PCR-based sensitive detection of Ralstonia solanacearum from soil,eggplant, seeds and weeds

Ralstonia solanacearum is an economically important, bacterial plant pathogen which affects a wide range of crop plants. R. solanacearum survives in the soil for many years and weeds serve as symptomless carrier. One of the important aspects in controlling R. solanacearum is its early detection. In this study, detection threshold of R. solanacearum in the soil was standardised using polymerase chain reaction (PCR) method. The minimum threshold limit ranged between 6.8 × 10 and 3.6 × 10² CFU g^?1 of soil. Using this standardised protocol R. solanacearum was detected from the rhizosphere soil of eggplants showing varying degrees of wilt. PCR method was quite sensitive to detect R. solanacearum from the xylem fluid of eggplant. Presence of R. solanacearum in the soil infected with capsicum wilt was also demonstrated successfully and the minimum detection limit was 4 × 10² CFU g^?1 of soil. The bacterium was not detected from the eggplant seeds collected during 2006 and 2007 seasons. However, the bacterium was detected from the weed (Alternanthera sessilis) grown in the eggplant field indicating the possibility of weeds serving as symptomless carrier. Using our method, it is possible to detect R. solanacearum from soil, plant and weeds grown in the field at an early stage so that proper management strategies could be taken to prevent the infection and further spread of the pathogen.     

Impact of commonly used agrochemicals on bacterial diversity in cultivated soils

The effects of three selected agrochemicals on bacterial diversity in cultivated soil have been studied. The selected agrochemicals are Cerox (an insecticide), Ceresate and Paraquat (both herbicides). The effect on bacterial population was studied by looking at the total heterotrophic bacteria presence and the effect of the agrochemicals on some selected soil microbes. The soil type used was loamy with pH of 6.0–7.0. The soil was placed in opaque pots and bambara bean (Vigna subterranean) seeds cultivated in them. The agrochemicals were applied two weeks after germination of seeds at concentrations based on manufacturer’s recommendation. Plant growth was assessed by weekly measurement of plant height, foliage appearance and number of nodules formed after one month. The results indicated that the diversity index (Di) among the bacteria populations in untreated soil and that of Cerox-treated soils were high with mean diversity index above 0.95. Mean Di for Ceresate-treated soil was 0.88, and that for Paraquattreated soil was 0.85 indicating low bacterial populations in these treatment-type soils. The study also showed that application of the agrochemicals caused reduction in the number of total heterotrophic bacteria population sizes in the soil. Ceresate caused 82.50% reduction in bacteria number from a mean of 40 × 10⁵ cfu g⁻¹ of soil sample to 70 × 10⁴ cfu g⁻¹. Paraquat-treated soil showed 92.86% reduction, from a mean of 56 × 10⁵ cfu g⁻¹ to 40 × 10⁴ cfu g⁻¹. Application of Cerox to the soil did not have any remarkable reduction in bacterial population number. Total viable cell count studies using Congo red yeast-extract mannitol agar indicated reduction in the number of Rhizobium spp. after application of the agrochemicals. Mean number of Rhizobium population numbers per gram of soil was 180 × 10⁴ for the untreated soil. Cerox-treated soil recorded mean number of 138 × 10⁴ rhizobial cfu g⁻¹ of soil, a 23.33% reduction. Ceresate- and Paraquat-treated soils recorded 20 × 10⁴ and 12 × 10⁴ cfu g⁻¹ of soil, respectively, representing 88.89% and 93.33% reduction in Rhizobium population numbers. Correspondingly, the mean number of nodules per plant was 44 for the growth in untreated soil, 30 for the plant in the Cerox-treated soil, 8 for the plant in Paraquat-treated soil and 3 for the plant in Ceresate-treated soil. The study has confirmed detrimental effect of insecticide on bacterial populations in the soil. Total heterotrophic counts, rhizobial counts as well as the number of nodules of all samples taken from the chemically treated soils were all low as compared to values obtained for the untreated soil. However, the effect of the insecticide was minimal in all cases as compared to the effects of the herbicides on the soil fauna. Indiscriminate use of agrochemicals on farms can therefore affect soil flora and subsequently food production.     

