Free-living Soil Nematode Research Articles

IMPACT OF PHYTOSANITARY TREATMENTS WITH NATURAL EXTRACTS ON SOIL NEMATODE COMMUNITY IN POT FARMING

The EU strongly encourages the use of natural products in plant protection. Natural extracts are increasingly used in controlling plant-parasitic nematodes, while the effects on the structure and function of non-target soil organisms have been poorly investigated. This work aimed at investigating the impact of abamectin, azadirachtin, and allium extract on the structure of soil free-living nematode community in potted ornamental plants of Acer palmatum and x Cupressocyparis leylandii by soil nematode indicators. Abamectin and Azadirachtin negatively affected the soil nematode community, but the effect was transitory. The nematode indicators showed that the nematode community responded quickly and negatively to treatments with natural extracts. The plant parasitic index (PPI) and enrichment index (EI) were the most representative due to their strong decrease after pest control treatment, especially after Fenamiphos applications. From a phytosanitary point of view, natural extract showed their potential in the IPM strategy only when they were applied in combination with other chemicals. Key Words: Azadiracthin, Allium extract, Abamectin, Pistoia Nursery-Ornamental District

The Effect of Varying Olive Mill Wastewater Concentrations on Soil Free-Living Nematode Communities and Lettuce Growth

We assessed the impact of increasing olive mill waste (OMW) concentrations (10%, 35%, 70%, and 100% v/v) on soil free-living nematode communities and Lactuca sativa (lettuce) growth, 10 and 45 days after application (DAA). L. sativa plants showed a survival threshold at OMW10%, with higher concentrations proving fatal. Contrary to expectations, nematode abundance increased with OMW concentration. OMW10% induced a rapid surge in nematode abundance, stabilizing at 45 DAA, resembling control values. OMW35%, OMW70%, and OMW100% plots exhibited persistent, gradual increases, surpassing control values at 45 DAA. All treatments favored fungal feeders, resulting in the overdominance of the genus Aphelenchus both at 10 and 45 DAA. Even though OMW did not exert a toxic effect on nematode populations, this shift in the community structure towards the dominance of a single genus could suggest an imbalance in the soil community, which could have negative implications for soil health and ecosystem functioning. Overall, our study provides insights into the complex interactions between OMW, soil nematode communities, and plant growth, emphasizing the importance of understanding soil ecology for sustainable agricultural management.

Почвенная нематода Caenorhabditis elegans как модель для изучения паразитических нематод

The free-living soil nematode Caenorhabditis elegans has been used as model organism in biological researches since middle of the 1960th. The short lifecycle, small body size, high fecundity, simplicity and cheapness of cultivation in laboratory, and safety for researchers are advantages of C. elegans as experimental model to study biology of Metazoa. The discussion about the possibility to use C. elegans as the model for parasitic nematodes started with the first mention of this nematode in scientific literature. The present article is the review of experimental studies demonstrating that in many cases substances toxic for C. elegans are also toxic for parasitic nematodes, and vice versa. This allows making a conclusion about the prospectivity to use C. elegans for initial screening for substances with nematicidal activity followed by their testing in experiments with parasitic nematodes. The possibility to use C. elegans for understanding mechanisms of nematicides action is also indisputable. On the whole one may conclude that C. elegans is a useful model both for searching new substances with anthelmintic activity and solution of the problem to overcome drug resistance of helmints.

Simple, inexpensive, and rapid approach to detect changes in the structure of soil free-living nematodes.

A general limitation of ecological investigations based on nematodes is related to the difficult and time-consuming taxonomic identification of species. Therefore, nematologists are investing many efforts to develop alternative approaches as proxies applicable in biomonitoring assessment. Recently, an alternative method that combines morpho-functional traits was proposed for detecting assemblage changes of marine nematodes. In view of the promising results, it was tested the same approach to document taxonomic structure changes of soil free-living and plant parasitic nematodes. Specifically, this attempt was carried out using three data sets that include studies from various European regions and different types of ecosystems: forests, grasslands and maize crops. Multivariate statistical analysis revealed that the simple combination of the four traits (i.e., buccal cavity cuticularization occurrence, amphideal fovea size and shape, morphology of the cuticle and pharynx) in a single code number perfectly mirrors the taxonomic structure trends of the nematode assemblage at genus level. Therefore, we predict that similar results can be also obtained by directly encoding nematode specimens with the selected traits and we point to new important advances if this procedure can be coupled with advanced machine learning.

