河西走廊酒泉地区盐碱土未培养放线菌多样性

采用免培养技术对河西走廊酒泉地区的原生盐碱土、次生盐碱土和农田土中的放线菌群落结构及其多样性进行分析.结果表明: 河西走廊酒泉地区原生盐碱土克隆文库分归于19个OTUs,分属于微球菌亚目、丙酸杆菌亚目、棒状杆菌亚目、弗兰克氏菌亚目、假诺卡氏菌亚目和放线菌目未知类群;次生盐碱土克隆文库分归于14个OTUs,分属于微球菌亚目、丙酸杆菌亚目和放线菌目未知类群;农田土克隆文库分归于7个OTUs,分属于微球菌亚目和棒状杆菌亚目;微球菌亚目是3种不同类型土壤中的共有种群,是原生盐碱土和农田土中的优势种群.多样性指数和稀释性曲线分析结果显示,3种不同类型土壤中放线菌种群丰富度为原生盐碱土>次生盐碱土>农田土;原生盐碱土、次生盐碱土的稀释性曲线均未趋于平稳,说明盐碱土中放线菌多样性比实际更加丰富.     

外加碳源对蚯蚓-污泥系统细菌群落结构的影响

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

三江源地区不同退化程度草地的土壤放线菌区系

用不同分离方法,对三江源地区不同退化程度草地土壤放线菌的数量和多样性进行了比较.从5份土样中共分离放线茵178株,根据表型特征和16S rRNA基因序列分析,分别归入7个已知属:小单孢菌属(Micromonospora)、原小单孢菌属(Promicromonospora)、诺卡氏菌属(Nocardia)、假诺卡氏菌属(Pseudonocardia)、游动放线菌属(Actinoplanes)、韩国生工茵属(Kribbella)和链霉菌属(Streptomyces).其中链霉菌属分离菌株可归入7个表型类群.发现轻度退化高寒草原的土壤放线菌数量,丰度和多样性高于重度退化高寒草原;针茅高寒草原的土壤放线菌数量和多样性高于蒿草高寒草甸,而其中链霉菌的种类低于后者.表明高寒草地的退化程度与其中土壤放线茵的数量和多样性呈负相关.     

连作龙牙百合与铁炮百合根际土壤真菌群落结构的差异分析

对连作龙牙百合(Long)与铁炮百合(Tie)根际土壤真菌ITS区进行扩增, 并利用Miseq ITS测序分析龙牙百合与铁炮百合根际土壤真菌群落的结构差异。结果表明: 测序百合根际土壤共得到69158条Clean Reads, 将其注释为277个操作分类单元(OTUs), 涵盖了5门、12纲、23目、25科、34属、36种; 在Alpha多样性指数上, Long的多样性指数高于Tie, 但均匀度低于Tie。在Beta多样性上, 两种百合间真菌群落结构差异较大; 在门水平子囊菌门、未知菌门、担子菌门为百合的优势菌群, 壶菌门为Tie特有。在属水平青霉菌属、炭疽菌属和未知菌属为两种百合真菌群落的优势菌属, 盘菌属仅出现在忌连作龙牙百合中, 青霉菌属和炭疽菌属在耐连作铁炮百合中含量增加, 未知菌属含量下降。研究表明, 连作状态下不同耐、忌连作百合根际土壤真菌群落存在差异, 且均有特异性的菌群, 研究结果为减轻或克服百合连作障碍提供一定的理论基础。     

