Bacterial diversity in Cr(VI) and Cr(III)-contaminated industrial wastewaters

The bacterial community structure of a chromium water bath, a chromium drainage waste system, a chromium pretreatment tank, and a trivalent chromium precipitation tank from the Hellenic Aerospace Industry S.A. was assessed using 16S rRNA libraries and a high-density DNA microarray (PhyloChip). 16S rRNA libraries revealed a bacterial diversity consisting of 14 distinct operational taxonomic units belonging to five bacterial phyla: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria, and Bacteroidetes. However, employing a novel microarray-based approach (PhyloChip), a high bacterial diversity consisting of 30 different phyla was revealed, with representatives of 181 different families. This made it possible to identify a core set of genera present in all wastewater treatment stages examined, consisting of members of Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria, and Bacteroidetes. In the chromium pretreatment tank, where the concentration of Cr(VI) is high (2.3 mg/l), we identified the presence of Pseudomonadales, Actinomycetales, and Enterobacteriales in abundance. In the chromium precipitation tank, where the concentration of Cr(III) is high, the dominant bacteria consortia were replaced by members of Rhodocyclales and Chloroflexi. The bacterial community structure changed significantly with changes in the chromium concentration. This in-depth analysis should prove useful for the design and development of improved bioremediation strategies.     

Mercury alters the bacterial community structure and diversity in soil even at concentrations lower than the guideline values

This study evaluated the effect of inorganic mercury (Hg) on bacterial community and diversity in different soils. Three soils—neutral, alkaline and acidic—were spiked with six different concentrations of Hg ranging from 0 to 200 mg kg⁻¹ and aged for 90 days. At the end of the ageing period, 18 samples from three different soils were investigated for bacterial community structure and soil physicochemical properties. Illumina MiSeq-based 16s ribosomal RNA (rRNA) amplicon sequencing revealed the alteration in the bacterial community between un-spiked control soils and Hg-spiked soils. Among the bacterial groups, Actinobacteria (22.65%) were the most abundant phyla in all samples followed by Proteobacteria (21.95%), Bacteroidetes (4.15%), Firmicutes (2.9%) and Acidobacteria (2.04%). However, the largest group showing increased abundance with higher Hg doses was the unclassified group (45.86%), followed by Proteobacteria. Mercury had a considerable negative impact on key soil functional bacteria such as ammonium oxidizers and nitrifiers. Canonical correspondence analysis (CCA) indicated that among the measured soil properties, Hg had a major influence on bacterial community structure. Furthermore, nonlinear regression analysis confirmed that Hg significantly decreased soil bacterial alpha diversity in lower organic carbon containing neutral and alkaline soils, whereas in acidic soil with higher organic carbon there was no significant correlation. EC₂₀ values obtained by a nonlinear regression analysis indicated that Hg significantly decreased soil bacterial diversity in concentrations lower than several guideline values.

     

Soil microbial community structure and enzymatic activity responses to nitrogen management and landscape positions in switchgrass (Panicum virgatum L.)

Switchgrass (Panicum virgatum L.) is usually grown on marginal land for biofuel system, in which nitrogen (N) is an essential management practice, and landscape position is a key topographical factor in impacting the production. However, limited information is available regarding how the N application and landscape positions affect soil microbial communities and enzyme activities under switchgrass. Thus, the specific objective of this study was to evaluate the responses of N rate (high, 112 kg N/ha; medium, 56 kg N/ha; and low, 0 kg N/ha) and landscape positions (shoulder and footslope) on soil biological health under switchgrass field. Data showed that N addition significantly influenced carbon and N fractions. The hot water‐soluble organic carbon (HWC) and nitrogen (HWN) fractions were significantly higher at footslope position than the shoulder position. The amount of total phospholipid fatty acid (PLFA), total bacterial, actinomycetes, gram‐negative and gram‐positive bacteria, total fungi, arbuscular mycorrhizal (AM) fungi, and saprophytes PLFAs were highest with medium and high N rates and footslope position. The N addition increased total PLFAs in N fertilizer treatments, viz. medium (5,946 ng PLFA‐C/g soil) and high N rates (5,871 ng PLFA‐C/g soil). Microbial biomass carbon and nitrogen and enzyme activities (urease, β‐glucosidase, acid phosphatase and arylsulfatase) were significantly enhanced by N fertilization (medium and high N rates) compared to control (low N rates) under footslope position. The urease activity under medium (36.3 µmol N‐NH₄⁺ g^?1 soil hr^?1) and high N rates (31.4 µmol N‐NH₄⁺ g^?1 soil hr^?1) was 42.9% and 23.6% higher than low N rates, respectively. This study suggests that the application of medium N rate in footslope position to switchgrass can enhance the soil biological properties and hence can protect the environment from the excessive use of N fertilizer.     

