Bacterial Feeding Research Articles

Soil nematode communities under monoculture agrocenoses (example of the Republic of Karelia)

The effect of crops cultivation on the soil free-living and plant-parasitic nematodes in agrocenoses of southern Karelia (fields with tilled crops, artificial grasslands) was studied. A comparison of monodominant plant communities in agrocenoses (tilled crops) and cenoses with alien species Heracleum sosnowskyi Manden was made. The characteristics reflecting the features of nematode communities in different types of agrocenoses were established. They include faunal composition with identification of constant and specific taxa determining the similarity/differences between agrocenoses, trophic structure of nematode communities, and ecological and population indices facilitating the assessment of soil ecosystem state. Bacterial and fungal feeders resistant to unfavourable conditions dominate under tilled crops and take part in organic matter decomposition, forming the core of the nematode fauna. In seeded meadows plant feeder nematodes become more significant in the community. The values of ecological and population indices show that the soil ecosystem is structured and stable. According to the characteristics of soil nematode communities the agroecosystem of the polycomponent seeded meadow corresponds to a late stage of ecological succession.

Anhydrobiosis and freezing-tolerance: adaptations that facilitate the establishment of Panagrolaimus nematodes in polar habitats.

Anhydrobiotic animals can survive the loss of both free and bound water from their cells. While in this state they are also resistant to freezing. This physiology adapts anhydrobiotes to harsh environments and it aids their dispersal. Panagrolaimus davidi, a bacterial feeding anhydrobiotic nematode isolated from Ross Island Antarctica, can survive intracellular ice formation when fully hydrated. A capacity to survive freezing while fully hydrated has also been observed in some other Antarctic nematodes. We experimentally determined the anhydrobiotic and freezing-tolerance phenotypes of 24 Panagrolaimus strains from tropical, temperate, continental and polar habitats and we analysed their phylogenetic relationships. We found that several other Panagrolaimus isolates can also survive freezing when fully hydrated and that tissue extracts from these freezing-tolerant nematodes can inhibit the growth of ice crystals. We show that P. davidi belongs to a clade of anhydrobiotic and freezing-tolerant panagrolaimids containing strains from temperate and continental regions and that P. superbus, an early colonizer at Surtsey island, Iceland after its volcanic formation, is closely related to a species from Pennsylvania, USA. Ancestral state reconstructions show that anhydrobiosis evolved deep in the phylogeny of Panagrolaimus. The early-diverging Panagrolaimus lineages are strongly anhydrobiotic but weakly freezing-tolerant, suggesting that freezing tolerance is most likely a derived trait. The common ancestors of the davidi and the superbus clades were anhydrobiotic and also possessed robust freezing tolerance, along with a capacity to inhibit the growth and recrystallization of ice crystals. Unlike other endemic Antarctic nematodes, the life history traits of P. davidi do not show evidence of an evolved response to polar conditions. Thus we suggest that the colonization of Antarctica by P. davidi and of Surtsey by P. superbus may be examples of recent “ecological fitting” of freezing-tolerant anhydrobiotic propagules to the respective abiotic conditions in Ross Island and Surtsey.

Relation between magnetic parameters and nematode abundance in agricultural soils of Portugal--a multidisciplinary study in the scope of environmental magnetism.

