Purpose: The objective of this study was to provide a baseline description of culture independent and culture dependent microflora associated with two commercially important and widely consumed fish; yellowfin and albacore tuna. A specific goal was the analysis of the anatomical incidence of histamine-producing bacterial species and co-occurring microbial community structure and diversity.
Methods: DNA was purified from gills, skin, and anal vent swabs of freshly caught yellowfin (n=3) and albacore (n=6) tuna. 16S rRNA gene amplicons were sequenced using the Illumina MiSeq V3 platform. Data were analyzed using the QIIME pipeline (Quantitative Insights Into Microbial Ecology). Enriched swab samples [48h at 25°C, Marine Broth (MB)+1% histidine] were analyzed for the presence of the histidine decarboxylase (hdc) gene using qPCR.
Results: Principal component analyses of 16S rRNA gene amplicons showed distinct taxonomic profiles for the three sampling locations: gills, skin, and anal vent. The most abundant class/order/family in all sampling locations was Gammaproteobacteria/Vibrionales/Vibrionaceae. Photobacterium was the most abundant genus (0.9%) observed in anal vent whereas only 0.1% of the OTUs from gills and skin were Photobacterium spp. Other important histamine-producing bacteria (HPB) such as Citrobacter, Enterobacter, and Morganella spp. comprised a small fraction of the observed OTUs at all sampling locations or 2-9 x 106, 0.1-5.8 x 106, and 0.4-1.1 x 106%, respectively. The hdc gene was only detected in anal vent enrichment samples from three albacore and two yellowfin tuna.
Significance: These data will be used to refine mitigation and detection strategies to control Photobacterium spp. and other histamine-producing bacteria in tuna and other fish species associated with SFP.