Anthropogenic nitrogen enrichment enhances soil carbon accumulation by impacting saprotrophs rather than ectomycorrhizal fungal activity

There is evidence that anthropogenic nitrogen (N) deposition enhances carbon (C) sequestration in boreal forest soils. However, it is unclear how free‐living saprotrophs (bacteria and fungi, SAP) and ectomycorrhizal (EM) fungi responses to N addition impact soil C dynamics. Our aim was to investigate how SAP and EM communities are impacted by N enrichment and to estimate whether these changes influence decay of litter and humus. We conducted a long‐term experiment in northern Sweden, maintained since 2004, consisting of ambient, low N additions (0, 3, 6, and 12 kg N ha^?1 year^?1) simulating current N deposition rates in the boreal region, as well as a high N addition (50 kg N ha^?1 year^?1). Our data showed that long‐term N enrichment impeded mass loss of litter, but not of humus, and only in response to the highest N addition treatment. Furthermore, our data showed that EM fungi reduced the mass of N and P in both substrates during the incubation period compared to when only SAP organisms were present. Low N additions had no effect on microbial community structure, while the high N addition decreased fungal and bacterial biomasses and altered EM fungi and SAP community composition. Actinomycetes were the only bacterial SAP to show increased biomass in response to the highest N addition. These results provide a mechanistic understanding of how anthropogenic N enrichment can influence soil C accumulation rates and suggest that current N deposition rates in the boreal region (≤12 kg N ha^?1 year^?1) are likely to have a minor impact on the soil microbial community and the decomposition of humus and litter.     

Influence of polyaluminum chloride on microbial characteristics in anaerobic membrane bioreactors for sludge digestion

In this study, two parallel lab-scale anaerobic membrane bioreactors (AnMBRs), one of which was dosed with polyaluminum chloride (PAC) for membrane fouling control, were operated for treating excess activated sludge collected from a wastewater treatment plant (WWTP). The AnMBRs were inoculated with anaerobic digested sludge collected from an anaerobic digester of another WWTP. The microbial community of digested sludge and cake layer in AnMBRs, as well as that of excess sludge, was analyzed through polymerase chain reaction coupled with denaturing gradient gel electrophoresis (PCR-DGGE) and Illumina MiSeq. The dynamic variation of archaeal community in AnMBRs was not as obvious as that of bacterial community based on the PCR-DGGE results. Under the circumstance of stable operation, Cloacimonetes, Chloroflexi, Bacteroidetes, Proteobacteria, Firmicutes, and Ignavibacteriae were observed as the predominant phyla in digested sludge based on the Illumina results. In addition to that, the cake layer possessed similar predominant phyla with the digested sludge but owned a higher diversity. Furthermore, overlapping bacterial communities were discovered between the excess sludge and digested sludge. However, the abundance of aerobic bacteria was substantially reduced, while the abundance of anaerobic microorganisms like phylum Cloacimonetes and Smithella was enriched in digested sludge over time. Additional PAC dosing, on the one hand, affected the bioavailable substrate, thus further changing the microbial community structure; on the other hand, aluminum itself also affected specific microbial communities. Besides, PAC dosing indirectly influenced the bacterial diversity in AnMBR as well.

     

