Soil Bacterial Populations Research Articles

Bacteria play a more important role than nutrients in the accumulation of tetracycline resistance in manure-treated soil

Manure application to agricultural soils can increase the abundance of antibiotic-resistance genes and resistant bacterial populations in soil. The aim of this study was to compare the contribution of nutrients and microorganisms of manure in the accumulation of tetracycline resistance in manure-treated soil. Soil microcosms were incubated for 77 days in a bench-scale mesocosm experiment and for 2 years in a greenhouse experiment and treated with manure or sterilized manure. In the manured soil, both aerobic tetracycline-resistant bacteria (TRB) and tetracycline-resistance genes (TRGs) (tetG, tetB(P), tetO, and tetL) were detected. Nutrients and TRGs not carried by live bacteria contribute little to the accumulation of TRB and TRGs, while microorganisms from manure contributed considerably. However, in soil with a long history of manure fertilization, the survival or dissemination of TRB and TRGs were prevented. The native soil microbial communities were probably more competitive than microbial species added with manure for nutrients of colonizing soil niches. Some bacterial species showed a significant negative correlation with the relative abundance of the four TRGs and TRB; probably, these bacterial species might have played a role in inhibiting the survival of TRB or dissemination of TRGs. These findings provide some clues for revealing the mechanisms of how manure application influences the abundance of TRGs and TRB in soil.

A lack of consensus in the literature findings on the removal of airborne benzene by houseplants: Effect of bacterial enrichment

Removal rates of benzene and formaldehyde gas by houseplants reported by several laboratories varied by several orders of magnitude. We hypothesized that these variations were caused by differential responses of soil microbial populations to the high levels of pollutant used in the studies, and tested responses to benzene by plants and soils separately. Five houseplant species and tobacco were exposed to benzene under hydroponic conditions and the uptake rates compared. Among the test plants, Syngonium podophyllum and Chlorophytum comosum and Epipremnum aureum had the highest benzene removal rates. The effects of benzene addition on populations of soil bacteria were determined using reverse transcription quantitative PCR (RT-qPCR) assays targeting microbial genes involved in benzene degradation. The total bacterial population increased as shown by increases in the levels of eubacteria 16S rRNA, which was significantly higher in the high benzene incubations than in the low benzene incubations. Transcripts (mRNA) of genes encoding phenol monooxygenases, catechol-2,3-dioxygenase and the housekeeping gene rpoB increased in all soils incubated with high benzene concentrations. Therefore the enrichment of soils with benzene gas levels typical of experiments with houseplants in the literature artificially increased the levels of total soil bacterial populations, and especially the levels and activities of benzene-degrading bacteria.

Impact of Repeated Applications of Metalaxyl on Its Dissipation and Microbial Community in Soil

Metalaxyl, an important phenylamide fungicide, is widely used for controlling fungal diseases caused by pathogens of the orders Peronosporales and Pythiales. Under laboratory conditions, metalaxyl was applied to soil samples at the recommended field rate (1×FR) and double of recommended field rate (2×FR) for two and three times. Soil subsamples were taken at 0, 1, 3, 7, 14, 28, and 45 days after the last application of metalaxyl for determination of metalaxyl residues and 7, 14, 28, and 56 days for enumeration of cultivable microorganisms and DGGE profile of soil microbial community. Soil incubation experiments revealed that metalaxyl was degraded faster in the third application than in the second application of the fungicide, half-lives of metalaxyl decreasing from 16.2 to 9.9 days for recommended field rate and 22.1 to 20.0 days for double of recommended field rate. Soil bacterial and fungal populations decreased in the first 14 days and then recovered to the control levels; population of actinomycetes did not alter in the first 28 days but increased at the end of the experiment after the second application. However, after the third treatment, temporary increase in soil bacteria population, nonsignificant inhibition effect on fungal population, and obvious stimulation effect on actinomycetes number were observed. DGGE results showed that successive inputs of metalaxyl altered the bacterial community structure. There were differences in the persistence and effects of metalaxyl on microbial community between the second and the third metalaxyl treatments.

Management Practices Affect Soil Nutrients and Bacterial Populations in Backgrounding Beef Feedlot.