峨眉山大蚯蚓肠道可培养细菌多样性研究

为探究峨眉山大蚯蚓秉前环毛蚓(Pheretima carnosa)肠道可培养细菌多样性,测定采样点土壤基本理化性质,从蚯蚓肠道中分离可培养细菌并进行16S r DNA系统发育分析,探究分离菌株的相似性、多样性、优势度及均匀度,绘制稀释曲线。结果显示:峨眉山大蚯蚓生活在有机质丰富的土壤环境中,其肠道中分离出的56株细菌分布在3门14属,其中芽孢杆菌属(Bacillus)为明显优势菌群;此外,Shannon-Wiener多样性指数(1.73)、Berger-Parker优势度指数(0.536)、Margalef指数(3.23)、Evenness均匀度指数(0.66)均表明峨眉山大蚯蚓肠道可培养细菌多样性丰富,而且稀释曲线表明尚有大量未分离细菌。上述研究为峨眉山大蚯蚓肠道微生物资源的开发利用奠定了基础。     

有机物料对设施番茄长期连作土壤细菌群落结构的影响

为研究稻草、鸡粪、牛粪和蚓粪对设施番茄长期连作(20年)土壤细菌群落结构的调节效果,应用高通量测序技术,对不同有机物料处理后的土壤细菌群落多样性和组成进行了研究,同时分析了土壤环境因子对微生物群落结构变化的贡献,为设施番茄生产的科学施肥提供理论依据。结果表明:(1)蚓粪和鸡粪对提高土壤细菌多样性和丰富度均有显著效果;牛粪显著降低了细菌多样性和丰富度;(2)与对照相比,稻草、鸡粪、蚓粪和牛粪使土壤优势菌群变形菌门(Proteobacteria)和放线菌门(Actinobacteria)的相对丰度增加了36.40%～44.27%和25.80%～29.35%,并显著降低了酸杆菌门(Acidobacteria)丰度;其中变形菌门和放线菌门丰度分别在稻草和蚓粪处理中最高,酸杆菌门在牛粪处理中最低。与化肥相比,施用有机物料不同程度地促进了土壤中有益菌属的生长,如鞘氨醇单胞菌属(Sphingomonas)、芽单胞菌属(Gemmatimonas)、芽孢杆菌属(Bacillus)、链霉菌属(Streptomyces)和紫杆菌属(Porphyrobacter),同时也抑制了酸杆菌门细菌的生长,如Gp6、Gp16和Gp4;(3)与化肥相比,有机物料处理显著提高了土壤pH,同时降低了电导率,其中蚓粪处理pH值最高,电导率最低。Pearson相关性分析表明,土壤pH、电导率、铵态氮、全碳和有机质含量是影响土壤细菌群落多样性和丰富度的主要环境因子。RDA分析表明,土壤铵态氮含量、电导率、pH和全碳含量对土壤细菌群落组成有重要作用。综上,蚓粪对番茄连作土壤细菌群落结构的调节效果优于其他有机物料,在设施番茄可持续生产中应引起更多关注。     

4种蚯蚓肠道微生物对砷毒性的响应差异研究

蚯蚓肠道是微生物多样性的一个潜在存储库。砷对蚯蚓肠道微生物群落的影响已被证实,但砷在不同蚯蚓肠道菌群中生物转化的差异仍不清楚。为了进一步阐述土壤中广泛存在的低浓度砷(浓度为5,15,25 mg/kg)对不同种类蚯蚓肠道微生物影响的差异,将4种典型蚯蚓暴露于砷污染土壤后,测定其肠道微生物组成变化,并分析砷对不同蚯蚓肠道内砷富集、形态和砷生物转化基因的影响。结果显示,所有蚯蚓组织内均存在明显的砷富集,其富集系数由高到低依次为:安德爱胜蚓(1.93)>加州腔蚓(0.80)>通俗腔蚓(0.78)>湖北远盲蚓(0.52),蚯蚓组织和肠道内砷形态主要以无机砷为主,其中As(III)含量比例> 80%,部分蚯蚓组织内还发现少量有机砷。4种蚯蚓肠道微生物群落在门水平上主要以变形菌、厚壁菌和放线菌为主,并与周围土壤细菌群落组成存在显著差异。同时,在土壤和肠道内共检测到17个砷转化基因,其中蚯蚓肠道内As(V)还原和砷转运相关基因相对丰度较高,而砷(去)甲基化基因丰度较低。此外,低浓度砷污染对蚯蚓生长无显著影响,却能引起蚯蚓肠道微生物群落的紊乱。蚯蚓种类和砷污染是引起蚯蚓肠道微生物...     