Soil is composed of different types of particles which are either natural or of anthropogenic origin. Anthropogenic particles are often related to the presence of heavy metals and thus provide information on soil quality. Magnetic parameters can detect the presence of such particles and may be used as a proxy for environmental pollution. This study explores the relationships between magnetic particles and the nematofauna of agricultural soils. Magnetic, pedological, microscopy and nematological analyses were conducted in soils collected from major regions of potato production in Portugal. The magnetic characterisation of soils identified regions with magnetic particles with possible anthropogenic origin. Microscopy analysis revealed the presence of spherical particles dominantly composed of Fe, O and C. A positive and significant relationship was found between saturation isothermal remanent magnetisation (SIRM) and mass-specific susceptibility (χ), confirming the importance the ferrimagnetic fraction to magnetic properties. The nematode communities were composed of nematodes belonging to four trophic groups (bacterial feeding, plant feeders, fungal feeders and omnivores/predators). The relationships between magnetic parameters and the nematodes showed that (1) S-25 has a linear correlation with number of nematodes per kilogram of soil and with plant feeders' trophic group and (2) SIRM correlates with the bacterial feeders trophic group. This study reveals that magnetic proxies may provide means for detecting regions with higher levels of pollution, possibly related to heavy metals. Due to the large background variability found in magnetic parameters, the sampling spacial mesh should to be further refined and the input of magnetic minerals needs to be locally calibrated.

Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto, Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100kgNha−1 for upland rice, and 0 and 20kgNha−1 for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.

Accidental Acarophagy ? Is it Safe for us?

Oribatid mites have successfully invaded almost all compartments of the biosphere. They are ubiquitous and, with the exception of the open oceans, they exist in every sort of terrestrial, aquatic, arboreal and parasitic habitat. They are found at every elevation and every latitude, from the Arctic to the Antarctic. Mites have a diversity of function in the ecosystem, as shown by the range of feeding guilds to which they belong. They include predators, parasites, fungal feeders, root feeders, bacterial feeders, omnivores, and scavengers. Ignoring mites, however, is a mistake. They are not passive inhabitants of ecosystems; rather they are strong interactors and major components of biological diversity.