模拟氮沉降和降雨变化对贝加尔针茅草原土壤细菌群落结构的影响

研究氮沉降和降雨变化对土壤细菌群落结构的影响,对未来预测多个气候变化因子对草地生态系统影响的交互作用具有重要意义。以施氮和灌溉分别模拟氮沉降和降雨增加,采用高通量测序技术,研究8个氮添加水平(0、15、30、50、100、150、200、300kg N hm-2a-1)和2个水分添加水平(不灌溉、模拟夏季增雨100 mm灌溉)对土壤细菌群落结构的影响。结果表明,氮素和水分输入增加后,土壤细菌群落组成、丰度均显著变化(P0.05)。在群落中占主导的细菌门类有疣微菌门Verrucomicrobia(30.61%—48.51%)、变形菌门Proteobacteria(21.37%—29.97%)、酸杆菌门Acidobacteria(9.54%—20.67%)和拟杆菌门Bacteroidetes(4.96%—9.74%)。在常规降雨和水分添加两种条件下,随着氮添加水平的增加,占主导的细菌门类(相对丰度1%)表现出不同的变化趋势。疣微菌门相对丰度在常规降雨N100—N300条件下显著降低,但在氮素和水分同时添加条件下随氮添加水平升高而逐渐升高,在N200—N300时显著升高。变形菌门和拟杆菌门相对丰度在常规降雨高氮添加条件下呈升高趋势,但在水分添加时却无明显变化。酸杆菌门相对丰度在常规降雨高氮添加条件下升高,但在水分添加后呈明显下降趋势。放线菌门Actinobacteria相对丰度在常规降雨N100—N300条件下显著升高,但在水分添加后高氮添加时显著降低。厚壁菌门Firmicutes相对丰度在常规降雨条件下无显著变化,但在水分和高氮添加条件下降低。浮霉菌门Planctomycetes相对丰度在两种不同的水分添加条件下均呈先升高后降低的趋势。氮素和水分添加对土壤细菌群落结构的变化存在明显的互作效应(P0.0001)。在不同氮素和水分输入条件下共有19个土壤细菌门类相对丰度有显著差异。土壤细菌群落结构的变化主要来自于疣微菌门和酸杆菌门的相对丰度变化,两者可作为土壤细菌群落结构变化的指示种。综上,氮素和水分添加显著改变了土壤细菌群落结构,氮素和水分对土壤细菌不同门类相对丰度变化存在明显的互作效应。     

Effect of coupled reduced irrigation and nitrogen fertilizer on soil mite community composition in a wheat field

Groundwater and nitrogen fertilizer overuse severely threatens crop productions; thus, current ecological agriculture requires low irrigation and nitrogen fertilizer inputs. The effects of combined reduced irrigation and nitrogen fertilizer addition on soil organism (e.g., mite) community and biodiversity remain poorly understood. We analyzed soil mite community composition, wheat grain yield, and soil characteristics in a 10‐year manipulation experiment with two levels of irrigation (reduced and conventional irrigation) and five nitrogen fertilizer levels (0, 70, 140, 210, and 280 kg N/ha). Reduced irrigation (20% reduction, from 280 to 220 mm) and nitrogen fertilizer (25% reduction, from 280 to 210 kg N/ha) addition did not significantly influence soil mite community and wheat yield. The relative abundances of fungivores and predators showed negative quadratic relationships with wheat yield, while that of plant parasites showed a positive relationship. The relationships between soil mite trophic groups and wheat yield revealed that we can evaluate the impacts of reduced irrigation and nitrogen fertilizer addition from the perspective of soil fauna. Soil mite community composition was altered by soil abiotic factors prior to reduced irrigation and nitrogen fertilizer addition. Overall, moderate reductions of irrigation and nitrogen fertilizer may not threaten to soil mite community and diversity or decrease crop production; in contrast, such reductions will benefit mite community development and the sustainable agriculture.     

呼伦贝尔沙地樟子松人工林土壤细菌群落结构与功能预测

为揭示呼伦贝尔沙地樟子松人工林土壤细菌群落结构和功能特征,以3种林龄（25 a、34 a和43 a）沙地樟子松人工林为研究对象,沙质草地为对照,采用野外调查、Illumina Miseq高通量测序和PICRUSt功能预测相结合的研究方法,鉴定分析土壤细菌群落结构,阐明土壤理化因子对土壤细菌群落结构的影响,预测土壤细菌功能特征。研究结果显示：（1）呼伦贝尔沙地樟子松人工林共获得土壤细菌35门92纲109目210科267属,主要细菌优势门为变形菌门（Proteobacteria）（24.29%±3.39%）、放线菌门（Actinobacteria）（23.72%±4.10%）和酸杆菌门（Acidobacteria）（23.40%±2.55%）。人工林与沙质草地的变形菌门和酸杆菌门相对丰度存在显著差异（P<0.05）,人工林间土壤细菌多样性指数不存在显著差异（P>0.05）。（2）研究区土壤细菌群落的主要影响因子是速效钾、全磷和全氮。（3）PICRUSt功能预测共获得5个一级功能层和31个二级功能层,主要涉及环境信息处理、代谢和遗传信息处理等功能。43 a人工林土壤细菌代谢功能活跃,有利于植物对养分的吸收和利用。在呼伦贝尔沙地种植樟子松人工林有助于改善土壤细菌群落结构,促进土壤细菌代谢功能,且表层土壤细菌群落对土壤环境变化更为敏感。     

