Impact of Sublethal Concentrations of Nitrite on Goldfish (Carassius auratus) Microbiomes

Effect of ectoparasite Ichthyophthirius multifiliis on the histopathology and gill and gut microbiota of goldfish (Carassius auratus)

Introduction

The ectoparasite Ichthyophthirius multifiliis, is the pathogen of white spot disease in freshwater fish, which parasitizes on gills, fins, and skins of fish, causing tissue damage and death of host. However, whether it influences gill and gut microbiota is still unknow.

Methods

In this study, H&E staining was used to show the gill and gut histopathological characteristics of I. multifiliis-infected and uninfected goldfish (Carassius auratus). Meanwhile, 16S rRNA gene amplicon sequencing was conducted to analyze the difference of gill and gut microbiota between I. multifiliis-infected and uninfected goldfish.

Results

Histopathological examination revealed that I. multifiliis has induced significant damage to the gills of goldfish, characterized by lamellae fusion, cell hyperplasia, cell hyperaemia, inflammatory infiltration, necrosis and desquamation. 16S rRNA gene sequencing result showed that alpha and beta diversity of gill microbiota was significantly reduced in the I. multifiliis-infected group, while no significant changes were observed in gut microbiota. Genus Candidatus Megaira exhibited the highest relative abundance in the I. multifiliis-infected group. Meanwhile, the abundance of opportunistic pathogens Aeromonas and Achromobacter were increased in the intestines of I. multifiliis-infected goldfish.

Discussion

The increased presence of Candidatus Megaira may originate from within the cells of I. multifiliis. The increase of opportunistic pathogens Aeromonas and Achromobacter may pose a threat to the health of goldfish. In summary, this study laid a foundation for further research on the interaction between I. multifiliis and host microbiota.

Divergent bacterial landscapes: unraveling geographically driven microbiomes in Atlantic cod

Establishing microbiome signatures is now recognized as a critical step toward identifying genetic and environmental factors shaping animal-associated microbiomes and informing the health status of a given host. In the present work, we prospectively collected 63 blood samples of the Atlantic cod population of the Southern Gulf of Saint Lawrence (GSL) and characterized their 16S rRNA circulating microbiome signature. Our results revealed that the blood microbiome signature was dominated at the phylum level by Proteobacteria, Bacteroidetes, Acidobacteria and Actinobacteria, a typical signature for fish populations inhabiting the GSL and other marine ecosystems. At the genus level, however, we identified two distinct cod groups. While the microbiome signature of the first group was dominated by Pseudoalteromonas, a genus we previously found in the microbiome signature of Greenland and Atlantic halibut populations of the GSL, the second group had a microbiome signature dominated by Nitrobacter and Sediminibacterium (approximately 75% of the circulating microbiome). Cods harboring a Nitrobacter/Sediminibacterium-rich microbiome signature were localized in the most southern part of the GSL, just along the northern coast of Cape Breton Island. Atlantic cod microbiome signatures did not correlate with the weight, length, relative condition, depth, temperature, sex, and salinity, as previously observed in the halibut populations. Our study provides, for the first time, a unique snapshot of the circulating microbiome signature of Atlantic cod populations and the potential existence of dysbiotic signatures associated with the geographical distribution of the population, probably linked with the presence of nitrite in the environment.