基于根际与凋落物际评价转Bt水稻对土壤线虫群落的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 基于根际与凋落物际评价转Bt水稻对土壤线虫群落的影响 DOI: 10.5846/stxb201305141061 作者: 作者单位: 南京农业大学资源与环境科学学院土壤生态实验室,南京农业大学资源与环境科学学院土壤生态实验室,南京农业大学资源与环境科学学院土壤生态实验室,南京农业大学资源与环境科学学院土壤生态实验室,南京白云化工环境监测有限公司,南京农业大学植物保护学院,南京农业大学资源与环境科学学院土壤生态实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 土壤与农业可持续发展国家重点实验室开放课题(0812201218); 转基因生物新品种培育重大专项(2013ZX08012-005); 南京农业大学SRT项目(201206); 江苏高校优势学科(PAPD). Influences of rhizosphere and detritusphere of Bt rice on soil nematode communities Author: Affiliation: Soil Ecology Lab,College of Resources and Environmental Sciences,Nanjing Agricultural University,Soil Ecology Lab,College of Resources and Environmental Sciences,Nanjing Agricultural University,Soil Ecology Lab,College of Resources and Environmental Sciences,Nanjing Agricultural University,Soil Ecology Lab,College of Resources and Environmental Sciences,Nanjing Agricultural University,Nanjing Baiyun Chemical Industry Environmental Monitoring Co. Ltd, Nanjing,,Soil Ecology Lab,College of Resources and Environmental Sciences,Nanjing Agricultural University 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:转基因作物在商业化推广前,有必要评价其对非靶标土壤生物的生态影响。根系和凋落物与土壤的界面是代表植物直接影响土壤的两个典型活性微域,即根际和凋落物际。基于室内盆栽实验构建水稻根际和凋落物际,比较了这两个高活性微域中转Bt水稻克螟稻(KMD)与亲本水稻秀水11(XSD)对土壤可利用资源、微生物学性质和线虫群落的影响。结果表明:转Bt水稻对土壤性质的影响依赖于水稻生育期和微域的变化。与XSD相比,KMD在苗期和拔节期显著提高了凋落物际土壤可溶性有机氮含量(P<0.05);在苗期显著降低了凋落物际土壤铵态氮含量,但在成熟期显著提高了凋落物际与交互微域土壤的铵态氮含量(P<0.05)。与亲本水稻相比,转Bt水稻分别在苗期和成熟期显著提高了凋落物际土壤微生物生物量碳和活性,而在拔节期和成熟期显著降低了根际土壤微生物生物量氮含量(P<0.05)。微域间的交互作用显著影响土壤微生物生物量、可溶性有机碳和氮、线虫总数和各食性线虫的数量(P<0.05)。转Bt水稻总体上降低了土壤线虫总数,尤其在苗期和拔节期的凋落物际土壤中达到显著水平。重复测量方差分析表明转Bt水稻显著影响土壤食细菌(P<0.01)和食真菌(P<0.05)线虫数量,及线虫群落的通道指数和富集指数。水稻收获后KMD秸秆的Bt蛋白含量显著高于亲本,全部KMD处理的土壤样品中Bt蛋白含量无显著变化,因而转Bt水稻对土壤生物学性质的影响可能并非来源于Bt蛋白的作用,而更可能来自于水稻生长性状和凋落物性质的差异。 Abstract:It is important to evaluate the ecological risks of transgenic Bt rice on soil non-target organisms before it is widely released in the market. Rhizosphere and detritusphere formed by plant roots and organic residues that contact soil directly, and represent two distinct microsites that are highly affected by plants. Pot experiments were established to investigate the effects of rice, a variety genetically modified to express the Bt protein, KMD, and its parental line, XSD, on soil chemical, microbial properties and nematode assemblages of the two microsites. Results indicated that effects of transgenic Bt rice on soil properties varied with plant growth stage and microsite type. Compared with XSD, KMD increased the concentrations of soil dissolved organic nitrogen in detritusphere (D) at seedling and elongation stages, whereas the concentrations of ammonium in the detritusphere were decreased significantly by KMD at seedling stage (P<0.05). At maturing stage, KMD increased the concentrations of ammonium in the detritusphere and overlapped microsite (DR, i.e. the area that affected by both rhizosphere and detritusphere) significantly (P<0.05). With regard to soil microbial biomass, KMD significantly increased the concentrations of soil microbial biomass carbon (MBC) in detritusphere at seedling and maturing stages (P<0.05), whereas significantly decreased microbial biomass nitrogen (MBN) in rhizosphere at elongation and maturing stages (P<0.05). Integrated effects of the two microsites had a significant effect on concentrations of microbial biomass carbon and nitrogen as well as dissolved organic matter, total nematode numbers and nematode numbers of different feeding groups (P<0.05). Generally, KMD decreased the total nematode numbers, especially there were significantly fewer nematodes in the detritusphere of KMD than XSD at seedling and elongation stages (P<0.05). Repeated-measure ANOVA indicated that transgenic Bt rice KMD had significant effects on numbers of bacterial feeders (P<0.01) and fungal feeders (P<0.05), nematode channel ratio (NCR) and enrichment index (EI). In addition, the genetically modified KMD significantly decreased (P<0.05) the proportions of bacterial feeders and fungal feeders in detritusphere at seedling and elongation stages, and such trends were consistent to the responses of ammonium concentrations of the same microsite and growth stage. In light of soil Bt protein concentrations under KMD treatments after maturing stage, Bt rice showed no significant effect, though the content of Bt protein in straw of KMD was significantly higher than that of XSD, indicating that significant differences of effects of KMD from XSD might not result from Bt protein itself, but from the difference of other traits such as rice growth and residue chemical composition. Together, we found that microsite studies combining the rhizosphere and detritusphere would facilitate to demonstrate the responses of soil microbial properties and nematode assemblages to explore the ecological impacts and mechanisms of growing genetically modified rice. 参考文献 相似文献 引证文献

