes belonging to the α-proteobacteria, γ-proteobacteria, and Cytophaga–Flavobacterium–Bacteroides (CFB) groups. We hypothesize that CFB bacteria may be successfully competing with 41-DBG2 (also a member of the CFB) for nutrients, thereby inhibiting growth of the latter and indirectly providing resistance against algicidal attack. We conclude that if algicidal bacteria play a significant role in regulating HAB dynamics, as some authors have inferred, bacterial community interactions are crucial factors that must be taken into consideration in future studies.     

Methanol removal efficiency and bacterial diversity of an activated carbon biofilter

Motivated by the need to establish an economical and environmentally friendly methanol control technology for the pulp and paper industry, a bench-scale activated carbon biofiltration system was developed. This system was evaluated for its performance in removing methanol from an artificially contaminated air stream and characterized for its bacterial diversity over time, under varied methanol loading rates, and in different spatial regions of the filter. The biofilter system, composed of a novel packing mixture, provided an excellent support for growth and activity of methanol-degrading bacteria, resulting in approximately 100% methanol removal efficiency for loading rates of 1–17 g/m³ packing/h, when operated both with and without inoculum containing enriched methanol-degrading bacteria. Although bacterial diversity and abundance varied over the length of the biofilter, the populations present rapidly formed a stable community that was maintained over the entire 138-day operation of the system and through variable operating conditions, as observed by PCR–DGGE methods that targeted all bacteria as well as specific methanol-oxidizing microorganisms. Phylogenetic analysis of bands excised and sequenced from DGGE gels indicated that the biofilter system supported a diverse community of methanol-degrading bacteria, with high similarity to species in the genera Methylophilus (β-proteobacteria), Hyphomicrobium and Methylocella (both α-proteobacteria).     

Phylogenetic Analysis of Bacterial Communities in Mesophilic and Thermophilic Bioreactors Treating Pharmaceutical Wastewater

The phylogenetic diversity of the bacterial communities supported by a seven-stage, full-scale biological wastewater treatment plant was studied. These reactors were operated at both mesophilic (28 to 32°C) and thermophilic (50 to 58°C) temperatures. Community fingerprint analysis by denaturing gradient gel electrophoresis (DGGE) of the PCR-amplified V3 region of the 16S rRNA gene from the domain Bacteria revealed that these seven reactors supported three distinct microbial communities. A band-counting analysis of the PCR-DGGE results suggested that elevated reactor temperatures corresponded with reduced species richness. Cloning of nearly complete 16S rRNA genes also suggested a reduced species richness in the thermophilic reactors by comparing the number of clones with different nucleotide inserts versus the total number of clones screened. While these results imply that elevated temperature can reduce species richness, other factors also could have impacted the number of populations that were detected. Nearly complete 16S rDNA sequence analysis showed that the thermophilic reactors were dominated by members from the β subdivision of the division Proteobacteria (β-proteobacteria) in addition to anaerobic phylotypes from the low-G+C gram-positive and Synergistes divisions. The mesophilic reactors, however, included at least six bacterial divisions, including Cytophaga-Flavobacterium-Bacteroides, Synergistes, Planctomycetes, low-G+C gram-positives, Holophaga-Acidobacterium, and Proteobacteria (α-proteobacteria, β-proteobacteria, γ-proteobacteria and δ-proteobacteria subdivisions). The two PCR-based techniques detected the presence of similar bacterial populations but failed to coincide on the relative distribution of these phylotypes. This suggested that at least one of these methods is insufficiently quantitative to determine total community biodiversity—a function of both the total number of species present (richness) and their relative distribution (evenness).     

