Search

Plasmids are mostly found in bacteria as extrachromosomal genetic elements and are widely used in genetic engineering. Exploring the mechanisms of plasmid-host interaction can provide crucial information for the application of plasmids in genetic engineering. However, many studies have generally focused on the influence of plasmids on their bacterial hosts, and the effects of plasmids on bacteria-feeding animals have not been explored in detail. Here, we use a "plasmid-bacteria- Caenorhabditis elegans " model to explore the impact of plasmids on their host bacteria and bacterivorous nematodes. First, the phenotypic responses of C. elegans were observed by feeding Escherichia coli OP50 harboring different types of plasmids. We found that E. coli OP50 harboring plasmid pEX18Gm unexpectedly increases the fecundity of C. elegans . Subsequently, we found that the plasmid pEX18Gm indirectly affects C. elegans fecundity via bacterial metabolism. To explore the underlying regulatory mechanism, we performed bacterial RNA sequencing and performed in-depth analysis. We demonstrated that the plasmid pEX18Gm upregulates the transcription of methionine synthase gene metH in the bacteria, which results in an increase in methionine that supports C. elegans fecundity. Additionally, we found that a pEX18Gm-induced increase in C. elegans can occur in different bacterial species. Our findings highlight the plasmid-bacteria- C. elegans model to reveal the mechanism of plasmids' effects on their host and provide a new pattern for systematically studying the interaction between plasmids and multi-species.

Caenorhabditis elegans, a free-living nematode, is commonly used as a model organism in ecotoxicological studies. The current literatures have provided useful insight into the relative sensitivity of several endpoints, but few direct comparisons of multiple endpoints under a common set of experimental conditions. The objective of this study was to determine appropriate sublethal endpoints to develop an ecotoxicity screening and monitoring system. C. elegans was applied to explore the sublethal toxicity of four heavy metals (copper, zinc, cadmium and chromium). Two physiological endpoints (growth and reproduction), three behavioral endpoints (head thrash frequency, body bend frequency and feeding) and two enzymatic endpoints (acetylcholine esterase [AChE] and superoxide dismutase [SOD]) were selected for the assessment of heavy metal toxicity. The squared correlation coefficients (R2) between the responses observed and fitted by Logit function were higher than 0.90 and the RMSE were lower than 0.10, indicating a good significance statistically. There was no significant difference among the half effect concentration (EC50) endpoints in physiological and behavioral effects of the four heavy metals, indicating similar sensitivity of physiological and behavioral effects. AChE enzyme was more sensitive to copper, zinc, and cadmium than to other physiological and behavioral effects, and SOD enzyme was most sensitive to chromium. The EC50 of copper, zinc, and cadmium, to the AChE enzyme in the nematodes were 0.68 mg/L, 2.76 mg/L, and 0.92 mg/L respectively and the EC50 of chromium to the SOD enzyme in the nematode was 1.58 mg/L. The results of this study showed that there was a good concentration-response relationship between all four heavy metals and the sublethal toxicity effects to C. elegans. Considering these sublethal endpoints in terms of simplicity, accuracy, repeatability and costs of the experiments, feeding is the relatively ideal sublethal toxicity endpoint of heavy metals to C. elegans.

Bacteria serve as live food and nutrients for bacterial-feeding nematodes (BFNs) in soils, and influence nematodes behavior and physiology through their metabolism. Five bacterial taxa (Bacillus amyloliquefaciens JX1, Variovorax sp. JX14, Bacillus megaterium JX15, Pseudomonas fluorescens Y1 and Escherichia coli OP50) and the typical BFN Caenorhabditis elegans were selected to study the effects of bacterial respiration and growth rates on the feeding preferences, brood size and lifespan of nematodes. P. fluorescens Y1 and E. coli OP50 were found to be more active, with high respiration and rapid growth, whereas B. amyloliquefaciens JX1 and B. megaterium JX15 were inactive. The nematode C. elegans preferred active P. fluorescens Y1 and E. coli OP50 obviously. Furthermore, worms that fed on these two active bacteria produced more offspring but had shorter lifespan, while inactive and less preferred bacteria had increased nematodes lifespan and decreased the brood size. Based on these results, we propose that the bacterial activity may influence the behavior and life traits of C. elegans in the following ways: (1) active bacteria reproduce rapidly and emit high levels of CO2 attracting C. elegans; (2) these active bacteria use more resources in the nematodes' gut to sustain their survival and reproduction, thereby reducing the worm's lifespan; (3) inactive bacteria may provide less food for worms than active bacteria, thus increasing nematodes lifespan but decreasing their fertility. Nematodes generally require a balance between their preferred foods and beneficial foods, only preferred food may not be beneficial for nematodes.

