Effects of nutritional input and diesel contamination on soil enzyme activities and microbial communities in antarctic soils

Pollution of Antarctic soils may be attributable to increased nutritional input and diesel contamination via anthropogenic activities. To investigate the effect of these environmental changes on the Antarctic terrestrial ecosystem, soil enzyme activities and microbial communities in 3 types of Antarctic soils were evaluated. The activities of alkaline phosphomonoesterase and dehydrogenase were dramatically increased, whereas the activities of β-glucosidase, urease, arylsulfatase, and fluorescein diacetate hydrolysis were negligible. Alkaline phosphomonoesterase and dehydrogenase activities in the 3 types of soils increased 3- to 10-fold in response to nutritional input, but did not increase in the presence of diesel contamination. Consistent with the enzymatic activity data, increased copy numbers of the phoA gene, encoding an alkaline phosphomonoesterase, and the 16S rRNA gene were verified using quantitative real-time polymerase chain reaction. Interestingly, dehydrogenase activity and 16S rRNA gene copy number increased slightly after 30 days, even under diesel contamination, probably because of adaptation of the bacterial population. Intact Antarctic soils showed a predominance of Actinobacteria phylum (mostly Pseudonorcarida species) and other phyla such as Proteobacteria, Chloroflexi, Planctomycetes, Firmicutes, and Verrucomicrobia were present in successively lower proportions. Nutrient addition might act as a selective pressure on the bacterial community, resulting in the prevalence of Actinobacteria phylum (mostly Arthrobacter species). Soils contaminated by diesel showed a predominance of Proteobacteria phylum (mostly Phyllobacterium species), and other phyla such as Actinobacteria, Bacteroidetes, Planctomycetes, and Gemmatimonadetes were present in successively lower proportions. Our data reveal that nutritional input has a dramatic impact on bacterial communities in Antarctic soils and that diesel contamination is likely toxic to enzymes in this population.     

Diversity of prokaryotes associated with soils around coal-fire gas vents in MaNasi county of Xinjiang, China

Bacterial and archaeal diversity in surface soils of three coal-fire vents was investigated by T-RFLP analysis and clone libraries of 16S rRNA genes. Soil analysis showed that underground coal fires significantly influenced soil pH, moisture and NO₃ ^? content but had little effect on other elements, organic matter and available nutrients. Hierarchical cluster analysis showed that bacterial community patterns in the soils were very similar, but abundance varied with geographic distance. A clone library from one soil showed that the bacterial community was mainly composed of Firmicutes, Proteobacteria, Acidobacteria, Bacteroidetes, Planctomycetes, Actinobacteria, and unidentified groups. Of these, Firmicutes was the most abundant, accounting for 71.4 % of the clones, and was mainly represented by the genera Bacillus and Paenibacillus. Archaeal phylotypes were closely related to uncultivated species of the phyla Crenarchaeota (97.9 % of clones) and Thaumarchaeota (2.1 %). About 28 % of archaeal phylotypes were associated with ammonia oxidization, especially phylotypes that were highly related to a novel, ammonia-oxidizing isolate from the phylum Thaumarchaeota. These results suggested that microbial communities in the soils were diverse and might contain a large number of novel cultivable species with the potential to assimilate materials by heterotrophic metabolism at high temperature.     

Crude Oil Treatment Leads to Shift of Bacterial Communities in Soils from the Deep Active Layer and Upper Permafrost along the China-Russia Crude Oil Pipeline Route

The buried China-Russia Crude Oil Pipeline (CRCOP) across the permafrost-associated cold ecosystem in northeastern China carries a risk of contamination to the deep active layers and upper permafrost in case of accidental rupture of the embedded pipeline or migration of oil spills. As many soil microbes are capable of degrading petroleum, knowledge about the intrinsic degraders and the microbial dynamics in the deep subsurface could extend our understanding of the application of in-situ bioremediation. In this study, an experiment was conducted to investigate the bacterial communities in response to simulated contamination to deep soil samples by using 454 pyrosequencing amplicons. The result showed that bacterial diversity was reduced after 8-weeks contamination. A shift in bacterial community composition was apparent in crude oil-amended soils with Proteobacteria (esp. α-subdivision) being the dominant phylum, together with Actinobacteria and Firmicutes. The contamination led to enrichment of indigenous bacterial taxa like Novosphingobium, Sphingobium, Caulobacter, Phenylobacterium, Alicylobacillus and Arthrobacter, which are generally capable of degrading polycyclic aromatic hydrocarbons (PAHs). The community shift highlighted the resilience of PAH degraders and their potential for in-situ degradation of crude oil under favorable conditions in the deep soils.     