Pyrosequence analysis of bacterial communities in aerobic bioreactors treating polycyclic aromatic hydrocarbon-contaminated soil

Two aerobic, lab-scale, slurry-phase bioreactors were used to examine the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil and the associated bacterial communities. The two bioreactors were operated under semi-continuous (draw-and-fill) conditions at a residence time of 35 days, but one was fed weekly and the other monthly. Most of the quantified PAHs, including high-molecular-weight compounds, were removed to a greater extent in the weekly-fed bioreactor, which achieved total PAH removal of 76%. Molecular analyses, including pyrosequencing of 16S rRNA genes, revealed significant shifts in the soil bacterial communities after introduction to the bioreactors and differences in the abundance and types of bacteria in each of the bioreactors. The weekly-fed bioreactor displayed a more stable bacterial community with gradual changes over time, whereas the monthly-fed bioreactor community was less consistent and may have been more strongly influenced by the influx of untreated soil during feeding. Phylogenetic groups containing known PAH-degrading bacteria previously identified through stable-isotope probing of the untreated soil were differentially affected by bioreactor conditions. Sequences from members of the Acidovorax and Sphingomonas genera, as well as the uncultivated “Pyrene Group 2” were abundant in the bioreactors. However, the relative abundances of sequences from the Pseudomonas, Sphingobium, and Pseudoxanthomonas genera, as well as from a group of unclassified anthracene degraders, were much lower in the bioreactors compared to the untreated soil.     

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.     

外加碳源对蚯蚓-污泥系统细菌群落结构的影响

蚯蚓是土壤生态系统中有机物质的重要分解者,并可通过物理运动和排泄蚓粪改变土壤的微生物群落组成。为研究蚓粪与污泥中微生物的相互关系,利用赤子爱胜蚓(Eisenia foetida)和人工湿地基质构建蚯蚓-污泥系统,采用高通量测序技术比较分析添加葡萄糖、乳糖、淀粉、纤维素4种碳源后污泥和蚓粪的细菌多样性及群落结构变化。结果表明,污泥的Chao和ACE指数明显高于蚓粪,添加不同碳源实验组间污泥的Chao和ACE指数差别不大,但均高于污泥对照组;添加葡萄糖、淀粉和纤维素实验组间蚓粪的Chao和ACE指数相近且高于蚯蚓对照组,乳糖实验组蚓粪的Chao和ACE指数则明显低于蚓粪对照组。添加葡萄糖、乳糖、淀粉和纤维素能够增加污泥中细菌多样性;添加葡萄糖、淀粉和纤维素能够增加蚓粪中细菌多样性,但添加乳糖会导致蚓粪中细菌多样性降低。蚓粪与污泥细菌群落结构组成存在明显差异,污泥中变形菌门、拟杆菌门、厚壁菌门、放线菌门、绿弯菌门、酸杆菌门、芽单胞菌门为优势菌门;除乳糖组外,蚓粪中变形菌门、拟杆菌门、厚壁菌门、放线菌门、疣微菌门为优势菌门(其中变形菌门和拟杆菌门占绝对优势),蚓粪乳糖组检测到柔膜菌门(2.6%),其他实验组均未检出。添加碳源后,污泥和蚓粪中能分解相应碳源的菌群增加,如葡萄糖实验组Lactococcus piscium,乳糖组Flavobacterium reichenbachii,淀粉组Alkanindiges illinoisensis和Zobellella taiwanensis,纤维素组Cellvibrio gandavensis等。     

The community composition of root-associated bacteria of the tomato plant

The objective of this study was to characterize the bacterial community composition in the bulk soil, rhizosphere soil and root tissue of the tomato plant (Lycopersicum esculentum Mill). 16S ribosomal DNA (rDNA) from the bacterial community was amplified using PCR, and sequence analysis of 16S rDNA clones was subsequently used for bacterial identification and phylogenetic classification. Phylogenetic analysis of clones (total of 68) from the bulk soil, rhizosphere and root tissues showed that about 50% of the bacteria belonged to the α-, β-, γ-, and δ-Proteobacteria or Cytophaga–Flavobacterium–Bacteroides (CFB) phyla, with only one high G+C clone identified. A number of diverse bacteria were identified within Proteobacteria, while 87% of the bacteria belonged to the genus Flavobacterium within the CFB phylum, which is a unique finding for tomato plants. Our results will be of interest to those wanting to identify bacteria that can promote plant growth or resistance to diseases.     

