Contrasting Diversity and Host Association of Ectomycorrhizal Basidiomycetes versus Root-Associated Ascomycetes in a Dipterocarp Rainforest

Root-associated fungi, including ectomycorrhizal and root-endophytic fungi, are among the most diverse and important belowground plant symbionts in dipterocarp rainforests. Our study aimed to reveal the biodiversity, host association, and community structure of ectomycorrhizal Basidiomycota and root-associated Ascomycota (including root-endophytic Ascomycota) in a lowland dipterocarp rainforest in Southeast Asia. The host plant chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) region and fungal internal transcribed spacer 2 (ITS2) region were sequenced using tag-encoded, massively parallel 454 pyrosequencing to identify host plant and root-associated fungal taxa in root samples. In total, 1245 ascomycetous and 127 putative ectomycorrhizal basidiomycetous taxa were detected from 442 root samples. The putative ectomycorrhizal Basidiomycota were likely to be associated with closely related dipterocarp taxa to greater or lesser extents, whereas host association patterns of the root-associated Ascomycota were much less distinct. The community structure of the putative ectomycorrhizal Basidiomycota was possibly more influenced by host genetic distances than was that of the root-associated Ascomycota. This study also indicated that in dipterocarp rainforests, root-associated Ascomycota were characterized by high biodiversity and indistinct host association patterns, whereas ectomycorrhizal Basidiomycota showed less biodiversity and a strong host phylogenetic preference for dipterocarp trees. Our findings lead to the working hypothesis that root-associated Ascomycota, which might be mainly represented by root-endophytic fungi, have biodiversity hotspots in the tropics, whereas biodiversity of ectomycorrhizal Basidiomycota increases with host genetic diversity.     

缺硼与低温对黄瓜幼苗—些生理反应的影响

营养液培养试验表明,缺硼明显降低黄瓜幼苗植株的生长量,植株叶片细胞质膜K 的渗漏增加,细胞结构受损。此外,叶片中蔗糖和还原糖都明显积累。缺硼的上述反应在低温胁迫（7－8℃,FX25－28℃为对照）时表现更为明显。试验结果表明硼对于细胞膜的完整性具有重要的作用;充分供硼可以减轻低温对细胞膜的伤害。     

低温胁迫下玉米幼苗的几种生理生化指标的变化

胚芽期和三叶期的玉米自交系‘齐319’幼苗经0、2、4、6℃冷处理后,测定过氧化物酶（POD）、过氧化氢酶（CAT）和超氧化物歧化酶（soD）活性以及可溶性蛋白和丙二醛（MDA）含量的结果表明：POD、CAT、SOD活性以及MDA和蛋白质含量均增加,0、2℃下胚芽期幼苗的抗寒性比三叶期的高,4和6℃下三叶期幼苗的抗寒能力更强;无论是胚芽期还是三叶期,温度越低,幼苗受冷伤害越大。     

Host Specificity and Source of Enterocytozoon bieneusi Genotypes in a Drinking Source Watershed

To assess the host specificity of Enterocytozoon bieneusi and to track the sources of E. bieneusi contamination, we genotyped E. bieneusi in wildlife and stormwater from the watershed of New York City''s source water, using ribosomal internal transcribed spacer (ITS)-based PCR and sequence analyses. A total of 255 specimens from 23 species of wild mammals and 67 samples from stormwater were analyzed. Seventy-four (29.0%) of the wildlife specimens and 39 (58.2%) of the stormwater samples from streams were PCR positive. Altogether, 20 E. bieneusi genotypes were found, including 8 known genotypes and 12 new ones. Sixteen and five of the genotypes were seen in animals and stormwater from the watershed, respectively, with WL4 being the most common genotype in both animals (35 samples) and stormwater (23 samples). The 20 E. bieneusi genotypes belonged to five genogroups (groups 1, 3, 4, and 7 and an outlier), with only 23/113 (20.4%) E. bieneusi-positive samples belonging to zoonotic genogroup 1 and 3/20 genotypes ever being detected in humans. The two genogroups previously considered host specific, groups 3 and 4, were both detected in multiple groups of mammals. Thus, with the exception of the type IV, Peru11, and D genotypes, which were detected in only 7, 5, and 2 animals, respectively, most E. bieneusi strains in most wildlife samples and all stormwater samples in the watershed had no known public health significance, as these types have not previously been detected in humans. The role of different species of wild mammals in the contribution of E. bieneusi contamination in stormwater was supported by determinations of host-adapted Cryptosporidium species/genotypes in the same water samples. Data from this study indicate that the host specificity of E. bieneusi group 3 is broader than originally thought, and wildlife is the main source of E. bieneusi in stormwater in the watershed.     