Bacterial Community Responses to Soils along a Latitudinal and Vegetation Gradient on the Loess Plateau,China

Soil bacterial communities play an important role in nutrient recycling and storage in terrestrial ecosystems. Loess soils are one of the most important soil resources for maintaining the stability of vegetation ecosystems and are mainly distributed in northwest China. Estimating the distributions and affecting factors of soil bacterial communities associated with various types of vegetation will inform our understanding of the effect of vegetation restoration and climate change on these processes. In this study, we collected soil samples from 15 sites from north to south on the Loess Plateau of China that represent different ecosystem types and analyzed the distributions of soil bacterial communities by high-throughput 454 pyrosequencing. The results showed that the 142444 sequences were grouped into 36816 operational taxonomic units (OTUs) based on 97% similarity. The results of the analysis showed that the dominant taxonomic phyla observed in all samples were Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria and Planctomycetes. Actinobacteria and Proteobacteria were the two most abundant groups in all samples. The relative abundance of Actinobacteria increased from 14.73% to 40.22% as the ecosystem changed from forest to sandy, while the relative abundance of Proteobacteria decreased from 35.35% to 21.40%. Actinobacteria and Proteobacteria had significant correlations with mean annual precipitation (MAP), pH, and soil moisture and nutrients. MAP was significantly correlated with soil chemical and physical properties. The relative abundance of Actinobacteria, Proteobacteria and Planctomycetes correlated significantly with MAP, suggesting that MAP was a key factor that affected the soil bacterial community composition. However, along with the MAP gradient, Chloroflexi, Bacteroidetes and Cyanobacteria had narrow ranges that did not significantly vary with the soil and environmental factors. Overall, we conclude that the edaphic properties and/or vegetation types are driving bacterial community composition. MAP was a key factor that affects the composition of the soil bacteria on the Loess Plateau of China.     

Pyrosequencing-based assessment of bacterial community structure along different management types in German forest and grassland soils

Background

Soil bacteria are important drivers for nearly all biogeochemical cycles in terrestrial ecosystems and participate in most nutrient transformations in soil. In contrast to the importance of soil bacteria for ecosystem functioning, we understand little how different management types affect the soil bacterial community composition.

Methodology/Principal Findings

We used pyrosequencing-based analysis of the V2-V3 16S rRNA gene region to identify changes in bacterial diversity and community structure in nine forest and nine grassland soils from the Schwäbische Alb that covered six different management types. The dataset comprised 598,962 sequences that were affiliated to the domain Bacteria. The number of classified sequences per sample ranged from 23,515 to 39,259. Bacterial diversity was more phylum rich in grassland soils than in forest soils. The dominant taxonomic groups across all samples (>1% of all sequences) were Acidobacteria, Alphaproteobacteria, Actinobacteria, Betaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, and Firmicutes. Significant variations in relative abundances of bacterial phyla and proteobacterial classes, including Actinobacteria, Firmicutes, Verrucomicrobia, Cyanobacteria, Gemmatimonadetes and Alphaproteobacteria, between the land use types forest and grassland were observed. At the genus level, significant differences were also recorded for the dominant genera Phenylobacter, Bacillus, Kribbella, Streptomyces, Agromyces, and Defluviicoccus. In addition, soil bacterial community structure showed significant differences between beech and spruce forest soils. The relative abundances of bacterial groups at different taxonomic levels correlated with soil pH, but little or no relationships to management type and other soil properties were found.

Conclusions/Significance

Soil bacterial community composition and diversity of the six analyzed management types showed significant differences between the land use types grassland and forest. Furthermore, bacterial community structure was largely driven by tree species and soil pH.     

