A Neurotoxic Insecticide Promotes Fungal Infection in Aedes aegypti Larvae by Altering the Bacterial Community.

Symbiotic bacteria have a significant impact on the formation of defensive mechanisms against fungal pathogens and insecticides. The microbiome of the mosquito Aedes aegypti has been well studied; however, there are no data on the influence of insecticides and pathogenic fungi on its structure. The fungus Metarhizium robertsii and a neurotoxic insecticide (avermectin complex) interact synergistically, and the colonization of larvae with hyphal bodies is observed after fungal and combined (conidia + avermectins) treatments. The changes in the bacterial communities (16S rRNA) of Ae. aegypti larvae under the influence of fungal infection, avermectin toxicosis, and their combination were studied. In addition, we studied the interactions between the fungus and the predominant cultivable bacteria in vitro and in vivo after the coinfection of the larvae. Avermectins increased the total bacterial load and diversity. The fungus decreased the diversity and insignificantly increased the bacterial load. Importantly, avermectins reduced the relative abundance of Microbacterium (Actinobacteria), which exhibited a strong antagonistic effect towards the fungus in in vitro and in vivo assays. The avermectin treatment led to an increased abundance of Chryseobacterium (Flavobacteria), which exerted a neutral effect on mycosis development. In addition, avermectin treatment led to an elevation of some subdominant bacteria (Pseudomonas) that interacted synergistically with the fungus. We suggest that avermectins change the bacterial community to favor the development of fungal infection.

[Phenotypic and genetic changes of entomopathogenic ascomycete Beauveria Bassiana under passaging through various hosts].

Phenotypic and genetic estimations of entomopathogenic ascomycete B.bassiana (strain Sar-31) after 6-passaging through four hosts were shown. Increasing of virulence, changes in morpho-cultural characteristics and variations in Inter Simple Sequence Repeats (ISSR) assay between initial and reisolated cultures were registered. Six passages of entomopathogenic ascomycete Beauveria bassiana (strain Sar-31) through four hosts (Galleria mellonella, Tenebrio molitor, Leptinotarsa decemlineata, Locusta migratoria) and following estimation of phenotypic and genetic differences of the initial strain and reisolated cultures were conducted. The passaging of strain through certain host led to increasing of virulence for both this host and other test-insects. Unidirectional changes of morpho-cultural characteristics: colonies pigmentation and relief strengthening, increasing of conidia production and lipolytic activity were registered in all passaged cultures. Genetic analysis with 6 ISSR markers revealed variations between initial and reisolated cultures in 3 markers. Taken together, the results of this study help us understand potential ways of fungi strains changes during epizootic process and possibilities of ISSR assay applying for investigation of pathogen transmission.

Analysis of mitochondrial DNA somatic mutations in OXYS and Wistar strain rats.

Rats of the OXYS strain are sensitive to oxidative stress and serve as a biological model of premature aging. We have compared spectra of somatic mutations in a control region of mtDNA from the liver of the OXYS rat strain and of Wistar rats as a control. The majority of nucleotide substitutions in the mutation spectra were represented by transitions: 94 and 97% in the OXYS and Wistar rats, respectively. It was shown that 40% of somatic mutations in the control region of mtDNA from Wistar rats were significantly consistent with the model of dislocation mutagenesis. No statistical support for this model was found for mutations in the control region of mtDNA from OXYS rats. The mutation frequency in the ETAS section was higher in the OXYS strain rats than in Wistar rats. These results suggest different mechanisms of mutagenesis in the two rat strains under study.