青藏铁路沿线唐古拉山口土壤微生物的ARDRA分析

通过构建16S rDNA文库及文库的限制性片段长度多态性分析（ARDRA）,对青藏铁路沿线唐古拉山口的土壤微生物多样性进行了研究。采用限制性内切酶HaeIII和RsaI对克隆文库中的90个克隆子进行了酶切分型,根据ARDRA酶切图谱的不同,可将其分为23个OTUs。16SrDNA序列分析结果表明,该克隆文库中主要包括变形菌门（Proteobacteria）的alpha、beta、detla亚类、厚壁菌门（Firmicutes）、放线菌门（Actinobacteria）、拟杆菌门（Bacteroidetes）、酸杆菌门（Acidobacteria）及浮霉菌门（Planctomycetes）等8类细菌及未培养细菌。Alpha变形细菌为该文库中的主要菌群,占克隆总数的33.3%;其次为未培养细菌,占克隆总数的22.2%,Bradyrhizobium为优势菌属。研究结果揭示,青藏铁路唐古拉山口的土壤微生物种群不仅具有丰富的多样性,还存在丰富的潜在新菌种。     

河北九莲城淖尔可培养放线菌多样性及抗菌活性筛选

【目的】勘探干涸的九莲城淖尔土壤放线菌多样性并进行活性筛选,以期发现药用微生物资源,为新抗生素的发现奠定基础。【方法】采用15种分离培养基,以稀释涂布法分离放线菌;根据分离菌株的16S rRNA基因序列同源性分析放线菌多样性;发酵液经乙酸乙酯萃取,菌丝体经丙酮浸提,获得提取浓缩物样品;样品通过纸片扩散法进行抗菌活性初筛;抗菌阳性菌株采用PCR技术进行Ⅰ型聚酮合酶(PKS I)KS域、Ⅱ型聚酮合酶(PKS II)KS域和非核糖体多肽合成酶(NRPS)A结构域抗生素生物合成基因的检测。【结果】从11份盐湖土壤样品中分离纯化到251株放线菌,其分布于放线菌纲的10个目15个科31个属,其中优势菌属为链霉菌属和拟诺卡氏菌属;251株放线菌中包括57株耐(嗜)盐放线菌,其优势菌属为拟诺卡氏菌属(22株)和涅斯捷连科氏菌属(15株)。基于16S r RNA基因序列的系统发育分析显示,菌株J11Y309为糖霉菌科潜在新属,菌株J12GA03为分枝杆菌科潜在新种。96株放线菌活性检测结果显示,56株至少对1株检定菌具有抗菌活性,阳性率为58.3%;56株有活性的放线菌中,47株至少含有1种抗生素生物合成基因,其中17株同时具有3种抗生素生物合成基因。【结论】干涸的九莲城淖尔土壤中含有较为丰富的药用放线菌资源,具有从中发现放线菌新物种和新抗生素的潜力。     

