Grazing of a common species of soil protozoa (Acanthamoeba castellanii) affects rhizosphere bacterial community composition and root architecture of rice (Oryza sativa L.)

We performed a controlled experiment with rice seedlings (Oryza sativa L.) growing in Petri dishes on homogeneous nutrient agar containing a simple rhizosphere food web consisting of a diverse bacterial community and a common soil protozoa, Acanthamoeba castellanii, as bacterial grazer. Presence of amoebae increased bacterial activity and significantly changed the community composition and spatial distribution of bacteria in the rhizosphere. In particular, Betaproteobacteria did benefit from protozoan grazing. We hypothesize that the changes in bacterial community composition affected the root architecture of rice plants. These effects on root architecture affect a fundamental aspect of plant productivity. Root systems in presence of protozoa were characterized by high numbers of elongated (L-type) laterals, those laterals that are a prerequisite for the construction of branched root systems. This was in sharp contrast to root system development in absence of protozoa, where high numbers of lateral root primordia and short (S-type) laterals occurred which did not grow out of the rhizosphere region of the axile root. As a consequence of nutrient release from grazed bacteria and changes in root architecture, the nitrogen content of rice shoots increased by 45% in presence of protozoa. Our study illustrates that interactions over three trophic levels, i.e. between plants, bacteria and protozoa significantly modify root architecture and nutrient uptake by plants.     

Comparison between direct counts of active soil ciliates (Protozoa) and most probable number estimates obtained by Singh's dilution culture method

The abundance of active soil ciliates was determined by Singh's dilution culture method any by the direct counting method of Lüftenegger et al. (1988) in 13 samples of 3 types of soil (meadow topsoil, spruce and beech litter). This comparative investigation revealed that the dilution culture methods are likely to overestimate active ciliates by orders of magnitude (with an average factor of 2000). One of the disadvantages of dilution methods is their difficulty meeting the assumptions of the MPN (most probable number) estimation model, on which they are based. A further serious problem is the proper separation of encysted and active cells. Due to a wide range of systematic errors, MPN estimates become seriously biased. But even if the basic assumptions could be met, the maximal precision of the estimate is far too low for a useful application within the context of soil ecology. This was revealed by the calculation of approximate confidence limits. Subjecting the data to analysis of variance showed that the direct counts can clearly differentiate ciliate abundances in forest litter versus meadow soil, whereas the dilution culture method is not precise enough to achieve this distinction. The MPN estimates did not even correlate significantly with the direct counts. Our investigation thus proved that dilution culture methods are beset with methodological deficiencies, resulting in unreliable estimates of protozoan abundances in soil.     

Fatty acid composition of ruminal bacteria and protozoa,and effect of defaunation on fatty acid profile in the rumen with special reference to conjugated linoleic acid in cattle

Objectives of this study were to compare fatty acid (FA) composition of ruminal bacterial (B) and protozoal (P) cells, and to investigate effect of protozoa on FA profile in the rumen of cattle. Three cows were used to prepare ruminal B and P cells. Four faunated and three defaunated cattle (half‐siblings) were used to study effect of protozoa on ruminal FA profile. Proportions of C16:0 and C18:0 in total fatty acids in B cells were 20.7% and 37.4%, whereas those in P cells were 33.4% and 11.6%, respectively. Proportions of trans‐vaccenic acid (VA) and cis‐9, trans‐11 conjugated linoleic acid (CLA) in B cells were 3.9% and 1.0%, and those in P cells were 5.5% and 1.6%, respectively, being higher in P cells. Proportions of C18:1, C18:2 and C18:3 in P cells were two to three times higher than in B cells. Proportions of unsaturated fatty acids, VA and CLA in B cells of faunated cattle were higher than those of defaunated. VA and CLA in the ruminal fluid of faunated were also 1.6 to 2.5 times higher than those of defaunated. This tendency was similar for cell‐free fraction of ruminal fluid. These results indicate that protozoa contribute greatly in VA and CLA production in the rumen.     

Prevalence of antibodies to Toxoplasma gondii in cats, dogs and horses in Sweden

Samples of serum or plasma taken during 1986 and 1987 from 244 pet cats, 303 dogs and 219 horses, randomly selected among animals referred to the Animal Clinics of the Swedish University of Agricultural Sciences, were screened by enzyme-linked immunosorbent assay (ELISA) for antibodies to Toxoplasma gondii. 42% of cats, 23% of dogs and 1% of horses examined were found seropositive.     