Narrow range of temperature and irradiance supports optimal development of Lessonia corrugata (Ochrophyta) gametophytes: implications for kelp aquaculture and responses to climate change

The kelp Lessonia corrugata (Ochrophyta, Laminariales) is being developed for integrated multi-trophic aquaculture (IMTA) trials in the vicinity of salmon cages in Tasmania, Australia. Gametophytes are vegetally maintained before seeding on hatchery twine; however, the optimal temperature and light conditions for growth and sexual development are unknown. We measured vegetative size of female and male gametophytes and sexual development of females over a range of temperatures and irradiances using a temperature gradient table and neutral density light filters. Over a 4-week experiment, gametophytes were exposed to a combination of thermal (5.7–24.9 °C) and irradiance (10–100 μmol photons m^?2 s^?1) gradients, to assess biological performance. At the temperature extremes (hottest = 24.9 °C, coldest = 5.7 °C), we observed the critical thermal limits for this species and the results reveal a narrow optimal temperature range for growth and sexual development between 15.7 and 17.9 °C, with irradiances between 40 and 100 μmol photons m^?2 s^?1 resulting in fertile female gametophytes. Lessonia corrugata inhabits a small geographic range, found only around Tasmania, south of the Australian mainland, hence oceanic changes such as ongoing increases in sea surface temperatures (SSTs), and altered irradiance regimes may limit recruitment of the early microscopic life stages in the future. Our findings provide optimised culture conditions for aquaculture and information to predict the future geographic range of L. corrugata under ocean global change.

     

Influence of inoculum density of the antagonistic bacteria Pseudomonas fluorescens and Pseudomonas corrugata on sugar beet seedling colonisation and suppression of Pythium damping off

The effect of initial inoculum density of the antagonistic bacterial strains Pseudomonas fluorescens B5 and Pseudomonas corrugata 2140 (10³ to 10⁸ CFU per seed pellet) on sugar beet seedling colonisation, in situ bioluminescence and antagonistic activity towards Pythium ultimum was investigated. Populations of the bacteria colonising sugar beet root systems approached an apparent carrying capacity of 10⁵ to 10⁶ CFU per plant after 12 d growth, irrespective of inoculum density. This meant an up to 320-fold population increase at low inoculum densities and a decrease at high densities. Population densities of both bacteria and their corresponding in situ bioluminescence (resulting from luciferase enzyme expression from the inserted luxAB genes) reached highest levels in the hypocotyl region and in the upper root region 0–20 mm below seed level (10⁴–10⁶ CFU/cm section, 10¹–10³ RLU/cm section) and decreased with root depth. In situ bioluminescence, which indicates physiological activity, was measurable at lowest antagonist initial inoculum density (10³ CFU per seed pellet) and did not increase significantly with increasing inoculum density. Bioluminescence was also significantly correlated with population density. For Pseudomonas fluorescens B5, the total population size per plant and downward colonisation of the root (below 40 mm depth) increased significantly with antagonist inoculum density applied to the seeds. For Pseudomonas corrugata 2140, no significant influence of initial inoculum density on root colonisation was observable. Survival and dry weight of sugar beet seedlings in Pythium infested soil increased significantly with increasing inoculum density of Pseudomonas fluorescens B5, whereas for Pseudomonas corrugata 2140, initial densities of 10⁴ to 10⁶ CFU per seed resulted in maximal survival of plants.     

黄河滩地和稻田土中铁还原菌、不产氧光合细菌分布机制

【目的】探讨沿黄流域土壤中铁还原菌(ferric reducing bacteria, Fe RB)、不产氧光合细菌(anoxygenic phototrophic bacteria, An PB)的分布机制。【方法】以沿黄流域(原阳段)为研究对象,采集黄河滩地和稻田土样,利用16Sr RNA基因高通量测序和实时荧光定量分析技术,结合统计学分析,揭示Fe RB、An PB菌群结构、丰度和主要环境影响因子。【结果】二者中的优势Fe RB在科(属)水平为Hydrogenophilaceae(Thiobacillus)、 Bacillaceae(Bacillus)、 Clostridiaceae、Rhodobactereace(Rhodobacter)、 Geobacteraceae(Geobacter),优势An PB为Rhodobactereace(Rhodobacter)、 Chloroflexaceae(Chloronema)、 Acetobacteraceae(Roseomonas)。An PB中Rhodobacteraceae与Fe RB中Bacillaceae、 Clostri...     