Ex-situ enzyme activity and bacterial community diversity through soil depth profiles in penguin and seal colonies on Vestfold Hills, East Antarctica

The soils impacted by sea animal excreta are important sources of nutrients in Antarctic terrestrial ecosystems, and soil microorganisms are the principal drivers of carbon and nitrogen cycling. However, microbial diversity and enzyme activities in these soils have still received little attention. In this paper, we investigated the distribution characteristics of bacterial community in four penguin and seal colony soil profiles collected in East Antarctica, using 16S rDNA-DGGE and real-time quantitative PCR. Soil microbial biomass carbon (C_mic), soil respiration (SR), and enzyme activities involved in carbon, nitrogen, and phosphorus metabolisms were also measured. Overall soil C_mic, SR, enzyme activities, and bacterial abundance decreased with depth. The bacterial abundance had a significant correlation with soil organic carbon and total nitrogen and highly corresponded to the relative content of penguin guano or seal excreta in these soil profiles. The 16S rDNA-DGGE revealed the complicated bacterial community structure in penguin and seal colony soils, and the band richness and dominant bands decreased with soil depth. Cluster analysis of DGGE profiles indicated that bacterial community in those soil profiles were divided into four main categories with the bacterial genetic similarity of 22 %, and the majority of the sequenced bands were Proteobacteria (α, β, γ), Actinobacteria, Bacteroidetes, Deinococcus-Thermus, Chloroflexi, and Firmicutes. Our results indicated that the deposition of penguin guano or seal excreta, which caused the variability in soil soil organic carbon, total nitrogen, pH, and soil moisture, might have an important effect on the vertical distribution pattern of bacterial abundance and diversity in Antarctic soil profiles.     

Taxonomic diversity of aerobic organotrophic bacteria from clean vietnamese soils and their capacity for oxidation of petroleum hydrocarbons

The dominant species and abundance of the cultured aerobic organotrophic bacteria were determined in the clean soils of the Republic of Vietnam. The total number of organotrophs varied from 2.0 × 10⁵ to 5.8 × 10⁸ CFU/g soil. A considerable fraction of the bacterial population (1.1 × 10⁵–9.5 × 10⁶ CFU/g soil) was able to utilize petroleum hydrocarbons as the sole carbon and energy source. Most of the organisms obtained in pure cultures were gram-positive bacteria; over 70% were hydrocarbon-oxidizing organisms. Analysis of 16S rRNA gene sequences resulted in tentative determination of the taxonomic position of 22 strains, with 12 belonging to the Firmicutes, 4, to the Proteobacteria, and 6 to the Actinobacteria. The most common bacteria capable of hydrocarbon oxidation belonged to the genera Acinetobacter, Bacillus, Brevibacillus, Chromobacterium, Cupriavidus, Gordonia, Microbacterium, Mycobacterium, and Rhodococcus. Some of the isolated Bacillus and Staphylococcus strains, as well as one Pseudomonas and one Sinomonas strain, did not utilize hydrocarbons. Gram-positive degraders, especially members of the order Actinomycetales, which exhibited high hydrocarbon-oxidizing activity, gained competitive advantage in the presence of hydrocarbons. This microbial group probably plays an important role in hydrocarbon degradation in tropical soils. Thus, Vietnamese soils, which had no history of petroleum contamination, support numerically significant and taxonomically diverse populations of h ydrocarbon-oxidizing bacteria.     

Ecology of algal communities of different soil types from Cierva Point, Antarctic Peninsula

