Both heat-shock and cold-shock influence trehalose metabolism in an entomopathogenic nematode

Entomopathogenic nematodes: Survival, virulence and immunity

As entomopathogenic nematodes (EPNs) are used as biological control agents, their survival and persistence are crucial to ensure success in application against insect pests. The survival of Heterorhabditis and Steinernema species is dependent on abiotic and biotic factors in the environment. Abiotic stress environments such as desiccation, temperature, and ultraviolet radiation (UV) severely impact their performance on field. EPNs produce and secrete effector molecules during the early stages of infection to interfere with the molecular mechanisms that control the insect innate immune function. Also, EPN effectors facilitate the subsequent release and spread of their symbiotic bacteria within the host. Hence, a comprehensive understanding of the underlying survival and virulence mechanisms enabling protection against environmental conditions and insect host immune responses is imperative to realistically enhance their performance on field. Thus, identifying key players regulating EPN survival, virulence and immunity could invariably contribute towards developing more robust, reliable solutions and application strategies including genetic tools and formulation technologies.

Stress tolerance in entomopathogenic nematodes: Engineering superior nematodes for precision agriculture

Entomopathogenic nematodes (EPNs) are soil-dwelling parasitic roundworms commonly used as biocontrol agents of insect pests in agriculture. EPN dauer juveniles locate and infect a host in which they will grow and multiply until resource depletion. During their free-living stage, EPNs face a series of internal and environmental stresses. Their ability to overcome these challenges is crucial to determine their infection success and survival. In this review, we provide a comprehensive overview of EPN response to stresses associated with starvation, low/elevated temperatures, desiccation, osmotic stress, hypoxia, and ultra-violet light. We further report EPN defense strategies to cope with biotic stressors such as viruses, bacteria, fungi, and predatory insects. By comparing the genetic and biochemical basis of these strategies to the nematode model Caenorhabditis elegans, we provide new avenues and targets to select and engineer precision nematodes adapted to specific field conditions.

Genistein Promotes Anti-Heat Stress and Antioxidant Effects via the Coordinated Regulation of IIS, HSP, MAPK, DR, and Mitochondrial Pathways in Caenorhabditis elegans

To determine the anti-heat stress and antioxidant effects of genistein and the underlying mechanisms, lipofuscin, reactive oxygen species (ROS), and survival under stress were first detected in Caenorhabditis elegans (C. elegans); then the localization and quantification of the fluorescent protein was determined by detecting the fluorescently labeled protein mutant strain; in addition, the aging-related mRNAs were detected by applying real-time fluorescent quantitative PCR in C. elegans. The results indicate that genistein substantially extended the lifespan of C. elegans under oxidative stress and heat conditions; and remarkably reduced the accumulation of lipofuscin in C. elegans under hydrogen peroxide (H₂O₂) and 35 °C stress conditions; in addition, it reduced the generation of ROS caused by H₂O₂ and upregulated the expression of daf-16, ctl-1, hsf-1, hsp-16.2, sip-1, sek-1, pmk-1, and eat-2, whereas it downregulated the expression of age-1 and daf-2 in C. elegans; similarly, it upregulated the expression of daf-16, sod-3, ctl-1, hsf-1, hsp-16.2, sip-1, sek-1, pmk-1, jnk-1 skn-1, and eat-2, whereas it downregulated the expression of age-1, daf-2, gst-4, and hsp-12.6 in C. elegans at 35 °C; moreover, it increased the accumulation of HSP-16.2 and SKN-1 proteins in nematodes under 35 °C and H₂O₂ conditions; however, it failed to prolong the survival time in the deleted mutant MQ130 nematodes under 35 °C and H₂O₂ conditions. These results suggest that genistein promote anti-heat stress and antioxidant effects in C. elegans via insulin/-insulin-like growth factor signaling (IIS), heat shock protein (HSP), mitogen-activated protein kinase (MAPK), dietary restriction (DR), and mitochondrial pathways.