Nematode colonisation of artificial water-filled tree holes

Nematodes inhabiting artificial water-filled tree holes were monitored over 16 months by placing 300 plastic cups in four forest areas. For the first time we investigated the importance of forest soils for nematode dispersal and colonisation of tree holes. On average, 91% of the cups were settled by a total of 35 species (maximum 58 336 individuals 100 cm−2). They were dominated by the bacterial feeder Dolichorhabditis dolichura (32.4%) and the hyphal feeders Laimaphelenchus penardi (23.6%) and Laimaphelenchus sp. (13.4%); 84.4% had lengths &lt; 0.75 mm and in only 6% of the water-filled tree holes were male nematodes found. None of the most common species was detected in the soils of the sampling sites. However, a meta-community analysis revealed a random turnover. The properties of the identified nematodes (small body size, anhydrobiosis, parthenogenesis) made them highly amenable to dispersal by wind and account for their rapid colonisation of a wide range of habitats.

Nematode functional guilds, not trophic groups, reflect shifts in soil food webs and processes in response to interacting global change factors

a b s t r a c t Soils store ∼80% of global terrestrial organic carbon and alterations in fluxes into and out of this pool may interact with ongoing climate change. Belowground food webs drive soil C dynamics, but little is known about their responses to co-occurring global change agents. We investigated open-air experi- mental grassland communities at ambient and elevated atmospheric CO2 concentration, ambient and enriched nitrogen input, and ambient and reduced summer precipitation to evaluate how these agents interactively affect soil nematodes, which are often used as an indicator group for soil food web structure and soil health. The aim of the study was to elucidate the response of the functional diversity of soil nematodes to changing environmental conditions by using nematode functional guilds and indices as indicators. The results suggest that nematode functional guilds surpass nematode trophic groups as soil indicators, suggesting that more detailed data on nematode community structure is essential to capture functional changes in response to environmental change. For instance, the density of opportunistic fungal feeders increased due to N addition with the response being more pronounced at elevated CO2, whereas densities of sensitive fungal-feeders were increased at ambient N and elevated CO2, illustrating opposing responses within one trophic group. Opportunistic bacterial feeders increased at elevated N, but did not respond to other environmental factors studied. Root-feeding Longidoridae were significantly reduced at elevated CO2 and elevated N compared to ambient conditions, whereas other plant feeders were little affected by the manipulations. Predacious nematodes were less abundant at elevated N, and the Structure Index (which indicates food web structure) suggested reduced top-down forces and simplified soil food webs, although omnivores did not vary significantly. Elevated CO2 buffered the effect of reduced precipitation on the Enrichment Index (which indicates increased resource availability) and the Channel Index (which indicates changes in decomposition channel) probably due to reduced stomatal conductance at elevated CO2. Further, the results suggest that the decomposer community switched from a bacterial-dominated to a fungal-dominated system at elevated N, indicating shifts in the microbial community as well as in the functioning of belowground food webs. Overall, the studied global change agents interactively and differentially affected functional guilds of soil nematodes, suggesting complex changes in soil processes. We highlight that detailed information on the functional guilds of nematodes is likely necessary to fully understand alterations in soil food webs and related processes due to global environmental change.

Spatial heterogeneity of soil quality around mature oil palms receiving mineral fertilization

The African oil palm (Elaeis guineensis Jacq.) is grown on a total area of 16 million ha; but data on soil quality in mature oil palm plantations are fragmentary and data concerning biota are almost non-existent. Consequently, no well-tested sampling method is available for soil diagnoses. We studied the spatial heterogeneity of the soil around the palm by measuring comprehensive soil quality in a 24-year-old oil palm plantation. Soil quality and litter were assessed in five zones with different plant cover, and different applications of herbicide or fertilizer. Physical-chemical characteristics, macrofauna, and nematofauna were analysed. A sampling method was developed and adapted to the way the cultivation practices are implemented: sampling by zone and weighting the plot mean by the respective area of each zone. The total density of macrofauna in the litter and in the 0–15 cm soil layer followed a gradient from the harvest pathway (29 ind m−²) to the windrow (1003 ind m−²). Ants (13–237 ind m−²), earthworms (11–120 ind m−²), Dermaptera (0–35 ind m−²), Coleoptera (3–24 ind m−²) and Chilopoda (0–43 ind m−²) were the main taxa. The termite population was very poor (3–4 ind m−²). The density of nematofauna was also heterogeneous (268–805 ind 100 g−1 of soil). Heterogeneity between zones was also reflected in the density of the functional groups, mainly soil engineers, detritivores and predators for macrofauna and bacterial feeders, and phytoparasites for nematofauna. The weeded circular zone around the palm had the highest soil nutrient content (P, K, Ca, Mg, Corg CEC, base saturation). Its biodiversity was average but it contained the highest density of earthworms and nematofauna. Possible relationships between chemicals and biological groups in the food web are discussed.