During summer 2005/2006, we characterized three sampling sites on mineral soils and four on ornithogenic soils from Cierva Point, Antarctic Peninsula, in terms of topographic and abiotic features (altitude, slope, magnetic direction, temperature, texture, pH, conductivity, organic matter, moisture and nutrient concentrations), and compared their microalgal communities through taxonomic composition, species richness, diversity, chlorophyll a content and their variation in time. Average values of pH, moisture, organic matter and nutrient concentrations were always significantly lower in mineral than in ornithogenic soils. Low N/P mass ratio showed potential N-limitation of biomass capacity in the former. On the other hand, the results suggested that physical stability is not as a key stress factor for mineral soil microalgae. Chlorophyll a concentration was not only higher in ornithogenic soils, but it also showed a wider range of values. As this parameter was positively correlated with temperature, pH, nutrients, organic matter and moisture, we cannot come to conclusions regarding the influence of each factor on algal growth. Communities of mineral soils were significantly more diverse than those of enriched ornithogenic soils due to higher species richness as well as higher equitability. Also, their structure was steadier over time, as shown by a cluster analysis based on relative frequency of algal taxa. Although Cyanobacteria and Bacillariophyceae dominated almost all samples, Chlorophyceae represented 34% of the 140 taxa recorded, and most of them observed only in cultures. The detection under controlled conditions of a high latent species richness in harsh mineral soil sites shows that the composition and equitability of these microalgal communities would be more prone to modification due to the manifold local consequences of climatic change than those of ornithogenic soils.     

Bacterial community of very wet and acidic subalpine forest and fire-induced grassland soils

The subalpine forest and grassland ecosystems at Tatajia in Yushan National Park, Taiwan, at an elevation of 2,700 m, mean annual precipitation of 4,100 mm, mean annual temperature of 9.5°C, and soil pH near 3.5, represent land types whose bacterial communities have not been previously characterized. To this end, small subunit (SSU) rRNA libraries were prepared from environmental DNA, and 319 clones were sequenced and characterized. Despite differences in vegetation, Acidobacteria, Proteobacteria and Firmicutes were the most abundant phyla in soil communities from the forest and grassland. Although not significantly different, on the basis of Chao1, Shannon and other indices and rarefaction analyses, the diversity of the bacterial community of grassland appeared higher than that of the forest. The composition of the most abundant operational taxonomic units (OTUs) also differed between the grassland and forest communities. Because the grassland was formed by fire 30 years ago from forest, these results indicated a different bacterial community could form within that time. Moreover, most of the OTUs abundant in Tatajia soils had been previously detected in other studies, but in lower numbers. Therefore, the bacterial communities in Tatajia differed in relative abundance but not in types of bacteria present. However, one acidobacterial OTU abundant in Tatajia had previously been found to be abundant in soils from around the world. Thus, this OTU may represent a particularly abundant and cosmopolitan bacterial phylotype.     

Microbial diversity in uterus of healthy and metritic postpartum Holstein dairy cows

Clone library of bacterial 16S rRNA gene was constructed to evaluate the bacterial diversity and community structure of uterus samples obtained from three postpartum healthy cows and three metritic cows on days 10 and 40. Sequences were assigned to five major groups (Bacteroidetes, Firmicutes, Fusobacteria, Proteobacteria, and Tenericutes) and to an uncultured group. On day 10, Bacteroidetes, Firmicutes, and Fusobacteria were the dominant group both in healthy and metritic cows. On day 40, the major sequences were affiliated with Bacteroidetes, Firmicutes, Tenericutes, and Proteobacteria. Tenericutes (Ureaplasma diversum) were revealed only from healthy cows, while Proteobacteria (Histophilus somni) were found only from metritic cows. Quantitative PCR revealed that metritic cows on day 10 showed higher value of total bacteria, Bacteroidetes, Peptostreptococcus, and Fusobacterium compared with healthy cows, while only a higher value of Fusobacterium spp. was observed from the metritic cows on day 40 compared with that from healthy cows (P?<?0.05). Our data indicates that great difference in the uterine bacterial community in both phyla level and species level exists between healthy and metritic postpartum cows, and dynamic changes in bacterial community occur over time.     

Characterization of feather-degrading bacteria from Brazilian soils

Studies on keratinolytic microorganisms have been mainly related to their biotechnological applications and association with animal pathologies. However, these organisms have an ecological relevance to recycling keratinous residues in nature. This work aimed to select and identify new culturable feather-degrading bacteria isolated from soils of Brazilian Amazon forest and Atlantic forest. Bacteria that were isolated from temperate soils and bacteria from Amazonian basin soil were tested for their capability to grow on feather meal agar (FMA). Proteolytic bacteria were tested for feather degradation and were further identified according to their morphological and biochemical characteristics. Also, molecular identification based on 16S rDNA gene sequencing was carried out. A total of 24 proteolytic and 20 feather-degrading isolates were selected; Most of the isolates were from the Bacillus genus (division Firmicutes), but one Aeromonas, two Serratia (??-Proteobacteria), and one Chryseobacterium (Cytophaga-Flavobacterium group).     