金龟子绿僵菌在森林土壤中的分布及对松墨天牛致病性测定

松墨天牛是重大森林植物检疫性病害——松材线虫病的主要媒介昆虫。本研究于2005年8月～2006年8月从福建、江西两省共110个林分样区(其中松林88个样区)采集土壤样品330份,采用选择性培养基分离土壤中的金龟子绿僵菌。从21个样区的26份土样中分离出的金龟子绿僵菌占采集样区的19．1％和样品的7．9％,成菌落数(CFU)500～72500CFU/g,表明金龟子绿僵菌在森林土壤中有较为广泛的分布。对分离到的9个产孢量高的菌株,采用浸渍法(1×10~7孢子/mL)接种3～4龄健康松墨天牛幼虫,采用跗节接种法接种2～15日龄健康成虫,测定其致病力。结果表明,MaYTTR-03、MaYTTR-04菌株对松墨天牛幼虫和成虫均有较高致病力,表现出良好的生防潜力。     

Phosphorus (P) uptake and growth of a root hairless barley mutant (bald root barley, brb) and wild type in low- and high-P soils

The recently isolated root‐hairless mutant of barley (Hordeum vulgare L), bald root barley, brb offers a unique possibility to quantify the importance of root hairs in phosphorus (P) uptake from soil. In the present study the ability of brb and the wild‐type, barley genotype Pallas producing normal root hairs to deplete P in the rhizosphere soil was investigated and the theory of diffusion and mass flow applied to compare the predicted and measured depletion profiles of diffusible P. Pallas depleted twice as much P from the rhizosphere soil as brb. The P depletion profile of Pallas uniformly extended to 0.8 mm from the root surface, which was equal to the root hair length (RHL). The model based on the theory of diffusion and mass flow explained the observed P‐depletion profile of brb, and the P depletion outside the root‐hair zone of Pallas, suggesting that the model is valid only for P movement in rhizosphere soil outside the root‐hair zone. In low‐P soil (P in soil solution 3 µm ) brb did not survive after 30 d, whereas Pallas continued to grow, confirming the importance of root hairs in plant growth in a P‐limiting environment. In high‐P soil (P in soil solution 10 µm ) both brb and Pallas maintained their growth, and they were able to produce seeds. At the high‐P concentration, RHL of the Pallas was reduced from 0.80 ± 0.2 to 0.68 ± 0.14 mm. In low‐P soil, P‐uptake rate into the roots of Pallas was 4.0 × 10^?7 g mm^?1 d^?1 and that of brb was 1.9 × 10^?7 g mm^?1 d^?1, which agreed well with the double amount of P depleted from the rhizosphere soil of Pallas in comparison with that of brb. In high‐P soil, the P uptake rates into the roots of brb and Pallas were 3.3 and 5.5 × 10^?7 g mm^?1 d^?1, respectively. The results unequivocally confirmed that in a low‐P environment, root hairs are of immense importance in P acquisition and plants survival, but under high‐P conditions they may be dispensable. The characterization of phenotypes brb and Pallas and the ability to reproduce seeds offers a unique possibility of molecular mapping of QTLs and candidate genes conferring root‐hair formation and growth of barley.     

金龟子绿僵菌在森林土壤中的分布及对松墨天牛致病性测定

松墨天牛是重大森林植物检疫性病害——松材线虫病的主要媒介昆虫。本研究于2005年8月～2006年8月从福建、江西两省共110个林分样区（其中松林88个样区）采集土壤样品330份,采用选择性培养基分离土壤中的金龟子绿僵菌。从21个样区的26份土样中分离出的金龟子绿僵菌占采集样区的19.1%和样品的7.9%,成菌落数（CFU）500～72500CFU/g,表明金龟子绿僵菌在森林土壤中有较为广泛的分布。对分离到的9个产孢量高的菌株,采用浸渍法（1×10⁷孢子/mL）接种3～4龄健康松墨天牛幼虫,采用跗节接种法接种2～15日龄健康成虫,测定其致病力。结果表明,MaYTTR-03、MaYTTR-04菌株对松墨天牛幼虫和成虫均有较高致病力,表现出良好的生防潜力。     

Application of immobilized tannase from <Emphasis Type="Italic">Aspergillus niger</Emphasis> for the removal of tannin from myrobalan juice

