Abstract
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.
Highlights
Water plays a vital role in the structural and functional stability of macromolecules and maintains the integrity of lipid membranes in biological systems [1]
We have examined S. feltiae for potential cryoprotectants following low-temperature acclimation and freezing regimes that result in cryoprotective dehydration or intracellular freezing [7]
Glycerol and glucose were detected by gas chromatography in the infective juveniles of S. feltiae
Summary
Water plays a vital role in the structural and functional stability of macromolecules and maintains the integrity of lipid membranes in biological systems [1]. Some nematodes are anhydrobiotic (survive without water); such as Aphelenchus avenae [3], Anguina tritici [4], Caenorhabditis elegans dauers [5] and Ditylenchus dipsaci [6], and some are freeze tolerant; such as Steinernema feltiae [7] and Panagrolaimus davidi [8] Most of these nematodes produce low molecular weight compounds in response to dehydration or freezing stress which act as cryoprotectants or anhydroprotectants [9,10,11]. Cryoprotectants are compounds that protect the organism from chilling and freezing injury and thereby enhances its cold tolerance [12] These include sugars such as trehalose, glucose, fructose, and polyhydric alcohols such as glycerol, sorbitol, myo-inositol, ethylene glycol, ribitol, erythritol and inositol [13]. There is no report on the synthesis of cryoprotectants in nematodes in response to freezing, as has been reported in some freezing tolerant earthworms [23]
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