Changes in Microbial Biofilm Communities during Colonization of Sewer Systems

The coexistence of sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) in anaerobic biofilms developed in sewer inner pipe surfaces favors the accumulation of sulfide (H₂S) and methane (CH₄) as metabolic end products, causing severe impacts on sewerage systems. In this study, we investigated the time course of H₂S and CH₄ production and emission rates during different stages of biofilm development in relation to changes in the composition of microbial biofilm communities. The study was carried out in a laboratory sewer pilot plant that mimics a full-scale anaerobic rising sewer using a combination of process data and molecular techniques (e.g., quantitative PCR [qPCR], denaturing gradient gel electrophoresis [DGGE], and 16S rRNA gene pyrotag sequencing). After 2 weeks of biofilm growth, H₂S emission was notably high (290.7 ± 72.3 mg S-H₂S liter⁻¹ day⁻¹), whereas emissions of CH₄ remained low (17.9 ± 15.9 mg COD-CH₄ liter⁻¹ day⁻¹). This contrasting trend coincided with a stable SRB community and an archaeal community composed solely of methanogens derived from the human gut (i.e., Methanobrevibacter and Methanosphaera). In turn, CH₄ emissions increased after 1 year of biofilm growth (327.6 ± 16.6 mg COD-CH₄ liter⁻¹ day⁻¹), coinciding with the replacement of methanogenic colonizers by species more adapted to sewer conditions (i.e., Methanosaeta spp.). Our study provides data that confirm the capacity of our laboratory experimental system to mimic the functioning of full-scale sewers both microbiologically and operationally in terms of sulfide and methane production, gaining insight into the complex dynamics of key microbial groups during biofilm development.     

Microbial Population Changes during Bioremediation of an Experimental Oil Spill

Three crude oil bioremediation techniques were applied in a randomized block field experiment simulating a coastal oil spill. Four treatments (no oil control, oil alone, oil plus nutrients, and oil plus nutrients plus an indigenous inoculum) were applied. In situ microbial community structures were monitored by phospholipid fatty acid (PLFA) analysis and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) to (i) identify the bacterial community members responsible for the decontamination of the site and (ii) define an end point for the removal of the hydrocarbon substrate. The results of PLFA analysis demonstrated a community shift in all plots from primarily eukaryotic biomass to gram-negative bacterial biomass with time. PLFA profiles from the oiled plots suggested increased gram-negative biomass and adaptation to metabolic stress compared to unoiled controls. DGGE analysis of untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. This banding pattern disappeared in all oiled plots, indicating that the structure and diversity of the dominant bacterial community changed substantially. No consistent differences were detected between nutrient-amended and indigenous inoculum-treated plots, but both differed from the oil-only plots. Prominent bands were excised for sequence analysis and indicated that oil treatment encouraged the growth of gram-negative microorganisms within the α-proteobacteria and Flexibacter-Cytophaga-Bacteroides phylum. α-Proteobacteria were never detected in unoiled controls. PLFA analysis indicated that by week 14 the microbial community structures of the oiled plots were becoming similar to those of the unoiled controls from the same time point, but DGGE analysis suggested that major differences in the bacterial communities remained.     

Community Structure and Activity Dynamics of Nitrifying Bacteria in a Phosphate-Removing Biofilm

The microbial community structure and activity dynamics of a phosphate-removing biofilm from a sequencing batch biofilm reactor were investigated with special focus on the nitrifying community. O₂, NO₂⁻, and NO₃⁻ profiles in the biofilm were measured with microsensors at various times during the nonaerated-aerated reactor cycle. In the aeration period, nitrification was oxygen limited and restricted to the first 200 μm at the biofilm surface. Additionally, a delayed onset of nitrification after the start of the aeration was observed. Nitrate accumulating in the biofilm in this period was denitrified during the nonaeration period of the next reactor cycle. Fluorescence in situ hybridization (FISH) revealed three distinct ammonia-oxidizing populations, related to the Nitrosomonas europaea, Nitrosomonas oligotropha, and Nitrosomonas communis lineages. This was confirmed by analysis of the genes coding for 16S rRNA and for ammonia monooxygenase (amoA). Based upon these results, a new 16S rRNA-targeted oligonucleotide probe specific for the Nitrosomonas oligotropha lineage was designed. FISH analysis revealed that the first 100 μm at the biofilm surface was dominated by members of the N. europaea and the N. oligotropha lineages, with a minor fraction related to N. communis. In deeper biofilm layers, exclusively members of the N. oligotropha lineage were found. This separation in space and a potential separation of activities in time are suggested as mechanisms that allow coexistence of the different ammonia-oxidizing populations. Nitrite-oxidizing bacteria belonged exclusively to the genus Nitrospira and could be assigned to a 16S rRNA sequence cluster also found in other sequencing batch systems.     