Fruit Fly in a Challenging Environment: Impact of Short-Term Temperature Stress on the Survival, Development, Reproduction, and Trehalose Metabolism of Bactrocera dorsalis (Diptera: Tephritidae)

An understanding of physiological damage and population development caused by uncomfortable temperature plays an important role in pest control. In order to clarify the adaptability of different temperatures and physiological response mechanism of B. dorsalis, we focused on the adaptation ability of this pest to environmental stress from physiological and ecological viewpoints. In this study, we explored the relationship between population parameters and glucose, glycogen, trehalose, and trehalose-6-phosphate synthase responses to high and low temperatures. Compared with the control group, temperature stress delayed the development duration of all stages, and the survival rates and longevity decreased gradually as temperature decreased to 0 °C and increased to 36 °C. Furthermore, with low temperature decrease from 10 °C to 0 °C, the average fecundity per female increased at 10 °C but decreased later. Reproduction of the species was negatively affected during high-temperature stresses, reaching the lowest value at 36 °C. In addition to significantly affecting biological characteristics, temperature stress influenced physiological changes of B. dorsalis in cold and heat tolerance. When temperature deviated significantly from the norm, the levels of substances associated with temperature resistance were altered: glucose, trehalose, and TPS levels increased, but glycogen levels decreased. These results suggest that temperature stresses exert a detrimental effect on the populations' survival, but the metabolism of trehalose and glycogen may enhance the pest's temperature resistance.

Protective effect of the stressed supernatant from Lactococcus lactis subsp. lactis and its metabolic analysis

There are numerous factors restricting wide application of lactic acid bacteria (LAB) in dairy industry, causing urgent demands for novel bioprotectants. Protective effects and metabolites of Lactococcus lactis subsp. lactis (L. lactis) from ultraviolet (UV)-induced supernatant were investigated and the protective mechanism was explored. The strain viability of the group treated with the supernatant of continuous UV irradiation (V1) and the group with intermittent UV irradiation (V2) was 8.45 and 14.13 times of the control group, respectively. Further exploration on the protective of L. lactis supernatant, under different dose of UV treatment, showed it was dose-dependent. The condition for the supernatant with best protective effect was vertical distance 50.00 cm, horizontal distance 25.00 cm, intermittent UV irradiation (30 s interval 30 s) for 4.5 min (V2), which was chose for untargeted metabolite analysis. And that in V1 was for comparative study. There were 181 up-regulated metabolites in V1 and 161 up-regulated metabolites in V2, respectively. Most of the up-regulated metabolites were related to secondary metabolite synthesis, environmental microbial metabolism, antibiotic synthesis and amino acid biosynthesis. Notably, production of dithiothreitol (DTT) in V2 was 65.2-fold higher than that in the control group. Trehalose in ABC transporter pathway was also up-regulated in the metabolites induced by UV. Results indicated that L. lactis could adapt to the UV stress by adjusting metabolic pathways and producing special metabolites to protect itself. This research offers the basis for robust strain development and contributes to initial study on potential bioprotectant.

Rapid Adjustments in Thermal Tolerance and the Metabolome to Daily Environmental Changes - A Field Study on the Arctic Seed Bug Nysius groenlandicus

Laboratory investigations on terrestrial model-species, typically of temperate origin, have demonstrated that terrestrial ectotherms can cope with daily temperature variations through rapid hardening responses. However, few studies have investigated this ability and its physiological basis in the field. Especially in polar regions, where the temporal and spatial temperature variations can be extreme, are hardening responses expected to be important. Here, we examined diurnal adjustments in heat and cold tolerance in the Greenlandic seed bug Nysius groenlandicus by collecting individuals for thermal assessment at different time points within and across days. We found a significant correlation between observed heat or cold tolerance and the ambient microhabitat temperatures at the time of capture, indicating that N. groenlandicus continuously and within short time-windows respond physiologically to thermal changes and/or other environmental variables in their microhabitats. Secondly, we assessed underlying metabolomic fingerprints using GC-MS metabolomics in a subset of individuals collected during days with either low or high temperature variation. Concentrations of metabolites, including sugars, polyols, and free amino acids varied significantly with time of collection. For instance, we detected elevated sugar levels in animals caught at the lowest daily field temperatures. Polyol concentrations were lower in individuals collected in the morning and evening and higher at midday and afternoon, possibly reflecting changes in temperature. Additionally, changes in concentrations of metabolites associated with energetic metabolism were observed across collection times. Our findings suggest that in these extreme polar environments hardening responses are marked and likely play a crucial role for coping with microhabitat temperature variation on a daily scale, and that metabolite levels are actively altered on a daily basis.

