Species Of Bacterial-feeding Nematodes Research Articles

Species-specific effects of long-term microplastic exposure on the population growth of nematodes, with a focus on microplastic ingestion

Microplastics (MPs; <5 mm) released into freshwaters undergo changes in their density that make them highly bioavailable to the fauna in the sediments. In fine sediments, nematodes account for up to 90% of the meiobenthic organisms and have an important position in benthic food webs, by connecting lower (bacteria) and higher (e.g., macrofauna, fish) trophic levels. Due to their high ecological relevance, ubiquitous occurrence and very high individual densities, nematodes can serve as bioindicators of environmental pollution and especially MP pollution, since the ingested microscopic particles can be easily detected in the transparent bodies of these organisms. Single-species toxicity tests with Caenorhabditis elegans have revealed dose-dependent inhibitory effects on reproduction in nematodes exposed for 96 h to relatively high concentrations of polystyrene (PS) beads. Thus, in this study, we examined whether longer-term multigenerational tests of nematodes under continuous PS bead exposure are able to reveal more subtle impacts of MPs on population growth and whether the observed effects can be linked to the species-specific life history traits of the nematodes.We therefore tested three bacterial-feeding nematode species (C. elegans, Acrobeloides nanus, Plectus acuminatus) by exposing them to 1.0-µm PS beads at an exposure concentration of 107 beads ml−1. The experiment was conducted in semi-fluid medium for 21–49 days depending on the life-cycle characteristics of each nematode species. Ingested PS beads were quantified by fluorescence microscopy observations. Population growth rates, carrying capacities as well as doubling time and the time at which the maximum sustainable yield was reached were used to assess the effects of PS bead exposure on nematode population dynamics.All three nematode species readily ingested 1.0-µm PS beads in semi-fluid medium, but the number of ingested PS beads varied between species. PS bead exposure significantly decreased the carrying capacity of C. elegans, whereas A. nanus populations grew significantly faster in the presence of the beads. Long-term multigeneration tests revealed more subtle impacts of MP on C. elegans than occurred following short-term exposure scenarios. Our results show that MP-induced changes in nematodes population dynamics can alter nematode communities, which in term may impact the benthic food web.

Nematophagous Pleurotus Species Consume Some Nematode Species but Are Themselves Consumed by Others

Pleurotus species are said to be nematophagous because they paralyze and consume some bacterial-feeding nematodes. It has never been clear whether that means all nematodes. Here we tested thirteen bacterial-feeding nematode species: seven of family Rhabditidae, three of Cephalobidae (one with three populations), two of Panagrolaimidae, and one of Diplogastridae. Nematodes interacted on water agar with toxin-producing isolates of Pleurotus pulmonarius (Fr.) Quél. and Pleurotus ostreatus (Jacq.) P. Kumm. Of the thirteen species, nine were susceptible to P. pulmonarius (all individuals were paralyzed) but four (four populations of two cephalobid species, one rhabditid, and one panagrolaimid) survived exposure to P. pulmonarius. The resistant four species not only survived but multiplied their numbers by consuming P. pulmonarius. A similar trend was observed with nematodes interacting with P. ostreatus; however, six species were resistant to P. ostreatus. Interestingly, four of these six species were susceptible to P. pulmonarius, and interactions overall were differential. Pleurotus species are nematophagous toward some nematodes but are also consumed by others in three of the four families assayed. Species-specific interactions point to the need for studies of the host ranges of both “nematophagous” fungi and “fungivorous” nematodes, especially if they are to be used for biological control.

Interactions among competing nematode species affect population growth rates.