Contaminants associated with manure in animal production sites are of significant concern. Unless properly managed, manure-derived soil nutrients in livestock production sites can deteriorate soil and water quality. This 3-yr study evaluated a soil nutrient management strategy with four sequentially imposed management practices: 12-mo backgrounding (BG), manure removal from the feeder area (FD), 12-mo destocking (DS), and 12-mo grass hay harvesting (H) in a small backgrounding feedlot. Resulting soil nutrient levels, total (), and N cycling bacterial ( and ) populations after each management practice in feedlot feeder and grazing (GR) areas and in crop grown at the control location (CT) were measured. Irrespective of management practice, FD contained greater soil nutrient concentrations than the GR and CT. Regardless of management practice, total bacteria cells (1.4 × 10 cells g soil) and nitrate reducers (5.2 × 10 cells g soil) were an order of magnitude higher in the FD than in the GR and CT, whereas nitrifying bacteria concentrations (1.4 × 10 cells g soil) were higher in the GR. Manure removal from the feeder area reduced M3-P (39%), total C (21%), total N (23%), NH-N (47%), and NO-N (93%) levels established in the FD during BG. Destocking lowered total C and N (45%) in the FD and NH-N (47%), NO-N (76%), and Zn (16%) in the GR. Hay harvesting reduced all soil nutrients in the FD and GR marginally. The management strategy has potential to lower soil nutrient concentrations, control soil nutrient buildup, and limit nutrient spread within the feedlot.

Differential responses of Oryza sativa secondary metabolism to biotic interactions with cooperative, commensal and phytopathogenic bacteria.

Profiling of plant secondary metabolite allows to differentiate the different types of ecological interactions established between rice and bacteria. Rice responds to ecologically distinct bacteria by altering its content of flavonoids and hydroxycinnamic acid derivatives. Plants' growth and physiology are strongly influenced by the biotic interactions that plants establish with soil bacterial populations. Plants are able to sense and to respond accordingly to ecologically distinct bacteria, by inducing defense pathways against pathogens to prevent parasitic interactions, and by stimulating the growth of root-associated beneficial or commensal bacteria through root exudation. Plant secondary metabolism is expected to play a major role in this control. However, secondary metabolite responses of a same plant to cooperative, commensal and deleterious bacteria have so far never been compared. The impact of the plant growth-promoting rhizobacteria (PGPR) Azospirillum lipoferum 4B on the secondary metabolite profiles of two Oryza sativa L. cultivars (Cigalon and Nipponbare) was compared to that of a rice pathogen Burkholderia glumae AU6208, the causing agent of bacterial panicle blight and of a commensal environmental bacteria Escherichia coli B6. Root and shoot rice extracts were analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC). Principal component analyses (PCAs) pinpointed discriminant secondary metabolites, which were characterized by mass spectrometry. Direct comparison of metabolic profiles evidenced that each bacterial ecological interaction induced distinct qualitative and quantitative modifications of rice secondary metabolism, by altering the content of numerous flavonoid compounds and hydroxycinnamic acid (HCA) derivatives. Secondary metabolism varied according to the cultivars and the interaction types, demonstrating the relevance of secondary metabolic profiling for studying plant-bacteria biotic interactions.

Effect of pesticides application on peanut (Arachis hypogaea L.) associated phosphate solubilizing soil bacteria

In the peanut-growing area of Córdoba, Argentina, herbicides and fungicides utilization is a common practice. This study analyses the effect of pesticides applied at recommended rates on the number and diversity of phosphate solubilizing soil bacteria from this area and the frequency of pyrroquinoline quinone genes (pqq). Pesticide soil treatment did not affect the abundance of culturable phosphate solubilizing bacteria but increased their genetic diversity and altered the frequency of pqqE and pqqC genes. The presence of the pqqE and pqqC genes was observed in a high percentage of isolated Gram-negative phosphate solubilizing bacteria. The analysis of the diversity of 16S rDNA and pqqE genes of soil DNA samples indicated a higher diversity in pesticides treated soil samples compared to control soil samples. Results obtained indicated that pesticides application increases diversity of soil bacterial community and therefore phosphate solubilizing soil bacterial population probably as a result of an increase of bacterial populations that use pesticides applied as carbon and energy source. Analysis of pqq genes frequency and diversity suggested that they would be potential molecular marker of Gram-negative phosphate solubilizing soil bacteria.