Microbial Succession in a Compost-packed Biofilter Treating Benzene-contaminated Air

Air artificially contaminated with increasing concentrations of benzene was treated in a laboratory scale compost-packed biofilter for 240 days with a removal efficiency of 81–100%. The bacterial community in the packing material (PM) at different heights of the biofilter was analysed every 60 days. Bacterial plate counts and ribosomal intergenic spacer analysis (RISA) of the isolated strains showed that the number of cultivable aerobic heterotrophic bacteria and the species diversity increased with benzene availability. Identification of the isolated species and the main bands in denaturing gradient gel electrophoresis (DGGE) profiles from total compost DNA during the treatment revealed that, at a relatively low volumetric benzene load (1.2≤VBL≤6.4 g m⁻³ _PM h⁻¹), besides low G+C Gram positive bacteria, originally present in the packing compost, bacteroidetes and β- and γ-proteobacteria became detectable in the colonising population. At the VBL value (24.8 g m⁻³ _PM h⁻¹) ensuring the maximum elimination capacity of the biofilter (20.1 g m⁻³ _PM h⁻¹), strains affiliated to the genus Rhodococcus dominated the microflora, followed by β-proteobacteria comprising the genera Bordetella and Neisseria. Under these conditions, more than 35% of the isolated strains were able to grow on benzene as the sole carbon source. Comparison of DGGE and automated RISA profiles of the total community and isolated strains showed that a complex bacterial succession occurred in the reactor in response to the increasing concentrations of the pollutant and that cultivable bacteria played a major role in benzene degradation under the adopted conditions.     

Impact of Substratum Surface on Microbial Community Structure and Treatment Performance in Biological Aerated Filters

The impact of substratum surface property change on biofilm community structure was investigated using laboratory biological aerated filter (BAF) reactors and molecular microbial community analysis. Two substratum surfaces that differed in surface properties were created via surface coating and used to develop biofilms in test (modified surface) and control (original surface) BAF reactors. Microbial community analysis by 16S rRNA gene-based PCR-denaturing gradient gel electrophoresis (DGGE) showed that the surface property change consistently resulted in distinct profiles of microbial populations during replicate reactor start-ups. Pyrosequencing of the bar-coded 16S rRNA gene amplicons surveyed more than 90% of the microbial diversity in the microbial communities and identified 72 unique bacterial species within 19 bacterial orders. Among the 19 orders of bacteria detected, Burkholderiales and Rhodocyclales of the Betaproteobacteria class were numerically dominant and accounted for 90.5 to 97.4% of the sequence reads, and their relative abundances in the test and control BAF reactors were different in consistent patterns during the two reactor start-ups. Three of the five dominant bacterial species also showed consistent relative abundance changes between the test and control BAF reactors. The different biofilm microbial communities led to different treatment efficiencies, with consistently higher total organic carbon (TOC) removal in the test reactor than in the control reactor. Further understanding of how surface properties affect biofilm microbial communities and functional performance would enable the rational design of new generations of substrata for the improvement of biofilm-based biological treatment processes.     