Microbial diversity of soil and water samples collected from pyrochemicals exposed areas of Virdhunagar district (Tamil Nadu, India) was studied. Soil and water samples from cultivable area, waste land and city area of the same region were also studied for a comparative acount. There is a remarkable reduction in total heterotrophic bacterial population (THB) in pyrochemicals exposed soil and water samples (42 × 10⁴ CFU/g and 5.6 × 10⁴ CFU/ml respectively), compared to the THB of cultivable area soil and water samples (98 × 10⁷ CFU/g and 38.6 × 10⁷ CFU/ml). The generic composition the THB of the pyrochemicals exposed samples too exhibited considerable change compared to other samples. Pseudomonas sp. was the predominant one (41.6%) followed by Achromobacter sp. (25%) in pyrochemical exposed soil and Pseudomonas sp. was the predominant one (25%) in pyrochemical exposed water samples followed by Bacillus sp. (25%) and Micrococcus sp. (16.6%). It was observed that Cornybacterium sp. and Micrococcus sp. were absent completely in pyrochemical exposed soil and Achromobacter sp. was missing in the pyrochemical exposed water samples, which were present in the other samples. The outcome of this study clearly demonstrates that pollutants such as chemicals used in pyrotechniques affect the microbial biodiversity and suitable measures have to be taken to control the pollution level and to save biodiversity.     

Growth Promotion of Fluorescent Pseudomonads and Control of Potato Common Scab in Field Soil with Non-antibiotic Actinomycete-biofertilizer

Field studies on the control of potato common scab were done with non-antibiotic Actinomycete biofertilizer, which was manufactured from swine feces with coprophilous actinomycetes and acidified to pH 5.0 with sulfuric acid. The field soil at pH 5.0 was mixed with 0.56 kg of the acidified biofertilizer per subplot (1.0 x 1.2 m) to a depth of the 15 cm. The scab severity, in terms of the percent coverage of the total surface area of potato tubers, was 10.7%, in the control, while the lesions were slight in the biofertilizer subplot, scab severity being only 2.30/0, and the potato production was increased 3 times with the biofertilizer. The viable counts of Streptomyces scabies in the biofertilizer subplot decreased to 1 × 10³ per gram soil from 5 × 10⁵ by 12 weeks, while the inhabitant fluorescent pseudomonads increased to 2.4 × 10⁷ per gram soil from 3 × 10⁴, and the increased fluorescent pseudomonads were antagonistic to the pathogenic strains.     

Stimulation of Growth of Peppermint (Mentha piperita) by Phosfon, a Growth Retardant

The shoot growth and fresh weight of Mentha piperita grown in soil were stimulated at concentrations of 1.26 × 10^?5M to 7.77 × 10^?4M phosfon (2,4-dichlorobenzyl tributyl phosphonium chloride) while higher concentrations resulted in retardation of growth. Concentrations of 6.30 × 10^?7M to 3.78 × 10^?5M caused retardation of growth in mineral nutrient solution, and even death at the highest concentrations. However, when the M. piperita plants were grown in mineral nutrient solutions at concentrations of phosfon which had been sequentially lowered from 2.52 × 10^?8M to 2.52 × 10^?12M, the shoot growth and fresh weight were stimulated as in the case of plants grown in phosfon treated soil.     

Comparison of Archaeal Populations in Soil and Their Encapsulated Iron-Manganese Nodules in Four Locations Spanning from North to South China

To characterize the archaeal community composition in soil originating iron-manganese nodules, four types of soils—brown soil, yellow-cinnamon soil, yellow brown soil and red soil—and their associated iron-manganese nodules were collected from Queyu (QY), Zaoyang (ZY), Wuhan (WH) and Guiyang (GY), China, respectively, and subjected to quantitative polymerase chain reaction, cloning and sequencing analyses. The results showed that the archaeal 16S rRNA gene copy numbers in nodules, ranging between 3.59 × 10² and 4.17 × 10³ copies g^?1 dry nodule, were about 50–1000 times lower than those in their corresponding soils (1.87 × 10⁵ to 1.08 × 10⁶ copies g^?1 dry soil), correlating with the low organic matter in the nodules, while archaea accounted for a relatively higher proportion of total prokaryote in nodules than in soils. Community composition analysis suggested that the archaeal diversity in both soils and nodules were much lower than bacterial, but archaeal community structures were similar to each other among the soils and nodules from the same location but varied among four locations, converse to the previous observation that bacterial community shifted markedly between nodules and soils as the result of habitat filtering. The archaeal communities in both soils and nodules were predominated by Thaumarchaeota Group I.1b with the relative abundance ranging between 73.88 and 94.17%, except that Euryarchaeota dominated the archaeal community in one nodule sample (WHn) developed from lake sediment. The finding shed new light on the archaeal diversity and their ecophysiology in different habitats, and further supported the opinion that archaea are more adaptable to stress and unfavorable conditions.     