Five Different Artemisia L. Species Ethanol Extracts' Phytochemical Composition and Their Antimicrobial and Nematocide Activity.

Among the plants that exhibit significant or established pharmacological activity, the genus Artemisia L. deserves special attention. This genus comprises over 500 species belonging to the largest Asteraceae family. Our study aimed at providing a comprehensive evaluation of the phytochemical composition of the ethanol extracts of five different Artemisia L. species (collected from the southwest of the Russian Federation) and their antimicrobial and nematocide activity as follows: A. annua cv. Novichok., A. dracunculus cv. Smaragd, A. santonica cv. Citral, A. abrotanum cv. Euxin, and A. scoparia cv. Tavrida. The study of the ethanol extracts of the five different Artemisia L. species using the methods of gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-MS/MS) allowed establishing their phytochemical profile. The obtained data on the of five different Artemisia L. species ethanol extracts' phytochemical composition were used to predict the antibacterial and antifungal activity against phytopathogenic microorganisms and nematocidal activity against the free-living soil nematode Caenorhabditis elegans. The major compounds found in the composition of the Artemisia L. ethanol extracts were monoterpenes, sesquiterpenes, flavonoids, flavonoid glycosides, coumarins, and phenolic acids. The antibacterial and antifungal activity of the extracts began to manifest at a concentration of 150 µg/mL. The A. dracunculus cv. Smaragd extract had a selective effect against Gram-positive R. iranicus and B. subtilis bacteria, whereas the A. scoparia cv. Tavrida extract had a selective effect against Gram-negative A. tumefaciens and X. arboricola bacteria and A. solani, R. solani and F. graminearum fungi. The A. annua cv. Novichok, A. dracunculus cv. Smaragd, and A. santonica cv. Citral extracts in the concentration range of 31.3-1000 µg/mL caused the death of nematodes. It was established that A. annua cv. Novichok affects the UNC-63 protein, the molecular target of which is the nicotine receptor of the N-subtype.

Upcycling of food waste streams to valuable biopigments pyocyanin and 1-hydroxyphenazine

Phenazines, including pyocyanin (PYO) and 1-hydroxyphenazine (1-HP) are extracellular secondary metabolites and multifunctional pigments of Pseudomonas aeruginosa responsible for its blue-green color. These versatile molecules are electrochemically active, involved in significant biological activities giving fitness to the host, but also recognized as antimicrobial and anticancer agents. Their wider application is still limited partly due to the cost of carbon substrate for production, which can be solved by the utilization of carbon from food waste within the biorefinery concept. In this study, a variety of food waste streams (banana peel, potato peel, potato washing, stale bread, yoghurt, processed meat, boiled eggs and mixed canteen waste) was used as sole nutrient source in submerged cultures of P. aeruginosa BK25H. Stale bread was identified as the most suitable substrate to support phenazine biopigments production and bacterial growth. This was further increased in 5-liter fermenter when on average 5.2 mg L-1 of PYO and 4.4 mg L-1 of 1-HP were purified after 24 h batch cultivations from the fermentation medium consisting of homogenized stale bread in tap water. Purified biopigments showed moderate antimicrobial activity, and showed different toxicity profiles, with PYO not being toxic against Caenorhabditis elegans, a free-living soil nematode up to 300 µg mL-1 and 1-HP showing lethal effects at 75 µg mL-1. Therefore, stale bread waste stream with minimal pretreatment should be considered as suitable biorefinery feedstock, as it can support the production of valuable biopigments such as phenazines.