It has been hypothesized that faunal activity in the rhizosphere influences root growth via an auxin-dependent pathway. In this study, two methods were used to adjust nematode and bacterial populations within experimental soils. One is “exclusion”, where soil mixed with pig manure was placed in two bags with different mesh sizes (1mm and 5μm diameter), and then surrounded by an outer layer of unamended soil resulting in soil with a greater populations of bacterial-feeding nematodes (1mm) and a control treatment (5μm). The second method is “inoculation”, whereby autoclaved soil was inoculated with bacteria (E. coli and Pseudomonas) and Nematodes (Cephalobus and C. elegans). In order to detect the changes in the rice’s perception of auxin under different nutrient and auxin conditions in the presence of soil bacterial-feeding nematodes, responses of soil chemistry (NH4+, NO3- and indole acetic acid (IAA)), rice root growth and the expression of an auxin responsive gene GH3-2 were measured. Results showed that, under low soil nutrient conditions (exclusion), low NO3- correlated with increased root branching and IAA correlated with increased root elongation and GH3-2 expression. However, under high soil nutrient conditions (inoculation), a high NH4+ to NO3- ratio promoted an increase in root surface area and there was an additional influence of NH4+ and NO3- on GH3-2 expression. Thus it was concluded that soil bacterial-feeding nematodes influenced soil nutritional status and soil IAA content, promoting root growth via an auxin dependent pathway that was offset by soil nitrogen status. [ABSTRACT FROM AUTHOR]

Inter-organismal metabolites play important roles in regulating organism behavior and the communication between organisms. Nematodes, the most abundant animals on earth, are crucial participants in soil ecosystems through their interactions with microbes. For example, bacterial-feeding nematodes increase the activity of indole-3-acetic acid (IAA)-producing bacteria and the IAA content in soil. However, the way in which these nematodes interact with bacteria and affect IAA biosynthesis is not well understood. Here, using the model nematode Caenorhabditis elegans and the plant-beneficial bacterium Arthrobacter pascens ZZ21, we examined the effects of nematode excretions or extracts on bacterial IAA biosynthesis. To explore the underlying regulatory mechanism in more detail, we performed transcriptome sequencing and metabolomic analysis. Our findings suggest that C. elegans extracts promote IAA biosynthesis in A. pascens ZZ21 by increasing the expression of genes and the abundance of intermediates involved in the indole-3-pyruvic acid (IPyA) pathway. C. elegans extracts also significantly influenced biosynthetic and metabolic activity in A. pascens ZZ21. Treatment with C. elegans extracts promoted pyruvate metabolism, the citrate cycle (TCA) cycle and the production of some TCA-cycle-related amino acids and inhibited oxidative phosphorylation, which induced the accumulation of reduced nicotinamide adenine dinucleotide (NADH). We propose that the extracts altered the metabolism of A. pascens ZZ21 to help the bacteria resist stress caused by their predator. Our findings indicate that bacterial-feeding nematodes mediate the interaction between nematodes and bacteria via their extracts, providing insights into the ecological function of C. elegans in soil. [ABSTRACT FROM AUTHOR]