补饲热处理大麦对延边黄牛瘤胃内环境的影响

该试验研究了补饲热处理大麦对瘤胃内环境的影响。选择2头健康无病、体重相近、安装永久性瘤胃瘘管的延边黄牛母牛，分别测定pH、原虫数及NH3-N浓度。对照组和试验组不同时间点pH值变化均不显著，两组pH值变化规律大致相同，变化范围在5．81～6．92之间。对照组和试验组不同时间点纤毛虫数量及NH3—N浓度无显著差异，试验组均低于对照组，但在各时间点，各组间差异均不显著。     

长江上游原生动物的群落生态学研究

于2003～2007年采集了长江上游通天河至三峡水库的原生动物样品,对长江上游地区原生动物的分布情况作了较全面的调查.该调查共设93个采样站点,其中通天河-重庆在长江干流设38个采样站,支流设22个采样站,三峡库区设33个采样点,每年丰水期和平水期各采集1次.调查结果表明,长江上游共检出309种原生动物,隶属于60科106属,其中通天河至金沙江段检出140种,水富-重庆江段检出90种,三峡水库检出245种.金沙江段优势种为砂壳虫、匣壳虫、表壳虫和圆壳虫;水富-重庆段优势种为砂壳虫、匣壳虫及巢居法帽虫;三峡库区种类较为丰富,除了砂壳虫科和表壳科依然占据优势外,简壳虫、变形虫、领鞭虫、吸管虫和钟虫也逐渐增多,成为一些区域的优势种.三峡水库检出的原生动物种类多于上游河流段,其中有125种只在三峡库区检出.与1990年三峡地区原生动物资料相比.库区的群落结构发生了明显变化.随着水库水文情势的变化,原生动物种类组成也由以有壳肉足虫为主的河流型逐渐转变为以纤毛虫占优势的静水型种类.     

瘤胃细菌、原虫和真菌降解植物细胞壁的相对贡献及其互作

采用体外产气量法 ,以球磨与未球磨玉米秸细胞壁为底物 ,对瘤胃微生物不同区系降解植物细胞壁的相对贡献和发酵特征进行了研究。用化学试剂和抗生素来分离瘤胃细菌、原虫和真菌 ,并设计下列微生物区系 :全瘤胃液 (WRF)、细菌 (B)、原虫 (P)、真菌 (F)、细菌 +原虫 (B +P)、细菌 +真菌 (B +F)、原虫 +真菌 (P +F)和负对照(CON)。结果表明 ,细胞壁经球磨后可以显著提高瘤胃微生物的产气量和降解率 (P <0 .0 1) ,但不改变发酵类型 ;不同微生物区系的产气量和降解率具有极显著的差异 (P <0 .0 1) ,WRF的产气量和降解率最高 ,其次是混合培养(B +P、P +F、B +F) ,而单培养 (B、P、F)的最低 (P <0 .0 1)。结果说明植物细胞壁在瘤胃内的降解是在细菌、原虫和真菌的协同作用下完成的 ,对植物细胞壁的降解程度可能不是某一种或二种微生物所能及第的。B +P的产气量和降解率仅次于WRF ,表明瘤胃细菌和原虫在降解植物细胞壁过程中存在协同效应 ,对细胞壁降解的贡献率较大。另外 ,随着产气量和降解率的提高 ,发酵液的pH值降低、总VFA、氨态氮和甲烷气体的含量升高 ,进一步证明植物细胞壁的发酵程度提高了。     

A Porous Simulation Experiment of Protozoa Movement with Glass Bead

Protozoa can move due to their flagella, cilia or pseudopodia, and play an important role in the transformation and cycling of matter and energy in ecosystems. In this study, the glass beads with the diameters of 1.0, 0.5, 0.25 and 0.1 mm were used to simulate soil pores of 0. 292 - 0. 258, 0. 155 - 0.116, 0. 056- 0. 040 and 0. 028 - 0.020 mm respectively. Three typical soil protozoa of Bodo edax, Colpoda cucullus and Amoeba proteus were examined for the relation of their movement to pores. It was found that the smallest protozoan of Bodo edax could be leached through all the pores. However, no more than 26% of the added protozoan was leached out of the column. The leached protozoa were decreased with the pore sizes and leaching duration. The bigger one of Colpoda cucullus was moved out from the column filled with the glass beads of ＞0.5 mm in diameter. Less than about 15 % of the added protozoa were leached out of the column. The biggest one of Amoeba proteus could not leached out from any of the pores. It is evident that most of the protozoa remained in the column due to their occupation of the pores.     

日粮类型对绵羊小肠内代谢性蛋白质的影响

以成年萨福克绵羊为试验对象,分别安装瘤胃瘘管、十二指肠近端T型瘘管和回肠远端T型瘘管,饲喂由鸭茅干草和配合饲料组成的不同瘤胃内可降解有机物/瘤胃内可降解粗蛋白质(OMR/CPR)比例的日粮,研究小肠可代谢性饲料蛋白质(MP)的变化规律.结果表明随着OMR/CPR的提高,小肠内微生物氮的消化量显著降低,而过瘤胃饲料蛋白质氮显著增加;表观MP量随着OMR/CPR的增加呈先增加后减少的变化趋势,表观MP量占CP、DCP摄取量分别为42.2%～59.6%、63.6%～87.8%.