One pot fabrication of optically active and efficient antibacterial poly(amide-benzimidazole-imide)/Ag bionanocomposite

Poly(amide-benzimidazole-imide) (PABI) containing silver nanoparticles was fabricated through in situ procedure using DMF as a common solvent which leads to spontaneous slow reduction at ambient temperature. UV/vis technique verified silver nanoparticles formation in the polymer matrix. The silver nanoparticles presence was also confirmed using various characterization techniques and their dispersion was verified by microscopic studies (TEM and FE-SEM analysis) which revealed good dispersion of Ag nanoparticles in PABI matrix without aggregation in nano scales sized. Antibacterial properties of the synthesized polymer and PABI/Ag bionanocomposite (BNC) were evaluated against two Gram-negative bacteria, Escherichia coli and Agrobacterium tumefaciens. Impregnation of silver nanoparticles inside the material caused a growth inhibition ring against both bacteria showing antibacterial effectiveness of the nano-material rather than the basic polymer. In addition, in vitro soil burial and weight loss tests were also performed for evaluation of PABI and PABI/Ag BNC biodegradation behavior. PABI/Ag BNC significantly decreased soil bacterial population but increased fungal population compared to PABI buried. However, weight loss was not significantly different for both compounds when they were exposed to colonization by fungal saprophytes for 3 months. At least in spite of having antibacterial behavior, nanoparticle-impregnated material could be decomposed in natural ecosystems due to fungal biodegradations.

Soil bacterial diversity patterns and drivers along an elevational gradient on Shennongjia Mountain, China.

Understanding biological diversity elevational pattern and the driver factors are indispensable to develop the ecological theories. Elevational gradient may minimize the impact of environmental factors and is the ideal places to study soil microbial elevational patterns. In this study, we selected four typical vegetation types from 1000 to 2800 m above the sea level on the northern slope of Shennongjia Mountain in central China, and analysed the soil bacterial community composition, elevational patterns and the relationship between soil bacterial diversity and environmental factors by using the 16S rRNA Illumina sequencing and multivariate statistical analysis. The results revealed that the dominant bacterial phyla were Acidobacteria, Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Verrucomicrobia, which accounted for over 75% of the bacterial sequences obtained from tested samples, and the soil bacterial operational taxonomic unit (OTU) richness was a significant monotonous decreasing (P < 0.01) trend with the elevational increasing. The similarity of soil bacterial population composition decreased significantly (P < 0.01) with elevational distance increased as measured by the Jaccard and Bray–Curtis index. Canonical correspondence analysis and Mantel test analysis indicated that plant diversity and soil pH were significantly correlated (P < 0.01) with the soil bacterial community. Therefore, the soil bacterial diversity on Shennongjia Mountain had a significant and different elevational pattern, and plant diversity and soil pH may be the key factors in shaping the soil bacterial spatial pattern.

Hardwood biochar and manure co-application to a calcareous soil

Biochar may affect the mineralization rate of labile organic C sources such as manures via microbial community shifts, and subsequently affect nutrient release. In order to ascertain the positive or negative priming effect of biochar on manure, dairy manure (2% by wt.) and a hardwood-based, fast pyrolysis biochar were applied (0%, 1%, 2%, and 10% by wt.) to a calcareous soil. Destructive sampling occurred at 1, 2, 3, 4, 6 and 12months to monitor for changes in soil chemistry, water content, microbial respiration, bacterial populations, and microbial community structure. Overall results showed that increasing biochar application rate improved the soil water content, which may be beneficial in limited irrigation or rainfall areas. Biochar application increased soil organic C content and plant-available Fe and Mn, while a synergistic biochar–manure effect increased plant-available Zn. Compared to the other rates, the 10% biochar application lowered concentrations of NO3-N; effects appeared masked at lower biochar rates due to manure application. Over time, soil NO3-N increased likely due to manure N mineralization, yet soil NO3-N in the 10% biochar rate remained lower as compared to other treatments. In the presence of manure, only the 10% biochar application caused subtle microbial community structure shifts by increasing the relative amounts of two fatty acids associated with Gram-negative bacteria and decreasing Gram-positive bacterial fatty acids, each by ∼1%. Our previous findings with biochar alone suggested an overall negative priming effect with increasing biochar application rates, yet when co-applied with manure the negative priming effect was eliminated.