Highly Heterogeneous Soil Bacterial Communities around Terra Nova Bay of Northern Victoria Land,Antarctica

Given the diminished role of biotic interactions in soils of continental Antarctica, abiotic factors are believed to play a dominant role in structuring of microbial communities. However, many ice-free regions remain unexplored, and it is unclear which environmental gradients are primarily responsible for the variations among bacterial communities. In this study, we investigated the soil bacterial community around Terra Nova Bay of Victoria Land by pyrosequencing and determined which environmental variables govern the bacterial community structure at the local scale. Six bacterial phyla, Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Cyanobacteria, and Bacteroidetes, were dominant, but their relative abundance varied greatly across locations. Bacterial community structures were affected little by spatial distance, but structured more strongly by site, which was in accordance with the soil physicochemical compositions. At both the phylum and species levels, bacterial community structure was explained primarily by pH and water content, while certain earth elements and trace metals also played important roles in shaping community variation. The higher heterogeneity of the bacterial community structure found at this site indicates how soil bacterial communities have adapted to different compositions of edaphic variables under extreme environmental conditions. Taken together, these findings greatly advance our understanding of the adaption of soil bacterial populations to this harsh environment.     

Bacterial diversity in dry modern freshwater stromatolites from Ruidera Pools Natural Park,Spain

Ruidera Pools Natural Park, Spain, constitutes one of the most representative systems of carbonate precipitation in Europe. The prokaryotic community of a dry modern stromatolite recovered from the park has been analyzed by molecular techniques that included denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analysis, together with microscopic observations from the sample and cultures. Ribosomal RNA was directly extracted to study the putatively active part of the microbial community present in the sample. A total of 295 16S rRNA gene sequences were analyzed. Libraries were dominated by sequences related to Cyanobacteria, most frequently to the genus Leptolyngbya. A diverse and abundant assemblage of non-cyanobacterial sequences was also found, including members of Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Acidobacteria,Planctomycetes and Chloroflexi groups. No amplification was obtained when using archaeal primers. The results showed that at the time of sampling, when the pool was dry, the bacterial community of the stromatolites was dominated by groups of highly related Cyanobacteria, including new groups that had not been previously reported, although a high diversity outside this phylogenetic group was also found. The results indicated that part of the Cyanobacteria assemblage was metabolically active and could thus play a role in the mineralization processes inside the stromatolites.     

Changes in the bacterial populations of the highly alkaline saline soil of the former lake Texcoco (Mexico) following flooding

Flooding an extreme alkaline-saline soil decreased alkalinity and salinity, which will change the bacterial populations. Bacterial 16S rDNA libraries were generated of three soils with different electrolytic conductivity (EC), i.e. soil with EC 1.7 dS m⁻¹ and pH 7.80 (LOW soil), with EC 56 dS m⁻¹ and pH 10.11 (MEDIUM soil) and with EC 159 dS m⁻¹ and pH 10.02 (HIGH soil), using universal bacterial oligonucleotide primers, and 463 clone 16S rDNA sequences were analyzed phylogenetically. Library proportions and clone identification of the phyla Proteobacteria, Actinobacteria, Acidobacteria, Cyanobacteria, Bacteroidetes, Firmicutes and Cloroflexi showed that the bacterial communities were different. Species and genera of the Rhizobiales, Rhodobacterales and Xanthomonadales orders of the α- and γ-subdivision of Proteobacteria were found at the three sites. Species and genera of the Rhodospirillales, Sphingobacteriales, Clostridiales, Oscillatoriales and Caldilineales were found only in the HIGH soil, Sphingomonadales, Burkholderiales and Pseudomonadales in the MEDIUM soil, Myxococcales in the LOW soil, and Actinomycetales in the MEDIUM and LOW soils. It was found that the largest diversity at the order and species level was found in the MEDIUM soil as bacteria of both the HIGH and LOW soils were found in it.     