Investigations of the interplay of organisms in an ecological community are a prerequisite to understanding the processes that shape the structures of those communities. Among several types of interactions, interest in the positive interactions of species that compete for the same resource has grown, as they may provide a mechanism enabling coexistence. In the laboratory experiment described herein, the effects of interspecific interaction on the population growth of two bacterial-feeding nematode species, Panagrolaimus cf. thienemanni and Poikilolaimus cf. regenfussi, were investigated. Specifically, we asked: (1) whether there is an interspecific interaction between organisms competing for a mutual resource and (2) whether these interactions are altered by the competitors' initial densities and (3) their variable growth rates (induced by different food supplies). Each treatment initially contained 48 nematode individuals, but at different species ratios (48:0; 32:16; 24:24; 16:32; 0:48). The populations were provided with three different bacterial densities (108, 109, and 1010cellsml-1) as food. The data were analyzed using a generalized linear mixed model. The best-fitting model revealed a significant decline in population growth rates with an increasing species ratio, but depending on the food density and species. These results provide strong evidence for positive interspecific interactions that vary with both species density and food-supply level. They also suggest important roles for positive interspecific interactions in habitat colonization and in maintaining the coexistence of species in the same trophic group.

Effect of Different Bacterial-Feeding Nematode Species on Soil Bacterial Numbers, Activity, and Community Composition

The effects of bacterial-feeding nematodes on bacterial number, activity, and community composition were studied through a microcosm experiment using sterilized soil inoculated with soil bacteria (soil suspension) and with bacteria and three species of bacterial-feeding nematodes (Cephalobus persegnis, Protorhabditis filiformis, and Caenorhabditis elegans). Catalyzed reporter deposition-fluorescence in situ hybridization, CO2 evolution, and denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16S rRNA gene fragments were used to investigate bacterial numbers, activity, and community composition, respectively. Our results showed that bacterial numbers and activity significantly increased in the presence of bacterial-feeding nematodes, which indicated that bacterial-feeding nematodes had a significant positive effect on soil bacteria. The different nematode species had different effects on bacterial numbers and activity. C. persegnis and P. filiformis, isolated from native soil, increased the bacterial number and activity more than C. elegans. The DGGE analysis results showed that dominant bacterial species significantly differed among the treatments, which suggested that bacterial-feeding nematode species modified the bacterial community composition in soil. Further gene sequence analysis results showed that the dominant bacterial species in this study were gram-negative bacteria. Given the completely same conditions except nematode species, the varied selective feeding behavior of different nematode species was the most likely reason for the altered bacterial community composition. Overall, the alteration of bacterial numbers, activity and community composition resulting from the bacterial-feeding nematodes may ultimately affect soil ecological functioning and processes.

Real‐time PCR as an effective technique to assess the impact of phoresy by Paenibacillus sp. bacteria on Steinernema diaprepesi nematodes in nature

Quantitative real-time PCR (qPCR) is a powerful tool to study species of cryptic organisms in complex food webs. This technique was recently developed to detect and quantify several species of entomopathogenic nematodes (EPNs), which are widely used for biological control of insects, and some natural enemies of EPNs such as nematophagous fungi and the phoretic bacteria Paenibacillus sp. and Paenibacillus nematophilus. A drawback to the use of primers and TaqMan probes designed for Paenibacillus sp. is that the qPCR also amplified Paenibacillus thiaminolyticus and Paenibacillus popilliae, two closely related species that are not phoretically associated with EPNs. Here, we report that the detection of Paenibacillus sp. DNA in nematode samples was two orders of magnitude greater (P < 0.001) when the bacterium was added to soil together with its EPN species-specific host Steinernema diaprepesi than when it was added concomitantly with other EPNs or with species of bacterial-feeding nematodes. Just 6% of samples detected trace amounts of P. thiaminolyticus and P. popilliae exposed to the same experimental conditions. Thus, although the molecular assay detects Paenibacillus spp. DNA in nonphoretic associations, the levels are essentially background compared to the detection of Paenibacillus sp. in association with its nematode host.

