Microbial Production of the Off-Flavor Geosmin in Tilapia Production in Brazilian Water Reservoirs: Importance of Bacteria in the Intestine and Other Fish-Associated Environments

Abstract

AimTo determine major sources of microbially produced geosmin in the commercially important aquaculture fish species tilapia.Methods and ResultsAbundance and composition of geosmin-producing bacteria in water and fish biosphere (intestine, digesta, and fins) of Nile tilapia (Oreachromis niloticus) raised in net cages in Brazilian freshwater farms were examined. By combining qPCR of the geosmin synthase geoA gene and 16S rRNA gene amplicon sequencing to identify potential geosmin-producing organisms, we observed that the proportion and composition of geosmin producers appeared to be rather similar in the water, digesta, intestinal mucous, and on skin, making up about 0.1–0.2% of the total bacterial densities. A high proportion of Cyanobacteria and other putative geosmin producers affiliated to the Actinomycetales were identified in the intestinal mucous layer. The main uptake site for geosmin in fish is traditionally assumed to be through the gill surface, but the present results suggest that uptake by the intestinal tract may represent a major source of geosmin uptake in fish.ConclusionThe high abundance of geosmin-producing bacteria in the intestinal mucous layer and digesta may indicate that the digestive system in fish is an important, but hitherto overlooked, source of geosmin and likely other off-flavors in fish.Significance and Impact of Study Tainting of fish by microbially produced off-flavors spoils fish quality and lowers consumer preferences for aquaculture-produced freshwater fish. Our results highlight the potential for the application of probiotic microorganisms for management of the intestinal microflora to improve the fish quality.HIGHLIGHTSOff-flavor producing bacteria are widely abundant in aquaculture.Off-flavor producers found on skin surface of fish.Off-flavor producing bacteria accumulate in the digestive system.Off-flavor producers might release significant amounts of off-flavor during lysis in the gut.Off-flavor uptake through the digestive system might be quantitatively significant.

The Impact of Sampling Season and Catching Site (Wild and Aquaculture) on Gut Microbiota Composition and Diversity of Nile Tilapia (Oreochromis niloticus)

“…At the genus level, the gut microbiota was dominated by Cetobacterium , Clostridium_sensu_stricto and Clostridium_XI , which was different from other studies. Lukassen et al [ 56 ] showed Cetobacterium as one of the predominant genera from the intestinal digesta of tilapia from a Brazilian reservoir. The observed discrepancies in microbiota composition may be due to several factors, including rearing environmental conditions, diet composition and genetic lineage.…”

Effects of the interaction between nutrient concentration and DIN:SRP ratio on geosmin production by freshwater biofilms

“…), they usually have a terrestrial origin or are present in sediments and foodstuffs. And while they can also be related to some geosmin episodes in aquatic systems, cyanobacteria are still considered the main geosmin producers in freshwater ecosystems (Lukassen et al, 2019;Olsen et al, 2016). The majority of these geosmin-producing cyanobacteria are benthic or epiphytic (70%), while the rest are planktonic (Jüttner and Watson, 2007).…”

The Role of Micronutrients and Toxic Metals in the Management of Epidemics in Cambodia

“…The immunonutrient could be zinc and the single cell microbe could act like a probiotic and physically block Streptomyces or other producers of geosmin and MIB from being adsorbed into fish. Lukasse et al [181] documented that geosmin mainly enters fish via their guts and proposed that probiotics in fish feeds should block geosmin bioaccumulation. Many probiotic treatments are used in aquaculture to change the microbial communities in animal guts to break down antimetabolites like phytase and to improve immunity [182].…”