Detection of microplastics in zebrafish housing systems: Can microplastic background contamination affect the final results of microplastic-related toxicological tests?

Concentrations of microplastics (MPs) were determined in three commonly used zebrafish housing systems to see if their levels could affect the final results of laboratory microplastic-related toxicology tests. MPs have received notable attention in the last few years, and their toxicology tests have also come to the fore. Zebrafish (Danio rerio), kept in fish housing systems, are widely used as models for MPs studies. Most of these systems contain a significant number of parts made of different polymers. As usage and amortization can erode these parts, MPs might appear in the keeping water or the fish body, which may represent a background load and possibly influence the results of microplastic-related toxicological tests. To take representative water samples from systems, two in-situ filtration techniques, a newly developed peristaltic pump-, and a jet pump-driven method were applied. The collected MP particles were analyzed with a Fourier-transform infrared microscope (detection limit 50 µm), and their possible origin was also investigated. The newly developed technique was more sufficient for sampling as it had a higher MPs recovery, especially in the smaller size range. Polyester, polyethylene and polypropylene were the most frequently detected polymers in the examined fish housing systems, the highest detected concentration was 0.31±0.12 particles/liter (0.22±0.16 µg/liter). These values are negligible compared to the literature data reporting enormously high applied MPs concentrations (104 - 2.21 × 108 particles/liter) during toxicology tests. The results also show that some detected MPs did not originate from the systems, their origin was presumed to be external.

Novel members of bacterial community during a short-term chilled storage of common carp (Cyprinus carpio).

This work aimed to identify the key members of the bacterial community growing on common carp (Cyprinus carpio) fillets during chilled storage with next-generation sequencing (NGS) and cultivation-dependent methods. Carp fillets were stored for 96 h at 2 °C and 6 °C with and without a vacuum package, and an additional frozen-thawed storage experiment was set for 120 days. Community profiles of the initial and stored fish samples were determined by amplicon sequencing. Conventional microbial methods were used parallelly for the enumeration and cultivation of the dominant members of the microbial community. Cultivated bacteria were identified with 16S rRNA sequencing and the MALDI-TOF MS method. Based on our results, the vacuum package greatly affected the diversity and composition of the forming microbial community, while temperature influenced the cell counts and consequently the microbiological criteria for shelf-life of the examined raw fish product. Next-generation sequencing revealed novel members of the chilled flesh microbiota such as Vagococcus vulneris or Rouxiella chamberiensis in the vacuum-packed samples. With traditional cultivation, 161 bacterial strains were isolated and identified at the species level, but the identified bacteria overlapped with only 45% of the dominant operational taxonomic units (OTUs) revealed by NGS. Next-generation sequencing is a promising and highly reliable tool recommended to reach a higher resolution of the forming microbial community of stored fish products. Knowledge of the initial microbial community of the flesh enables further optimization and development of processing and storage technology.