腾格里沙漠东南缘藻结皮与藓结皮放线菌多样性及其潜在代谢功能

放线菌作为干旱、半干旱环境中生物土壤结皮(Biological Soil Crusts,BSCs)组成的重要生命存在形式之一,不仅是潜在临床有用天然产物化学多样性的重要来源,也是该生态系统物质循环与能量流动的重要参与者。以腾格里沙漠东南缘广泛分布的藻结皮和藓结皮为研究对象,通过宏基因组测序比较分析两种BSCs放线菌种群的分布特征、组成及其潜在代谢功能。结果表明,腾格里沙漠东南缘藻结皮与藓结皮土壤微生物组主要形成以地嗜皮菌属、红色杆菌属、类诺卡氏菌属、游动放线菌属、芽生球菌属、链霉菌属、贫养杆菌属、糖丝菌属、土壤红杆菌属、假诺卡氏菌属、小单孢子菌属、康奈斯氏杆菌属、大理石雕菌属、小月菌属以及弗兰克氏菌属等为主要类群的放线菌群落结构,在两种BSCs类型之间各属分布存在差异。藓结皮中放线菌参与的氨基糖与核苷酸糖代谢、原核生物中的碳固定途径、丁酸代谢、丙酸代谢、丙氨酸/天门冬氨酸和谷氨酸代谢、甲烷代谢、2-羰基羧酸代谢、肽聚糖生物合成、淀粉与蔗糖代谢以及缬氨酸/亮氨酸与异亮氨酸降解显著高于藻结皮。藓结皮中地嗜皮菌属和红色杆菌属对相对丰度前10的代谢功能分类的贡献度显著低于藻结皮,而类诺卡氏菌属、芽生球菌属、贫养杆菌属、游动放线菌属、链霉菌属、假诺卡氏菌属和糖丝菌属等对这些功能的相对贡献在藓结皮中具有重要作用。这些结果可为全面、深入理解腾格里沙漠东南缘藻结皮与藓结皮放线菌资源多样性及其潜在功能多样性提供科学数据,也为理解放线菌在不同类型BSCs中的生态功能提供参考。     

Earthworm invasions of ecosystems devoid of earthworms: effects on soil microbes

Recent studies document North American earthworm invasions and their profound effects on the structure of the soil profile, which is the habitat for soil microorganisms (mainly fungi and bacteria). Dramatic alterations made to these layers during earthworm invasion significantly change microbial community structure and therefore microbial activities such as C transformations. Understanding the impacts of earthworm invasion on the microbes themselves will give insight into earthworm effects on microbial activities. Bacterial and actinomycete communities in earthworm guts and casts have not been studied in environments recently invaded by earthworms. Earthworm invasion tended to decrease fungal species density and fungal species diversity and richness. The presence of earthworms decreased zygomycete species abundance probably due to disruption of fungal hyphae. Physical disruption of hyphae may also explain decreased mycorrhizal colonization rates, decreased mycorrhizal abundance and altered mycorrhizal morphology in the presence of earthworms. Mixing of organic layers into mineral soil during earthworm invasion tended to decrease microbial biomass in forest floor materials while increasing it in mineral soil. In newly invaded forest soils, microbial respiration and the metabolic quotient tended to decline. In forests where either the microbial community has had time to adapt to earthworm activities, or where the destruction of the forest floor is complete, as in invasions by the Asian Amynthas hawayanus, the presence of earthworms tends to increase the metabolic quotient indicating a shift to a smaller, more active microbial community.     

Carbon availability controls the growth of detritivores (Lumbricidae) and their effect on nitrogen mineralization

Activity of soil decomposer microorganisms is generally limited by carbon availability, but factors controlling saprophagous soil animals remain largely unknown. In contrast to microorganisms, animals are unable to exploit mineral nutrient pools. Therefore, it has been suggested that soil animals, and earthworms in particular, are limited by the availability of nitrogen. In contrast to this view, a strong increase in density and biomass of endogeic earthworms in response to labile organic carbon addition has been documented in field experiments. The hypothesis that the growth of endogeic earthworms is primarily limited by carbon availability was tested in a laboratory experiment lasting for 10 weeks. In addition, it was investigated whether the effects of earthworms on microbial activity and nutrient mineralization depend on the availability of carbon resources. We manipulated food availability to the endogeic earthworm species Octolasion tyrtaeum by using two soils with different organic matter content, providing access to different amounts of soil, and adding labile organic carbon (glucose) enriched in ¹³C.Glucose addition strongly increased the growth of O. tyrtaeum. From 8 to 17% of the total C in earthworm tissue was assimilated from the glucose added. Soil microbial biomass was not strongly affected by the addition of glucose, though basal respiration was significantly increased and up to 50% of the carbon added as glucose was incorporated into soil organic matter. The impact of earthworms on the mineralization and leaching of nitrogen depended on C availability. As expected, in C-limited soil, the presence of earthworms strongly increased nitrogen leaching. However, when C availability was increased by the addition of glucose, this pattern was reversed, i.e. the presence of O. tyrtaeum decreased nitrogen leaching and its availability to soil microflora. We conclude that irrespective of the total carbon content of soils, O. tyrtaeum was primarily limited by carbon, and that increased carbon availability allowed earthworms to be more effective in mobilizing N. The presence of earthworms increases C limitation of soil microorganisms, due to increased availability of N and P in earthworm casts or a direct depletion of easily available carbon resources by earthworms.     