Elevated Trehalose Levels in C. elegans daf-2 Mutants Increase Stress Resistance, Not Lifespan

The C. elegans insulin/IGF-1 (insulin-like growth factor 1) signaling mutant daf-2 recapitulates the dauer metabolic signature—a shift towards lipid and carbohydrate accumulation—which may be linked to its longevity and stress resistance phenotypes. Trehalose, a disaccharide of glucose, is highly upregulated in daf‑2 mutants and it has been linked to proteome stabilization and protection against heat, cold, desiccation, and hypoxia. Earlier studies suggested that elevated trehalose levels can explain up to 43% of the lifespan extension observed in daf-2 mutants. Here we demonstrate that trehalose accumulation is responsible for increased osmotolerance, and to some degree thermotolerance, rather than longevity in daf-2 mutants. This indicates that particular stress resistance phenotypes can be uncoupled from longevity.

Synchrotron-Radiation Vacuum-Ultraviolet Circular-Dichroism Spectroscopy for Characterizing the Structure of Saccharides

Circular-dichroism (CD) spectroscopy is a powerful tool for analyzing the structures of chiral molecules and biomolecules. The development of CD instruments using synchrotron radiation has greatly expanded the utility of this method by extending the spectra to the vacuum-ultraviolet (VUV) region below 190 nm and thereby yielding information that is unobtainable by conventional CD instruments. This technique is especially advantageous for monitoring the structure of saccharides that contain hydroxy and acetal groups with high-energy transitions in the VUV region. Combining VUVCD spectra with theoretical calculations provides new insight into the contributions of anomeric hydroxy groups and rotational isomers of hydroxymethyl groups to the dynamics, intramolecular hydrogen bonds, and hydration of saccharides in aqueous solution.

Infective larvae of Anisakis simplex (Nematoda) accumulate trehalose and glycogen in response to starvation and temperature stress

Anisakis simplex L3 larvae infect fish and other seafood species such as squid or octopi; therefore, humans consuming raw or undercooked fish may become accidental hosts for this parasite. These larvae are induced to enter hypometabolism by cold temperatures. It is assumed that sugars (in particular trehalose and glycogen) are instrumental for survival under environmental stress conditions. To elucidate the mechanisms of environmental stress response in A. simplex, we observed the effects of starvation and temperature on trehalose and glycogen content, the activity of enzymes metabolizing those sugars, and the relative expression of genes of trehalose and glycogen metabolic pathways. The L3 of A. simplex synthesize trehalose both in low (0°C) and high temperatures (45°C). The highest content of glycogen was observed at 45°C at 36 h of incubation. On the second day of incubation, tissue content of trehalose depended on the activity of the enzymes: TPS was more active at 45°C, and TPP was more active at 0°C. The changes in TPP activity were consistent with the transcript level changes of the TPP gene, and the trehalose level, while glycogen synthesis correlates with the expression of glycogen synthase gene at 45°C; this suggests that the synthesis of trehalose is more essential. These results show that trehalose plays a key role in providing energy during the thermotolerance and starvation processes through the molecular and biochemical regulation of trehalose and glycogen metabolism.

