Abstract
The GI microbiota of abalone contains a highly complex bacterial assemblage playing an essential role in the overall health of these gastropods. The gut bacterial communities of abalone species characterized so far reveal considerable interspecific variability, likely resulting from bacterial interactions and constrained by the ecology of their abalone host species; however, they remain poorly investigated. Additionally, the extent to which structural changes in the microbiota entail functional shifts in metabolic pathways of bacterial communities remains unexplored. In order to address these questions, we characterized the gut microbiota of the northeast Pacific blue (Haliotis fulgens or HF) and yellow (Haliotis corrugata or HC) abalone by 16S rRNA gene pyrosequencing to shed light on: (i) their gut microbiota structure; (ii) how bacteria may interact among them; and (iii) predicted shifts in bacterial metabolic functions associated with the observed structural changes. Our findings revealed that Mycoplasma dominated the GI microbiome in both species. However, the structure of the bacterial communities differed significantly in spite of considerable intraspecific variation. This resulted from changes in predominant species composition in each GI microbiota, suggesting host-specific adaptation of bacterial lineages to these sympatric abalone. We hypothesize that the presence of exclusive OTUs in each microbiota may relate to host-specific differences in competitive pressure. Significant differences in bacterial diversity were found between species for the explored metabolic pathways despite their functional overlap. A more diverse array of bacteria contributed to each function in HC, whereas a single or much fewer OTUs were generally observed in HF. The structural and functional analyses allowed us to describe a significant taxonomic split and functional overlap between the microbiota of HF and HC abalone.
Highlights
The gastro-intestinal tract of metazoans may be considered a highly complex ecosystem inhabited by a large number of bacteria (Backhed, 2005)
Pyrosequencing yielded 451,095 raw 16S rRNA reads of which 239,125 met quality criteria and were non-chimeric, these were assigned to 1,508 operational taxonomic units (OTUs)
A number of these OTUs were removed from subsequent analyses, 1,066 because their read number was
Summary
The gastro-intestinal tract (or GI) of metazoans may be considered a highly complex ecosystem inhabited by a large number of bacteria (Backhed, 2005). Functional studies have revealed that the relationship between the gut microbiome and its host may be so close that bacteria may be directly involved in the maturation of the GI tract of the hosts species (Bates et al, 2006; Bry et al, 1996; Bano et al, 2007). Adult abalone are considered ecosystem engineers, as they graze macro and microalgae at species-specific depths, which maintains open habitat exploited by other benthic organisms (Crosson & Friedman, 2017; Cox, 1962). Several abalone species support valuable fisheries and aquaculture production in many countries around the world (Crosson & Friedman, 2017). The peninsula of Baja California harbors seven exploitable abalone species (Morales-Bojórquez, Muciño Díaz & Vélez-Barajas, 2008), two of which, the blue abalone Haliotis fulgens (HF, ) and the yellow abalone Haliotis corrugata (HC, ), sustain the high-valued fishery in the NW Mexican Pacific coast (MoralesBojórquez, Muciño Díaz & Vélez-Barajas, 2008; SAGARPA, 2009)
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