Biology subjects

Kormas, K.

Publications and source records attributed to Kormas, K..

7 recordsLinked to original sources

bioRxiv2026

Consistent gut bacterial microbiota in European sea bass fed aquafeeds containing sustainable plant and invasive fish-based ingredients

The aim of this study was to evaluate the impact of two sustainable dietary protein sources on the structure and composition of the gut microbiota in European sea bass (Dicentrarchus labrax) juveniles. These protein sources were incorporated to the aquafeeds containing (a) Lupinus albus meal, treated with either exogenous enzymes (Solid state hydrolysis-SSH) or fermented with Saccharomyces cerevisiae (Solid state fermentation, SSF) and (b) Lagocephalus sceleratus meal. In the first case (a), the control aquafeed simulated a standard commercial diet, containing soybean meal whereas in the rest of the diets soybean meal was partially or totally replaced by hydrolysed or fermented Lupin meal. In the second case (b) the fish were fed Lagocephalus sceleratus unprocessed fishmeal as well as treated at different temperatures to deactivate tetrodotoxin (TTX). A control diet with 30% commercial fish meal was also fed as a reference diet. Both diets in all inclusion levels did not cause any significant gut microbiota change, suggesting their neutral role in this aspect. However, the gut bacterial communities of the fish fed with 12.5% lupin meal inclusion, had increased amino acid biosynthetic pathways suggesting a beneficial effect.

microbiology↗

bioRxiv2026

Distinct Daphnia spp. whole-body bacterial microbiota in two contrasting Mediterranean lakes

The microbiota and microbiome associated with zooplankton remains rather understudied compared to other animal groups and/or taxa. The present study aimed at investigating the whole-body bacterial microbiota of Daphnia spp. in two contrasting Greek lakes, the shallow and hypertrophic Lake Koronia vs. the deep and mesotrophic Lake Vegoritida, including both egg-bearing and non-egg-bearing individuals. In both lakes, 2,060 bacterial operational taxonomic units (OTUs) were found, with 223 of them being conditionally rare (crOTUs) with low contribution even for the dominant phyla, with L. Vegoritida having more crOTUs than L. Koronia. The individuals microbiota had inconsiderable overlap with the surrounding water microbiota in both lakes. The two lakes showed significant differences in their Daphnia -associated microbiota. L. Koronia had richer OTUs and rather homogeneous bacterial communities, with higher occupancy. Overall, no significant differences in between the microbiota of egg-bearing and non-egg-bearing Daphnia individuals in both lakes. However, regarding the most important OTUs (miOTUs), the L. Koronia miOTUs were highly overlapped between the individuals with and without eggs, with only one missing from the individuals without eggs. In L. Vegoritida the individuals without eggs had only six miOTUs and while egg-bearing individuals had nine different ones; the two lakes had no shared miOTUs., considerable differences occurred.. A total of 27 miOTUs, was found and belonged to the Pseudomonadota, unclassified Bacteria, Cyanobacteria, Bacteroidota, Bacillota and Actinomycetota. Those miOTUs, where assignment to the genus level was possible, they were related to Cyanobium, Mucilaginibacter, Flavobacterium and Staphylococcus. This study showed that lake morphotype and ecological status can exert some impact on Daphnia-associated bacterial microbiota, with more pronounced effects on egg-bearing and non-egg-bearing individuals.

microbiology↗

bioRxiv2025

Sex-related gut microbiota in three geographically separated Norway lobster (Nephrops norvegicus) populations

Despite the ecological and economic interest of the Norway lobster (Nephrops norvegicus), its gut microbiota remains largely understudied. The current study aimed at investigating the gut bacterial microbiota in three geographically separated N. norvegicus populations from the Mediterranean and the North Sea and detecting any potential sex-related microbiota differences, by high-throughput sequencing of the V3-V4 16S rRNA gene diversity of the gut tissue. From the Greek population, egg-bearing females were also caught. A total of 2,385 operational taxonomic units (OTUs) were identified and between 417 and 1290 occurred in each population/sex group. The dominant OTUs belonged to the Fusobacteriia and Bacteroidia (Sweden), Bacilli and Gammaproteobacteria (Italy) and Spirochaetia and Bacilli (Greece) bacterial classes. In the eggs, the Actinobacteria, Alphaproteobacteria and Gammproteobacteria prevailed. Four OTUs related to the Oceanispirochaeta, Kordiimonas, Desulfovibrio, Carboxylicivirga genera and one unafilliated OTU were positively correlated (p values between 0.001 and 0.04) to body size indicating their potential role in the animals nutrition and growth. No statistically significant differences were found between males-females in each of the three populations. However, statistically significant differences between populations for each sex, were found for all females (p values between 0.008 and 0.032) and for the males between the most distant populations, i.e. Italy-Sweden (p=0.021) and Greece-Sweden (p=0.015). The eggs microbiota was statistically different from both the adult females (p=0.027) and males (p=0.046) gut microbiota. Overall, this study showed that N. norvegicus gut microbiota are differentiated between geographically distant populations and that sex-related differences are not significant.