Abundance and Diversity of Methanotrophs and Propanotrophs in Soils above Yangxin Oil Reservoir,China

Methanotrophs have long been used as an important biological indicator for prospecting of oil and gas, while the indication of propanotrophs in hydrocarbon micro-seep systems is still poorly investigated. In this study, the abundance and diversity of the methanotrophic pmoA gene and the propanotrophic prmA gene as target genes were investigated in soils above Yangxin oil reservoir and Beiguan non-petroliferous area using molecular biological techniques. A total of 14 soil samples were collected at different depths (5, 20, 50, 100, 150, 200 and 250 cm) of two 2.5-m soil profiles located separately within the oil field and the non-petroliferous area for analysis of fluorescent quantitative real-time polymerase chain reaction (RT-PCR) (14 samples) and clone libraries (4 samples). The results demonstrated high presence of the propanotrophic prmA gene ranging from 7.68 × 10⁵ to 2.29 × 10⁷ copies/g dw (gene copies per gram soil of dry weight) in soil from the oil field relative to the non-petroliferous area for which the same measurements yielded results all below detection limit except for the 5-cm sample. On the other hand, oil field soil yielded much lower content of the methanotrophic pmoA gene (below detection limit to 5.6 × 10² copies/g dw) than the non-petroliferous area (1.14 × 10³ copies/g dw to 1.26 × 10⁵ copies/g dw) below 20-cm depth due to influence of biogenic methane, implying that propanotrophs may be better indicator bacteria for prospecting of oil and gas. Almost all pmoA clones of two 50-cm soil samples phylogenetically belonged to Gamma-Proteobacteria and the predominant pmoA OTUs were all uncultured bacteria. All prmA clones of two 5-cm soil samples were derived predominantly from Actinobacteridae (25.7%) and Alpha-Proteobacteria (74.3%), and all dominant prmA OTUs were also clustered with uncultured bacteria. Our results confirm that propanotrophs may be better indicator bacteria for prospecting of oil and gas and enrich the knowledge on diversity of methanotrophs and propanotrophs in the oil field and the non-petroliferous area.     

Spore-forming bacteria in soil cultivated with GM white poplars: Isolation and characterization

The impact of transgenic white poplars (Populus alba L. cv. ‘Villafranca’) was assessed on the soil aerobic spore-forming bacteria (SFB). The genetically modified poplars, expressing either the StSy gene for resveratrol production or the bar gene for herbicide tolerance, were cultivated in greenhouse. The occurrence of SFB was monitored in soil samples collected at eight different timepoints over a two-year period. The total culturable bacterial population of the StSy and bar trials underwent significant seasonal fluctuations in the range of 10⁶−2.5 × 10⁸ CFU/g dry soil and of 10⁴−5 × 10⁸ CFU/g dry soil, respectively. Changes occurred also within the culturable SFB population with size varying at 10³−5 × 10⁴ CFU/g dry soil and 10²−2 × 10⁵ CFU/g dry soil in the StSy and bar trials, respectively. No significant differences in the size of the total and SFB culturable populations were observed when comparing each transgenic line with the nontransformed control line while seasonal shifts of soil bacterial populations were evident in both trials. The culturable SFB fraction included three isolates (SFB-1, SFB-2 and SFB-3) classified by 16S rDNA sequence analysis as members of the Bacillus genus. According to the reported data, cultivation of both herbicide-resistant and resveratrol-producing GM white poplars did not affect the culturable SFB population at the soil level.     

Evaluation of soil bacterial biomass using environmental DNA extracted by slow-stirring method

A simple and rapid method (slow-stirring method) for extracting environmental DNA (eDNA) from soils was constructed by physical mild stirring with chemical treatment. eDNA was extracted efficiently with minimal damage from various kinds of soil. The amount of eDNA and soil bacterial biomass showed a linear proportional relation [Y=(1.70×10⁸)X, r ²=0.96], indicating that bacterial biomass could be evaluated by quantifying levels of eDNA. Consequently, the average bacterial biomass in an agricultural field was calculated as 5.95×10⁹ cells/g sample, approximately 10–100 times higher than that in non- and oil-polluted fields.     