Actinomycetes isolated from medicinal plant rhizosphere soils: diversity and screening of antifungal compounds,indole-3-acetic acid and siderophore production

A total of 445 actinomycete isolates were obtained from 16 medicinal plant rhizosphere soils. Morphological and chemotaxonomic studies indicated that 89% of the isolates belonged to the genus Streptomyces, 11% were non-Streptomycetes: Actinomadura sp., Microbispora sp., Micromonospora sp., Nocardia sp, Nonomurea sp. and three isolates were unclassified. The highest number and diversity of actinomycetes were isolated from Curcuma mangga rhizosphere soil. Twenty-three Streptomyces isolates showed activity against at least one of the five phytopathogenic fungi: Alternaria brassicicola, Collectotrichum gloeosporioides, Fusarium oxysporum, Penicillium digitatum and Sclerotium rolfsii. Thirty-six actinomycete isolates showed abilities to produce indole-3-acetic acid (IAA) and 75 isolates produced siderophores on chrome azurol S (CAS) agar. Streptomyces CMU-PA101 and Streptomyces CMU-SK126 had high ability to produced antifungal compounds, IAA and siderophores.     

Effects of earthworms on biomass production,nitrogen allocation and nitrogen transfer in wheat-clover intercropping model systems

The effects of earthworms (Lumbricidae) on plant biomass production and N allocation in model intercropping systems of winter wheat and white clover were evaluated in two pot experiments. Wheat and wheat-clover mixtures were grown in a low-organic loam soil, earthworms were added at densities comparable to field population densities and the experiments were terminated 48 and 17 d after earthworm introductions. In both experiments, earthworms significantly increased the biomass and N uptake of wheat while they had generally no effects on clover. As a result, earthworm activity increased the proportion of wheat biomass in the total plant biomass of the mixture. Nitrogen budgets of the experiment lasting 48 d indicated that additional N in the system made available by earthworm activity was primarily taken up by the wheat. Earthworms also affected intra-plant N allocation in wheat which had significantly higher shoot:root N ratios when earthworms were present. When clover was labelled with ¹⁵N in the experiment which lasted 17 d, endogeic earthworms significantly reduced the amounts of ¹⁵N excess transferred from living or decomposing clover roots to accompanying wheat plants. Earthworms assimilated small quantities of ¹⁵N tracer from decomposing clover roots but not from living clover roots. The results of these model experiments suggest that earthworms can affect the balance between intercropped cereals and legumes by altering intra- and inter-plant N allocation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigation of actinomycete diversity in the tropical rainforests of Singapore