Soil nematode community structure affected by tillage systems and cover crop managements in organic soybean production

Information associating the tillage disturbance and its effect over soil nematode communities in different tillage systems has not been thoroughly discussed, especially in Asian countries. We investigated the effect of three tillage systems, i.e., moldboard plow/rotary harrow (MP), rotary cultivation (RC), and no-tillage (NT), and three cover crop treatments (fallow, rye, and hairy vetch) with two manure applications (0 and 1Mgha−1) on nematode communities and degree of surface soil translocation (DTL). This study was conducted in Japanese Kanto region (Andosols) in 2009–2011. We calculated nematode community indices, including channel index, enrichment index, and structure index (SI), based on the composition of nematode assemblages, to infer soil ecosystem condition. DTL was calculated from data on the variation of vertical soil distribution of radioactive cesium-137 deposited following the Fukushima Daiichi nuclear power plant accident in 2011. Tillage system influenced nematode abundance of all feeding groups. Cover crop also affected abundance of bacterial feeders (BAC), fungal feeders and facultative root feeders (FFR), predators (PRD), and obligatory root feeders (ORF). SI was bigger in NT, which was 22% and 47% higher than in MP and RC, respectively. DTL negatively correlated with abundance of BAC, omnivores, ORF, total number of nematode species, and SI, but positively correlated with the abundance ratio of FFR to FFR+BAC. Our results suggested that tillage inversion exerted stronger effects on nematode community and structure of soil ecosystem than cover crop treatment and manure application.

Evaluation of feeding regimes to enhance PHA production using acetic and butyric acids by a pure culture of Cupriavidus necator

In this study volatile fatty acids (VFAs), which are by-products from anaerobic fermentations, have been used as the carbon source for polyhydroxyalkanoates (PHA) production by pure culture bacteria, Cupriavidus necator. A number of factors influence the conversion efficiencies of VFAs to PHAs including the bacterial feeding regimes. When VFA was supplied as a single feed, it was found that concentrations higher than 2% v/v VFA led to substrate inhibition and only 18% acetic acid and 12% of butyric acid was converted into PHA. This resulted in less than 65% (w/w) of PHA content within the microbial cells. Hence, the single VFA feeding strategy was found to provide low conversion rates of VFA into polymer. An improved feeding strategy was found to be the use of an automatic VFA feed based on the pH control of the medium, which led to a more continuous feeding regime. The conversion of VFA to PHA was increased by almost 2-fold to 33 and 22% for acetic acid and butyric acid respectively, with up to 75% (w/w) of PHA resultant within the microbial cells.

Aerobic cloacal and pharyngeal bacterial flora in six species of free-living birds.