Earthworms naturally secrete substantial amounts of mucus (relative to their body size) from the cuticle when moving through the soil. However, how the metabolites in the epidermally derived mucus affect soil microfauna is largely unknown. The objective of this study was to determine how earthworm mucus affected the physiology of the model nematode Caenorhabditis elegans and that of two soil-dwelling bacterial-feeding nematodes: Mesorhabditis sp. and Protorhabditis sp. The traits examined included phobotaxis, reproduction, mortality, body size, feeding inhibition rate, and feeding preference. Two nematode species escaped from the earthworm mucus, whereas earthworm mucus reduced the reproduction of C. elegans and increased the mortality of C. elegans and Mesorhabditis sp. Moreover, earthworm mucus reduced the feeding rate of C. elegans and Protorhabditis sp. and changed the feeding preferences of all three species of nematodes. At 48 h, earthworm mucus increased feeding on Bacillus amyloliquefaciens JX1 for C. elegans and Protorhabditis sp. and reduced feeding on Escherichia coli OP50 for Mesorhabditis sp. These results suggest that earthworm mucus can be detrimental to bacterial-feeding nematodes and provide insights into the non-trophic interactions between earthworms and other soil biota. • Two of the three bacterial-feeding nematodes escaped from earthworm mucus. • Earthworm mucus reduced the reproduction of C. elegans. • Earthworm mucus increased the mortality of the C. elegans and Mesorhabditis sp. • Earthworm mucus inhibited the feeding rate of C. elegans and Protorhabditis sp and changed the feeding preferences of all the bacterial-feeding nematodes. [ABSTRACT FROM AUTHOR]

Ability to identify familiar foods is a major driver of animal feeding behavior. Animals show preference for familiar foods over novel ones, presumably to avoid poisonous substances and better support their growth and reproduction. However, we do not know how their feeding behavior is affected when the familiar food is inferior to a novel food with regards to its palatability and nutritional properties. We tested the hypothesis that feeding preference is determined by specific food characteristics rather than food familiarity with fast-growing soil-dwelling nematodes. Two sequential experiments were designed to test the feeding behavior of soil bacterial-feeding nematodes ( Mesorhabditis sp. and Acrobeloides sp.) resulting from familiar food recognition, including a 6-months training period to develop their food familiarity and a feeding experiment to test their food preference for five bacterial species. Nematodes showed clear preference for specific food sources, which were not necessarily the familiar food. Their feeding behavior was not affected by food familiarity, but correlated highly with bacterial traits such as cell size, growth rates, and water content. We conclude that nematode feeding behavior was controlled by food specificity rather than familiarity. We further suggest that physiological factors, possibly the physical size and presence of chemical receptors in the buccal cavity, allow nematodes to rapidly assess their food supply and switch from a familiar food to a preferred, novel food that is easier to ingest and better suited to support their growth and reproduction. [ABSTRACT FROM AUTHOR]

Animals are expected to choose foods that optimize their growth, reproduction and survival, but their dietary choice changes when suffering stress. Here, we provide the first report of nematode stress resulting from exposure to earthworm-produced cyclic peptides, and confirm that this stress changes the dietary choice of the model animal Caenorhabditis elegans and other soil-dwelling bacterial-feeding nematodes. When allowed free choice in a stress-free environment, nematodes prefer feeding on high-quality bacteria to support a higher reproduction and a shorter lifespan, supporting a reproduction-dominated energy allocation pattern. However, they feed less on preferred food (high-quality bacteria) and include more unpreferred food (low-quality bacteria) in the diet when stressed by the toxic cyclic peptides. Nematodes that eat more unpreferred bacteria appear to shift towards a survival-dominated energy allocation pattern. Specifically, limited resources obtained from low-quality bacteria are preferentially allocated to repair cyclic peptide-induced damage of their DNA and complete their lifespan, although at significantly reduced reproduction level. Our results demonstrate that nematodes can actively change their dietary strategy to maintain survival at the cost of reproduction when they experience acute stress. This stress-driven adjustment of dietary choice may be the key to understand feeding ecology and food web structure. • Earthworm mucus changed the 'normal' feeding preference of soil nematodes. • Earthworm mucus caused DNA damage of soil nematodes. • Cyclic peptides were responsible for changing nematode dietary choice. • Nematodes chose more unpreferred food when exposed to cyclic peptides. • Nematodes reallocated energy resource to somatic repair at the cost of reproduction. [ABSTRACT FROM AUTHOR]