Effects of cadmium on the fitness of, and interactions between, two bacterivorous nematode species

Interactions between species contribute to macro- and microevolution as well as to community structure and functioning. In addition to direct predator–prey relations, many other interactions (competition, facilitation, inhibition, etc.) may be key to the structure and functioning of communities. Such interactions often occur between species belonging to the same trophic level, and have already been demonstrated between species of bacterial-feeding nematodes, but the exact mechanisms remain poorly understood. Hence, it is difficult to predict their outcome under changing environmental conditions like pollution. Scientists and policy makers have come up with standardized tests to establish environmentally acceptable levels of pollution. In this experiment, we demonstrate how sublethal levels of contaminants can affect not only the fitness of two nematode species but also the way in which these species interact. We performed monospecific and combined culture experiments with two species of soil bacterivorous nematodes, Acrobeloides nanus and Plectus parvus, under optimal conditions and compared the outcome with trials in which the nematodes were exposed to a series of sublethal cadmium concentrations. By evaluating fitness and outcome of interspecific interactions based on their abundance, our results (a) confirm the considerably higher tolerance of A. nanus than that of P. parvus to Cd; (b) demonstrate mutual facilitation between both species; (c) highlight that differential tolerance to pollution between bacterivorous species may affect the balance and outcome of their interactions leading to counterintuitive results such as a higher population fitness of one species (A. nanus) under increased pollution.

Interactions among bacterial-feeding nematode species at different levels of food availability

Accurate prediction of the biodiversity–ecosystem functioning relationship requires adequate understanding of the interactions among species in a community. Effects of species diversity on ecosystem functioning are usually considered more pronounced with increasing functional dissimilarity, although species within functional groups may also perform non-identical functions and interact with each other. Here we present results of a laboratory experimental study aimed at elucidating whether interspecific interactions among species within a single nematode trophic group, bacterivores, (1) affect population development and community structure, and (2) depend on food availability. We studied the population growth of Rhabditis (Pellioditis) marina, a rhabditid nematode known to favour very high food densities when in monoculture, and of Diplolaimelloides meyli and D. oschei, congeneric Monhysteridae known to perform better in monocultures at intermediate food availability. Both Diplolaimelloides species showed significantly different patterns of food-density dependence in combination culture compared to monoculture. At very high food availability, the rhabditid nematode facilitated growth of both monhysterid species, probably as a result of down-regulation of bacterial density. At the lowest food availabilities, the presence of even low numbers of monhysterid nematodes lead to exclusion of the rhabditid, which at such low food availability has a very inefficient food uptake. At intermediate food availabilities, abundances of both Diplolaimelloides species were strongly depressed in the combination culture, as a result of food depletion by the rhabditid, indirect inhibitory interactions between the two congeneric species, or both. The complexity of the species interactions render predictions on the outcome and functional consequences of changes in within-trophic-group diversity highly problematic.

Differential effects of food availability on population growth and fitness of three species of estuarine, bacterial-feeding nematodes

The significance of bottom-up controls on biological communities has been a long-standing topic of interest in ecology. However, before environmental effects on communities can be properly assessed, a thorough knowledge of the individual species' responses is required. We studied effects of food availability on population development and on different life-history traits in three species of bacterial-feeding nematodes, Diplolaimelloides oschei, Diplolaimelloides meyli (both Monhysteridae) and Pellioditis marina (Rhabditidae), which co-occur on macrophyte detritus in the Westerschelde Estuary (SW Netherlands). The bacteria Escherichia coli was offered in five food-availability treatments corresponding to initial cell densities from 3 × 10 10 cells ml − 1 to 3 × 10 7 cells ml − 1 . The three bacterial-feeding nematode species studied here showed differential responses to food availability, which agreed with the general idea that Rhabditidae have extreme colonization abilities under very high food availability, while Monhysteridae tend to have a somewhat slower population development and comparatively lower food requirements. Several life-history traits, including juvenile mortality and development time, did not exhibit a clear food-availability dependence, but bioenergetics-related parameters did. Results on the F1 generation may, however, be affected by strong maternal effects on life-history traits of their progeny. Patterns of food-availability dependence of population increase and size at maturity were similar in P. marina. Both Diplolaimelloides species, however, exhibited a large body size at maturity but a very low population increase at the highest food availability, suggesting a trade-off between biomass and reproduction. Comparison with published data on other nematode species reveals that nematode responses to food availability as well as to other environmental factors are highly species-specific.