English

Cocoa, the &lsquo;Food of Gods&rsquo; is one of the important plantation crops consumed worldwide and around 40 - 50 million people depend on cocoa for their livelihood. An experiment was conducted during 2010 and 2011 to investigate the impact of N, P and K fertilizers through fertigation on soil microbial population of cocoa at Tamil Nadu Agricultural University, India. The study was laid out in randomized block design with 13 treatment combinations. The study shows that, fertigation with 125% recommended fertilizer dose as water soluble fertilizer through fertigation by micro sprinkler irrigation (T10) had the highest soil bacterial population (60.10 &times; 10-6 CFU g-1), fungal population (16.61&times; 10-4 CFU g-1) and actinomycetes population (8.07 &times; 10-3 CFU g-1). The same treatment recorded higher yield characters viz., beans per pod (47.81), bean length (2.47 cm), bean girth (3.57 cm), single bean wet weight (3.15 g), single bean dry weight (1.31 g), dry bean weight per pod (62.23 g), dry bean yield per tree (3273.63 g). Key words: Fertigation, drip irrigation, micro sprinkler irrigation, bacteria, fungi, actinomycetes.

Influence of Organic Manures (Biofertilizers) on Soil Microbial Population in the Rhizosphere of Mulberry (Morus Indica L.)

The effect of different kinds of organic manures on soil microbial population and mulberry production was assessed. A field experiment wascarried out at Periyar EVR College, Tamil Nadu, India in basic soil to study the influence of organic manures on soil bacterial population andmulberry production. The 4 groups of mulberry plants of MR2 variety were biofertilized with FYM, Azospirillum, Phosphobacteria andVermicompost respectively. The biofertilizers lodged bacteria on the rhizosphere of mulberry plants. When the root microorganism areanalyzed Farm yard manure biofertilized mulberry plant root tips had Gluconacobacter diazotrophicus, Bacillus pumilus, Pseudomonas putida,Bacillus coagulans, Bacillus sonorensis, Azotobacter chrococcum; Azospirillum biofertilized mulberry plants root tips had Bacillus coaculans,Azotobactor chrococcum, Azotobactor vinelandii, Bacillus subtilis and Azospirillum brasilense. Phosphobacteria biofertilized mulberry plantroot tips had Pseudomonas putida, Bacillus stearothermophilus, Brevibacillus borslelansis and Streptomycies thermonitrificans andvermicompost biofertilized mulberry plant root tips had lodged bacterias like Bacillus megaterium, Bacillus subtilis, Gluconacobacterdiazotrophicus, Pseudomonas putida, Azotobacter chrococcum, Azotobacter vinelandi, Bacillus stearothermophilus, Brevibacillus borslelansisand Bacillus sonorensis. Microbiology work reveals luxuriant growth of bacteria in all the biofertizer treated rhizosphere in the order FYM &lt;Azospirillum &lt; Phosphobacteria &lt; Vermicompost. Increased availability of NPK and other micronutrients were noticed in T4 treated plantscompared to other treatments.DOI: http://dx.doi.org/10.3126/ijasbt.v3i1.12137 Int J Appl Sci Biotechnol, Vol. 3(1): 61-66

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.

