Toxicological effects of tire rubber-derived 6PPD-quinone, a species-specific toxicant, and dithiobisbenzanilide (DTBBA) in the marine rotifer Brachionus koreanus.

The ingredients of tire-rubber products include a complex range of chemicals additives, most of which are leached into surrounding water as unmeasured toxicants with unexplored ecotoxicological impacts. The present study summarizes the reported species-specific acute toxicity of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), the ozonation product of anti-oxidant 6PPD used in tire rubber. Also, chronic toxicity and oxidative response of 6PPD-Q and another tire-rubber derivative, 2',2'''-dithiobisbenzanilide (DTBBA), in rotifer Brachionus koreanus were investigated. Although 6PPD-Q has been reported to be highly toxic to several species of salmonids, only moderate chronic toxicity was observed in B. koreanus. In contrast, DTBBA significantly retarded the population growth and fecundity. The varying toxicity of 6PPD-Q and DTBBA was linked to the level of reactive oxygen species in which DTBBA exposure caused a significant concentration-dependent increase. Our results imply unanticipated risks to aquatic species posed by chemical additives in tire-rubber which may be considered emerging contaminants of toxicological concern.

Exploring the gut microbiota composition of Indian major carp, rohu (Labeo rohita), under diverse culture conditions.

Gut microbiota of freshwater carps are often investigated for their roles in nutrient absorption, enzyme activities and probiotic properties. However, little is known about core microbiota, assembly pattern and the environmental influence on the gut microbiota of the Indian major carp, rohu. The gut microbial composition of rohu reared in different culture conditions was analysed by 16S rRNA amplicon sequencing. There was variation on gut microbial diversity and composition. A significant negative correlation between dissolved oxygen content (DO) and alpha diversity was observed, thus signifying DO content as one of the key environmental factors that regulated the diversity of rohu gut microbial community. A significant positive correlation was observed between phosphate concentration and abundance of Actinobacteria in different culture conditions. Two phyla, Proteobacteria and Actinobacteria along with OTU750868 (Streptomyces) showed significant (p < 0.05) differences in their abundance among all culture conditions. The Non-metric multidimensional scaling ordination (NMDS) analysis using Bray-Curtis distances, showed the presence of unique gut microbiota in rohu compared to other herbivorous fish. Based on niche breadth, 3 OTUs were identified as core generalists, persistent across all the culture conditions whereas the specialists dominated in the rohu gut microbiota assembly. Co-occurrence network analysis revealed positive interaction within core members while mutual exclusion between core and non-core members. Predicted microbiota function revealed that different culture conditions affected the metabolic capacity of gut microbiota of rohu. The results overall indicated the significant effect of different rearing environments on gut microbiota structure, assembly and inferred community function of rohu which might be useful for effective manipulation of gut microbial communities of rohu to promote better health and growth under different husbandry settings.

Alteration of gut microbiota composition and function of Indian major carp, rohu (Labeo rohita) infected with Argulus siamensis.

Gut microbiome homeostasis is critical in preventing diseases. However, the effect of disease on gut microbiota assembly remains unclear. At present, there are no reports on the composition and functional analysis of intestinal microbiota of Indian major carp, rohu (L. rohita) infected with ectoparasite, Argulus. In this study, we analysed and compared the intestinal microbiota of healthy and Argulus-infected rohu by 16S rRNA amplicon sequencing. Argulus infection could significantly influence the diversity and richness of the gut microbiota. However, abundance of Actinobacteria and Patescibacteria were enriched significantly in Argulus-infected fish. Venn diagram revealed that there were many more unique genera in the infected group as compared to control fish. The genera, Stenotrophomonas and Pirellula were significantly increased in infected fish while the abundance of Reyranella was decreased. LEfSe analysis showed a significant enrichment in abundances of 11 taxa in healthy group and 17 taxa in infected group. Furthermore, genera Rubellimicrobium, Dielma, Hyphomicrobium, Reyranella, Streptomyces and Cloacibacterium performed the best in differentiating between both the groups. Predicted microbiota function by PICRUSt revealed that the gut microbiota of infected fish was mainly associated with enriched synthesis of chitinases, chitin binding proteins, osmoprotectant proteins and sulfatases enzymes. There was a positive association between the structural and functional composition of the gut microbiota. The results indicated that the Argulus infection could affect the intestinal microbiota composition and function of rohu.