The cold tolerance of the northern root-knot nematode, Meloidogyne hapla

The northern root-knot nematode, Meloidogyne hapla, is one of the most important nematode pathogens occurring in cold regions. It is a sedentary, biotrophic parasites of plants and overwinter in the soil or in diseased roots. This study showed that the cold tolerance for the second-stage juveniles (J2) of M. hapla was moderate with the 50% survival temperature (S₅₀) of -2.22°C and the fatal temperature was -6°C when cooling at 0.5°C min^-1. Cryoprotective dehydration significantly enhance cold tolerance of M. hapla J2 with the lowest S₅₀ of -3.28°C after held being at -1°C for 6 h. Moreover, cold shock and cold acclimation had significant effects on the freezing survival of M. hapla J2. The lethal temperature of eggs was -18°C. Therefore, the cold tolerance of M. hapla is sufficiently favorable to withstand winters in cold temperature environments.

Enzyme characteristics of pathogen-specific trehalose-6-phosphate phosphatases

Owing to the key role of trehalose in pathogenic organisms, there has recently been growing interest in trehalose metabolism for therapeutic purposes. Trehalose-6-phosphate phosphatase (TPP) is a pivotal enzyme in the most prominent biosynthesis pathway (OtsAB). Here, we compare the enzyme characteristics of recombinant TPPs from five important nematode and bacterial pathogens, including three novel members of this protein family. Analysis of the kinetics of trehalose-6-phosphate hydrolysis reveals that all five enzymes display a burst-like kinetic behaviour which is characterised by a decrease of the enzymatic rate after the pre-steady state. The observed super-stoichiometric burst amplitudes can be explained by multiple global conformational changes in members of this enzyme family during substrate processing. In the search for specific TPP inhibitors, the trapping of the complex conformational transitions in TPPs during the catalytic cycle may present a worthwhile strategy to explore.

Expression of Genes Encoding the Enzymes for Glycogen and Trehalose Metabolism in L3 and L4 Larvae of Anisakis simplex

Trehalose and glycogen metabolism plays an important role in supporting life processes in many nematodes, including Anisakis simplex. Nematodes, cosmopolitan helminths parasitizing sea mammals and humans, cause a disease known as anisakiasis. The aim of this study was to investigate the expression of genes encoding the enzymes involved in the metabolism of trehalose and glycogen—trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), glycogen synthase (GS), and glycogen phosphorylase (GP)—in stage L3 and stage L4 larvae of A. simplex. The expression of mRNA all four genes, tps, tpp, gs, and gp, was examined by real-time polymerase chain reaction. The A. simplex ribosomal gene (18S) was used as a reference gene. Enzymatic activity was determined. The expression of trehalose enzyme genes was higher in L3 than in L4 larvae, but an inverse relationship was noted for the expression of gs and gp genes.

Freeze-thaw Caenorhabditis elegans freeze-thaw stress response is regulated by the insulin/IGF-1 receptor daf-2

BACKGROUND

Adaption to cold temperatures, especially those below freezing, is essential for animal survival in cold environments. Freezing is also used for many medical, scientific, and industrial purposes. Natural freezing survival in animals has been extensively studied. However, the underlying mechanisms remain unclear. Previous studies demonstrated that animals survive in extremely cold weather by avoiding freezing or controlling the rate of ice-crystal formation in their bodies, which indicates that freezing survival is a passive thermodynamic process.

RESULTS

Here, we showed that genetic programming actively promotes freezing survival in Caenorhabditis elegans. We found that daf-2, an insulin/IGF-1 receptor homologue, and loss-of-function enhanced survival during freeze-thaw stress, which required the transcription factor daf-16/FOXO and age-independent target genes. In particular, the freeze-thaw resistance of daf-2(rf) is highly allele-specific and has no correlation with lifespan, dauer formation, or hypoxia stress resistance.

CONCLUSIONS

Our results reveal a new function for daf-2 signaling, and, most importantly, demonstrate that genetic programming contributes to freezing survival.

