Dimethyl sulfoxide and ascarosides improve the growth and yields of entomopathogenic nematodes in liquid cultures

Increasing the infective juvenile (IJ) yields of entomopathogenic nematodes in monoxenic culture systems would reduce their production cost for the market. Ascarosides act as universal nematode pheromones with developmental and behavioral effects of nematodes. Dimethyl sulfoxide (DMSO) is unexpectedly found to enhance the IJ yields of entomopathogenic nematodes on fortified nutrient broth plates. In this study, the influence of selected ascarosides (ascr#7, ascr#9 and ascr#11) and DMSO in three concentrations on the IJ yields of S. carpocapsae All and H. bacteriophora H06 in liquid culture flasks was determined, and the critical development parameters (IJ recovery rate, number of hermaphrodites, number of visible eggs in a hermaphrodite) were examined for H. bacteriophora H06. The results demonstrated that IJ yields were significantly improved in the liquid medium containing 0.01 % DMSO, and 0.02 nM ascr#11 for S. carpocapsae All, and 0.1 % and 0.01 % DMSO and 0.02 pM ascr#11 for H. bacteriophora H06 in proper concentrations. Furthermore, it was discovered that increased recovery rate, hermaphrodite numbers and eggs in the hermaphrodites may contribute to the improved IJ yields of H. bacteriophora H06 in DMSO-supplemented liquid medium. Compared with the control flasks, the IJ yields from the flasks containing 0.01 % DMSO were 15 % and 35 % higher for S. carpocapsae All and H. bacteriophora H06 respectively in 15 days. The cost for ascarosides and DMSO is almost negligible. The results would provide practical technology for low-cost commercial production of these nematodes for pest management program.

Influence of the ascarosides on the recovery, yield and dispersal of entomopathogenic nematodes

Recovery, yield, and dispersal are crucial developmental and behavioral indices for the infective juveniles of entomopathogenic nematodes, which are used as biocontrol agents against a variety of agricultural pests. Ascarosides and isopropylstilbene (ISO) function as nematode pheromones with developmental and behavioral effects. In this study, 11 synthesized ascarosides identified from Caenorhabditis elegans, together with ISO identified from Photorhabdus luminescens, were used to determine their influence on the IJ recovery, growth on agar plates, and dispersal of S. carpocapsae All, H. bacteriophora H06 and H. indica LN2 nematodes. Compared with the controls, significant differences in IJ recovery of three nematode species were detected from the supernatants of their corresponding bacterial cultures with almost all ascarosides or isopropylstilbene (ISO) at 0.04 nM in 6 days. The highest IJ recovery percentages was obtained from ISO and ascr#3 for All strain, ascr#5 and ascr#6 for LN2 strain, and ISO and ascr#12 for H06 strain. The ISO detected from Photorhabdus bacteria also induced IJ recovery of S. carpocapsae All. IJ yields was significantly stimulated by all synthesized compounds for S. carpocapsae All, and by most compounds for H. bacteriophora H06. The higher IJ yields varied with ascarosides. Ascr#7 and DMSO was common for the improved IJ yields of both nematode species. The three nematode species showed marked differences in dispersal behavior. In response to the ascarosides or ISO, S. carpocapsae All IJs actively moved with different dispersal rates, H. indica LN2 IJs in very low dispersal rates, and H. bacteriophora H06 IJs in variable and even suppressed rates on the agar plates at least during the assay period. Based on the synthesized standards, ascr#1, ascr#9 and ascr#10 were detected from three nematode species, ascr#5 and ascr#11 also from S. carpocapsae All and H. bacteriophora H06, and ascr#12 also from H. bacteriophora H06 and H. indica LN2. Ascr#9 was most abundant in three nematode species. Compared with the sterile PBS, significantly more ascr#1, ascr#9 and ascr#10 were detected from S. carpocapsae All and H. indica LN2, but less ascr#5 and ascr#11 from S. carpocapsae All, ascr#1, ascr#5, ascr#11 and ascr#12 from H. bacteriophora H06, in the corresponding bacterial supernatant. It seems that the bacterial supernatants could regulate the ascaroside secretion by the three nematode species. These results will provide useful clues for selecting suitable ascarosides to induce the recovery, improve the yield, and enhance the dispersal of the IJs of these nematodes.