Temporal dynamics of soil nematode population in an Acacia saligna invaded Mediterranean sand dune ecosystem

Summary The invasive Australian tree, Acacia saligna, has been the subject of numerous studies investigating its ecological impact. However, the effect of its invasion on the soil free-living nematode population has yet to be researched. In this study, we examined the impact of A. saligna on the soil free-living nematode population in a coastal dune site with a Mediterranean climate during three sampling periods. Soil samples were collected from beneath the canopies of A. saligna trees, the native dominant shrub Retama raetam, and bare soil plots as a control. Our findings reveal that A. saligna increases the density of the soil free-living nematode population and changes its trophic and taxonomic composition. While the nematode diversity and functional index scores did not significantly differ between sampling locations, they did differ between the different sampling times, highlighting the seasonal dynamics of the soil nematode population in Mediterranean sand dunes.

Seasonal fluctuations attenuate stimulatory or inhibitory impacts of colonial birds on abundance, structure and diversity of soil biota.

Soil microorganisms and free-living nematodes were investigated in association with the nesting and roosting habitats of the following piscivorous and omnivorous colonial birds: black kite (Milvus migrans), great cormorant (Phalacrocorax carbo), black-crowned night heron (Nycticorax nycticorax) and little egret (Egretta garzetta), in Israel's Mediterranean region. Abiotic variables, abundance, trophic structure, sex ratio and genus diversity of soil free-living nematodes, and total abundance of bacteria and fungi, were measured during the wet season, following our previous study conducted during the dry season. The observed soil properties were important drivers of soil biota structure. Presence of the most efficient elements for soil organisms, such as phosphorus and nitrogen, was strongly dependent on the diet of the compared piscivorous and omnivorous bird colonies; levels of these nutrients were notably higher in the bird habitats than in their respective control sites during the study period. Ecological indices showed that the different species of colonial birds can have different (stimulatory or inhibitory) impacts on abundance and diversity of the soil biota, affecting the structure of the soil free-living nematode population at the generic, trophic and sexual levels during the wet season. A comparison with results from the dry season illustrated that seasonal fluctuations can change, and even attenuate the effect of bird activity on the abundance, structure and diversity of the soil communities.

A new free-living nematode species, Terschellingia didistalamphida sp. nov. (Nematoda: Linhomoeidae), with female intersexuality from West Bengal, India

A new species of free-living soil nematode, Terschellingia didistalamphida sp. nov., is described from paddy field in West Bengal, India. It is characterized by moderate body length (L=1.0–3.5 mm), possesses two amphids, only four cephalic setae. Amphideal fovea distant from the anterior end, stoma small and narrow, pharynx with well-developed terminal bulb. Females with amphidelphic ovaries. Males with paired testes, ventrally arcuate, short and stout spicules, gubernaculum with clearly developed dorso-caudal apophysis. Tail long and filiform, similar in both sexes. Fourteen female intersexes of Terschellingia didistalamphida sp. nov., with a prominent female reproductive structure and a less conspicuous male reproductive system, were found. These female intersexes are with well-developed vulva and prominent spicules, however, lack apophysis. A checklist for known cases of intersex across various nematode orders has been appended.

Population Density of Free-Living Nematodes and their Relationships with Some Soil Physicochemical Properties of Alfalfa

The present study was conducted to evaluate the soil’s suitability for the alfalfa crop in Nomal Valley, Gilgit Baltistan (GB), using a variety of physicochemical parameters and free-living soil nematodes as indicators. Ten soil samples from different sites (A1-A10) of the valley were collected in zip-lock plastic bags to test for free-living soil nematodes and physicochemical characteristics. Each sample’s free-living nematodes were extracted using the modified Baermann funnel method and counted using a compound microscope (at 40 and 100X). About 100 nematodes were identified from each sample to the family level. Based on feeding behavior, nematodes were divided into groups. Nematode population densities ranged from 102 to 507. The most prevalent feeding group members were bacterivores, while predators were the least common. Cephalobidae was the most frequently occurring family, which indicates soil’s fertility. Various physiochemical parameters, including soil temperature, pH, electrical conductivity (EC), moisture, bulk density, and texture, were also measured. The ranges for the selected soil parameters were as follows: pH 7.20-7.80, EC 68-252 mS/m, bulk density 0.91-1.37g/cm2, and soil temperature 22-30 ℃. All sites had slit loam soil texture except A-5, which had sandy loam.

The FMRFamide-like peptide FLP-1 modulates larval development by regulating the production and secretion of the insulin-like peptide DAF-28 in Caenorhabditis elegans.

