A multiscale study of the effects of a diet containing CdSe/ZnS-COOH quantum dots on Salmo trutta fario L.: Potential feed-related nanotoxicity

Quantum dots (QDs) receive widespread attention in industrial and biomedical fields, but the risks posed by the use of nanoparticles to aquatic organisms and the associated toxicological effects are still not well understood. In this study, effects of the 7-day dietary exposure of Salmo trutta fario L. juveniles to CdSe/ZnS-COOH QDs were evaluated at molecular, cellular, physiological and whole-organism levels. Fish feeding with QDs-contaminated feed resulted in an increased somatic index of the liver, a genotoxic effect on peripheral blood erythrocytes, altered enzyme activity and decreased MDA level. Furthermore, Cd levels in the gills and liver tissues of the exposed fish were found to be significantly higher than in those of the control fish. Alpha diversity indexes of the gut microbiota of the QDs-exposed S. trutta fario L. individuals exhibited a decreasing trend. The principal coordinate analysis (PCoA) showed that the gut microbiota of the control fish was significantly different from that of the fish exposed to QDs (p < 0.05). Additionally, the linear discriminant analysis (LDA) performed using an effect size (LEfSe) algorithm unveiled 19 significant taxonomic differences at different taxonomic levels between the control group and the QDs-exposed group. In the QDs-exposed group, the relative abundance of the genus Citrobacter (Proteobacteria phylum) in the gut microbiota was found to be significantly increased whereas that of the genus Mycoplasma (Tenericutes phylum) significantly decreased compared to the control group. In summary, QDs-contaminated diet affects the gut microbiota of fish by significantly changing the relative abundance of some taxa, potentially leading to dysbiosis. This, together with morphophysiological, cytogenetic and biochemical changes, poses a risk to fish health.

Gut Microbiome of Wild Baltic Salmon (Salmo salar L.) Parr

Gut microbiota of wild Baltic salmon (a sub-population of Atlantic salmon Salmo salar L.) parr was first analyzed using microbial profiling of the 16S rRNA gene (V3-V4 region) and high taxonomic richness was revealed. At the phylum level, the gut microbiota was dominated by Firmicutes, Actinobacteria, and Proteobacteria, the most numerous of which were Firmicutes. The phylum Tenericutes (mainly assigned to Mycoplasmataceae), which is common both in wild North- and East- Atlantic salmon parr, was not detected in Baltic salmon parr. Across all samples, unique amplicon sequence variants (ASVs) belonging to the unclassified Bacilli, Actinomycetales, and Rhizobiales were identified as the major taxa. Fifteen ASVs at the family level were found in all gut samples of Baltic salmon parr, the majority of which were Mycobacteriaceae, Cryptosporangiaceae, Microbacteriaceae, and Planctomycetaceae. At the genus level, Mycobacterium, Clostridium sensu stricto, and Hyphomicrobium were dominant but at low levels in all gut samples. Our study has revealed that the gut microbial community of wild Baltic salmon parr differs from those of wild North- and East-Atlantic salmon parr. This can be due to biogeographical differences or host-selective pressures, as the Baltic salmon population is believed to have split from the Atlantic salmon population in the Ancylian period.

Interactions of semiconductor Cd-based quantum dots and Cd2+ with gut bacteria isolated from wild Salmo trutta fry

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.

Impact evaluation of marking Salmo trutta with Alizarin Red S produced by different manufacturers

Fish otolith marking with the alizarin dye is a commonly used tool in sustainable fishery management. However, the reported effects of this dye on fish health are rather controversial and are possibly linked to differences in the composition of different brands of Alizarin red S (ARS). Laboratory experiments designed to elucidate effects of different concentrations of theoretically the same ARS as indicated by the CAS (Chemical Abstracts Service) number on fish at different development stages were carried out. The acute toxicity of ARS to Salmo trutta was found to be concentration- and fish developmental stage-dependant. Our study results showed that S. trutta sensitivity to ARS varies depending on its developmental stages as follows: fry (50-days after hatching) > alevins (30-days after hatching) > alevins (1-day after hatching). One of the tested ARS brands (purchased from VWR International LLC (Matsonford Road, USA)) was found to be several times more toxic to fish than another (purchased from Sigma-Aldrich (St. Louis, USA)), although according to the certificates of analysis, the tested substances were identical. Survival and growth of the S. trutta fry, which was marked with different ARS brands and stocked in the same natural stream, was investigated for two consecutive years. The results obtained indicate remarkable differences (p < 0.05) in the effects produced by the tested ARS brands, thus confirming our laboratory findings. The performed elemental analysis of the tested ARS dyes revealed significant differences in chemical impurities that these dyes contain. This study has, for the first time, expressed concern about the probable long-term impact of some ARS brands on the marked fish and their potential to bias the results of the studies dealing with ARS-marked fish.

Erwinia typographi sp. nov., isolated from bark beetle (Ips typographus) gut

Gram-negative-staining bacteria that were resistant to monoterpene myrcene (7-methyl-3-methylene-1.6-octadiene, C10H16, at concentrations of up to 10 µl ml−1 in TSB) were isolated from the gut contents of adult bark beetles Ips typographus (Coleoptera, Scolytidae). The beetles were collected from the bark of Norway spruce (Picea abies) in Lithuania. Bark beetles feed on conifers, which produce myrcene among many other defensive compounds. It has been suggested that the micro-organisms present within the beetles’ guts could be involved in their resistance towards this plant defensive compound. The most resistant bacterial strains were isolated and characterized by phenotypic assays as well as fatty acid analysis, 16S rRNA gene sequencing, multilocus sequence analyses (MLSA) based on the rpoB, atpD and infB genes and DNA–DNA hybridization. Biochemical characterization indicated that the bacteria belonged to the family Enterobacteriaceae . Phylogenetic analyses of the 16S rRNA gene sequences and MLSA of the novel strains revealed that they belonged to the genus Erwinia , but represented a novel species. The dominant cellular fatty acids were C16 : 0 and C17 : 0 cyclo. The DNA G+C content was 49.1 mol%. The results obtained in this study indicated that these bacteria from the bark beetle gut represented a novel species, for which the name Erwinia typographi sp. nov. is proposed, with the type strain DSM 22678T ( = Y1T = LMG 25347T).