Bacterial succession during curing process of a skate (Dipturus batis) and isolation of novel strains

Abstract

Aims: To study the succession of cultivated and uncultivated microbes during the traditional curing process of skate. Methods and Results: The microbial diversity was evaluated by sequencing 16Sr RNA clone libraries and cultivation in variety of media from skate samples taken periodically during a 9-day curing process. A pH shift was observed (pH 6·64-9·27) with increasing trimethylamine (2·6 up to 75·6 mg N per 100 g) and total volatile nitrogen (TVN) (from 58·5 to 705·8 mg N per 100 g) but with relatively slow bacterial growth. Uncured skate was dominated by Oceanisphaera and Pseudoalteromonas genera but was substituted after curing by Photobacterium and Aliivibrio in the flesh and Pseudomonas on the skin. Almost 50% of the clone library is derived from putative undiscovered species. Cultivation and enrichment strategies resulted in isolation of putatively new species belonging to the genera Idiomarina, Rheinheimera, Oceanisphaera, Providencia and Pseudomonas. The most abundant genera able to hydrolyse urea to ammonia were Oceanisphaera, Psychrobacter, Pseudoalteromonas and isolates within the Pseudomonas genus. Conclusions: The curing process of skate is controlled and achieved by a dynamic bacterial community where the key players belong to Oceanisphaera, Pseudoalteromonas, Photobacterium, Aliivibrio and Pseudomonas. Significance and Impact of the Study: For the first time, the bacterial population developments in the curing process of skate are presented and demonstrate a reservoir of many yet undiscovered bacterial species.

Sequence Variants in TAAR5 and Other Loci Affect Human Odor Perception and Naming

“…Our results are consistent with a role for TAAR5 in aversion to TMA in humans. Carriers of the TAAR5 variant rated the fish odor as less unpleasant and were less likely to describe it as fermented skate or shark, which contain high levels of TMA [33,35] and are generally considered to have a very foul odor. In contrast, carriers were more likely to use non-seafood-related descriptors with neutral or positive odor valence.…”

“…The lead missense variant at the locus is presented. S6) showed that carriers were less likely to use fermented fish descriptors such as ''fermented skate'' and ''shark'' (p = 4.1 3 10 À4 , OR = 0.51, 95% CI = 0.35, 0.74), which contain high levels of TMA and have a foul odor due to ammonia and TMA produced during fermentation [33][34][35]. Carriers were more likely to use descriptors that are generally not considered foul-smelling (i.e., have neutral or positive odor valence) and are not seafood-related, such as ''potatoes,'' ''ketchup,'' ''caramel,'' and ''rose'' (p = 3.1 3 10 À8 , OR = 2.17, 95% CI = 1.65, 2.85).…”

Exploring the Brine Microbiota of a Traditional Norwegian Fermented Fish Product (Rakfisk) from Six Different Producers during Two Consecutive Seasonal Productions

“…Compared to LAB, there are few studies reporting Gammaproteobacteria to be dominating in fermented food. This taxon has been found dominant in shellfish [18] and in cured skate [41]. However, several studies found Gammaproteobacteria as a non-dominant part of the bacteria in fermented food [42,43,44] or found that the domination of this taxon has been replaced by Firmicutes towards the end of the fermentation [15,45,46].…”

Changes in protein compositions and textural properties of the muscle of skate fermented at 10°C

“…While a much higher ammonia nitrogen content in fermented skate samples was observed than that of fresh skates. According to Reynisson et al [20] and Cho et al, [25] Genus Pseudomonas and Thiopseudomonas were a predominant bacterium in fermented skate sample. And those two genera have been reported that predominantly produces alkaline proteolytic enzymes, which catalyze the cleavage of peptide bonds in meat proteins.…”

“…[19] Unlike other fish species, skate retains high urea and trimethylamine N-oxide (TMAO) in their muscle tissue as organic osmolytes at relatively high concentrations urea at 292-369 mmol/kg wet mass and TMAO at 85-168 mmol/kg wet mass, which leads to a significant increase in pH values and formation of unique ammonia flavors by the action of microorganisms during the fermentation. [7] A bacterial succession during the curing process of a skate has been investigated by Reynisson et al [20] that the key players in skate samples during fermentation are organisms belonging to Oceanisphaera, Psychrobacter, Pseudoalteromonas genera and some species within the Pseudomonas genus. Both Oceanisphaera and Pseudoalteromonas had a strong urease activity and were present in high relative quantity in the beginning of the fermentation.…”