Potency of Bacillus thuringiensis and Bacillus subtilis against the cotton leafworm,Spodoptera littoralis (Bosid.) Larvae

The biological activities of two species of bacteria isolated from soil of cotton fields identified as Bacillus subtilis strain NRC313 (BS NRC313) and Bacillus thuringiensis strain NRC335 (BT NRC335) were evaluated against the third larval instar of the cotton leafworm, Spodoptera littoralis (Boisd.). The different entomopathogenic bacteria of BS NRC313and BT NRC335 contained 10 × 10⁸ cell/ml, and caused mortality of 100 and 97.3% for the above mentioned strains, respectively. Concentrations of 2.5 × 10⁸ to 10 × 10⁸ cell/ml of strains BS NRC313 and BT NRC335 were applied to the larvae: LC₅₀ were 3.3 × 10⁸ and 3.9 × 10⁸ cell/ml respectively. The influence of exposure to toxin concentrations manifested in terms of decreasing the adult emergence and prolongation of the generation period. The percentage of larvae that survived and succeeded to pupate increased by decreasing the concentration. The longevity of adult emergence that resulted from larvae treated with Bacillus subtilis were 6.0 ± 0.51 and 9.0 ± 0.63 days at 5 × 10⁸ and 2.5 × 10⁸ cell/ml, respectively compared with 9.8 ± 0.47 in control. The results indicated that Bacillus subtilis was more potent than Bacillus thuringiensis. Field applications of B. thuringiensis, B. subtilis and Reldan achieved 55.6, 67.4 and 89.4% reduction of the cotton leafworm larvae Spodoptera littoralis in clover plants under field conditions.     

Effects of nitrogen nutrition and root medium water potential on growth, nitrogen uptake and osmotic adjustment of rice

The effects of nitrogen (N) nutrition on growth, N uptake and leaf osmotic potential of rice plants (Oryza sativa L. ev. IR 36) during simulated water stress were determined. Twenty-one-day-old seedlings in high (28.6 × 10 ^?4M) and low (7.14 × 10 ⁴M) N levels were exposed to decreased nutrient solution water potentials by addition of polyethylene glycol 6000. The roots were separated from the solution by a semi-permeable membrane. Nutrient solution water potential was ?0.6 × 10⁵ Pa and was lowered stepwise to ?1 × 10⁵, ?2 × 10⁵, ?4 × 10⁵ and ?6 × 10⁵ Pa at 2-day intervals. Plant height, leaf area and shoot dry weight of high and low nitrogen plants were reduced by lower osmotic potentials of the root medium. Osmotic stress caused greater shoot growth reduction in high N than in low N plants. Stressed and unstressed plants in 7.14 × 10⁴M N had more root dry matter than the corresponding plants in 28.6 × 10⁴M N. Dawn leaf water potential of stressed plants was 1 × 10⁵ to 5.5 × 10⁵ Pa lower than nutrient solution water potential. Nitrogen-deficient water-stressed plants, however, maintained higher dawn leaf water potential than high nitrogen water-stressed plants. It is suggested that this was due to higher root-to-shoot ratios of N deficient plants. The osmotic potentials of leaves at full turgor for control plants were about 1.3 × 10⁵ Pa higher in 7.14 × 10^?4M than in 28.6 × 10^?4M N and osmotic adjustment of 2.6 × 10⁵ and 4.3 × 10⁵ Pa was obtained in low and high N plants, respectively. The nitrogen status of plants, therefore, affected the ability of the rice plant to adjust osmotically during water stress. Plant water stress decreased transpiration and total N content in shoots of both N treatments. Reduced shoot growth as a result of water stress caused the decrease in amount of water transpired. Transpiration and N uptake were significantly correlated. Our results show that nitrogen content is reduced in water-stressed plants by the integrated effects of plant water stress per se on accumulation of dry matter and transpiring leaf area as well as the often cited changes in soil physical properties of a drying root medium.     

