Microbial ecology of intestinal tract of gilthead sea bream (Sparus aurata Linnaeus, 1758) from two coastal lagoons of Sardinia (Italy)

Abstract

1 - The bacterial flora of the digestive tract of aquatic organisms reflects various factors, such as the aqueous environment (temperature, salinity, etc.), seasonal variation, diet, fish species and anatomy of gastrointestinal section.
2 - In the present work, culturable bacteria isolated from intestinal samples of gilthead sea bream caught in two coastal lagoons of Sardinia, were quantified and identified in order to detect the effect of different habitats on the microbial ecology of fish gut.
3 - A total of 120 bacterial colonies coming from intestinal tracts of Sparus aurata specimens captured in the Tortoli (Eastern Sardinia: Lat 39°56’ 854’’N, Long 9°41’160’’E) and Porto Pino (Southern Sardinia: Lat 39°02’ 54’’N, Long 08°32’54’’E) lagoons during the winter season, were identified by means of amplified ribosomal DNA restriction analysis and 16S rRNA gene sequencing.
4 - The results showed no significant differences in the bacterial loads, while a diverse composition of microbial gut flora was detected between the two groups of gilthead sea bream. Indeed, intestinal microbiota from the Tortoli lagoon showed high genetic variation with a total of 13 different taxonomic bacterial groups identified as Pseudomonas spp. (33.3%), Sphingomonas paucimobilis (10.5%), Proteus spp. (8.8%), Chryseobacterium sp. B-G-R2A3 (5.3%), Arctic soil bacterium A1T3 (5.3%), Sphingobacterium spp. (5.3%), Psychrobacter spp. (3.5%), Psychrobacter maritimus (3.5%), Leucobacter spp. (3.5%), Yersinia bercovieri (3.5%), Aeromonas spp. (3.5%), Aeromonas molluscorum (1.7%), and Erwinia persicina (1.7%). On the other hand, 16S rRNA gene analyses of bacterial flora performed on the Porto Pino gut samples, revealed a lower variability when compared with those from Tortoli, since only 3 different taxonomic groups were distinguished and ascribed to Pseudomonas spp. (90%), Janthinobacterium spp. (8%) and Psychrobacter maritimus (2%).
5 - Our findings indicate that the aqueous habitat highly selects fish microbial gut flora which represents a peculiar ecosystem and a possible biomarker of environmental origin.