A polymerase chain reaction (PCR) application for free‐living nematodes (Rhabditida) discrimination

AbstractSynthetic primers were designed and constructed based on Caenorhabditis elegans genomic sequences, targeting HSP70 related sequences. Genomic DNA derived from several free‐living bacterial feeding nematode species was subjected to polymerase chain reaction (PCR), attempting discrimination among them. The amplified DNA fragments exhibited a distinct and reproducible pattern that characterizes different nematode species and populations.

Influence of Ectomycorrhiza on the Structure of Detrital Food Webs in Pine Rhizosphere

Trees infected with ectomycorrhizal (EM) fungi are known to direct several times more energy into the soil than non-ectomycorrhizal trees. Since energy-rich substrates are required by most biological processes, it is widely speculated that the flow of carbon from plants through EM mycelia into soils should have a wide range of effects in the below-ground milieu. In this study we investigated whether EM fungi of effects in the below-ground milieu. In this study we investigated whether EM fungi of Scots pine (Pinus sylvestris) seedlings exert a short-term influence on the biomass and composition of a detrital food web consisting of up to three trophic levels. The experiment was conducted in microcosms with raw humus, perlite and sandy soil (1:1:1; vol.). The soil was defaunated. reinoculated with 10 species of soil bacteria. and 11 species of saprophytic soil fungi, and pine seedlings, either infected or non-infected with six taxa of EM fungi, were separately planted in the microcosms. Five different food webs were established: 1) saprophytic microbes alone. 2) as 1) but with two species of bacterial-feeding nematodes. 3) as 2) but two species of fungal-feeding nematodes included. 4) as 2) but with predatory nematodes, and 5) as 3) but with predatory nematodes. The microcosms were incubated in a climate chamber with varying illumination and temperature regimes for two annual cycles of the pine. After 37 weeks, ca 15 times more fungal biomass was detected on pine roots growing in the systems inoculated with EM fungi than in non-inoculated systems, and there was a significantly greater total biomass of pines in the EM systems. Despite this clearly enhanced autotroph production, neither the total nematode biomass nor the length of the food chain were affected by the EM fungi. The presence of nematodes. independent of the composition of this fauna, enhanced the production of pine biomass significantly, but only in the absence of mycorrhizal fungi. Neither the species composition nor the trophic group architecture of the fauna influenced EM production or growth of EM infected pines, except for fungal-feeding nematodes which had a slight negative influence on the biomass of EM fungi. Our results infer that the role of EM fungi in affecting the amount of energy entering the soils is significant in the long run only, i.e. through increased litter production. We hypothesize that the short-term insensitivity of the decomposer food web to the presence of EM fungi reflects the nature of EM fungi as an efficient sink, preventing the additional production of plant-derived photosynthates from-reaching the organisms of the detrital food web.

Thermal constraints to population growth of bacterial-feeding nematodes

Bacterial-feeding nematodes are important participants in decomposition pathways and nutrient cycles in soils. The contribution of each species to component processes depends upon the physiology of individuals and the dynamics of populations. Having determined the effects of temperature on metabolic rates of several species of bacterial-feeding nematodes, we now present the effects of temperature on population growth rates and relate those data to observed field dynamics. Of nine species of bacterial-feeding nematodes screened for reproductive performance at 20°C, finite rates of population increase ranged from 4.833 d −1 for Caenorhabditis elegans Dougherty to 1.160 d −1 for Panagrolaimus detritophagus Fuchs. Species in the family Rhabditidae generally reproduced more rapidly than those in the Cephalobidae. From the nine species, finite rates of population increase and instantaneous population growth rates were measured at temperatures between 10 and 35°C for Acrobeloides bodenheimeri Thorne, A. buetschlii Steiner and Buhrer, Bursilla labiata Andrássy. Caenorhabditis elegans, Cephalobus persegnis Bastian, and Rhabditis cucumeris Andrássy. Caenorhabditis elegans at 20°C had the maximum finite rate of population increase while R. cucumeris at 35°C had the minimum rate (4.540 × 10 −25 d −1). We utilize the geometric mean of the finite rates of population increase (d −1) as an integral measure of the innate capacity of a species to maintain reproduction across temperatures. The geometric mean varied from 1.03 × 10 −4 for R. cucumeris to 1.45 for Cephalobus persegnis. In the field, temperatures exceeded the upper thermal threshold of R. cucumeris for a significant portion of the 1993 growing season. Population dynamics of this nematode closely matched predicted trajectories. Differences in population growth rates may partially explain the amount of N mineralized by each species.