Morphologic, Host Specificity, and Molecular Characterization of a Hungarian Cryptosporidium meleagridis Isolate

This study was undertaken in order to characterize Cryptosporidium meleagridis isolated from a turkey in Hungary and to compare the morphologies, host specificities, organ locations, and small-subunit RNA (SSU rRNA) gene sequences of this organism and other Cryptosporidium species. The phenotypic differences between C. meleagridis and Cryptosporidium parvum Hungarian calf isolate (zoonotic genotype) oocysts were small, although they were statistically significant. Oocysts of C. meleagridis were successfully passaged in turkeys and were transmitted from turkeys to immunosuppressed mice and from mice to chickens. The location of C. meleagridis was the small intestine, like the location of C. parvum. A comparison of sequence data for the variable region of the SSU rRNA gene of C. meleagridis isolated from turkeys with other Cryptosporidium sequence data in the GenBank database revealed that the Hungarian C. meleagridis sequence is identical to a C. meleagridis sequence recently described for a North Carolina isolate. Thus, C. meleagridis is a distinct species that occurs worldwide and has a broad host range, like the C. parvum zoonotic strain (also called the calf or bovine strain) and Cryptosporidium felis. Because birds are susceptible to C. meleagridis and to some zoonotic strains of C. parvum, these animals may play an active role in contamination of surface waters not only with Cryptosporidium baileyi but also with C. parvum-like parasites.     

Growth Characteristics and Intraspecies Host Specificity of a Large Virus Infecting the Dinoflagellate Heterocapsa circularisquama

The growth characteristics and intraspecies host specificity of Heterocapsa circularisquama virus (HcV), a large icosahedral virus specifically infecting the bivalve-killing dinoflagellate H. circularisquama, were examined. Exponentially growing host cells were more sensitive to HcV than those in the stationary phase, and host cells were more susceptible to HcV infection in the culture when a higher percent of the culture was replaced with fresh medium each day, suggesting an intimate relationship between virus sensitivity and the physiological condition of the host cells. HcV was infective over a wide range of temperatures, 15 to 30°C, and the latent period and burst size were estimated at 40 to 56 h and 1,800 to 2,440 infective particles, respectively. Transmission electron microscopy revealed that capsid formation began within 16 h postinfection, and mature virus particles appeared within 24 h postinfection at 20°C. Compared to Heterosigma akashiwo virus, HcV was more widely infectious to H. circularisquama strains that had been independently isolated in the western part of Japan, and only 5.3% of the host-virus combinations (53 host and 10 viral strains) showed resistance to viral infection. The present results are helpful in understanding the ecology of algal host-virus systems in nature.     

低磷和高照度光下两种不同磷效率玉米幼苗的几种光合参数变化

以完全培养液（HP,1000μmol·L^-1KH2PO4）培养15d的玉米自交系KH5（磷高效）和SD502（磷低效）幼苗转入低磷（LP,5μmol·L^-1KH2PO4）条件下培养20d后,检测叶中几种与光合作用有关参数的结果表明,低磷下两自交系玉米叶中无机磷含量、植株生物量和叶片的净光合速率（Pn）均下降,KH5的降幅小于SD502。两自交系玉米叶片以高照度光（1600μmol·m^-2·s^-1）照射1h后,叶片的PSII实际光化学效率（ФPSII）、PSII最大光化学效率（Fv/Fm）和表观光合电子传递速率（ETR）均下降,而初始荧光（F0）、非光化学猝灭（NPQ）和天线热耗散（HDR）均升高。在强光胁迫过程中,玉米幼苗叶片发生光抑制,自交系SD502在低磷下的光抑制比KH5严重。     