Infective Juveniles of the Entomopathogenic Nematode, Steinernema feltiae Produce Cryoprotectants in Response to Freezing and Cold Acclimation

Steinernema feltiae is a moderately freeze-tolerant entomopathogenic nematode which survives intracellular freezing. We have detected by gas chromatography that infective juveniles of S. feltiae produce cryoprotectants in response to cold acclimation and to freezing. Since the survival of this nematode varies with temperature, we analyzed their cryoprotectant profiles under different acclimation and freezing regimes. The principal cryoprotectants detected were trehalose and glycerol with glucose being the minor component. The amount of cryoprotectants varied with the temperature and duration of exposure. Trehalose was accumulated in higher concentrations when nematodes were acclimated at 5°C for two weeks whereas glycerol level decreased from that of the non-acclimated controls. Nematodes were seeded with a small ice crystal and held at -1°C, a regime that does not produce freezing of the nematodes but their bodies lose water to the surrounding ice (cryoprotective dehydration). This increased the levels of both trehalose and glycerol, with glycerol reaching a higher concentration than trehalose. Nematodes frozen at -3°C, a regime that produces freezing of the nematodes and results in intracellular ice formation, had elevated glycerol levels while trehalose levels did not change. Steinernema feltiae thus has two strategies of cryoprotectant accumulation: one is an acclimation response to low temperature when the body fluids are in a cooled or supercooled state and the infective juveniles produce trehalose before freezing. During this process a portion of the glycerol is converted to trehalose. The second strategy is a rapid response to freezing which induces the production of glycerol but trehalose levels do not change. These low molecular weight compounds are surmised to act as cryoprotectants for this species and to play an important role in its freezing tolerance.

Divergent thermal specialisation of two South African entomopathogenic nematodes

Thermal physiology of entomopathogenic nematodes (EPN) is a critical aspect of field performance and fitness. Thermal limits for survival and activity, and the ability of these limits to adjust (i.e., show phenotypic flexibility) depending on recent thermal history, are generally poorly established, especially for non-model nematode species. Here we report the acute thermal limits for survival, and the thermal acclimation-related plasticity thereof for two key endemic South African EPN species, Steinernema yirgalemense and Heterorhabditis zealandica. Results including LT50 indicate S. yirgalemense (LT50 = 40.8 ± 0.3 °C) has greater high temperature tolerance than H. zealandica (LT50 = 36.7 ± 0.2 °C), but S. yirgalemense (LT50 = -2.4 ± 0 °C) has poorer low temperature tolerance in comparison to H. zealandica (LT50 = -9.7 ± 0.3 °C), suggesting these two EPN species occupy divergent thermal niches to one another. Acclimation had both negative and positive effects on temperature stress survival of both species, although the overall variation meant that many of these effects were non-significant. There was no indication of a consistent loss of plasticity with improved basal thermal tolerance for either species at upper lethal temperatures. At lower temperatures measured for H. zealandica, the 5 °C acclimation lowered survival until below -12.5 °C, where after it increased survival. Such results indicate that the thermal niche breadth of EPN species can differ significantly depending on recent thermal conditions, and should be characterized across a broad range of species to understand the evolution of thermal limits to performance and survival in this group.

Sex differences in carbohydrate metabolism are linked to gene expression in Caenorhabditis elegans

The male and the hermaphrodite forms of the nematode Caenorhabditis elegans (C. elegans) differ markedly in anatomy, nervous system and behavior at adulthood. Using the male mutants fog-2, him-5, and him-8, we compared body proportions and composition, and aspects of carbohydrate metabolism and gene expression between the C. elegans sexes in three adult stages. In all experiments, both sexes were grown on the same plate and separated using flow cytometry. The fat to fat-free mass ratio and the body volume-adjusted fat mass is similar between the sexes, although the body size is more than 50% smaller in adult males than in age-matched hermaphrodites. The volume-adjusted total RNA content is approximately 2-fold lower in males. Biochemical and NMR-based analyses reveal higher trehalose levels and much lower glucose levels in males than in hermaphrodites. The resulting trehalose-to-glucose ratio is 5.4-fold higher in males. These sex differences are reflected in gene expression data because the genes encoding key enzymes of the glycolysis and trehalose synthesis pathways are more highly expressed in males than in hermaphrodites. Notably, expression of the phosphofructokinase gene (C50F4.2) is 29-fold higher in males. Comparative analysis of gene expression data identifies 285 male-specific and 160 hermaphrodite-specific genes. These include transcription factor and C-type lectin-encoding genes. More than 35% of all C-type lectin genes are more highly expressed in males. The expression of many C-type lectin genes differs by a factor of >100 between the sexes. In conclusion, we found sex differences in carbohydrate metabolism that are linked to gene expression and identified certain lectin genes that are differentially expressed by the C. elegans sexes.