The purpose of this study was to investigate the culturable aerobic pharyngeal and cloacal bacterial flora of free-living birds, to determine the physiological bacterial microbiota, to identify possible interactions between feeding behaviour and the composition of the pharyngeal and cloacal microflora and to investigate the occurrence of pathogenic bacteria. Cloacal and pharyngeal swabs of 167 free-living birds, including water rails (Rallus aquaticus), spotted crakes (Porzana porzana), mute swans (Cygnus olor), barn swallows (Hirundo rustica), reed warblers (Acrocephalus scirpaceus) and black cormorants (Phalacrocorax carbo) from Germany, were cultured to determine the prevalence of aerobic bacteria. Statistical analysis of bacterial findings and feeding behaviour was performed. A widespread soil and water bacteria were isolated, which are expected to be present in the habitat and food. However, some potentially avian- and human-pathogenic bacteria, such as Aeromonas hydrophila, Elizabethkingia meningoseptica, Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli, were also recovered. Free-living birds of the examined species harbour several environmental bacteria, which could be facultative pathogenic. Prevalence of bacteria in healthy free-living birds of the species included in this survey is influenced by environmental and alimentary factors.

Adaptive value of a predatory mouth-form in a dimorphic nematode.

Polyphenisms can be adaptations to environments that are heterogeneous in space and time, but to persist they require conditional-specific advantages. The nematode Pristionchus pacificus is a facultative predator that displays an evolutionarily conserved polyphenism of its mouthparts. During development, P. pacificus irreversibly executes either a eurystomatous (Eu) or stenostomatous (St) mouth-form, which differ in the shape and number of movable teeth. The Eu form, which has an additional tooth, is more complex than the St form and is thus more highly derived relative to species lacking teeth. Here, we investigate a putative fitness trade-off for the alternative feeding-structures of P. pacificus. We show that the complex Eu form confers a greater ability to kill prey. When adults were provided with a prey diet, Eu nematodes exhibited greater fitness than St nematodes by several measures, including longevity, offspring survival and fecundity when followed by bacterial feeding. However, the two mouth-forms had similar fecundity when fed ad libitum on bacteria, a condition that would confer benefit on the more rapidly developing St form. Thus, the two forms show conditional fitness advantages in different environments. This study provides, to our knowledge, the first functional context for dimorphism in a model for the genetics of plasticity.

Systematic comparison of bacterial feeding strains for increased yield of Caenorhabditis elegans males by RNA interference-induced non-disjunction

Rare Caenorhabditis elegans males arise when sex chromosome non-disjunction occurs during meiosis in self-fertilizing hermaphrodites. Non-disjunction is a relatively rare event, and males are typically observed at a frequency of less than one in five hundred wild-type animals. Males are required for genetic crosses and phenotypic analysis, yet current methods to generate large numbers of males can be cumbersome. Here, we identify RNAi reagents (dsRNA-expressing bacteria) with improved effectiveness for eliciting males. Specifically, we used RNAi to systematically reduce the expression of over two hundred genes with meiotic chromosome segregation functions, and we identified a set of RNAi reagents that robustly and reproducibly elicited male progeny.

Phylogenetic structures of soil nematode communities along a successional gradient in an unreclaimed copper mine tailings site

Analysis of the phylogenetic structure of biological communities by examining the extent to which community members are more closely related (phylogenetically clustered) or less closely related (phylogenetically overdispersed) than expected by chance has recently been proven to be a promising approach to gain insight into the factors governing the community assembly. However, to date there aren't any studies that have quantitatively examined the community structure of soil nematodes in a phylogenetic framework, despite their crucial roles in soil food webs and nutrient cycling processes. Here, we explored the phylogenetic structures of soil nematode communities along a successional gradient in an unreclaimed copper (Cu) mine tailings site to reveal the potential determinants of the soil nematode community assembly. Unexpectedly, we found little evidence that the phylogenetic distance of the co-occurring soil nematodes increased along this gradient. In contrast, phylogenetic structures of the soil nematode communities along the gradient appeared to show a weak tendency toward clustering (i.e. nematodes tend to co-occur with other closely related nematodes more often than expected by chance). On the other hand, when different soil nematode groups characterized by feeding habits were taken into account separately, we unveiled contrasting phylogenetic community structures: bacterial-feeding (BF), plant-feeding (PF), and omnivore-predator (OP) nematode communities tended to be phylogenetically clustered; whereas, fungal-feeding (FF) nematode communities exhibited a tendency toward phylogenetic overdispersion. Moreover, the net relatedness indices of nematode communities characterized by different feeding habits were shown to be correlated with distinct soil chemical properties (such as diethylene triamine pentaacetic acid extractable Cu for BF and cation exchange capacity for FF), indicating that the assembly processes of these communities were not neutral and might have been largely driven by the respective soil chemical properties. Collectively, our results provided novel insight into the factors driving the assembly of soil nematode communities, highlighting the potential for future studies on nematodes to benefit from a community phylogenetics approach.