The FMRFamide-like peptides (FLPs) are conserved in both free-living and parasitic nematodes. This molecular genetic study verified the relevance of the flp-1 gene, which is conserved in many nematode species, to the larval development of the free-living soil nematode Caenorhabditis elegans. Using C. elegans as a model, we found that: (1) FLP-1 suppressed larval development, resulting in diapause; (2) the secretion of FLP-1, which is produced in AVK head neurons, was suppressed by the presence of food (Escherichia coli) as an environmental factor to continue larval development; (3) the FLP-1 reduced the production and secretion of DAF-28, which is produced in ASI head neurons and is the predominant insulin-like peptide (INS) present. FLP-1 is conserved in many species of plant-parasitic root-knot nematodes that cause severe damage to crops. Therefore, our findings may provide insight into the development of new nematicides that can disturb their infection and development.

Ecological stoichiometry drives the evolution of soil nematode life history traits

Ecological stoichiometry is a useful theoretical framework for understanding the sources and controls on nutrient availability that structure the composition and diversity of biotic communities. One such relationship is that organismal development rate is positively linked to cellular Phosphorus (P). We hypothesized that P availability, relative to other nutrients, e.g., nitrogen and carbon, would drive the evolution of traits associated with organismal growth and development. We examined the effects of P availability both in situ and in vitro, on free-living soil nematodes. We found that P-deficient environments produce predictable changes in the ecology and evolution of important life history traits. Our results identify altered rRNA gene copy number and subsequent changes in gene expression and protein synthesis as mechanisms by which P-deficiency influences these traits. These findings have important implications for explaining soil ecological and evolutionary patterns across multiple levels of organization, including the structure and functioning of organisms, populations, communities, and ecosystems.

Redox and Metabolic Regulation of Intestinal Barrier Function and Associated Disorders.

The intestinal epithelium forms a physical barrier assembled by intercellular junctions, preventing luminal pathogens and toxins from crossing it. The integrity of tight junctions is critical for maintaining intestinal health as the breakdown of tight junction proteins leads to various disorders. Redox reactions are closely associated with energy metabolism. Understanding the regulation of tight junctions by cellular metabolism and redox status in cells may lead to the identification of potential targets for therapeutic interventions. In vitro and in vivo models have been utilized in investigating intestinal barrier dysfunction and in particular the free-living soil nematode, Caenorhabditis elegans, may be an important alternative to mammalian models because of its convenience of culture, transparent body for microscopy, short generation time, invariant cell lineage and tractable genetics.

Free-living nematode community structure and distribution within vineyard soil aggregates under conventional and organic management practices

Soil biota play a crucial role in soil ecosystem stability, promoting decomposition of organic matter and nutrient cycling. The influence of organic farming versus conventional farming is known to improve soil properties such as aggregation. Despite the importance of soil microbial communities in soil biogeochemical processes, our knowledge of their community dynamics is rudimentary especially under different agricultural managements. Here we studied the effect of two types of vineyard managements (conventional, and organic), and three soil aggregate sizes (macro – LMA, 8,000-9,800 μm; meso – SMA, 500-2000 μm and micro – MA, <500 μm) on free-living soil nematodes. The abundance, diversity, and indices of free-living soil nematodes were determined. We found that the abundance of free-living soil nematodes increased with organic treatment, and that the nematode community guild structure altered toward changes in the Wasilewska index, where plant parasites were found to increase macro-aggregates in the agricultural practices that may be attributed to weed management (no-tillage and no herbicides) in the organic treatment. The network connectivity increased in complexity with increasing aggregate sizes, highlighting the importance of the interplay between nematodes and soil inter-aggregate pore size and connectivity.