DAF-16 and Δ9 desaturase genes promote cold tolerance in long-lived Caenorhabditis elegans age-1 mutants

In Caenorhabditis elegans, mutants of the conserved insulin/IGF-1 signalling (IIS) pathway are long-lived and stress resistant due to the altered expression of DAF-16 target genes such as those involved in cellular defence and metabolism. The three Δ⁹ desaturase genes, fat-5, fat-6 and fat-7, are included amongst these DAF-16 targets, and it is well established that Δ⁹ desaturase enzymes play an important role in survival at low temperatures. However, no assessment of cold tolerance has previously been reported for IIS mutants. We demonstrate that long-lived age-1(hx546) mutants are remarkably resilient to low temperature stress relative to wild type worms, and that this is dependent upon daf-16. We also show that cold tolerance following direct transfer to low temperatures is increased in wild type worms during the facultative, daf-16 dependent, dauer stage. Although the cold tolerant phenotype of age-1(hx546) mutants is predominantly due to the Δ⁹ desaturase genes, additional transcriptional targets of DAF-16 are also involved. Surprisingly, survival of wild type adults following a rapid temperature decline is not dependent upon functional daf-16, and cellular distributions of a DAF-16::GFP fusion protein indicate that DAF-16 is not activated during low temperature stress. This suggests that cold-induced physiological defences are not specifically regulated by the IIS pathway and DAF-16, but expression of DAF-16 target genes in IIS mutants and dauers is sufficient to promote cross tolerance to low temperatures in addition to other forms of stress.

The oatmeal nematode Panagrellus redivivus survives moderately low temperatures by freezing tolerance and cryoprotective dehydration

The cold tolerance abilities of only a few nematode species have been determined. This study shows that the oatmeal nematode, Panagrellus redivivus, has modest cold tolerance with a 50% survival temperature (S (50)) of -2.5°C after cooling at 0.5°C min(-1) and freezing for 1 h. It can survive low temperatures by freezing tolerance and cryoprotective dehydration; although freezing tolerance appears to be the dominant strategy. Freezing survival is enhanced by low temperature acclimation (7 days at 5°C), with the S (50) being lowered by a small but significant amount (0.42°C). There is no cold shock or rapid cold hardening response under the conditions tested. Cryoprotective dehydration enhances the ability to survive freezing (the S (50) is lowered by 0.55°C, compared to the control, after 4 h freezing at -1°C) and this effect is in addition to that produced by acclimation. Breeding from survivors of a freezing stress did not enhance the ability to survive freezing. The cold tolerance abilities of this nematode are modest, but sufficient to enable it to survive in the cold temperate environments it inhabits.

Trehalose extends longevity in the nematode Caenorhabditis elegans

Trehalose is a disaccharide of glucose found in diverse organisms and is suggested to act as a stress protectant against heat, cold, desiccation, anoxia, and oxidation. Here, we demonstrate that treatment of Caenorhabditis elegans with trehalose starting from the young-adult stage extended the mean life span by over 30% without any side effects. Surprisingly, trehalose treatment starting even from the old-adult stage shortly thereafter retarded the age-associated decline in survivorship and extended the remaining life span by 60%. Demographic analyses of age-specific mortality rates revealed that trehalose extended the life span by lowering age-independent vulnerability. Moreover, trehalose increased the reproductive span and retarded the age-associated decrease in pharyngeal-pumping rate and the accumulation of lipofuscin autofluorescence. Trehalose also enhanced thermotolerance and reduced polyglutamine aggregation. These results suggest that trehalose suppressed aging by counteracting internal or external stresses that disrupt protein homeostasis. On the other hand, the life span-extending effect of trehalose was abolished in long-lived insulin/IGF-1-like receptor (daf-2) mutants. RNA interference-mediated inactivation of the trehalose-biosynthesis genes trehalose-6-phosphate synthase-1 (tps-1) and tps-2, which are known to be up-regulated in daf-2 mutants, decreased the daf-2 life span. These findings indicate that a reduction in insulin/IGF-1-like signaling extends life span, at least in part, through the aging-suppressor function of trehalose. Trehalose may be a lead compound for potential nutraceutical intervention of the aging process.

