Microbial community structure in a host-parasite system: the case of Prussian carp and its parasitic crustaceans.

AIMS: The aim of the study was to investigate the skin microbiota of Prussian carp infested by ectoparasites from the genera Argulus and Lernaea. METHODS AND RESULTS: Associated microbiota of skin of Prussian carp and ectoparasites were investigated by sequencing of the V3, V4 hypervariable regions of 16S rRNA using Illumina MiSeq sequencing platform. CONCLUSIONS: According to the Spearman rank correlation test, the increasing load of ulcerations of the skin of Prussian carp was weakly negatively correlated with reduction in the abundance of the following taxa: Acrobacter, bacteria C39 (Rhodocyclaceae), Rheinheimera, Comamonadaceae, Helicobacteraceae and Vogesella. In this study, the microbiota of ectoparasites from the genera Lernaea and Argulus were characterized for the first time. The microbiota associated with L. cyprinacea was significantly different from microbial communities of intact skin mucosa of both infested and uninfested fish and skin ulcers (ADONIS, P ≤ 0·05). The microbiota associated with parasitic crustaceans L. cyprinacea were dominated by unclassified bacteria from Comamonadaceae, Aeromonadaceae families and Vogesella. The dominant microbiota of A. foliaceus were represented by Flavobacterium, Corynebacterium and unclassified Comamonadaceae. SIGNIFICANCE AND IMPACT OF THE STUDY: Results from these studies indicate that ectoparasites have the potential to alter skin microbiota, which can play a possible role in the transmission of secondary bacterial infections in fish, caused by pathogenic bacteria.

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.

The Change in the Entomopathogenic Properties in Streptomycin Resistant Bacillus thuringiensis.

Streptomycin-resistant strains (StrR) of the entomopathogenic bacteria Bacillus thuringiensis ssp. galleriae (Btg) have been obtained. Assessment of growth rate of Btg 69-6 colonies revealed significant difference between the initial strain StrS sensitive to antibiotics and StrR. Decrease in susceptibility of instar IV larvae of Galleria mellonella to Btg 69-6 StrR by a factor of eight compared to Btg 69-6 StrS has also been recorded. In Btg 190 StrR, the insecticidal activity decreased by a factor of five. In StrR, the biochemical properties changed after acquisition of resistance compared to the initial strain.

[THE PROOF OF VERTICAL TRANSMISSION OF THE NUCLEOPOLYHEDROVIRUS IN MANY GENERATIONS OF THE GYPSY MOTH LYMANTRIA DISPAR L].

INTRODUCTION: Insect viruses can play an important role in population dynamics of their hosts. That is why the problem of permanent viral infection support among virus-positive insects is associated with one of the intriguing problems of general biology and virology. MATERIALS AND METHODS: Under laboratory conditions, the modeling of the vertical transmission of the nucleopolyhedrovirus (NPV) gypsy moth was implemented at relatively high level of mortality among insects of parental generation (60%). The diagnostics of the occult virus was executed by the PCR method among insects before their infection under laboratory conditions, as well as among insects that survived after inoculation. RESULTS: The NPV-caused mortality among insects that survived after infection in generations F1, F2, and F3 was 14 ± 4%, 10 ± 4%, and 5 ± 0.5%, respectively. In the following three generations NPV-induced mortality was not noticed. DISCUSSION: The level of the virus-positive individuals among the gypsy moth embryos in all occasions was higher than the NPV-induced mortality of insects. Thus, the given results show that the presence of virus among insect does not mean inevitable mortality of their hosts. Perhaps, the viral DNA can completely or partly lose its infectivity but may exist in the analyzed insect samples. CONCLUSIONS: The viral infection can be formed among progeny surviving after inoculation of insects. It can be actuated during three generations of the gypsy moth. The level of the virus-positive individuals among the gypsy moth embryos determined by the PCR method in daughter generations was higher than the NPV- induced mortality of insects.

[Demonstration of the remote effect of baculovirus vertical transmission, with gypsy moth Lymantria dispar L. (Lepidoptera, Lymantriidae) as an example].

It is demonstrated for the first time that viral infection can be formed in insects survived after infection of gypsy moth larvae by nucleopolyhedrovirus (NPV), and cause subsequent mortality of individuals during, at minimum, two generations (the period of observations). The vertical virus transmission is carried by both male and female insects survived after infection. It is shown by means of PCR that the level of virus carrying in gypsy moth embryos of generations F1 and F2 is higher than the number of insects killed by NPV.