Photobacterium predominate the microbial communities of muscle of European plaice (Pleuronectes platessa) caught in the Norwegian sea independent of skin and gills microbiota, fishing season, and storage conditions

Isolation of an endophytic yeast for improving the antibacterial activity of water chestnut Jiaosu: Focus on variation of microbial communities

Recent years have seen an increase in the development of functional Jiaosu products, including eco-friendly Jiaosu and antimicrobial healthcare fermentation products. As a result, research on the antibacterial activity of Jiaosu has attracted attention. In the present study, the endophytic yeast WCF016, which exhibits antibacterial activity against Escherichia coli and Staphylococcus aureus, was isolated from the peel of water chestnut and identified as Candida sake via morphological and phylogenetic analyses based on 26S rDNA D1/D2 region sequencing. Water chestnut Jiaosu with or without WCF016 inoculation exhibited similar flavor and physicochemical properties. However, inoculation significantly enhanced the antibacterial activity of water chestnut Jiaosu, especially in group D (inoculate of both fruit and vegetable enzyme starter and WCF016), which showed the largest diameter in its inhibition zone for both E. coli and S. aureus, reaching 25 ± 0 mm and 24 ± 1.0 mm. Moreover, inoculation with WCF016 influenced the abundance of the microbial community, especially Lactiplantibacillus and Zygoascus, which reached 51.76 % and 24.46 %, respectively, in group B (inoculated WCF016), thereby improving the antibacterial activity and flavor quality of the water chestnut Jiaosu. Notably, final pH, total sugar, and all organic acids effectively promoted fungal diversity and exhibited a positive correlation with most of the fungal genera. These results indicate that conditions conducive to the formation of organic acid-producing microbes and the synthesis of organic acids promote the antibacterial activity of Jiaosu.

Spatio-temporal plasticity of gill microbiota in estuarine fish

Coastal marine and estuarine systems are subject to enormous endogenous and exogenous pressures, particularly climate change, while at the same time being highly productive sources and nurseries for fish populations. Interactions between host and microbiome are increasingly recognized for their importance for fish health, with growing evidence indicating that increasing environmental pressures impact host resilience and favor the raise of opportunistic bacterial taxa. The microbial composition of the gill mucus reflects environmental conditions and represents an entry route for pathogens into the fish body. High-throughput sequencing of prokaryotic populations from 250 samples of two fish species with highly different habitat preferences, as well as seasonal and spatial distributions in the Elbe estuary system, allowed us to describe the variation of the microbiota along a salinity gradient and under fluctuating environmental conditions. The analysis of estuarine fish core microbiota in relation to variable bacterial components indicated dysbiotic states under sustained hypoxia and high nutrient loads largely driven by increased prevalence of facultatively aerobic (Acinetobacter) and anaerobic heterotrophs (Shewanella, Aeromonas). By correlating bacterial abundances with environmental and physiological parameters in a co-occurrence network approach, we describe plasticity in microbiota composition, identify potential biomarkers for fish health monitoring and reconstruct movement patterns of the fish. Our results can help to shape future minimal-invasive and cost-effective monitoring programs, and identify factors that need to be controlled in the estuary to promote fish and stock health.

Effect of harvesting season and location on the microbial quality and community composition of the edible sea urchin (Echinus esculentus) gonads

Despite the crucial role of microbial community composition in the quality and stability of seafood, little emphasis has been given to the microbiota profile of sea urchin gonads. This study investigates the microbial quality and community composition of sea urchin gonads (Echinus esculentus) as a function of harvesting season (autumn, winter, spring, and summer) and location (one site proximal to urban activity areas while the other is located in open water close to the coastline). Significant season-dependent variations were found in psychrotrophic and aerobic plate counts, with higher counts in summer, followed by autumn, spring, and winter. H2S-producing bacteria and Pseudomonas spp. counts were unaffected by harvesting season or location. Sea urchin gonad microbial composition proved resilient and dynamic, primarily shaped by seasonal variations, and minimally influenced by location. Winter and spring samples exhibited higher diversity than autumn and summer. Key genera like Pseudomonas, Psychromonas, Vibrio, Chryseobacterium, Shewanella, and Photobacterium varied seasonally. Pseudomonas, Vibrio, and Photobacterium are crucial in assessing microbial quality and safety due to their roles as specific spoilage organisms (SSOs) and, in some cases, human pathogens. Though relative abundances differed slightly between locations, harvesting location did not notably impact microbial community shaping in gonads. However, the results suggest that harvesting locations near areas with urban activity may lead to contamination with specific bacterial species, possibly due to water quality variations. These findings emphasize the importance of considering seasonality when evaluating sea urchin gonad microbial quality. Identifying key genera enhances insights into potential SSOs and human pathogens, enhancing food safety considerations in the consumption of raw or lightly processed sea urchin gonads and guiding the development of preservation methods to extend shelf life.