Vertical profiles of microbial communities in perfluoroalkyl substance-contaminated soils

Poly- and perfluoroalkyl compounds (PFASs) are ubiquitous in the environment, but their influences on microbial community remain poorly known. The present study investigated the depth-related changes of archaeal and bacterial communities in PFAS-contaminated soils. The abundance and structure of microbial community were characterized using quantitative PCR and high-throughput sequencing, respectively. Microbial abundance changed considerably with soil depth. The richness and diversity of both bacterial and archaeal communities increased with soil depth. At each depth, bacterial community was more abundant and had higher richness and diversity than archaeal community. The structure of either bacterial or archaeal community displayed distinct vertical variations. Moreover, a higher content of perfluorooctane sulfonate (PFOS) could have a negative impact on bacterial richness and diversity. The rise of soil organic carbon content could increase bacterial abundance but lower the richness and diversity of both bacterial and archaeal communities. In addition, Proteobacteria, Actinobacteria, Chloroflexi, Cyanobacteria, and Acidobacteria were the major bacterial groups, while Thaumarchaeota, Euryarchaeota, and unclassified Archaea dominated in soil archaeal communities. PFASs could influence soil microbial community.     

Characterization of the bacterial and archaeal communities in rice field soils subjected to long-term fertilization practices

The bacterial and archaeal communities in rice field soils subjected to different fertilization regimes for 57 years were investigated in two different seasons, a non-planted, drained season (April) and a rice-growing, flooded season (August), by performing soil dehydrogenase assay, real-time PCR assay and pyrosequencing analysis. All fertilization regimes increased the soil dehydrogenase activity while the abundances of bacteria and archaea increased in the plots receiving inorganic fertilizers plus compost and not in those receiving inorganic fertilizers only. Rice-growing and flooding decreased the soil dehydrogenase activity while they increased the bacterial diversity in rice field soils. The bacterial communities were dominated by Chloroflexi, Proteobacteria, and Actinobacteria and the archaeal communities by Crenarchaeota at the phylum level. In principal coordinates analysis based on the weighted Fast UniFrac metric, the bacterial and archaeal communities were separated primarily by season, and generally distributed along with soil pH, the variation of which had been caused by long-term fertilization. Variations in the relative abundance according to the season or soil pH were observed for many bacterial and archaeal groups. In conclusion, the microbial activity, prokaryotic abundance and diversity, and prokaryotic community structure in the rice field soils were changed by season and long-term fertilization.     

Identification of nitrogen-incorporating bacteria in petroleum-contaminated arctic soils by using [15N]DNA-based stable isotope probing and pyrosequencing

Arctic soils are increasingly susceptible to petroleum hydrocarbon contamination, as exploration and exploitation of the Arctic increase. Bioremediation in these soils is challenging due to logistical constraints and because soil temperatures only rise above 0°C for ∼2 months each year. Nitrogen is often added to contaminated soil in situ to stimulate the existing microbial community, but little is known about how the added nutrients are used by these microorganisms. Microbes vary widely in their ability to metabolize petroleum hydrocarbons, so the question becomes: which hydrocarbon-degrading microorganisms most effectively use this added nitrogen for growth? Using [¹⁵N]DNA-based stable isotope probing, we determined which taxonomic groups most readily incorporated nitrogen from the monoammonium phosphate added to contaminated and uncontaminated soil in Canadian Forces Station-Alert, Nunavut, Canada. Fractions from each sample were amplified with bacterial 16S rRNA and alkane monooxygenase B (alkB) gene-specific primers and then sequenced using lage-scale parallel-pyrosequencing. Sequence data was combined with 16S rRNA and alkB gene C quantitative PCR data to measure the presence of various phylogenetic groups in fractions at different buoyant densities. Several families of Proteobacteria and Actinobacteria that are directly involved in petroleum degradation incorporated the added nitrogen in contaminated soils, but it was the DNA of Sphingomonadaceae that was most enriched in ¹⁵N. Bacterial growth in uncontaminated soils was not stimulated by nutrient amendment. Our results suggest that nitrogen uptake efficiency differs between bacterial groups in contaminated soils. A better understanding of how groups of hydrocarbon-degraders contribute to the catabolism of petroleum will facilitate the design of more targeted bioremediation treatments.     

