The dark European honey bee Apis mellifera mellifera L. is the native subspecies in Lithuania. Region-specific conditions, such as cold winters, variable spring weather and wintering on honeydew ho...

Background With the rapid development of nanotechnology, more and more nanoproducts are being released into the environment where they may both pose ecological risks and be toxic to living organisms. The ecotoxicological impact of quantum dots (QDs), a class of nanoparticles (NPs), on aquatic organisms is becoming an emerging issue, this due to their nano-specific properties, to the physico-chemical transformation in the environment and to the possible release of toxic metals from their structure such as Cd. Methods In this work, (i) spectroscopic measurements of commercially available Cd-based QDs (CdSe/ZnS-COOH) were made at various pH values (5.0 and 7.0) to study their interactions (at a concentration of 4 nm) with various strains of Gram-positive and Gram-negative gut bacteria after short-term exposure and (ii) the antibacterial efficacy of QDs and Cd2+ (at a concentration 0.09–3.56 mM) against gut bacteria isolated from wild freshwater Salmo trutta fry was studied at different temperatures (15 °C and 25 °C) and pH values (5.0 and 7.0) by applying a well-established disc diffusion assay. Results Twenty-six gut bacterial isolates from wild Salmo trutta fry were identified as Aeromonas spp., A. popoffii, A. salmonicida, A. sobria, Carnobacterium maltaromaticum, Buttiauxella sp., Listeria sp., Microbacterium sp., Shewanella putrefaciens and Serratia sp. Cd-based (CdSe/ZnS-COOH) QDs at a concentration of 4 nm were found to be stable in aqueous media (with pH 7.0) or starting to form aggregates (at pH 5.0), thus, apparently, did not release heavy metals (HMs) into the media over 48 h in conditions of light or dark and did not show antibacterial efficacy on the gut bacteria isolated from wild Salmo trutta fry after short-term (9 h and 48 h) incubations. Cd2+ was found to produce significant dose-dependent toxic effects on bacterial growth, and the size of the inhibition zones on some of the tested strains significantly correlated with temperature. The most sensitive and the most resistant to Cd2+ were the Gram-positive bacteria, for which the minimum inhibitory concentration (MIC) values of Cd2+ were 0.09–0.27 mM and 3.11–3.29 mM respectively and varied significantly between the tested temperatures (15 °C and 25 °C). The MIC values of Cd2+ for the Gram-negative bacteria (18 out of 22 strains) ranged from 0.44 to 0.71 mM and did not differ significantly between the tested temperatures. Among the selected Gram-positive and Gram-negative strains, those with the higher sensitivity towards Cd2+ also revealed relatively stronger signals of QDs photoluminescence (PL) when transferred after incubation into fresh medium without QDs. In addition, the formation of endogenous metalloporphyrins observed spectroscopically in some bacterial strains indicates certain differences in metabolic activity that may play a protective role against potential oxidative damage.

Insect guts are colonized by different species of microorganisms, most of which are benign or beneficial to their host. However, little is known about how the microbial gut communities vary among different host species. In this study, using 16S metagenomic sequencing, we compared the indigenous gut microbiota in adult of two solitary cavity-nesting Hymenoptera, a bee (Megachile centuncularis) and a wasp (Ancistrocerus antilope). The richness of operational taxonomic units (OTUs) was estimated in the guts of freshly eclosed imagoes, which had had no contact with the environment. We obtained 123,237 total reads from M. centuncularis and 125,942 from A. antilope. Three phyla, Proteobacteria, Actinobacteria, and Firmicutes, were dominant. Nine OTUs in M. centuncularis and five OTUs in A. antilope represented ≥1% of all reads. Wolbachia, a well-known insect endosymbiont, dominated in both species, representing 27% of reads in M. centuncularis and 48% in A. antilope. The most abundant in the gut of M. centuncularis was Arthrobacter (38%), while the dominants in the gut of A. antilope were Microbacterium (18%) and Erwinia (14%). These differences in microbiota richness and composition between bee and wasp are likely to be caused by their disparate trophic specialization.

The application of alizarin dye for the marking of fish is a widely adopted practice in post-stocking monitoring programmes. Nevertheless, concerns regarding the welfare implications of alizarin staining persist. The present study conclusively demonstrated that ARS dye exerts instantaneous and protracted deleterious effects on the physiological parameters (gill ventilation frequency, homeostasis in the gut microbiota, total number of erythrocytes and leukocytes) and body fitness (total length, weight and Fulton’s condition factor) of S. trutta fry. The validity of the dye-marked fish stocking effectiveness studies is called into question by these findings.