Novelty and Uniqueness Patterns of Rare Members of the Soil Biosphere

Soil bacterial communities typically exhibit a distribution pattern in which most bacterial species are present in low abundance. Due to the relatively small size of most culture-independent sequencing surveys, a detailed phylogenetic analysis of rare members of the community is lacking. To gain access to the rarely sampled soil biosphere, we analyzed a data set of 13,001 near-full-length 16S rRNA gene clones derived from an undisturbed tall grass prairie soil in central Oklahoma. Rare members of the soil bacterial community (empirically defined at two different abundance cutoffs) represented 18.1 to 37.1% of the total number of clones in the data set and were, on average, less similar to their closest relatives in public databases when compared to more abundant members of the community. Detailed phylogenetic analyses indicated that members of the soil rare biosphere either belonged to novel bacterial lineages (members of five novel bacterial phyla identified in the data set, as well as members of multiple novel lineages within previously described phyla or candidate phyla), to lineages that are prevalent in other environments but rarely encountered in soil, or were close relatives to more abundant taxa in the data set. While a fraction of the rare community was closely related to more abundant taxonomic groups in the data set, a significant portion of the rare biosphere represented evolutionarily distinct lineages at various taxonomic cutoffs. We reason that these novelty and uniqueness patterns provide clues regarding the origins and potential ecological roles of members of the soil's rare biosphere.     

Effects of wetland degradation on bacterial community in the Zoige Wetland of Qinghai-Tibetan Plateau (China)

Wetland degradation makes significant impacts on soil, and bacterial communities in soil are likely to respond to these impacts. The purpose of this study was to investigate the impacts of soil property, soil type and soil depth on bacterial community in different stages of soil degradation in the Zoige Wetland. Microbial biomass carbon was estimated from chloroform fumigation-extraction. Bacterial communities were evaluated by cluster and principal component analysis of DGGE banding patterns and sequencing of partial 16S rDNA PCR amplicons. Experimental results showed that microbial biomass carbon decreased with the soil types (Peat soil > Swamp soil > Meadow soil > Sandy soil) and declined with soil depths (0–20 > 20–40 > 40–60 cm). Bacterial community was affected by soil type more primarily than by soil depth. In addition, the microbial biomass carbon was strongly correlated with soil water content, soil organic carbon and total nitrogen. Sequence analysis of DGGE bands indicated that bacterial phyla of α-Proteobacteria, γ-Proteobacteria, Bacteroidetes, Flavobacterium and Unidentified bacterium predominantly existed in the soil. All these results suggest that specific changes in soil property, soil type and soil depth affected soil bacterial community both quantitatively and qualitatively.     

洮河上游不同海拔紫果云杉根际与非根际土壤细菌多样性及影响因子

【背景】紫果云杉天然林在维护洮河上游生态环境安全方面发挥着重要作用,不同海拔梯度如何影响紫果云杉根际与非根际细菌多样性、土壤养分因子及三者之间的相关性尚不清楚。【目的】深入探索紫果云杉根际与非根际土壤细菌群落结构组成及受控因子。【方法】采用Illumina Miseq平台对洮河上游不同海拔紫果云杉天然林根际与非根际土壤细菌进行测序分析,分析土壤理化因子与细菌多样性随海拔的变化趋势,并通过相关性与冗余分析探究环境因子对细菌群落的影响。【结果】土壤养分因子随海拔升高呈先增加后降低趋势;根际土养分因子组间差异显著(P<0.05),非根际组间差异不显著(P>0.05)。随海拔升高根际微生物物种多样性指数(H)、均匀度指数(E)、丰富度指数(Chao1/ACE)和OTU数目呈单峰型变化趋势;非根际多样性指数随海拔升高呈双峰型变化趋势。土壤细菌多样性与养分因子密切相关,其中有机质、全氮和碱解氮呈显著正相关(P<0.05),而土壤pH和有效磷与细菌多样性呈负相关但不显著(P>0.05)。不同海拔梯度下紫果云杉天然林细菌群落结构一致性较高,从30个样本中获得7 159个细菌OTU,注释到37个门;细菌优势类群为放线菌门、变形菌门、酸杆菌门和绿弯菌门。不同细菌门对土壤养分因子的响应各不相同,有机质、全氮和碱解氮与变形菌门呈显著正相关(P<0.05)。【结论】土壤理化因子能够显著影响紫果云杉根际与非根际细菌多样性和组成,海拔和水热条件等环境因子对植物和土壤的驱动影响是细菌群落结构稳定组成的重要原因。本研究有助于深入理解紫果云杉天然林土壤细菌多样性的变化和驱动机制,为洮河上游天然林恢复与生态恢复提供借鉴。     