Analysis and succession of nitrifying bacteria community structure in sequencing biofilm batch reactor

To reveal the succession procedure of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) community structure in sequencing biofilm batch reactor (SBBR), the molecular biological techniques of denaturing gradient gel electrophoresis (DGGE), cloning, and real-time PCR were applied. DGGE showed that the structural diversity of the bacterial community increased during the biofilm formation period, and some kinds of populations had been highly preponderant consistently. The results of cloning and sequencing revealed that Nitrosomonas was the dominant species. The real-time PCR analysis indicated that the amount of the AOB increased significantly after the cultivation period, and the NOB gradually decreased. The AOB content on the 25th day was 17 times that of the 6th day. It also showed the biofilm formed successfully with accumulating nitrite and prepared to achieve the achievement of simultaneous nitrification and denitrification in SBBR. Furthermore, the ammonia-oxidizing rate was in correspondence with the NH₄ ⁺-N removal efficiency.     

Characterization of microbial community in an aerobic moving bed biofilm reactor applied for simultaneous nitrification and denitrification

A continuous-flow moving bed biofilm reactor (MBBR) under aerobic conditions was established for simultaneous nitrification and denitrification (SND), and microbial communities were investigated by a combination of denaturing gel gradient electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). DGGE analysis has revealed more similar microbial community structures formed in the biofilms with more similar carbon nitrogen (C/N) ratios. FISH analysis shows that the dominance of both Betaproteobacteria ammonia-oxidizing bacteria and Nitrospira-like nitrite-oxidizing bacteria were negatively correlated to C/N ratios. Sequence analysis of DGGE bands has indicated the presence of anoxic denitrifying bacteria Agrobacterium tumefaciens and Rhizobium sp., suggesting that the oxygen gradient inside the biofilm may be responsible for the mechanism of SND in aerobic MBBRs. The study confirms that appropriate control of microbial community structure resulting from optimal C/N ratio is beneficial in improving SND, thus optimizing nitrogen removal in aerobic MBBR. The established SND-based MBBR can save operation space and time in comparison to the traditional nitrogen removal process, and might be very attractive for future practical applications.     

In Situ Activity and Spatial Organization of Anaerobic Ammonium-Oxidizing (Anammox) Bacteria in Biofilms

We investigated autotrophic anaerobic ammonium-oxidizing (anammox) biofilms for their spatial organization, community composition, and in situ activities by using molecular biological techniques combined with microelectrodes. Results of phylogenetic analysis and fluorescence in situ hybridization (FISH) revealed that “Brocadia”-like anammox bacteria that hybridized with the Amx820 probe dominated, with 60 to 92% of total bacteria in the upper part (<1,000 μm) of the biofilm, where high anammox activity was mainly detected with microelectrodes. The relative abundance of anammox bacteria decreased along the flow direction of the reactor. FISH results also indicated that Nitrosomonas-, Nitrosospira-, and Nitrosococcus-like aerobic ammonia-oxidizing bacteria (AOB) and Nitrospira-like nitrite-oxidizing bacteria (NOB) coexisted with anammox bacteria and accounted for 13 to 21% of total bacteria in the biofilms. Microelectrode measurements at three points along the anammox reactor revealed that the NH₄⁺ and NO₂⁻ consumption rates decreased from 0.68 and 0.64 μmol cm⁻² h⁻¹ at P2 (the second port, 170 mm from the inlet port) to 0.30 and 0.35 μmol cm⁻² h⁻¹ at P3 (the third port, 205 mm from the inlet port), respectively. No anammox activity was detected at P4 (the fourth port, 240 mm from the inlet port), even though sufficient amounts of NH₄⁺ and NO₂⁻ and a high abundance of anammox bacteria were still present. This result could be explained by the inhibitory effect of organic compounds derived from biomass decay and/or produced by anammox and coexisting bacteria in the upper parts of the biofilm and in the upstream part of the reactor. The anammox activities in the biofilm determined by microelectrodes reflected the overall reactor performance. The several groups of aerobic AOB lineages, Nitrospira-like NOB, and Betaproteobacteria coexisting in the anammox biofilm might consume a trace amount of O₂ or organic compounds, which consequently established suitable microenvironments for anammox bacteria.     

