Biology subjects

Riiser, E. S.

Publications and source records attributed to Riiser, E. S..

3 recordsLinked to original sources

bioRxiv2019

Metagenomic shotgun analyses reveal complex patterns of intra- and interspecific variation in the intestinal microbiomes of codfishes

The relative importance of host-specific selection or environmental factors in determining the composition of the intestinal microbiome in wild vertebrates remains poorly understood. Here, we use metagenomic shotgun sequencing of individual specimens to compare the intra- and interspecific variation of intestinal microbiome communities in two ecotypes (NEAC and NCC) of Atlantic cod (Gadus morhua) - that have distinct behavior and habitats- and three Gadidae species that occupy a range of ecological niches. Interestingly, we find significantly diverged microbiomes amongst the two Atlantic cod ecotypes. Interspecific patterns of variation are more variable, with significantly diverged communities for most species comparisons, apart from the comparison between coastal cod (NCC) and Norway pout (Trisopterus esmarkii), whose community compositions are not significantly diverged. The absence of consistent species-specific microbiomes suggests that external environmental factors, such as temperature, diet or a combination there-off comprise major drivers of the intestinal community composition of codfishes. ImportanceThe composition of the intestinal microbial community associated with teleost fish is influenced by a diversity of factors, ranging from internal factors (such as host-specific selection) to external factors (such as niche occupation). These factors are often difficult to separate, as differences in niche occupation (e.g. diet, temperature or salinity) may correlate with distinct evolutionary trajectories. Here, we investigate four gadoid species with contrasting levels of evolutionary separation and niche occupation. Using metagenomic shotgun sequencing, we observe distinct microbiomes amongst two Atlantic cod (Gadus morhua) ecotypes (NEAC and NCC) with distinct behavior and habitats. In contrast, interspecific patterns of variation are more variable. For instance, we do not observe interspecific differentiation between the microbiomes of coastal cod (NCC) and Norway pout (Trisopterus esmarkii) whose lineages have evolutionary separated over 20 million years ago. The observed pattern of microbiome variation in these gadoid species is therefore most parsimoniously explained by differences in niche occupation.

microbiology↗

bioRxiv2019

Switching on the light: using metagenomic shotgun sequencing to characterize the intestinal microbiome of Atlantic cod

The biological roles of the intestinal microbiome and how it is impacted by environmental factors are yet to be determined in wild marine fish species. Atlantic cod (Gadus morhua) is an ecologically important species with a wide-spread distribution in the North Atlantic Ocean. 16S rRNA-based amplicon analyses found no geographical differentiation between the intestinal microbiome of Atlantic cod from different locations. Nevertheless, it is unclear if this lack of differentiation results from an insufficient resolution of this method to resolve fine-scaled biological complexity. Here, we take advantage of the increased resolution provided by metagenomic shotgun sequencing to investigate the intestinal microbiome of 19 adult Atlantic cod individuals from two coastal populations in Norway - located 470 km apart. Our results show that the intestinal microbiome is dominated by the Vibrionales order, consisting of varying abundances of Photobacterium, Aliivibrio and Vibrio species. Moreover, resolving the species community to unprecedented resolution, we identify two abundant species, P. iliopiscarium and P. kishitanii, which comprise over 50% of the classified reads. Interestingly, genomic data shows that the intestinal P. kishitanii strains have functionally intact lux genes, and its high abundance suggests that fish intestines form an important part of its ecological niche. These observations support a hypothesis that bioluminescence plays an ecological role in the marine food web. Despite our improved taxonomical resolution, we identify no geographical differences in bacterial community structure, indicating that the intestinal microbiome of these coastal cod is colonized by a limited number of closely related bacterial species with a broad geographical distribution that are well suited to thrive in this host-associated environment.

microbiology↗

bioRxiv2017

A single Vibrionales 16S rRNA oligotype dominates the intestinal microbiome in two geographically separated Atlantic cod populations

BackgroundHost-microbe interactions are particularly intriguing in Atlantic cod (Gadus morhua), as it lacks the MHC II complex involved in presentation of extracellular pathogens. Nonetheless, little is known about the diversity of its microbiome in natural populations. Here, we use 16S rRNA high-throughput sequencing to investigate the microbial community composition in gut content and mucosa of 22 adult individuals from two coastal populations in Norway, located 470 km apart.\n\nResultsWe identify a core microbiome of 23 OTUs (97% sequence similarity) in all individuals that comprises 93% of the total number of reads. The most abundant orders are classified as Vibrionales, Fusobacteriales, Clostridiales and Bacteroidales. While mucosal samples show significantly lower diversity than gut content samples, no differences in OTU community composition are observed between the two populations. The differential abundance of oligotypes within two common OTUs does reveal limited spatial segregation. Remarkably, the most abundant OTU consists of a single oligotype (order Vibrionales, genus Photobacterium) that represents nearly 50% of the reads in both locations.\n\nConclusionsOur results show that the intestinal bacterial community of two geographically separated coastal populations of Atlantic cod is dominated by a limited number of highly abundant 16S rRNA oligotypes shared by all specimens examined. The ubiquity of these oligotypes suggests that the northern coastal Atlantic cod gut microbiome is colonized by a limited number of species with excellent dispersal capabilities that are well suited to thrive in their host environment.

microbiology↗