Characterization of culturable heterotrophic bacteria in hydrocarbon-contaminated soil from an alpine former military site

We characterized the culturable, heterotrophic bacterial community in soil collected from a former alpine military site contaminated with petroleum hydrocarbons. The physiologically active eubacterial community, as revealed by fluorescence-in situ-hybridization, accounted for 14.9 % of the total (DAPI-stained) bacterial community. 4.0 and 1.2 % of the DAPI-stained cells could be attributed to culturable, heterotrophic bacteria able to grow at 20 and 10 °C, respectively. The majority of culturable bacterial isolates (23/28 strains) belonged to the Proteobacteria with a predominance of Alphaproteobacteria. The remaining isolates were affiliated with the Firmicutes, Actinobacteria and Bacteroidetes. Five strains could be identified as representatives of novel species. Characterization of the 28 strains demonstrated their adaptation to the temperature and nutrient conditions prevailing in the studied soil. One-third of the strains was able to grow at subzero temperatures (?5 °C). Studies on the effect of temperature on growth and lipase production with two selected strains demonstrated their low-temperature adaptation.     

西宁南山4种灌木根际和非根际土壤微生物、酶活性和养分特征

西宁南山区植被退化情况严重,人工造林植被恢复被看作是最有效的恢复手段,其中选择合适造林树种尤为关键。选择人工种植的唐古特白刺Nitraria tangutorum、柠条Caragana korshinskii、西北小蘗Berberis vernae和短叶锦鸡儿Caragana brevifolia共4种灌木树种造林试验区为研究对象,通过测定根际和非根际土壤微生物数量、酶活性及养分含量,综合比较种植4种灌木树种根际和非根际土壤肥力差异,科学评价其对土壤的改善效果。研究表明:(1)土壤微生物数量和酶活性总体呈现出根际高于非根际的规律,仅放线菌数量和脲酶活性出现了根际低于非根际现象。(2)土壤养分方面,4种灌木根际土壤和非根际土壤p H值、全N、全P、全K含量差异不显著,有机质、有效P、速效K含量均呈现出根际非根际,而碱解N则是根际非根际。(3)土壤酶活性与土壤微生物数量相关性不显著,土壤有机质含量与土壤细菌、真菌数量呈极显著正相关,有效P含量与土壤细菌、真菌和放线菌数量呈极显著正相关,速效K含量与过氧化氢酶、酸性磷酸酶活性呈显著正相关,全N、碱解N含量均与脲酶活性呈显著正相关。(4)从土壤肥力综合水平来看,根际非根际,其中根际土壤中西北小蘗柠条短叶锦鸡儿唐古特白刺,研究结果表明西北小蘗和柠条能大幅提高土壤肥力,改良土壤效果较好。     

Identification of Household Bacterial Community and Analysis of Species Shared with Human Microbiome

Microbial populations in indoor environments, where we live and eat, are important for public health. Various bacterial species reside in the kitchen, and refrigerators, the major means of food storage within kitchens, can be a direct source of food borne illness. Therefore, the monitoring of microbiota in the refrigerator is important for food safety. We investigated and compared bacterial communities that reside in the vegetable compartment of the refrigerator and on the seat of the toilet, which is recognized as highly colonized by microorganisms, in ten houses using high-throughput sequencing. Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes were predominant in refrigerator and toilet samples. However, Proteobacteria was more abundant in the refrigerator, and Firmicutes was more abundant in the toilet. These household bacterial communities were compared with those of human skin and gut to identify potential sources of household bacteria. Bacterial communities from refrigerators and toilets shared more species in common with human skin than gut. Opportunistic pathogens, including Propionibacterium acnes, Bacteroides vulgatus, and Staphylococcus epidermidis, were identified as species shared with human skin and gut microbiota. This approach can provide a general background of the household microbiota and a potential method of source-tracking for public health purposes.