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.     

Impact of Protists on the Activity and Structure of the Bacterial Community in a Rice Field Soil

Flooded rice fields have become a model system for the study of soil microbial ecology. In Italian rice fields, in particular, aspects from biogeochemistry to molecular ecology have been studied, but the impact of protistan grazing on the structure and function of the prokaryotic community has not been examined yet. We compared an untreated control soil with a γ-radiation-sterilized soil that had been reinoculated with a natural bacterial assemblage. In order to verify that the observed effects were due to protistan grazing and did not result from sterilization, we set up a third set of microcosms containing sterilized soil that had been reinoculated with natural assemblage bacteria plus protists. The spatial and temporal changes in the protistan and prokaryotic communities were examined by denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) analysis, respectively, both based on the small-subunit gene. Sequences retrieved from DGGE bands were preferentially affiliated with Cercozoa and other bacteriovorous flagellates. Without protists, the level of total DNA increased with incubation time, indicating that the level of the microbial biomass was elevated. Betaproteobacteria were preferentially preyed upon, while low-G+C-content gram-positive bacteria became more dominant under grazing pressure. The bacterial diversity detectable by T-RFLP analysis was greater in the presence of protists. The level of extractable NH₄⁺ was lower and the level of extractable SO₄²⁻ was higher without protists, indicating that nitrogen mineralization and SO₄²⁻ reduction were stimulated by protists. Most of these effects were more obvious in the partially oxic surface layer (0 to 3 mm), but they could also be detected in the anoxic subsurface layer (10 to 13 mm). Our observations fit well into the overall framework developed for protistan grazing, but with some modifications pertinent to the wetland situation: O₂ was a major control, and O₂ availability may have limited directly and indirectly the development of protists. Although detectable in the lower anoxic layer, grazing effects were much more obvious in the partially oxic surface layer.     

Characterization of an Autotrophic Nitrogen-Removing Biofilm from a Highly Loaded Lab-Scale Rotating Biological Contactor

In this study, a lab-scale rotating biological contactor (RBC) treating a synthetic NH₄⁺ wastewater devoid of organic carbon and showing high N losses was examined for several important physiological and microbial characteristics. The RBC biofilm removed 89% ± 5% of the influent N at the highest surface load of approximately 8.3 g of N m⁻² day⁻¹, with N₂ as the main end product. In batch tests, the RBC biomass showed good aerobic and anoxic ammonium oxidation (147.8 ± 7.6 and 76.5 ± 6.4 mg of NH₄⁺-N g of volatile suspended solids [VSS]⁻¹ day⁻¹, respectively) and almost no nitrite oxidation (< 1 mg of N g of VSS⁻¹ day⁻¹). The diversity of aerobic ammonia-oxidizing bacteria (AAOB) and planctomycetes in the biofilm was characterized by cloning and sequencing of PCR-amplified partial 16S rRNA genes. Phylogenetic analysis of the clones revealed that the AAOB community was fairly homogeneous and was dominated by Nitrosomonas-like species. Close relatives of the known anaerobic ammonia-oxidizing bacterium (AnAOB) Kuenenia stuttgartiensis dominated the planctomycete community and were most probably responsible for anoxic ammonium oxidation in the RBC. Use of a less specific planctomycete primer set, not amplifying the AnAOB, showed a high diversity among other planctomycetes, with representatives of all known groups present in the biofilm. The spatial organization of the biofilm was characterized using fluorescence in situ hybridization (FISH) with confocal scanning laser microscopy (CSLM). The latter showed that AAOB occurred side by side with putative AnAOB (cells hybridizing with probe PLA46 and AMX820/KST1275) throughout the biofilm, while other planctomycetes hybridizing with probe PLA886 (not detecting the known AnAOB) were present as very conspicuous spherical structures. This study reveals that long-term operation of a lab-scale RBC on a synthetic NH₄⁺ wastewater devoid of organic carbon yields a stable biofilm in which two bacterial groups, thought to be jointly responsible for the high autotrophic N removal, occur side by side throughout the biofilm.     