Small molecule signals mediate social behaviors in C. elegans

The last few decades have seen the structural and functional elucidation of small-molecule chemical signals called ascarosides in C. elegans. Ascarosides mediate several biological processes in worms, ranging from development, to behavior. These signals are modular in their design architecture, with their building blocks derived from metabolic pathways. Behavioral responses are not only concentration dependent, but also are influenced by the current physiological state of the animal. Cellular and circuit-level analyses suggest that these signals constitute a complex communication system, employing both synergistic molecular elements and sex-specific neuronal circuits governing the response. In this review, we discuss research from multiple laboratories, including our own, that detail how these chemical signals govern several different social behaviors in C. elegans. We propose that the ascaroside repertoire represents a link between diverse metabolic and neurobiological life-history traits and governs the survival of C. elegans in its natural environment.

Influence of symbiotic and non-symbiotic bacteria on pheromone production in Steinernema nematodes (Nematoda, Steinernematidae)

In this study, we assessed the effect of symbiotic (cognate and non-cognate) and non-symbiotic bacteria on ascaroside production of first-generation adults in two Steinernema spp.: S. carpocapsae All strain and S. feltiae SN strain. Each nematode species was reared under three bacterial scenarios: (1) cognate symbiotic, (2) non-cognate symbiotic strain and (3) non-cognate symbiotic species. Our results showed S. carpocapsae produced four quantifiable ascaroside molecules: asc-C5, asc-C6, asc-C7 and asc-C11, whereas in S. feltiae only three molecules were detected: asc-C5, asc-C7 and asc-C11. Bacterial conditions did not significantly affect the quantity of the secreted ascarosides in first-generation adults of S. carpocapsae However, in S. feltiae, Xenorhabdus nematophila All strain influenced the production of two ascaroside molecules: asc-C5 and asc-C11.

Chemical mating cues in C. elegans

In the natural environment it is vital that organisms are capable of locating mates to reproduce and, consequently, increase the diversity of their gene pool. Many species make use of audio and visual communication for mate location. However, the more ancient form of chemical communication is used by all forms of life, from bacteria to mammals. In the past decade, much information has been discovered regarding pheromones in the nematode Caenorhabditis elegans. In this review, chemical signals that govern mating behavior in C. elegans will be discussed, from the existence and identification of mating cues, to the neurons involved in the behavioral response. Specifically, mate attraction is dictated by specific glycosides and side chains of the dideoxysugar ascarylose, a class of molecules known as ascarosides. Intriguingly, modifications of the ascarosides can dictate different behaviors such as male attraction, hermaphrodite attraction, and dauer formation. In general, interactions between core sensory neurons such as ASK and sex-specific neurons like CEM are critical for detecting these small molecules. These data reveal the existence of a complex, synergistic, chemical mating cue system between males and hermaphrodites in C. elegans, thereby highlighting the importance of mate attraction in a primarily hermaphroditic population.

Ascaroside activity in Caenorhabditis elegans is highly dependent on chemical structure

The nematode Caenorhabditis elegans secretes ascarosides, structurally diverse derivatives of the 3,6-dideoxysugar ascarylose, and uses them in chemical communication. At high population densities, specific ascarosides, which are together known as the dauer pheromone, trigger entry into the stress-resistant dauer larval stage. In order to study the structure-activity relationships for the ascarosides, we synthesized a panel of ascarosides and tested them for dauer-inducing activity. This panel includes a number of natural ascarosides that were detected in crude pheromone extract, but as yet have no assigned function, as well as many unnatural ascaroside derivatives. Most of these ascarosides, some of which have significant structural similarity to the natural dauer pheromone components, have very little dauer-inducing activity. Our results provide a primer to ascaroside structure-activity relationships and suggest that slight modifications to ascaroside structure dramatically influence binding to the relevant G protein-coupled receptors that control dauer formation.