Pathogenicity and Host Specificity of Mycovellosiella lantanae var. lantanae,a Potential Biocontrol Agent for Lantana camara in South Africa

Lantana camara is a poisonous, bushy shrub from South and Central America that has invaded much of the moist, warm sub-tropical areas of South Africa. In the last decade, evidence of a conspicuous and damaging mycobiota on lantana in the Neotropics has persuaded biocontrol researchers to consider fungi as potential biocontrol agents for this plant. Samples of diseased L. camara leaves were collected during field surveys in South, North and Central America from 1987 to 1997. Pathogenicity tests showed the leaf spot fungus, Mycovellosiella lantanae var. lantanae to be a promising biocontrol pathogen. Inoculations onto South African biotypes of L. camara and a number of closely related species within the family Verbenaceae were made under quarantine conditions to determine the pathogenicity and host specificity of the fungus. Inoculation of L. camara biotypes resulted in necrotic, grey lesions (20-60 per leaf), necrosis of flower buds and stalks, as well as defoliation of certain biotypes after three weeks. None of the other plant species tested showed any disease symptoms. This indicates a very restricted host range, making this pathogen a suitable candidate for application as a biological control agent. It is expected that the fungus will reduce the vigour and reproductive potential of L. camara. Due to the variation in virulence of M. lantanae var. lantanae when tested on South African lantana biotypes, release strategies may include the use of combinations of the isolates to target a wider range of lantana biotypes in the field. Permission to release M. lantanae var. lantanae in South Africa was granted in September 2001. The pathogen will be released as a classical biocontrol agent in South Africa.     

Ectomycorrhizal and endophytic fungi associated with <Emphasis Type="Italic">Alnus glutinosa</Emphasis> growing in a saline area of central Poland

Alnus glutinosa (black alder) is a mycorrhizal pioneer tree species with tolerance to high concentrations of salt in the soil and can therefore be considered to be an important tree for the regeneration of forests areas devastated by excessive salt. However, there is still a lack of information about the ectomycorrhizal fungi (EMF) associated with mature individuals of A. glutinosa growing in natural saline conditions. The main objective of this study was to test the effect of soil salinity and other physicochemical parameters on root tips colonized by EMF, as well as on the species richness and diversity of an EMF community associated with A. glutinosa growing in natural conditions. We identified a significant effect of soil salinity (expressed as electrical conductivity: EC_e and EC_1:5) on fungal taxa but not on the total level of EM fungal colonization on roots. Increasing soil salinity promoted dark-coloured EMF belonging to the order Thelephorales (Tomentella sp. and Thelephora sp.). These fungi are also commonly found in soils polluted with heavy-metal. The ability of these fungi to grow in contaminated soil may be due to the presence of melanine, a natural dark pigment and common wall component of the Thelephoraceae that is known to act as a protective interface between fungal metabolism and biotic and abiotic environmental stressors. Moreover, increased colonization of fungi belonging to the class of Leotiomycetes and Sordiomycetes, known as endophytic fungal species, was observed at the test sites, that contained a larger content of total phosphorus. This observation confirms the ability of commonly known endophytic fungi to form ectomycorrhizal structures on the roots of A. glutinosa under saline stress conditions.     