Humoral responses in Rhodnius prolixus: bacterial feeding induces differential patterns of antibacterial activity and enhances mRNA levels of antimicrobial peptides in the midgut.

BackgroundThe triatomine, Rhodnius prolixus, is a major vector of Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. It has a strictly blood-sucking habit in all life stages, ingesting large amounts of blood from vertebrate hosts from which it can acquire pathogenic microorganisms. In this context, the production of antimicrobial peptides (AMPs) in the midgut of the insect is vital to control possible infection, and to maintain the microbiota already present in the digestive tract.MethodsIn the present work, we studied the antimicrobial activity of the Rhodnius prolixus midgut in vitro against the Gram-negative and Gram-positive bacteria Escherichia coli and Staphylococcus aureus, respectively. We also analysed the abundance of mRNAs encoding for defensins, prolixicin and lysozymes in the midgut of insects orally infected by these bacteria at 1 and 7 days after feeding.ResultsOur results showed that the anterior midgut contents contain a higher inducible antibacterial activity than those of the posterior midgut. We observed that the main AMP encoding mRNAs in the anterior midgut, 7 days after a blood meal, were for lysozyme A, B, defensin C and prolixicin while in the posterior midgut lysozyme B and prolixicin transcripts predominated.ConclusionOur findings suggest that R. prolixus modulates AMP gene expression upon ingestion of bacteria with patterns that are distinct and dependent upon the species of bacteria responsible for infection.

The meiofauna of artificial water-filled tree holes: colonization and bottom-up effects

The meiofaunal community of artificial water-filled tree holes was determined, and the bottom-up effects of different amounts of leaf litter on abundance and diversity were estimated. We assume a positive impact of leaf litter on meiofaunal abundances, species diversity, and trophic links. Plastic cups with different amounts of leaf litter were placed in a beech forest (Teutoburg Forest, Bielefeld, Germany) for 24 weeks. As early as 1 week later, the artificial tree holes were colonized by bdelloid rotifers, tardigrades, and nematodes. Rotifers were dominant throughout the experiment, followed by nematodes and tardigrades. The 29 nematode species that were identified included bacterial and hyphal feeders, with common species such as Plectus cirratus/accuminatus and Aphelenchoides parietinus predominating. Impacts of water volume (up to complete desiccation), pH, and O2 on the meiofaunal community were not detected, whereas the addition of leaf litter resulted in bottom-up effects. Nematode abundance, especially that of bacterial feeders, and species number increased with increasing leaf input. The predatory nematode Prionchulus muscorum was found only in treatments containing high leaf content. Rotifer abundances were partly negatively affected by the amount of added leaves and, like tardigrades, showed a reversal in their correlation at higher leaf inputs. Our study revealed the fast colonization of small water bodies by meiofaunal organisms and the importance of passively distribution. Furthermore, the results provide a comparison with the meiofaunal community in lakes and soil.