Uncovering the microbiome landscape in sashimi delicacies

It is widely believed that a significant portion of the gut microbiota, which play crucial roles in overall health and disease, originates from the food we consume. Sashimi is a type of popular raw seafood cuisine. Its microbiome, however, remained to be thoroughly explored. The objective of this study is to explore the microbiome composition in sashimi at the time when it is served and ready to be eaten. Specifically, our tasks include investigating the diversity and characteristics of microbial profiles in sashimi with respect to the fish types. We utilized the Sanger-sequencing based DNA barcoding technology for fish species authentication and next-generation sequencing for sashimi microbiome profiling. We investigated the microbiome profiles of amberjack, cobia, salmon, tuna and tilapia sashimi, which were all identified using the MT-CO1 DNA sequences regardless of their menu offering names. Chao1 and Shannon indexes, as well as Bray-Curtis dissimilarity index were used to evaluate the alpha and beta diversities of sashimi microbiome. We successfully validated our previous observation that tilapia sashimi has a significantly higher proportions of Pseudomonas compared to other fish sashimi, using independent samples (P = 0.0010). Salmon sashimi exhibited a notably higher Chao1 index in its microbiome in contrast to other fish species (P = 0.0031), indicating a richer and more diverse microbial ecosystem. Non-Metric Multidimensional Scaling (NMDS) based on Bray-Curtis dissimilarity index revealed distinct clusters of microbiome profiles with respect to fish types. Microbiome similarity was notably observed between amberjack and tuna, as well as cobia and salmon. The relationship of microbiome similarity can be depicted as a tree which resembles partly the phylogenetic tree of host species, emphasizing the close relationship between host evolution and microbial composition. Moreover, salmon exhibited a pronounced relative abundance of the Photobacterium genus, significantly surpassing tuna (P = 0.0079), observed consistently across various restaurant sources. In conclusion, microbiome composition of Pseudomonas is significantly higher in tilapia sashimi than in other fish sashimi. Salmon sashimi has the highest diversity of microbiome among all fish sashimi that we analyzed. The level of Photobacterium is significantly higher in salmon than in tuna across all the restaurants we surveyed. These findings provide critical insights into the intricate relationship between the host evolution and the microbial composition. These discoveries deepen our understanding of sashimi microbiota, facilitating our decision in selecting raw seafood.

Effects of collagen-based coating with chitosan and ε-polylysine on sensory, texture, and biochemical changes of refrigerated Nemipterus virgatus fillets

In order to evaluate the effects of chitosan, ε-polylysine, and collagen on the preservation properties of refrigerated Nemipterus virgatus, samples were tested with different treatments for 10 days, namely chitosan, ε-polylysine and collagen (CH + ε-PL + CA), chitosan and ε-polylysine (CH + ε-PL), chitosan and collagen (CH + CA), ε-polylysine and collagen (ε-PL + CA), and the uncoated sample (CK). The results demonstrated that the bio-coating exhibited better preservation effects. The CH + ε-PL + CA, CH + ε-PL, CH + CA, ε-PL + CA treatments could significantly inhibit bacterial growth and retard the increase of total volatile base nitrogen (TVB-N), 2-thiobarbituric acid (TBA), K-value, and total viable counts (TVC) in N. virgatus fillets. The pH of all samples decreased and reached its lowest value on day 6, then increased significantly at the end of the experiment (p < .05). Water-holding capacity (WHC) of all the groups decreased continuously throughout storage, and CK reached 66.03% on day 6, which is significantly lower than CH + ε-PL + CA, CH + ε-PL, CH + CA, and ε-PL + CA (p < .05). On the contrary, the sensory scores of CH + ε-PL + CA, CH + ε-PL, CH + CA, and ε-PL + CA were significantly higher than the control, and the score of CH + ε-PL + CA (p < .05) was the best among all the groups. In terms of texture, CH + PL + CA also showed less cell shrinkage and tighter muscle fiber arrangement compared to other treatments. To sum up, the CH + PL + CA bio-coating proved to be a promising method for maintaining the storage quality of N. virgatus under refrigerated storage conditions.

Insight to the diversity of Photobacterium spp. isolated from European plaice (Pleuronectes platessa) based on phylogenetic analysis, phenotypic characterisation and spoilage potential

This study aimed to explore the diversity of fifty-four Photobacterium strains isolated from muscle tissue of European plaice (Pleuronectes platessa) caught at different fishing seasons and stored 14-days under various conditions. Single phylogenetic markers (16S rRNA, gapA, gyrB and recA) and multilocus sequence analysis (MLSA) were employed to classify isolates at species level. Furthermore, intra- and interspecies variability in the phenotypic traits, maximum specific growth rate (μmax) and spoilage potential of the Photobacterium isolates were investigated. The isolates were classified into the P. iliopiscarium (53.7 %), P. phosphoreum (40.7 %) and P. piscicola (5.6 %) clades using MLSA. Two housekeeping genes, gyrB and recA, exhibited a consistent phylogenetic relationship with MLSA, suggesting that they might be used as individual phylogenetic markers for the Photobacterium genus. Intra- and interspecies variability in the expression of phenotypic characteristics and the production of trimethylamine (TMA), inosine (HxR), and hypoxanthine (Hx) were observed. A growth optimum temperature for P. iliopiscarium was approximately 20 °C, while those for P. phosphoreum and P. piscicola were closer to 15 °C. All isolates exhibited the highest growth density at 1.5 % NaCl, followed by 0.5 %, 3 %, and 6 % NaCl. However, P. phosphoreum demonstrated a higher NaCl tolerance than the other two species. Although, the high CO2 atmosphere significantly inhibited the growth of all strains at 4 °C, P. phosphoreum and P. piscicola showed higher growth density at 15 °C than P. iliopiscarium. Notably, all strains demonstrated H2S production. The μmax varied considerably within each species, highlighting the significance of strain-level variability. This study demonstrates that P. iliopiscarium and P. piscicola, alongside P. phosphoreum, are efficient TMA-, HxR-, Hx-, and H2S-producers, suggesting their potential contribution to synergistic off-odour generation and spoilage. Moreover, the Photobacterium isolates seem to exhibit diverse adaptations to their environments, resulting in fluctuated growth and spoilage potential. Understanding intra- and interspecies variability will facilitate modelling seafood spoilage in microbial risk assessments and developing targeted hurdles to prolong products' shelf-life.