Free-living nematodes research: State of the art, prospects, and future directions. A bibliometric analysis approach

Nematodes are among the most successful metazoans inhabiting the Earth and they are pivotal components as in terrestrial as in aquatic (both in marine and freshwater) environments providing important ecosystem services. The aim of this study was to understand major research trends and topics on free-living nematodes inhabiting soil, marine and freshwater environments and to highlight possible differences among them. To achieve this objective, a bibliometric analysis was performed using Scopus database. The indexed global scientific literature on free-living nematodes from 1912 to 2021 was explored using VOSviewer software, allowing a comprehensive overview of the topic. The analyses of co-authorship (among researchers and countries), the co-occurrence of keywords and the analysis of citation of journals were performed. Overall, free-living soil nematodes found a wider audience in high ranked journals especially when compared with freshwater nematodes. Marine nematodes stand in between them and many aspects of biodiversity research in marine ecosystems are covered by high-medium ranked journals (i.e. taxonomy, systematic, phylogeny, morphological and genetic diversity). Although, the estimation of the taxonomic diversity of the phylum Nematoda enumerated a high number of documents, an increasing attention emerged for the investigation of pollution effects (i.e. nematodes as bioindicators of environmental status) and the use of nematodes as model organisms for addressing scientific questions in line with the Eco-Evo-Devo (Ecological Evolutionary Developmental biology) approach. These fundamental themes were indirectly confirmed by the co-authorship analysis, which revealed that taking integrative approaches between taxonomy (both morphological and molecular), ecological and evolutionary aspects attracted a higher number of citations.

The Free-Living Nematodes as Indicators of the Soil Quality in Relation to the Clay Content, When Coffee Waste Is Applied

Coffee waste is an organic material that can potentially be used in agricultural systems as an organic amendment. This study investigated the effects of the application of three concentrations of coffee waste (1%, 2%, and 4% w/v), used as an organic amendment, on soil free-living nematode communities, and in two different soil types (clay and sandy loam). Coffee waste incorporation did not appear to be toxic to the soil’s free-living nematodes; on the contrary, it favored the nematode populations; this increase was greater in the sandy loam soil type. Our results show that the abundance of the cp-1 bacteria-feeding nematodes can be used as an indicator of the soil’s enrichment or depletion phase. Panagrolaimus was the most promising genus to describe quality differentiations that occur in the soil system. Three months after coffee waste application, Panagrolaimus was found to be dominant in all coffee waste applications, indicating that the soil was in a phase of enrichment. Six months after the application, nematode community structure indices (enrichment and structure) showed that coffee waste was decomposed in the 1 and 2% treatments and that these systems were in a stage of nutrient depletion. In terms of agricultural practices, when a coffee waste dose is lesser than 4%, a second application is recommended before 6 months to avoid soil degradation.

Year-Long Assessment of Soil Nematode Diversity and Root Inhibition-Indicator Nematode Genera in Rice Fields.

Soil nematodes contribute to nutrient cycling. This year-long study aimed to investigate the changes in the diversity of soil nematodes during the spring, summer, and winter seasons in rice fields at 24 sites and to determine the indicator nematode genera that inhibit the roots of rice plants. A total of 216 soil samples were collected during three seasons, and the collection of 72 root samples was carried out during rice cropping. Forty-four soil nematode genera were identified. They exhibited significant changers in their abundance, which were dependent on the seasons and on soil characteristics. In particular, the abundance of plant-parasitic nematodes (PPNs) and free-living soil nematodes was 49% and 15% higher during the summer than during the spring and winter seasons, respectively. Soil characteristics, such as soil nitrogen (N) contents, carbon (C) contents, and soil moisture were significantly higher during the summer than in the spring and winter seasons, but soil pH was significantly lower during the summer than in the spring and winter seasons. Moreover, Hirschmanniella,Meloidogyne, and Heterodera emerged as good indicators for rice root inhibition, corroborating the frequency, density, and prominence value of PPNs of the sampled soil and rice roots. This study also indicated that free-living nematode genera, such as Rhabdolaimus, Diplogaster, and Rhabditis, might function as ecological indicators for soil health.

The FMRFamide-like peptide FLP-2 is involved in the modulation of larval development and adult lifespan by regulating the secretion of the insulin-like peptide INS-35 in Caenorhabditis elegans.