Dynamics of nematode communities in tomatoes grown in conventional and organic farming systems, and their impact on soil fertility

Nematode communities were monitored intensively through a tomato ( Lycopersicon esculentum L.) growing season in plots managed by conventional and organic farming practices. The temporal dynamics of individual species of bacterial-feeding nematodes differed and suggested differing importance of species in their contribution to N-mineralization in the organically managed soil. Species with r-selected, colonizer characteristics were most responsive to incorporation of organic matter and the subsequent increase of microbial biomass. Bacterial-feeding nematode populations were lowest early in the growing season, when tomato plants exhibited symptoms of nitrogen deficiency. We hypothesize that increasing abundance, biomass and activity of these nematodes in the spring by organic matter incorporation at the end of the previous crop would reduce the observed nitrogen stress. Fungal-feeding nematodes were more abundant in the conventional than the organic plots during periods of organic matter decomposition, possibly related to the higher carbon:nitrogen ratios of the crop residues incorporated into the conventional soils than of the manures and leguminous cover crops incorporated into the organic soils. Predaceous and omnivore nematode populations were low in both farming systems, and plant-parasitic nematode species reflected the crop sequences in rotations used in each system.

Population energetics of bacterial-feeding nematodes: Respiration and metabolic rates based on CO 2 production

By grazing on bacteria, bacterial-feeding nematodes participate in decomposition food webs and N mineralization to an extent determined by metabolic and behavioral attributes and by life history. We studied the respiratory and metabolic activities of 8 species of bacterial-feeding nematodes at 5 temperatures by measuring the rate of CO 2 evolution with an IR gas analyzer. We developed a method for determining size- or stage-specific respiration rates from measurements made on populations of varied stage-structure. Species from a single field site exhibited different thermal optima and temperature-niche breadths for respiratory and metabolic activity. Respiration rates of adults ranged between 1.25–8.80 nl O 2 h −1 at 20°C among the species. Metabolic rates of adults ranged from 1.15 nl O 2 μg(fresh wt) −1 h −1 for Rhabditis cucumeris Andrassy to 4.43 nl O 2 μg(fresh wt) −1 h −1 for Bursilla labiata Andrassy at 20°C. At each temperature, metabolic rates of nematodes of similar size varied with thermal adaptation of the species. Metabolic rates of Cruznema tripartitum Zullini and Cephalobus persegnis Bastian were more sensitive to temperature change than were those of Acrobeloides bodenheimeri Thorne, A. buetschlii Steiner and Buhrer and Panagrolaimus detritophagus Fuchs. C. persegnis exhibited the greatest total metabolic activity cross a range of temperatures, and P. detritophagus the least. Observed differences in thermal adaptation may contribute to the predominance of species in the nematode community at different times during the year or at different depths in the soil.

Biology of Seinura Demani (Nematoda : Aphelenchoididae)

Seinura demani was reared on five species of bacterial feeding nematodes and 3 fungus feeding species. Under culture conditions prey were recognised on contact; there was no evidence of an ability to track victims. S. demani is a bisexual species, its life-history includes one juvenile stage within the egg, two post-hatch juvenile stages, and the adult. Development of all stages are described and measurements given. In cultures incubated at 20°C, the generation time is 41/2-5 days. Male S. demani are attracted to pre-adult moulting females and are retained in their immediate vicinity until the moult is completed. Mating behaviour and copulation are described. Descriptions of behaviour are based on observation, not on experiments, and should therefore be considered as items for further research. Conclusions drawn from the observations are tentative at this stage.