Five thousand actinomycetes were isolated from soil samples collected from rainforests in Singapore and the generic identities of these isolates were determined by using a procedure that combined morphological, chemotaxonomic and 16S rDNA sequence-based phylogenetic analyses. Actinomycetes belonging to a total of 36 genera were identified. The most abundant isolates are members of Streptomyces, Micromonospora, Actinoplanes, Actinomadura, Nonomuria, Nocardia and Streptosporangium. By phylogenetic analysis of 16S rDNA sequences of our isolates together with those of known actinomycete species, we also evaluated the species diversity of several genera including Streptomyces, Micromonospora, Nonomuria, and Actinomadura. We found that: first, the tropical isolates are present in most clades represented by known species; and second, many tropical isolates form new clades distant from the known species, indicating the presence of unidentified taxa at both species and genus levels. Based on these results, we conclude that actinomycete diversity in the tropical rainforest is very great and should represent an excellent source for discovery of novel bioactive compounds. Received 17 March 1999/ Accepted in revised form 24 June 1999     

秸秆和生草覆盖对桃园土壤养分含量、微生物数量及土壤酶活性的影响

以秸秆(覆盖重量分别为小麦(Triticum aestivum)秸3.25 kg·m^-2、玉米(Zea mays)秸1.97 kg·m^-2、禾本科杂草3.67 kg·m^-2)和生草(白三叶草(Trifolium repens)、高羊茅(Festuca arundincea)和紫花苜蓿(Medicago sativa), 播种量均为50 kg·hm^-2)为覆盖材料, 以不覆盖为对照, 研究了不同覆盖材料对桃园土壤微生物数量和酶活性的影响, 及其与土壤养分的关系。结果表明, 与对照相比, 除覆盖生草根际和非根际土壤全磷和速效磷含量差异均不显著外, 其他处理根际和非根际土壤碱解氮、速效钾、全氮、全钾和有机质含量差异均达到显著水平; 所有处理根际和非根际土壤氨化细菌、真菌和放线菌数量、土壤含水率和pH值、土壤脲酶和磷酸酶活性差异均达到显著水平。白三叶草处理的根际和非根际土壤碱解氮、速效钾、全氮、全钾、有机质含量, 土壤氨化细菌和真菌数量, 土壤脲酶和磷酸酶活性的平均升幅均最高, 分别为99%、270%、267%、117%、272%、158%、141%、156%和64%。氨化细菌、真菌、放线菌、脲酶和磷酸酶分别与土壤碱解氮、速效钾(放线菌和磷酸酶除外)、全氮、全钾和有机质呈显著或极显著的正相关。通径分析表明, 在3种土壤微生物和2种酶对养分含量的影响中, 脲酶是影响土壤碱解氮、速效钾、全氮、全钾和有机质的主要因子。     

Effects of Exotic Earthworms on Soil Phosphorus Cycling in Two Broadleaf Temperate Forests

We compared the biogeochemical cycling of phosphorus (P) in northern hardwood forest plots invaded by exotic earthworms versus adjacent uninvaded reference plots. In three of the six pairs of plots, earthworm invasion resulted in significantly more total P in the upper 12 cm of soil. The finding of increased amounts of unavailable and occluded inorganic P forms in the invaded plots suggests that earthworm activity mobilized unweathered soil particles from deeper layers of the soil, increasing the stocks of total P in surface soils. In two pairs of plots, the earthworm-invaded soils had less total P than the reference soils. In these plots, earthworm activity resulted in augmented rates of P cycling and alteration of the physical structure of the soil that increased loss of P in leaching water, reducing the total amount of P. We hypothesize that the different effects of earthworm invasion on the soil P cycle result from unique characteristics of the ecological groups of earthworms dominating each site. The invaded plots with increased total P were dominated by the anecic species Lumbricus terrestris, a large earthworm that constructs deep, vertical burrows and is effective at moving soil materials from and to deeper layers of the profile. In contrast, the earthworm-invaded plots where the total P in the surface soil decreased were dominated by the epi-endogeic species L. rubellus, which feeds and lives in the upper organic layers of the soil. In these plots, earthworms significantly increased the amount of readily exchangeable P in the soil, increasing the loss of this element in leaching water.     