In the animal kingdom, neuropeptides regulate diverse physiological functions. In invertebrates, FMRFamide and its related peptides, a family of neuropeptides, play an important role as neurotransmitters. The FMRFamide-like peptides (FLPs) are one of the most diverse neuropeptide families and are conserved in nematodes. Our screen for flp genes of the free-living soil nematode Caenorhabditis elegans revealed that the flp-2 gene is involved in the larval development. The gene is also conserved in plant-parasitic root-knot nematodes. Our molecular genetic analyses of the C. elegans flp-2 gene demonstrated as follows: (1) the production and secretion of FLP-2, produced in the head neurons, are controlled by environmental factors (growth density and food); (2) the FLP-2 is involved in not only larval development but also adult lifespan by regulating the secretion of one of the insulin-like peptides INS-35, produced in the intestine. These findings provide new insight into the development of new nematicides.

Impact of Super-High Density Olive Orchard Management System on Soil Free-Living and Plant-Parasitic Nematodes in Central and South Italy.

Simple SummarySuper-high density olive orchards are spreading in Italy to reduce production costs and increase yields per hectare. The objective of this study was to assess the orchards’ effect on the soil nematode community in five sites located in the main Italian olive cultivation areas compared to the adjacent traditional olive orchard system. Super-high density olive orchard management combined with conventional tillage and mineral fertilization decreased total organic carbon compared to traditional management. The soil nematode community was affected by the depletion of organic matter, especially for plant-parasitic nematodes, which increased. Moreover, this investigation evidenced that the Super-high density olive orchard management system could change the soil plant-parasitic nematode composition of olive orchards. In fact, the families Telotylenchidae, Paratylenchidae, Meloidogynidae, and Criconematidae were favored in the Super-high density olive orchard system, while Longidoridae, Heteroderidae, and Pratylenchidae were disadvantaged. However, conservative and sustainable soil management might maintain or improve the soil nematode community functionality and reduce plant-parasitic nematodes.The soil nematode community plays an important role in ecosystem services. The objective of this study was to assess the effect of Super-high density (SHD) olive orchards on the nematode community in five sites with different soils, climates, and cultivars. At each site, the SHD management system was compared to the adjacent olive orchard traditional (TRAD) system, in which the same soil management and phytosanitary measures were applied. Soil management was assessed by total organic carbon content (TOC), while the soil nematode community was evaluated using the nematode taxa abundances and soil nematode indicators. TOC was significantly decreased in the SHD olive orchard system compared to TRAD in the sites characterized by conventional tillage and mineral fertilization. The two-way ANOSIM analysis on nematode abundance showed no difference between the two olive management methods, instead showing only a significant difference per site mainly due to variabilities in plant-parasitic nematode assemblage. However, a negative impact of SHD management was evident in environments stressed by summer droughts and conventional tillage: the ratio of obligate plant-parasites to bacterivores and fungivores (Pp/(B+F)) was significantly higher in SHD than in the TRAD olive orchard system, and the prey-to-predator θ mass ratio showed the lowest values in the sites under organic fertilization or green manure. The canonical correspondence analysis showed that the free-living nematodes were only slightly affected by SHD olive orchards; instead, the presence of plant-parasitic nematodes families such as Telotylenchidae, Paratylenchidae, Meloidogynidae, and Criconematidae was favored, in comparison to Longidoridae, Heteroderidae, and Pratylenchidae.

Stochasticity dominates assembly processes of soil nematode metacommunities on three Asian mountains

Nematodes play an important role in ecosystems, yet very little is known about their assembly processes and the factors influencing them. We studied nematode communities in bulk soil from three Asian mountain ecosystems to study the assembly processes of free-living nematode metacommunities and their driving factors. On each mountain, elevations span a range of climatic conditions with the potential to reveal the assembly processes predominating across multiple biomes. A phylogenetic null modeling framework was used to analyze 18S rRNA gene amplicons to quantify various assembly processes. We found that phylogenetic turnover between nematode communities on all mountains was dominated by stochastic processes, with “undominated processes” as the most predominant stochastic factor. Elevation has a significant impact on the relative importance of deterministic and stochastic processes. A variety of climatic and edaphic variables significantly influenced the variation of community assembly processes with elevation, even though their impacts were not consistent between the mountains. Overall, our results indicated that free-living nematode metacommunities in a wide range of environments are largely structured by stochastic processes, rather than by niche-based deterministic processes, which suggests that metacommunities of soil free-living nematodes may respond to climate change in a largely unpredictable way.