The Impact of Long-Term Hypoxia on the Antioxidant Defense System in the Siberian Frog Rana amurensis.

The Siberian frog Rana amurensis has a uniquely high tolerance to hypoxia among amphibians, as it is able to withstand several months underwater with almost no oxygen (0.2 mg/liter) vs. several days for other studied species. Since it was hypothesized that hypoxia actives the antioxidant defense system in hypoxia-tolerant animals, one would expect similar response in R. amurensis. Here, we studied the effect of hypoxia in the Siberian frog based on the transcriptomic data, activities of antioxidant enzyme, and content of low-molecular-weight antioxidants. Exposure to hypoxia upregulated expression of three relevant transcripts (catalase in the brain and two aldo-keto reductases in the liver). The activities of peroxidase in the blood and catalase in the liver were significantly increased, while the activity of glutathione S-transferase in the liver was reduced. The content of low-molecular-weight antioxidants (thiols and ascorbate) in the heart and liver was unaffected. In general, only a few components of the antioxidant defense system were affected by hypoxia, while most remained unchanged. Comparison to other hypoxia-tolerant species suggests species-specific adaptations to hypoxia-related ROS stress.

Fungus Metarhizium robertsii and neurotoxic insecticide affect gut immunity and microbiota in Colorado potato beetles.

Fungal infections and toxicoses caused by insecticides may alter microbial communities and immune responses in the insect gut. We investigated the effects of Metarhizium robertsii fungus and avermectins on the midgut physiology of Colorado potato beetle larvae. We analyzed changes in the bacterial community, immunity- and stress-related gene expression, reactive oxygen species (ROS) production, and detoxification enzyme activity in response to topical infection with the M. robertsii fungus, oral administration of avermectins, and a combination of the two treatments. Avermectin treatment led to a reduction in microbiota diversity and an enhancement in the abundance of enterobacteria, and these changes were followed by the downregulation of Stat and Hsp90, upregulation of transcription factors for the Toll and IMD pathways and activation of detoxification enzymes. Fungal infection also led to a decrease in microbiota diversity, although the changes in community structure were not significant, except for the enhancement of Serratia. Fungal infection decreased the production of ROS but did not affect the gene expression of the immune pathways. In the combined treatment, fungal infection inhibited the activation of detoxification enzymes and prevented the downregulation of the JAK-STAT pathway caused by avermectins. The results of this study suggest that fungal infection modulates physiological responses to avermectins and that fungal infection may increase avermectin toxicosis by blocking detoxification enzymes in the gut.

The effect of trematode infection on the markers of oxidative stress in the offspring of the freshwater snail Lymnaea stagnalis.

Most invertebrate species exhibit immunological responses that can inactivate and eliminate penetrating parasites. Such immune responses in particular involve the formation of potentially toxic reactive oxygen species (ROS). We explored the immune capabilities of the first-generation (F1) offspring of naturally infected freshwater snails, Lymnaea stagnalis, in response to infection by trematode cercariae under laboratory conditions. The rates of ROS formation and peroxidase activity in the hemolymph of the F1 offspring of L. stagnalis parents infected by an asexual stage of trematodes were significantly higher than in F1 offspring of uninfected parents. Compared to offspring from uninfected parents, the growth rate of F1 snails from infected parents was higher, but survival was lower. After infection of F1 snails by trematode cercariae of Echinoparyphium aconiatum under laboratory conditions, the rate of ROS formation and peroxidase activity in the hemolymph of F1 offspring of uninfected parents increased compared to control snails. This pattern persisted throughout the entire 3-week observation period. In contrast, the rate of ROS formation in the hemolymph of F1 snails from infected parents after experimental infection by E. aconiatum cercariae did not differ from controls, and peroxidase activity even decreased. Thus, trematode parthenitae infection of parents could alter the immune response of their offspring.

Vairimorpha ephestiae is a synonym of Vairimorpha necatrix (Opisthosporidia: Microsporidia) based on multilocus sequence analysis.

An isolate of the microsporidium Vairimorpha ephestiae (originally isolated from Ephestia kühniella) from collection of Prof. J. Weiser was propagated in a laboratory culture of Galleria mellonella. Only disporoblastic sporogony was observed and formation of octospores, characteristic of the genus Vairimorpha, never occurred. A partial nucleotide sequence of the small subunit rRNA gene (1247 bp) for this microsporidium showed 100% identity to the homologous sequences of Vairimorpha (Nosema) necatrix (Genbank accession # U11051 and # DQ996241), a microsporidium with a broad host range within the Lepidoptera. Sequence similarity of protein-coding genes (RPB1, HSP70 and actin) between V. ephestiae and V. necatrix was about 98-100%. The level of genetic polymorphism in the RPB1 locus between these two species was essentially the same as between isolates of V. necatrix. It is therefore concluded that V. ephestiae is in fact an isolate of V. necatrix and the former species should be synonymized with the latter. Though described later, V. necatrix has prevailing usage and its precedence over V. ephestiae is proposed to conserve stability and avoid confusion.