Temperature-Sensitive Mutants for the Replication of Plasmids in ESCHERICHIA COLI I. Isolation and Specificity of Host and Plasmid Mutations

Temperature-sensitive mutants of Escherichia coli defective in the replication of the plasmid colicinogenic factor E1 (ColE(1)) were isolated following mutagenesis of E. coli K12 strain carrying the ColE(1) factor. Following the mutagenic treatment an enrichment procedure utilizing the replacement of thymine with bromouracil in the ColE(1) DNA duplicated at the restrictive temperature was used. The mutants isolated following this enrichment step were the result of a mutation event either in the host chromosome or in the ColE(1) plasmid. The host mutants fell into three phenotypic classes based on the effect each mutation had on the maintenance of a variety of other extrachromosomal DNA elements. Phenotypic class I mutations affected all E. coli plasmids, both the I and F sex factor types as well as the ColE(1) factor. Phenotypic class II mutations affected the maintenance of the ColE(1) and the F sex factor type plasmids and not the I type, while phenotypic class III mutations affected only ColE(1) replication. None of these mutations was found to have a significant effect on the replication of the E. coli chromosome. The plasmid-linked mutations fell into two phenotypic classes on the basis of the ability of the Flac episome to complement the mutation in the ColE(1) plasmid.     

Sensitivity and Specificity of a Urine Circulating Anodic Antigen Test for the Diagnosis of Schistosoma haematobium in Low Endemic Settings

Background

Elimination of schistosomiasis as a public health problem and interruption of transmission in selected areas are key goals of the World Health Organization for 2025. Conventional parasitological methods are insensitive for the detection of light-intensity infections. Techniques with high sensitivity and specificity are required for an accurate diagnosis in low-transmission settings and verification of elimination. We determined the accuracy of a urine-based up-converting phosphor-lateral flow circulating anodic antigen (UCP-LF CAA) assay for Schistosoma haematobium diagnosis in low-prevalence settings in Zanzibar, Tanzania.

Methodology

A total of 1,740 urine samples were collected in 2013 from children on Pemba Island, from schools where the S. haematobium prevalence was <2%, 2–5%, and 5–10%, based on a single urine filtration. On the day of collection, all samples were tested for microhematuria with reagent strips and for the presence of S. haematobium eggs with microscopy. Eight months later, 1.5 ml of urine from each of 1,200 samples stored at -20°C were analyzed by UCP-LF CAA assay, while urine filtration slides were subjected to quality control (QCUF). In the absence of a true ‘gold’ standard, the diagnostic performance was calculated using latent class analyses (LCA).

Principal Findings

The ‘empirical’ S. haematobium prevalence revealed by UCP-LF CAA, QCUF, and reagent strips was 14%, 5%, and 4%, respectively. LCA revealed a sensitivity of the UCP-LF CAA, QCUF, and reagent strips of 97% (95% confidence interval (CI): 91–100%), 86% (95% CI: 72–99%), and 67% (95% CI: 52–81%), respectively. Test specificities were consistently above 90%.

Conclusions/Significance

The UCP-LF CAA assay shows high sensitivity for the diagnosis of S. haematobium in low-endemicity settings. Empirically, it detects a considerably higher number of infections than microscopy. Hence, the UCP-LF CAA employed in combination with QCUF, is a promising tool for monitoring and surveillance of urogenital schistosomiasis in low-transmission settings targeted for elimination.     

Sequence Variation of the tRNALeu Intron as a Marker for Genetic Diversity and Specificity of Symbiotic Cyanobacteria in Some Lichens

We examined the genetic diversity of Nostoc symbionts in some lichens by using the tRNA^Leu (UAA) intron as a genetic marker. The nucleotide sequence was analyzed in the context of the secondary structure of the transcribed intron. Cyanobacterial tRNA^Leu (UAA) introns were specifically amplified from freshly collected lichen samples without previous DNA extraction. The lichen species used in the present study were Nephroma arcticum, Peltigera aphthosa, P. membranacea, and P. canina. Introns with different sizes around 300 bp were consistently obtained. Multiple clones from single PCRs were screened by using their single-stranded conformational polymorphism pattern, and the nucleotide sequence was determined. No evidence for sample heterogenity was found. This implies that the symbiont in situ is not a diverse community of cyanobionts but, rather, one Nostoc strain. Furthermore, each lichen thallus contained only one intron type, indicating that each thallus is colonized only once or that there is a high degree of specificity. The same cyanobacterial intron sequence was also found in samples of one lichen species from different localities. In a phylogenetic analysis, the cyanobacterial lichen sequences grouped together with the sequences from two free-living Nostoc strains. The size differences in the intron were due to insertions and deletions in highly variable regions. The sequence data were used in discussions concerning specificity and biology of the lichen symbiosis. It is concluded that the tRNA^Leu (UAA) intron can be of great value when examining cyanobacterial diversity.     

