Relative diversity of bacterial 16S rRNA gene clones associated with <i>Nitocra spinipes</i> in antibiotics and control treatments.

<p>Unc., Uncultured; nd, 16S rRNA sequence not detected; Treatments: ciprofloxacin (Cipr), Sulfomethoxazole (Sulf), trimethoprim (Trim); Controls: synthetic seawater (SS), acetone (Ac), dimethylsulfoxid (DMSO). Percentages are rounded to the nearest whole number and the corresponding number of clones per library is given in brackets.</p

Survival and development of antibiotic-treated and control groups of <i>Nitocra spinipes</i>.

<p>(A) Survivorship, %; (B) percentage of copepodites (%Copepodites); and (C) copepod developmental index (DI). All data are shown as median and range observed at the termination of experiments, i.e., day 13 for ciprofloxacin (Cipro) and sulfamethoxazole (Sulf), and day 11 for trimethoprim (Trim) treatments, whereas statistical comparisons are based on the Box Cox transformed data; * (p<0.05) and *** (p<0.001) denote significant differences from the respective controls.</p

Bacterial diversity indices (<i>H_B</i> and <i>V</i>) based on clone library analysis.

<p>Treatments: ciprofloxacin (Cipr); Sulfomethoxazole (Sulf); trimethoprim (Trim); Controls: synthetic seawater (SS), acetone (Ac), dimethylsulfoxid (DMSO).</p

Unrooted 16S rRNA gene tree based on maximum likelihood analyses of bacteria associated with <i>Nitocra spinipes</i>.

<p>Treatments: ciprofloxacin (orange), sulfomethoxazole (blue), trimethoprim (red); Controls: SS (grey), acetone (purple) and DMSO (green). Reference sequences are in black. Sequences are presented with their GenBank accession numbers followed by identity descriptions. Number of 16S rRNA gene sequences identified in each clone library is indicated in brackets following the clone number. Identical sequences found within a clone library were not included in the tree. One thousand bootstrapped replicate resampled datasets were analyzed. Bootstrap values are indicated as percentage and not shown if below 50%.</p

Bacteria-Mediated Effects of Antibiotics on <i>Daphnia</i> Nutrition

In polluted environments, contaminant effects may be manifested via both direct toxicity to the host and changes in its microbiota, affecting bacteria–host interactions. In this context, particularly relevant is exposure to antibiotics released into environment. We examined effects of the antibiotic trimethoprim on microbiota of Daphnia magna and concomitant changes in the host feeding. In daphnids exposed to 0.25 mg L^–1 trimethoprim for 24 h, the microbiota was strongly affected, with (1) up to 21-fold decrease in 16S rRNA gene abundance and (2) a shift from balanced communities dominated by <i>Curvibacter</i>, <i>Aquabacterium,</i> and <i>Limnohabitans</i> in controls to significantly lower diversity under dominance of <i>Pelomonas</i> in the exposed animals. Moreover, decreased feeding and digestion was observed in the animals exposed to 0.25–2 mg L^–1 trimethoprim for 48 h and then fed ¹⁴C-labeled algae. Whereas the proportion of intact algal cells in the guts increased with increased trimethoprim concentration, ingestion and incorporation rates as well as digestion and incorporation efficiencies decreased significantly. Thus, antibiotics may impact nontarget species via changes in their microbiota leading to compromised nutrition and, ultimately, growth. These bacteria-mediated effects in nontarget organisms may not be unique for antibiotics, but also relevant for environmental pollutants of various nature

Multi-level toxicity assessment of engineered cellulose nanofibrils in <i>Daphnia magna</i>

<p>Cellulose nanofibril (CNF)-based materials are increasingly used in industrial and commercial applications. However, the impacts of CNF on aquatic life are poorly understood, and there are concerns regarding their potential toxicity. Using a combination of standard ecotoxicological tests and feeding experiments, we assessed the effects of CNF exposure (0.206–20.6 mg/L) on the feeding (food uptake and gut residence time) and life-history traits (growth and reproduction) in the cladoceran <i>Daphnia magna.</i> No mortality was observed in a 48 h acute exposure at 2060 mg/L. Moreover, a 21-day exposure at low food and moderate CNF levels induced a stimulatory effect on growth, likely driven by increased filtration efficiency, and, possibly, partial assimilation of the CNF by the animals. However, at low food levels and the highest CNF concentrations, growth and reproduction were negatively affected. These responses were linked to caloric restriction caused by dilution of the food source, but not an obstruction of the alimentary canal. Finally, no apparent translocation of CNF past the alimentary canal was detected. We conclude that CNF displays a low toxic potential to filter-feeding organisms and the expected environmental risks are low.</p