Polymerase chain reaction-denaturing gradient gel electrophoresis analysis of bacterial community structure in the food,intestines, and feces of earthworms

The bacterial communities in the food, intestines, and feces of earthworms were investigated by PCR-denaturing Gradient gel electrophoresis (DGGE). In this study, PCR-DGGE was optimized by testing 6 universal primer sets for microbial 16S rRNA in 6 pure culture strains of intestinal microbes in earthworms. One primer set effectively amplified 16S rRNA from bacterial populations that were found in the food, intestines, and feces of earthworms. Compared with the reference markers from the pure culture strains, the resulting DGGE profiles contained 28 unique DNA fragments. The dominant microorganisms in the food, intestines, and feces of earthworms included Rhodobacterales bacterium, Fusobacteria, Ferrimonas marina, Aeromonas popoffii, and soil bacteria. Other straisn, such as Acinetobacter, Clostridium, and Veillonella, as well as rumen bacteria and uncultured bacteria also were present. These results demonstrated that PCR-DGGE analysis can be used to elucidate bacterial diversity and identify unculturable microorganisms.     

Effects of European Earthworm Invasion on Soil Characteristics in Northern Hardwood Forests of Minnesota, USA

European earthworms are colonizing worm-free hardwood forests across North America. Leading edges of earthworm invasion in forests of northern Minnesota provide a rare opportunity to document changes in soil characteristics as earthworm invasions are occurring. Across leading edges of earthworm invasion in four northern hardwood stands, increasing total earthworm biomass was associated with rapid disappearance of the O horizon. Concurrently, the thickness, bulk density and total soil organic matter content of the A horizon increased, and it’s percent organic matter and fine root density decreased. Different earthworm species assemblages influenced the magnitude and type of change in these soil parameters. Soil N and P availability were lower in plots with high earthworm biomass compared to plots with low worm biomass. Decreases in soil nitrogen availability associated with high earthworm biomass were reflected in decreased foliar nitrogen content for Carex pensylvanica, Acer saccharum and Asarum canadense but increased foliar N for Athyrium felix-femina. Overall, high earthworm biomass resulted in increased foliar carbon to nitrogen ratios. The effects of earthworm species assemblages on forest soil properties are related to their feeding and burrowing habits in addition to effects related to total biomass. The potential for large ecosystem consequences following exotic earthworm invasion has only recently been recognized by forest ecologists. In the face of rapid change and multiple pressures on native forest ecosystems, the impacts of earthworm invasion on forest soil structure and function must be considered.     

Microwave irradiation is a useful tool for improving isolation of actinomycetes from soil

Actinomycetes are an important source of novel, biologically active compounds. New methods need to be developed for isolating previously unknown actinomycetes from soil. The objective of this experiment was to study microwave irradiation of soil as a means for isolating previously unknown actinomycetes. Soil samples were collected at ten elevations between 800 m and 3670 m on Taibai Mountain, Shaanxi Province, China. Moistened soil samples were irradiated at 120 W heating power (2450 MHz) for 3 min using a household microwave oven. Irradiation increased total actinomycete, streptomycete, and antagonistic actinomycete counts on three types of culture media. Irradiation also increased the number of culturable actinomycete isolates. Some actinomycete isolates were culturable only after the soil was irradiated, whereas other isolates could not be cultured after irradiation. Irradiation of soil from elevations >3000 m increased actinomycete counts significantly but had little effect on the number of culturable actinomycete isolates. In contrast, irradiation of samples from elevations <3000 m had relatively little effect on actinomycete counts, but significantly increased the number of culturable actinomycete isolates. We used 16S rDNA sequence analysis to identity 14 actinomycete isolates that were only culturable after irradiation. Microwave irradiation of soil was helpful for isolating Streptomyces spp., Nocardia spp., Streptosporangium spp., and Lentzea spp. Slightly more than 90% of the identified actinomycete species were biologically active. In conclusion, microwave irradiation is a useful tool for isolating biologically active actinomycetes from soil.