Effects of UV pretreatment on microbial community structure and metabolic characteristics in a subsequent biofilter treating gaseous chlorobenzene

To provide insight into effects of UV pretreatment on microorganisms in subsequent biofilters, the changes of microbial community structure and metabolic characteristics of biofilters with (UV–BF) and without (BF) UV pretreatment were studied. The respiratory quinone and BIOLOG methods were used to analyze microbial community structure and metabolic characteristics, respectively. The results indicated the quinone profiles, the species of dominant quinone and its molar fraction of the biofilm in both biofilters showed different behaviors. Ubiquinones-8 and menaquinone-9(H₂) was the dominant quinones in BF and UV–BF processes, respectively. The dissimilarity index of two biofilters markedly increased to nearly 60 after turning on the UV lamp. The microbial samples from UV–BF process showed higher metabolic activities of 0.040 cm⁻¹ h⁻¹ than 0.028 cm⁻¹ h⁻¹ in BF process. Moreover, the microorganisms in both biofilters demonstrated distinct metabolic characteristics. Further, the performance of biofilters showed good correlation with microbial community structure and metabolic characteristics.     

Influence of temperature on process efficiency and microbial community response during the biological removal of chlorophenols in a packed-bed bioreactor

Two reactors, initially operated at 14 and 23±1°C (RA and RB, respectively), were inoculated with a bacterial consortium enriched and acclimatized to the respective temperatures over 4 months. The biofilms, formed in the reactors, were studied using scanning electron microscopy, cultivation of the biofilm microflora, and physiological analysis of the isolates. Two bacteria able to mineralize chlorophenols under a large range of temperature (10–30°C) were isolated from the biofilm communities of reactors RA and RB and characterized as Alcaligenaceae bacterium R14C4 and Cupriavidus basilensis R25C6, respectively. When temperature was decreased by 10°C, the chlorophenols removal capacity was reduced from 51.6 to 22.8 mg l⁻¹ h⁻¹ in bioreactor RA (from 14 to 4°C) and from 59.3 to 34.7 mg l⁻¹ h⁻¹ in bioreactor RB (from 23±1 to 14°C). Fluorescence in situ hybridization (FISH) of the biofilm communities showed that, in all temperatures tested, the β-proteobacteria were the major bacterial community (35–47%) followed by the γ-proteobacteria (12.0–6.5%). When the temperature was decreased by 10°C, the proportions of γ-proteobacteria and Pseudomonas species increased significantly in both microbial communities.     

Succession of Bacterial Community Structure along the Changjiang River Determined by Denaturing Gradient Gel Electrophoresis and Clone Library Analysis

Bacterial community structure along the Changjiang River (which is more than 2,500 km long) was studied by using denaturing gradient gel electrophoresis (DGGE) and clone library analysis of PCR-amplified 16S ribosomal DNA (rDNA) with universal bacterial primer sets. DGGE profiles and principal-component analysis (PCA) demonstrated that the bacterial community gradually changed from upstream to downstream in both 1998 and 1999. Bacterial diversity, as determined by the Shannon index (H′), gradually decreased from upstream to downstream. The PCA plots revealed that the differences in the bacterial communities among riverine stations were not appreciable compared with the differences in two adjacent lakes, Lake Dongting and Lake Poyang. The relative stability of the bacterial communities at the riverine stations was probably due to the buffering action of the large amount of water flowing down the river. Clone library analysis of 16S rDNA revealed that the dominant bacterial groups changed from β-proteobacteria and the Cytophaga-Flexibacter-Bacteroides group upstream to high-G+C-content gram-positive bacteria downstream and also that the bacterial community structure differed among the stations in the river and the lakes. The results obtained in this study should provide a reference for future changes caused by construction of the Three Gorges Dam.