渭北塬区不同龄苹果园土壤微生物空间分布特征

PDF HTML阅读 XML下载 导出引用 引用提醒 渭北塬区不同龄苹果园土壤微生物空间分布特征 DOI: 10.5846/stxb201402160268 作者: 作者单位: 宝鸡文理学院、陕西省灾害监测与机理模拟重点实验室,宝鸡文理学院、陕西省灾害监测与机理模拟重点实验室,宝鸡文理学院、陕西省灾害监测与机理模拟重点实验室,宝鸡文理学院、陕西省灾害监测与机理模拟重点实验室,宝鸡文理学院、陕西省灾害监测与机理模拟重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家“十一五”科技支撑计划资助项目（2006BAD09B09）；陕西省教育厅自然科学专项（2010JK402）；宝鸡文理学院重点项目（ZK1041，ZK0846） Spatial distribution of soil microorganisms in apple orchards of different ages on the Weibei rainfed tableland of the Loess Plateau, China Author: Affiliation: Key Laboratory of Disaster Survey and Mechanism Simulation of Shaanxi Province / Baoji University of Arts and Sciences,Key Laboratory of Disaster Survey and Mechanism Simulation of Shaanxi Province / Baoji University of Arts and Sciences,Key Laboratory of Disaster Survey and Mechanism Simulation of Shaanxi Province / Baoji University of Arts and Sciences,Key Laboratory of Disaster Survey and Mechanism Simulation of Shaanxi Province / Baoji University of Arts and Sciences,Key Laboratory of Disaster Survey and Mechanism Simulation of Shaanxi Province / Baoji University of Arts and Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以渭北塬区塬面5、10、15和20龄苹果园为对象,距树干1.0、1.5、2.0 m处用土钻法分层采集0-30 cm土样,稀释平板法测定土壤微生物数量,平行测定土壤有机碳、总氮和总磷,分析不同龄果园土壤微生物的空间分布状况及其与土壤碳、氮、磷的关系。结果表明:土壤真菌数量随树龄增大而增加,龄间差异显著(P<0.05);与对照农田相比,各龄果园放线菌数量及5龄和20龄果园细菌数量偏低,10龄和15龄果园细菌数量偏高;各龄果园土壤真菌、细菌和放线菌数量均随深度增加而减小。就相同深度土层而言,真菌数量随果园年限增大而增加,细菌则以10龄和15龄果园较多,同深度土层的放线菌龄间差异随深度增加而减小。在沿树干向外的径向水平方向上,真菌数量随果园年限的增加相应增多;10龄和15龄果园土壤细菌和放线菌高于5龄果园和20龄果园。5龄果园土壤总氮有沿树干向外、沿表层向下逐步降低的趋势,果园从5龄经10龄到15龄,其"高氮点"则逐步向外、向下移动。塬区果园土壤C : N比偏低。 Abstract:Soil microorganisms are vital for orchard ecosystems, as they determine and promote the material cycle and energy flow. The Weibei Loess Plateau is one of the main regions producing high-quality apples since the 1980s. The planting structure of apple orchards has following characteristics: simple and long-term fertilizer, high quality management, and "double high" (high investment and high harvest) production, which results in different soil fertility and quality in orchards of different ages, leading to different habitat conditions for microorganisms. Consequently, different aged orchards have different soil microbial species composition, quality, and spatial distributions. Yet, differences in soil microorganism parameters affect apple yield and quality, because of their involvement in maintaining and improving the feedback effect on soil properties and fertility in orchards. To maintain sustainable development, prevent soil quality degradation, and reform orchard degradation, it is essential to understand the long-term dynamics and trends of microorganisms in orchards. This work investigated the spatial distribution of soil microorganisms in different apple orchards of different ages (5, 10, 15, and 20 years old) on the Weibei rainfed tableland of the Loess Plateau. Soil samples were first collected from the 0-30cm soil layer at root radial distances of 1.0, 1.5, and 2.0 m away from the main tree trunk using a soil coring method. Soil total nitrogen (TN), soil total phosphorus (TP), and soil organic carbon (SOC) were then determined using the Flowsys III and Liqui TOC II analyzer. Relationships between soil microorganisms and soil nutrients (i.e., TN, TP, and SOC) were also analyzed. The results showed that the soil fungal population increased with increasing apple orchard age. There were significant differences in soil fungal population among orchard ages, at the P=0.05 level. The soil actinomycete population in orchards of all ages and soil bacterial population in 5-year and 20-year old apple orchards was lower than that in agricultural fields (control check). In comparison, the soil bacterial population in 10-year and 15-year old apple orchards was higher than that in the agricultural field. Fungal, actinomycete and bacterial populations decreased with increasing soil depth. At the same soil depth, the soil fungal population increased with increasing orchards age, with the soil bacterial population in 10-year and 15-year old apple orchards being higher than that in 5-year and 20-year old orchards. Soil actinomycete populations declined with the increasing in soil depth in all ages of apple orchards. In the radial horizontal direction, the soil fungal population in all apple orchards increased with age, while the soil bacterial population during the full fruit bearing period (10 and 15-years old) was higher than that in 5-year and 20-year old orchards, with soil actinomycetes exhibiting the same trend. The TP in 5-year old apple orchards declined outward from the apple trunk and downward from the topsoil. The "High spot of TN" moved outward from the apple trunk and downward from the topsoil for 5-year to 15-year old apple orchards. The soil C : N ratio was low in apple orchards on the Weibei rainfed tableland of the Loess Plateau. 参考文献 相似文献 引证文献