Cold tolerance in sealworm (Pseudoterranova decipiens) due to heat-shock adaptations

Third-stage larvae ofPseudoterranova decipienscommonly infect whitefish such as cod, and the parasite can be transferred to humans through lightly prepared (sushi) meals. Because little is known about the nematode's cold tolerance capacity, we examined the nematode's ability to supercool, and whether or not cold acclimation could induce physiological changes that might increase its ability to tolerate freezing conditions. Even if third-stagePseudoterranova decipienslarvae have some supercooling ability, they show no potential for freezing avoidance because they are not able to withstand inoculative freezing. Still, they have the ability to survive freezing at high subzero temperatures, something which suggests that these nematodes have a moderate freeze tolerance. We also show that acclimation to high temperatures triggers trehalose accumulation to an even greater extent than cold acclimation. Trehalose is a potential cryoprotectant which has been shown to play a vital role in the freeze tolerance of nematodes. We suggest that the trehalose accumulation observed for the cold acclimation is a general response to thermal stress, and that the nematode's moderate freeze tolerance may be acquired through adaptation to heat rather than coldness.

Discovering genes associated with dormancy in the monogonont rotifer Brachionus plicatilis

BACKGROUND

Microscopic monogonont rotifers, including the euryhaline species Brachionus plicatilis, are typically found in water bodies where environmental factors restrict population growth to short periods lasting days or months. The survival of the population is ensured via the production of resting eggs that show a remarkable tolerance to unfavorable conditions and remain viable for decades. The aim of this study was to generate Expressed Sequence Tags (ESTs) for molecular characterisation of processes associated with the formation of resting eggs, their survival during dormancy and hatching.

RESULTS

Four normalized and four subtractive libraries were constructed to provide a resource for rotifer transcriptomics associated with resting-egg formation, storage and hatching. A total of 47,926 sequences were assembled into 18,000 putative transcripts and analyzed using both Blast and GO annotation. About 28-55% (depending on the library) of the clones produced significant matches against the Swissprot and Trembl databases. Genes known to be associated with desiccation tolerance during dormancy in other organisms were identified in the EST libraries. These included genes associated with antioxidant activity, low molecular weight heat shock proteins and Late Embryonic Abundant (LEA) proteins. Real-time PCR confirmed that LEA transcripts, small heat-shock proteins and some antioxidant genes were upregulated in resting eggs, therefore suggesting that desiccation tolerance is a characteristic feature of resting eggs even though they do not necessarily fully desiccate during dormancy. The role of trehalose in resting-egg formation and survival remains unclear since there was no significant difference between resting-egg producing females and amictic females in the expression of the tps-1 gene. In view of the absence of vitellogenin transcripts, matches to lipoprotein lipase proteins suggest that, similar to the situation in dipterans, these proteins may serve as the yolk proteins in rotifers.

CONCLUSION

The 47,926 ESTs expand significantly the current sequence resource of B. plicatilis. It describes, for the first time, genes putatively associated with resting eggs and will serve as a database for future global expression experiments, particularly for the further identification of dormancy related genes.

Genomics of reproduction in nematodes: prospects for parasite intervention?