Soil hydrological properties as influenced by long‐term nitrogen application and landscape positions under switchgrass seeded to a marginal cropland

Switchgrass (Panicum virgatum L.) has the potential to recover the soil hydrological properties of marginal lands. Nitrogen (N) and landscape position are the key factors in impacting these soil properties under switchgrass. The specific objective of this study was to investigate the responses of N rate (low, 0 kg N/ha and high, 112 kg N/ha) and landscape positions (shoulder and footslope) on near‐surface soil hydrological properties that included: infiltration rate (q_s), saturated hydraulic conductivity (K_sat), bulk density (ρ_b), penetration resistance (SPR), water retention (SWR), pore‐size distribution (PSD), and carbon (C) and nitrogen (N) fractions under switchgrass production. Data showed that, in general, the N and landscape position significantly influenced soil hydrological properties. Higher N rate decreased ρ_b (1.23 and 1.36 g/cm³ at 0–5 and 5–15 cm, respectively) and SPR (1.06 and 1.53 MPa at 0–5 and 5–15 cm, respectively) at both depths and increased the q_s, K_sat and Green–Ampt estimated sorptivity (S) and hydraulic conductivity (K_s) parameters, and SWR (0–5 cm depth) at 0 and ?0.4 kPa matric potentials (ψ_m). Furthermore, footslope position significantly decreased ρ_b, SPR at 0–5 and 5–15 cm depths, and increased the q_s, K_sat, S, K_s, and SWR (0–5 cm depth) at every ψ_m ranged from 0 to ?30.0 kPa. The higher N rate increased the coarse mesopores (60–1,000 μm) and total pores, whereas, footslope position increased the coarse mesopores, micropores (<60 μm), and total pores. Data from this study showed that planting switchgrass with 112 kg N/ha under footslope position helped in improving the soil hydrological properties, those can be beneficial in enhancing the biomass yield under marginal lands.     

Detection of monochlorobenzene metabolizing bacteria under anoxic conditions by DNA-stable isotope probing

Cultivation-independent analyses were applied to study the structural diversity of the bacterial community which developed in groundwater inoculated microcosms actively metabolizing monochlorobenzene (MCB) under anaerobic conditions. Addition of ¹³C-labelled MCB demonstrated that the community produced ¹³CO₂ as a metabolite at slightly increasing rates over a period of 1,051 days while no ¹³C-methane evolved. Genetic profiles of partial 16S rRNA genes generated with the single-strand conformation polymorphism (SSCP) technique by PCR from directly extracted total DNA revealed that, despite the long incubation period, six replicate microcosms were characterized by almost the same microbial members. Nine distinguishable contributors to the SSCP-profiles were characterized by DNA sequencing, revealing the presence of different members from the phyla Proteobacteria, Fibrobacteres and from the candidate division OD1. DNA-stable isotope probing (SIP) was applied to distinguish the actual MCB metabolizing bacteria from the other community members. This study reveals for the first time the structural diversity of an anaerobic MCB metabolizing bacterial community. However, it also demonstrates the limitations of SIP to detect bacteria slowly metabolizing carbon sources under anaerobic conditions.     