Higher Abundance of Ammonia Oxidizing Archaea than Ammonia Oxidizing Bacteria and Their Communities in Tibetan Alpine Meadow Soils under Long-term Nitrogen Fertilization

Increasing usage of nitrogen fertilizer for food production has resulted in severely environmental problems of nutrients enrichment. This study aimed to examine the response of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to a long-term nitrogen fertilization in Tibetan alpine meadow. The abundance and composition of both AOB and AOA were assessed using quantitative real-time PCR, cloning and sequencing techniques based on amoA gene under different fertilization gradient (0, 30, 60, 90, and 120 g m^?2 year^?1). Our results showed that, abundances of AOA amoA genes (ranging from 1.48 × 10⁹ to 2.00 × 10⁹ copies per gram of dry soil) were significantly higher than those of AOB amoA genes (1.25 × 10⁷ to 2.62 × 10⁸ copies per gram of dry soil) under fertilization scenario. The abundance of AOB amoA genes increased with increasing nitrogen fertilization, whereas fertilization had little effect on AOA abundance. Sequences of clone libraries of the different treatments revealed that AOB communities were dominated by representatives of Cluster 4, constituting 48.94–64.44% in each clone library. Sequences of Clusters 9, 1 and 2 were prevalent in soils under higher fertilization. All archaeal amoA sequences recovered were affiliated with the soil/sediment clade and marine sediment clade, and no significant difference was observed on the community structure among different fertilization treatments. Variations in the AOB community structure and abundance were linked to ammonium-N and soil pH induced by different fertilization treatments. These results showed that the abundance and structure of the AOB community respond to the fertilization gradient, not AOA.     

Field evaluation of different application methods of the mixture of Bacillus cereus strain AR156 and Bacillus subtilis strain SM21 on pepper growth and disease resistance

The mixture of Bacillus subtilis strain SM21 and Bacillus cereus strain AR156, referred to as ASB, is a biopesticide in the process of registration in China, which has the capacity of controlling root-knot nematode in cucumber, Phytophthora wilt in pepper and Ralstonia wilt in tomato. In this study, we tested its effects on a range of physiological indicators of plant growth including biomass, yield, chlorophyll content and fruit nutrients of pepper, as well as, its efficacy in controlling bacterial wilt caused by Ralstonia solanacearum under field conditions in 2009 and 2010 by a variety of inoculation methods. Three application methods – soaking seeds, drenching soil around seeds right after sowing and drenching the rhizosphere of transplanted seedling with the aqueous solution (as a soil drench) –and three concentrations of ASB (1.0 × 10⁶ CFU/mL, 1.0 × 10⁷ CFU/mL, and 1.0 × 10⁸ CFU/mL) were employed. The results showed that both soaking seeds with ASB at 1.0 × 10⁷ CFU/mL as well as drenching rhizosphere with ASB at 1.0 × 10⁶ CFU/mL and 1.0 × 10⁷ CFU/mL promoted growth, increased yield and fruit nutrient contents of pepper. The combination of these two inoculation methods led to significant increases in growth and fruit nutrient contents. We found that the most effective way was the combination of soaking seeds with the ASB at 1.0 × 10⁷ CFU/mL and drenching rhizosphere with it at 1.0 × 10⁶ CFU/mL, which is also easy for Chinese farmers to implement.     

Characterisation of acidic sites of Pseudomonas biomass capable of binding protons and cadmium and removal of cadmium via biosorption

Summary The ability of Pseudomonas aeruginosa to accumulate Cd(II) ions from wastewater industries was experimentally investigated and mathematically modelled. From the potentiometric titration and non-ideal competitive analysis (NICA) model, it was found that the biomass contains three acidic sites. The values of proton binding (pK _i =1.66±3.26×10⁻³, 1.92±1.63×10⁻⁴ and 2.16±3.79×10⁻⁴) and binding constant of cadmium metal ions (pK _M1=1.99±2.45×10⁻³ and pK _M2=1.67±4.08×10⁻³) on the whole surface of biomass showed that protonated functional groups and biosorption of Cd(II) ions could be attributed to a monodentate binding to one acidic site, mainly the carboxylic group. From the isothermal sorption experimental data and Langmuir model, it was also found that the value of Langmuir equilibrium (pK _f) constant is 2.04±2.1×10⁻⁵ suggesting that the carboxyl group is the main active binding site. In addition, results showed that the maximum cadmium capacity (q _max) and affinity of biomass towards cadmium metal ions (b) at pH 5.1 and 20 min were 96.5±0.06 mg/g and 3.40×10⁻³± 2.10×10⁻³, respectively. Finally, interfering metal ions such as Pb(II), Cu(II), Cr(III), Zn(II), Fe(II), Mn(II), Ca(II) and Mg(II) inhibited Cd(II) uptake. Comparing the biosorption of Cd(II) by various Pseudomonas isolates from contaminated environment samples (soil and sewage treatment plant) showed that maximum capacities and equilibrium times were different, indicating that there was a discrepancy in the chemical composition between biomasses of different strains.