Understanding reproductive processes in parasitic nematodes has the potential to lead to the informed design of new anthelmintics and control strategies. Little is known, however, about the molecular mechanisms underlying sex determination, gametogenesis and reproductive physiology for most parasitic nematodes. Together with comparative analyses of data for the free-living nematode Caenorhabditis elegans, molecular investigations are beginning to provide insights into the processes involved in reproduction and development in parasitic nematodes. Here, we review recent developments, focusing on technological aspects and on molecules associated with sex-specific differences in adult nematodes.

Characterisation of the fluorescence from freshwater, planktonic bacteria

Amino acid-like fluorescence has been used as an indicator of biological activity in wastewater effluent and in natural waters, and can be detected using fluorescence spectroscopy. Little or no work has been able to state conclusively that these so called 'amino acid-like' fluorophores are associated with proteins present as a result of bacterial activity. This work aims to ascertain whether bacteria are one possible cause of these 'amino acid-like' peaks observed in natural waters. In addition, fluorescence derived solely from one bacterial source was determined as a function of the growth time and temperature. The bacterium Pseudomonas aeruginosa was isolated from the urban River Tame, Birmingham, UK, and planktonic bacteria were grown in sterile, sealed glass jars, in 100 ml growth media. Bacteria were grown at 11, 25 and 37 degrees C, over a maximum of 10 days. A 3D Excitation-Emission Matrix (EEM) plot was generated from fluorescence analysis of the samples. Both tryptophan and tyrosine-like fluorescence, resembling that observed in natural and waste waters, was observed in these samples, indicating that observed fluorescence signals from aquatic systems in the literature were of biotic origin. Significant differences in fluorescence signals were obtained from planktonic cells grown at different temperatures. At 25 and 37 degrees C, cells were found to produce predominantly tryptophan-like fluorescence, with some tyrosine-like fluorescence also detected. A further unknown fluorophore was also detected (emission wavelength of approximately 460 nm, with three excitation centres at 225, 260 and 390 nm), likely to be a bacterially produced metabolite. At 11 degrees C, a more environmentally realistic temperature in temperate environments, quantitative and qualitative differences were observed in fluorescence signals when compared with the higher temperatures, indicating that laboratory observations conducted at higher temperatures may not be easily used to interpret environmental processes.

GENETIC VARIATION AND RELATIONSHIPS BETWEEN ISOLATES AND SPECIES OF THE ENTOMOPATHOGENIC NEMATODE GENUS HETERORHABDITIS DECIPHERED THROUGH ISOZYME PROFILES

We studied variation in isozyme patterns of 8 metabolic enzymes in 5 species of Heterorhabditis (H. bacteriophora, H. indica, H. marelata, H. megidis, and H. zealandica) comprising 18 isolates. Isozyme banding patterns of all the 8 enzymes were species specific; however, 3 enzymes, i.e., arginine kinase, fumarate hydratase, and malate dehydrogenase, displayed distinct patterns among all the 18 isolates. Phylogenetic analysis of the isozyme patterns produced dendrograms depicting a high degree of genetic variation among Heterorhabditis species, with the average pairwise distance of 0.2000. Trees constructed using different phylogenetic methods showed a relatively close genetic relationship between H. megidis and H. zealandica and between H. bacteriophora and H. indica. Also, H. bacteriophora HP88 was the most distant species from H. megidis (UK isolate), H. marelatus (Oregon isolate), and H. zealandica (X1 isolate) with pairwise distance of 0.1957, 0.2228, and 0.2120, respectively. Phylogenetic analysis also revealed genetic variation among H. bacteriophora isolates with the average pairwise distance of 0.1507. GPS2 and GPS3 were the most closely related isolates with the average distance of only 0.0870, followed by GPS1 and GPS2 with average distance of 0.1087. In contrast, KMD19 and HP88, OH25, and HP88, and OH25 and Acows isolates were the most divergent populations with a pairwise distance of 0.2011 and 37 character differences. Pairwise distance analysis also revealed that genetic divergence among populations of H. bacteriophora is relatively independent of geographic distance. Overall, these results demonstrate strong subspecies structuring in H. bacteriophora.