火电厂周边不同生物结皮细菌群落特征差异及其影响因素

为探究大气降尘重金属污染对矿区周边不同类型生物结皮细菌群落结构的影响,利用高通量测序技术分析位于宁东能源化工基地典型火电厂周边的3类生物结皮(藻结皮ZB、混生结皮HB、苔藓结皮TB)和对照(CK,裸土)的细菌丰度和群落结构,并探讨了影响细菌群落结构的环境因子。结果表明: 不同类型生物结皮的理化性质和重金属含量存在差异,且由于生物结皮对大气降尘重金属的富集作用造成各类结皮均达重度污染级别。在相对丰度排名前10的优势细菌门中,芽单胞菌门、蓝细菌门在不同类型生物结皮之间差异显著。细菌群落α多样性由高到低排序依次为CK>TB>HB>ZB。非度量多维排序(NMDS)结果显示,裸土细菌群落与其他3种生物结皮存在明显差异。相关性分析表明,生物结皮演替对细菌群落组成具有显著影响,细菌多样性和组成与pH、养分、重金属含量等密切相关。放线菌门、绿弯菌门相对丰度与pH值呈显著正相关关系,而与全氮(TN)、全磷(TP)、Pb、Zn、Cd均呈显著负相关关系;冗余分析结果表明,TN、pH、TP、有机碳(SOC)是影响3种生物结皮细菌群落α多样性以及一些优势菌群相对丰度的主要土壤环境因子,而重金属Pb、Zn、Cd是影响细菌群落结构的主要重金属元素,对细菌群落数量和多样性有抑制或刺激作用。说明pH、重金属和养分是影响结皮细菌群落组成的关键因子。总体而言,长期的重金属富集作用会对生物结皮的细菌多样性和群落组成产生影响。     

呼和浩特市大青山白桦根际土壤细菌群落结构研究

采用高通量测序技术对天然次生林生态系统演替过程中先锋树种白桦的根际土壤细菌多样性及群落结构进行了分析。研究结果表明:白桦根际土壤细菌隶属于28门、90纲、126目、213科、286属,在3个采样地中排名前8的优势细菌门的相对丰度均大于1%,分别为变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、放线菌门(Actinobacteria)、芽单胞菌门(Gemmatimonadetes)、绿弯菌门(Chloroflexi)、硝化螺旋菌门(Nitrospirae)、疣微菌门(Verrucomicrobia)和拟杆菌门(Bacteroidetes)。各样地中前3个门的相对丰度之和均在60%以上。对白桦根际土壤细菌的α多样性指数、门水平的聚类热图以及PCoA聚类结果的分析表明,3个采样地中,小井沟(B2)和哈达门森林公园(C2)白桦根际土壤细菌的物种组成更为接近,与井儿梁(A2)的物种组成有一定差异;且小井沟和哈达门森林公园的物种多样性及丰度(ACE指数)显著高于井儿梁,表明细菌对不同环境的适应能力有明显差异。对细菌群落结构与土壤理化性质的RDA分析及相关性分析表明,环境因子对白桦根际土壤细菌的影响顺序为:全氮TN酸碱度pH含水量WC速效钾AK硝态氮NN铵态氮AN有机质OM有效磷EP,其中,TN、pH和WC是白桦根际土壤优势细菌的主要影响因子。研究结果为深入认识森林生态系统中根际土壤细菌的群落结构和影响因子提供了理论依据。     

Start-up and stabilization of an Anammox process from a non-acclimatized sludge in CSTR

Development of an Anammox (anaerobic ammonium oxidation) process using non-acclimatized sludge requires a long start-up period owing to the very slow growth rate of Anammox bacteria. This article addresses the issue of achieving a shorter start-up period for Anammox activity in a well-mixed continuously stirred tank reactor (CSTR) using non-acclimatized anaerobic sludge. Proper selection of enrichment conditions and low stirring speed of 30 ± 5 rpm resulted in a shorter start-up period (82 days). Activity tests revealed the microbial community structure of Anammox micro-granules. Ammonia-oxidizing bacteria (AOB) were found on the surface and on the outer most layers of granules while nitrite-oxidizing bacteria (NOB) and Anammox bacteria were present inside. Fine-tuning of influent NO₂ ⁻/NH₄ ⁺ ratio allowed Anammox activity to be maintained when mixed microbial populations were present. The maximum nitrogen removal rate achieved in the system was 0.216 kg N/(m³ day) with a maximum specific nitrogen removal rate of 0.434 g N/(g VSS day). During the study period, Anammox activity was not inhibited by pH changes and free ammonia toxicity.