Carbon Dioxide Evolution and Oxidoreductase Enzyme Activities in Relation to Herbicides Application in an Alluvial Soil of Varanasi

Laboratory incubation study was carried out in Gangetic alluvial soil of Varanasi at recommended and double the recommended dose of glyphosate, paraquat and pendimethalin to assess their impact on carbon dioxide (CO2) evolution, dehydrogenase & catalase activities and the soil bacterial population. Both stimulating and inhibiting effects were noticed from the application of herbicides glyphosate, paraquat and pendimethalin on the decomposition of organic matter. The rate of periodical changes of CO2 evolution (mg CO2-C g−1 soil) from the herbicides applied soil, followed the order pendiemthalin > paraquat >glyphosate. The dehydrogenase activity (mg TPF g−1 day−1) was more stimulant at double the recommended dose of the herbicides after 42 days of incubation. Both stimulating and/or inhibiting effects were observed on catalase activity (i mole H2O2 consumed min−1 g−1 soil) and bacterial population in soil as influenced by the herbicides.

Relationship between Soil Bacterial Population and Various Physico- Chemical Properties at Two Broadleaved Forest Stands of Meghalaya Differing in Altitudes

Although soil bacterial communities are one of the important biotic components that influence decomposition and nutrient mineralization in the terrestrial ecosystems, factors driving this biotic community in the broadleaved forest stands of Meghalaya are not well studied. The present study examined the importance of physico-chemical properties in driving soil bacterial communities in the broadleaved forest stands of Meghalaya differing in altitudes. Soils were collected at two different (0-10 cm and 10-20 cm) depths monthly for a period of two years. Results showed that bacterial CFU was higher in the high altitude forest stand at 0-10 cm depth as compared to the low altitude forest stand at 10-20 cm depth. It also showed significant positive correlation with organic carbon and total nitrogen in both the two forest stands indicating that these two constitute the major driving factors of bacterial communities in the broad leaved forest stand of Meghalaya.

Long-Term Effects of Spent Wash Liquor on Soil Bacterial Population in Sugar Cane Production Systems

Long-Term Effects of Spent Wash Liquor on Soil Bacterial Population in Sugar Cane Production Systems

Treated agro-industrial wastewater irrigation of tomato crop: Effects on qualitative/quantitative characteristics of production and microbiological properties of the soil

A comparative study was carried out to evaluate the effects of two water irrigation sources on the quality and microbiological safety of tomato plants and fruit, and on the microbiological soil properties: irrigation with groundwater (GW) and with treated agro-industrial wastewater (TW). In a field experiment in southern Italy (Apulia region), the physico-chemical characteristics of the irrigation waters and the fruit quality parameters were determined. Escherichia coli, fecal Enterococci and Salmonella spp. were also monitored in the irrigation waters, tomato plant and fruit, and root-zone soil. Bacteriological analysis for total heterotrophic counts (THCs) were determined for plant, fruit, and soil samples. The irrigation water source did not significantly affect yield quantitative traits. However, with GW, the marketable fruit yield was higher than with TW (∼82 vs. ∼79Mgha−1, respectively). For both irrigation treatments, the most important qualitative parameters that characterize the processing tomato fruit (i.e., dry matter content, pH, soluble solid content, color parameters) were in agreement with reports in the literature. For the microbiological results, the mean levels of E. coli and fecal Enterococci were 4408 and 3804CFU 100ml−1, respectively, for TW (above the Italian guidelines for TW re-use). For the tomato plant and fruit, no E. coli isolated in either, and fecal coliforms and THC were not influenced by the irrigation waters (P>0.05). Total bacterial enumeration by quantitative PCR was lower in soil irrigated with GW, than TW (3.69 vs. 4.02, ×106, respectively). Moreover, soil microbial community patterns substantially differed between the two water treatments. These data show that while fecal indicators are not affected, the community composition and dynamics of the whole bacterial population in soil is influenced by the different qualities of these waters used for irrigation.

Soil bacterial community response to differences in agricultural management along with seasonal changes in a Mediterranean region.