聚乙二醇模拟干旱对耐低钾水稻幼苗的根系生长及某些生理特性的影响

以早籼品种‘瑰宝八号’及其变异后代耐低钾的水稻为材料,用20%PEG6000模拟干旱,测定幼苗根系形态和部分生理特性的指标并对其抗旱能力进行比较的结果表明:耐低钾水稻幼苗的超氧化物歧化酶活性、根系活力和活跃吸收面积相对较高,而丙二醛含量相对较低,其根重和根体积也高,比其亲本‘瑰宝八号’有更高的抗旱能力.     

Temporal Effects of a Begomovirus Infection and Host Plant Resistance on the Preference and Development of an Insect Vector,Bemisia tabaci,and Implications for Epidemics

Persistent plant viruses, by altering phenotypic and physiological traits of their hosts, could modulate the host preference and fitness of hemipteran vectors. A majority of such modulations increase vector preference for virus-infected plants and improve vector fitness, ultimately favouring virus spread. Nevertheless, it remains unclear how these virus-induced modulations on vectors vary temporally, and whether host resistance to the pathogen influences such effects. This study addressed the two questions using a Begomovirus-whitefly-tomato model pathosystem. Tomato yellow leaf curl virus (TYLCV) -susceptible and TYLCV-resistant tomato genotypes were evaluated by whitefly-mediated transmission assays. Quantitative PCR revealed that virus accumulation decreased after an initial spike in all genotypes. TYLCV accumulation was less in resistant than in susceptible genotypes at 3, 6, and 12 weeks post inoculation (WPI). TYLCV acquisition by whiteflies over time from resistant and susceptible genotypes was also consistent with virus accumulation in the host plant. Furthermore, preference assays indicated that non-viruliferous whiteflies preferred virus-infected plants, whereas viruliferous whiteflies preferred non-infected plants. However, this effect was prominent only with the susceptible genotype at 6 WPI. The development of whiteflies on non-infected susceptible and resistant genotypes was not significantly different. However, developmental time was reduced when a susceptible genotype was infected with TYLCV. Together, these results suggest that vector preference and development could be affected by the timing of infection and by host resistance. These effects could play a crucial role in TYLCV epidemics.     

豚草卷蛾寄主专一性风险评价

在以往豚草生物防治研究的基础上 ,为评价防治恶性豚草的外来天敌昆虫的安全性 ,以及探索外来生防作用物的风险评价方法 ,以豚草卷蛾为案例 ,进一步对其寄主安全性进行了风险评估。基于与豚草的近缘关系及以往的研究结果 ,选用 9科 36种常见经济作物、观赏植物和杂草 ,采用室内非选择性取食测定、田间开放条件下多选择性取食测定和室外非选择性取食分龄接虫的生命表等研究方法 ,对豚草卷蛾的寄主专一性作了深入研究。 ( 1 )室内非选择性取食测定结果表明 ,豚草卷蛾仅能在豚草和苍耳上完成整个幼虫的发育 ;但在强迫将高龄幼虫 ( 4～ 6龄 )接入黄花蒿、菊花 (黄莲 )和向日葵 (白 97-1和天委 F2 )时 ,有少量幼虫能发育化蛹 ,但不发生取食 ,在这些植物上完成发育只是一种假象。 ( 2 )田间开放条件下多选择性取食测定结果表明 ,豚草卷蛾的寄主选择性随种群数量不同而异 ,当种群数量增大 ,受取食条件胁迫时 ,出现风险“扩散”现象。田间供试的 1 6种 (含品种 )植物中 ,第 2、3和 4代出现虫瘿 (被幼虫选择 )的供试植物依次为 :豚草(第 2代 ) ;豚草和苍耳 (第 3代 ) ;豚草、苍耳和黄花蒿 (第 4代 )。按产卵单因子选择性风险指数 ( SEFRI(1) )值分析表明 ,豚草卷蛾成虫产卵对豚草、苍耳和黄花蒿表现出选择性风险     