Effect of mine tailing on the spatial variability of soil nematodes from lead pollution in La Union (Spain)

The Cartagena–La Union mining district, exploited since the end of the 3rd century BC, was one of the world's largest lead producers in the 19th century. Although activity ceased in 1991, today mining residues pose a huge pollution problem. This study characterises lead contents (total and DPTA) and other soil parameters (N, P, K, pH, SOM, CaCO3, granulometric fraction, etc.) using multivariate geostatistical methods in relation to nematode diversity. In this work, trophic groups and metabolic footprints of soil nematodes were measured using 193 samples from the mining, natural and agricultural areas in this district. We explored the relationship between soil health and nematode communities. High lead concentrations were quantified: mean 8500mgkg−1 for total and 340mgkg−1 for DPTA in this mining area. Although nematode diversity was broad (81 taxa), their diversity, abundance and metabolic footprints significantly reduced in the mining area. Significant differences in the nematode community structure were observed, and the relative abundance of predators was sensitive to mine and agricultural activities, whilst omnivores reduced only in the agricultural area, and bacterial feeders exhibited a differential response to both anthropogenic disturbances. The total abundance of nematodes, trophic groups and c–p groups correlated negatively with soil Pb contents, and a positive relationship was found with SOM and N, P and K contents.

Significance and Survival of Enterococci During the House Fly Development

House flies are among the most important nonbiting insect pests of medical and veterinary importance. Larvae develop in decaying organic substrates and their survival strictly depends on an active microbial community. House flies have been implicated in the ecology and transmission of enterococci, including multi-antibiotic-resistant and virulent strains of Enterococcus faecalis. In this study, eight American Type Culture Collection type strains of enterococci including Enterococcus avium, Enterococcus casseliflavus, Enterococcus durans, Enterococcus hirae, Enterococcus mundtii, Enterococcus gallinarum, Enterococcusfaecalis, and Enterococcusfaecium were evaluated for their significance in the development of house flies from eggs to adults in bacterial feeding assays. Furthermore, the bacterial colonization of the gut of teneral flies as well as the importance of several virulence traits of E. faecalis in larval mortality was assessed. Overall survival of house flies (egg to adult) was significantly higher when grown with typically nonpathogenic enterococcal species such as E. hirae (76.0% survival), E. durans (64.0%), and E. avium (64.0%) compared with that with clinically important species E. faecalis (24.0%) and E. faecium (36.0%). However, no significant differences in survival of house fly larvae were detected when grown with E. faecalis strains carrying various virulence traits, including isogenic mutants of the human clinical isolate E. faecalis V583 with in-frame deletions of gelatinase, serine protease, and capsular polysaccharide serotype C. Enterococci were commonly detected in fly puparia (range: 75-100%; concentration: 103-105 CFU/puparium);however, the prevalence of enterococci in teneral flies varied greatly: from 25.0 (E. casseliflavus) to 89.5% (E. hirae). In conclusion, depending on the species, enterococci variably support house fly larval development and colonize the gut of teneral adults. The human pathogenic species, E. faecalis and E. faecium, poorly support larval development and are likely acquired in nature by adult flies during feeding. House fly larvae do not appear to be a suitable model organism for assessment of enterococcal virulence traits.

The responses of soil nematode assemblages to disturbance in Liaohe estuary wetlands

To improve the knowledge of nematode communities in the Liaohe estuary, the spatiotemporal variations of free-living nematode communities (density, diversity and trophic structure) in the protected zone (PZ) and the development zone (DZ) were seasonally studied. Soil nematode communities were analysed at the depths of 0–10 and 10–20 cm. The results showed that bacterial feeder nematodes were the most abundant trophic groups in both depths and at both sites. Nematode abundance and plant-parasitic nematodes maturity index/maturity index in the DZ were higher than that in the PZ (p < 0.05); trophic diversity, Shannon index, fungivore/bacterivore ratio and Wasilewska index in the PZ were higher than those in the DZ (p < 0.05). No significant differences were found in nematode indices between soil layers. Structural equation modelling (SEM) revealed that season, plant biomass and soil properties explained 78% of the variation in soil nematode, and plant biomass controlled nematodes indirectly through affecting soil properties. In general, anthropogenic activities could affect nematode communities, but the degree of influence varied with seasonal change.