Land-use change is considered likely to be one of main drivers of biodiversity changes in grassland ecosystems. To gain insight into the impact of land use on the underlying soil bacterial communities, we aimed at determining the effects of agricultural management, along with seasonal variations, on soil bacterial community in a Mediterranean ecosystem where different land-use and plant cover types led to the creation of a soil and vegetation gradient. A set of soils subjected to different anthropogenic impact in a typical Mediterranean landscape, dominated by Quercus suber L., was examined in spring and autumn: a natural cork-oak forest, a pasture, a managed meadow, and two vineyards (ploughed and grass covered). Land uses affected the chemical and structural composition of the most stabilised fractions of soil organic matter and reduced soil C stocks and labile organic matter at both sampling season. A significant effect of land uses on bacterial community structure as well as an interaction effect between land uses and season was revealed by the EP index. Cluster analysis of culture-dependent DGGE patterns showed a different seasonal distribution of soil bacterial populations with subgroups associated to different land uses, in agreement with culture-independent T-RFLP results. Soils subjected to low human inputs (cork-oak forest and pasture) showed a more stable bacterial community than those with high human input (vineyards and managed meadow). Phylogenetic analysis revealed the predominance of Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes phyla with differences in class composition across the site, suggesting that the microbial composition changes in response to land uses. Taken altogether, our data suggest that soil bacterial communities were seasonally distinct and exhibited compositional shifts that tracked with changes in land use and soil management. These findings may contribute to future searches for bacterial bio-indicators of soil health and sustainable productivity.

Carbon Mineralization and Microbial Attributes in Straw-Amended Soils as Affected by Moisture Levels

An 80-d incubation experiment was conducted to investigate straw decomposition, the priming effect and microbial characteristics in a non-fertilized soil (soil 1) and a long-term organic manure-fertilized soil (soil 2) with and without 13C-labeled maize straw amendment under different moisture levels. The soil 2 showed a markedly higher priming effect, microbial biomass C (Cmic), and β-glucosidase activity, and more abundant populations of bacteria and fungi than the soil 1. Also, soil CO2 emission, Cmic, β-glucosidase activity, and bacterial and fungal population sizes were substantially enhanced by straw amendment. In the presence of straw, the amount of straw mineralization and assimilation by microbes in the soil at 55% of water holding capacity (WHC) were significantly higher by 31% and 17%, respectively, compared to those at 25% of WHC. In contrast, β-glucosidase activity and fungal population size were both enhanced as the moisture content decreased. Cmic decreased as straw availability decreased, which was mainly attributed to the reduction of straw-derived Cmic. Amended soils, except the amended soil 2 at 25% of WHC, had a more abundant fungal population as straw availability decreased, indicating that fungal decomposability of added straw was independent of straw availability. Non-metric multidimensional scaling analysis based on fungal denatured gradient gel electrophoresis band patterns showed that shifts in the fungal community structure occurred as water and straw availability varied. The results indirectly suggest that soil fungi are able to adjust their degradation activity to water and straw availability by regulating their community structure.

Sensitive quantitative detection of Ralstonia solanacearum in soil by the most probable number-polymerase chain reaction (MPN-PCR) method

We developed a sensitive quantitative assay for detecting Ralstonia solanacearum in soil by most probable number (MPN) analysis based on bio-PCR results. For development of the detection method, we optimized an elution buffer containing 5g/L skim milk for extracting bacteria from soil and reducing contamination of polymerase inhibitors in soil extracts. Because R. solanacearum can grow in water without any added nutrients, we used a cultivation buffer in the culture step of the bio-PCR that contained only the buffer and antibiotics to suppress the growth of other soil microorganisms. To quantify the bacterial population in soil, the elution buffer was added to 10g soil on a dry weight basis so that the combined weight of buffer, soil, and soil-water was 50g; 5mL of soil extract was assumed to originate from 1g of soil. The soil extract was divided into triplicate aliquots each of 5mL and 500, 50, and 5μL. Each aliquot was diluted with the cultivation buffer and incubated at 35 °C for about 24h. After incubation, 5μL of culture was directly used for nested PCR. The number of aliquots showing positive results was collectively checked against the MPN table. The method could quantify bacterial populations in soil down to 3cfu/10g dried soil and was successfully applied to several types of soil. We applied the method for the quantitative detection of R. solanacearum in horticultural soils, which could quantitatively detect small populations (9.3cfu/g), but the semiselective media were not able to detect the bacteria.