Growth Cycle of Predacious Bdellovibrios in a Host-Free Extract System and Some Properties of the Host Extract

Host-free growth and reproduction of a host-dependent strain of Bdellovibrio bacteriovorus incubated with an extract from host cells were studied. The morphological changes occurring in the cells were correlated with deoxyribonucleic acid (DNA) synthesis as measured by labeled nucleotide or orthophosphate incorporation. The host-free developmental cycle of Bdellovibrio is similar to that of the two-membered system; the early loss of flagella, the elongation into filaments, and multiple fission into flagellated progeny are typical for both host-free and intraperiplasmic development of bdellovibrios. Filament length and time of division appear to depend on the concentration of the host extract. Host extract was found to be heat stable and DNase stable, and Pronase sensitive and RNase sensitive. Addition of ribonucleic acid to the extract medium at various times during the Bdellovibrio growth cycle demonstrated that host extract is required continuously during the cycle for growth. The observations reported give a unified picture of Bdellovibrio development and allow for the suggestion that wild-type bdellovibrios depend upon the presence of some host factor for induction of DNA synthesis, whereas depletion of host factor triggers division. The ecological implications of such host dependence are discussed.     

The Quest for a Suitable Host: Size Distributions of Host Trees and Secondary Hemiepiphytes Search Strategy

As climbing plants lack the capacity to hold themselves upright, they need to encounter a suitable host. Vines, lianas, and secondary hemiepiphytes need, therefore, an effective searching strategy. Various hypotheses have been put forward on searching strategies, including ‘skototropism’—growth toward darkness—and random searching. We studied host searching strategies of three secondary hemiepiphyte species belonging to the genus Heteropsis. We recorded information on the diameter distribution of host and evaluated whether these hosts were ‘suitable’, i.e., sufficiently tall for Heteropsis individuals to reach reproductive size. The diameter distribution of host trees bearing Heteropsis seedlings was similar to that of the trees in our study plots. Also, we found that 72–81 percent of the Heteropsis seedlings were present on unsuitable hosts (seedlings, saplings, herbs). These results suggest that Heteropsis seedlings search hosts in a random manner and not by skototropism. We found quite a distinct pattern for adult Heteropsis individuals, which predominantly occur on host trees bigger than 10 cm dbh. Host diameter distribution for Heteropsis adults differed significantly from that of the entire tree community. This difference suggests that Heteropsis individuals may change hosts if they are initially present on nonsuitable hosts. We observed that Heteropsis seedlings and juveniles on unsuitable hosts often produced vegetative shoots that searched for another host. In many cases, such shoots did not find a suitable host. For Heteropsis, our results suggest that host tree searching is a long‐term trial and error process that is governed by a random searching strategy. Abstract in Spanish is available in the online version of this article.     

Specificity of a ctyochemical bioassay for arginine-vasopressin and its validation for plasma measurement

The total Na+/K + ATP-ase activity of the thick ascending limb of the loop of Henlé may be stimulated by arginine-vasopressin (AVP). Lysine-vasopressin (LVP), oxytocin (OT), and arginine-vasotocin (AVT) produce less than 5% of the enzyme activity induced by the same concentration of AVP. Physiological concentrations of a mixture of other hormones with known activity on the kidney (T₃, T₄ aldosterone, angiotensin II, and OT) did not significantly increase total Na+/K + ATP-ase activity. Specific AVP antiserum consistently removed greater than 90% of the stimulatory effect of plasma. The concentration of AVP in plasmas from dehydrated subjects was greater than l0 times that of the same subjects hydrated. Intra-assay coefficient of variation was 35% and 52% from 200 l and 20 l of plasma respectively. The interassay coefficient of variation was 53% and 55% from plasma pools with high and low AVP content.