microbiology↗

bioRxiv2024

Distinct communities of Bacteria and unicellular eukaryotes in the different water masses of Cretan Passage water column (Eastern Mediterranean Sea)

Understanding the diversity and dynamics of marine microbiota holds significant importance due to their role in maintaining vital ecosystem functions and services including climate regulation and bioremediation. Here, we studied the diversity and associations between Bacteria and unicellular eukaryotes in the different water masses of the Cretan Passage water column in the Eastern Mediterranean Sea (EMS). Samples were collected from two stations in the Hellenic Exclusive Economic Zone (EEZ) at various depths down to 1000 m during two sampling expeditions in August 2019 and February 2020. Through high-throughput 16S and 18S rRNA gene analysis, we unveiled vertical variations in both bacterial and unicellular eukaryotes diversity respectively. Additionally, interspecies co-occurrence patterns were evaluated between the top and bottom water masses. Our results revealed species fluctuations indicative of seasonality in the surface water mass while the deepest water layers were enriched in heterotrophic taxa and grazers related to organic matter degradation and nutrient cycling. Finally, we found a higher number of microbial associations in surface waters indicating abundant ecological niches compared to the deepest layer, possibly related to the lack of bottom-up resources in the oligotrophic deep ocean.

ecology↗

bioRxiv2024

The effect of dietary fish oil replacement by microalgae on the gilthead sea bream midgut bacterial microbiota

It is well known that the gut microbiome and its interaction with the host influence several important factors for fish health such as nutrition and metabolism. Diet is one of the main factors influencing the composition of the gut microbiome in reared fish. Microalgae, due to their high fatty acid content, appear to be a promising alternative for replacing fish oil in aquafeed. Thus, the aim of this work was to evaluate the effects of dietary microalgae blends as fish oil replacers on the midgut bacterial microbiota of the gilthead sea bream (Sparus aurata). The control diet (FO) contained only fish oil as source of lipids, EPA and DHA fatty acids, while three experimental diets were used where fish oil was replaced at 67% by one of the following microalgae biomass blends: Microchloropsis gaditana and Isochrysis sp. (Tisochrysis lutea) (MI), Phaeodactylum tricornutum and Isochrysis sp. (PI) and Schizochytrium sp. and P. tricornutum (SP). The midgut bacterial community composition of the experimental diets was altered compared to the control diet. There were 11 operational taxonomic units (OTUs) which were highly abundant in FO compared to the three experimental diets (FO, MI, SP) and two OTUs that were found in high abundance in both FO and the experimental diets in all comparisons (FO-MI, FO-PI, FO-SP). Most of the highly abundant OTUs in the experimental diets were unique to each experimental diet, with two OTUs being found in common between FO-MI and FO-PI. Additional evidence from the presumptive bacterial functional metabolic pathways suggested that the microalgae-based diets resulted in one over-expressed and one under-expressed pathway. The overexpressed pathway was related to the metabolism of fucose, a major constituent of the polysaccharide content of several microalgal species. Peptidoglycan biosynthesis was the under-expressed metabolic pathway. This suggests that a new gut microbiota profile was selected due to the microalgae inclusion in the provided diet. This study showed that, with the absence of mortality in fish, the gilthead sea bream gut microbiome can smoothly adapt its function according to the metabolic capacity of the dietary microalgae combinations that were used. The MI feed seems to promote several beneficial bacteria with potential probiotic abilities in the fish gut, belonging to the Pseudoalteromonas, Pseudomonas, Bacillus and Rhodopseudomonas genera.

microbiology↗

bioRxiv2023

Fecal and skin microbiota of two rescued Mediterranean monk seal pups during rehabilitation

The role of animal host-associated microbiomes is becoming more apparent and defined for wild animals, especially for the species under conservation strategies. This study investigated the succession of fecal and skin bacterial microbiota of two rescued female Mediterranean monk seal (Monachus monachus) pups for most of their rehabilitation period. Bacterial species richness and diversity was assessed by high-throughput sequencing of nine freshly collected fecal samples and four skin swabs per individual. Both the fecal and skin microbiota highly overlapped in their containing operational taxonomic units (OTUs) and abundance patterns. The fecal microbiota was separated in two distinct periods, and was dominated by OTUs related to the Shigella, Streptococcus, Enterococcus, Lactobacillus and Escherichia genera in the first period, while in the second period the dominating genera were the Clostridium, Blautia, Fusobacterium, Edwardsiella and Bacteroides. The skin microbiota was highly similar between the two individuals in each sampling and were dominated by Psychrobacter-, Elizabethkingia- and Bergeyella-related OTUs. The provided antibiotic treatment along with the provided probiotics and nutritional supplements, resulted in a major turnover of the bacterial microbiota with the potentially detrimental OTUs being eliminated towards the end of the rehabilitation period, prior to the release of the pups in the wild.

microbiology↗

bioRxiv2022

Midgut bacterial microbiota of 12 fish species from a marine protected area in the Aegean Sea (Greece)

Fish microbiome science is progressing fast, but it is biased toward farmed or laboratory fish species against natural fish populations, which remain considerably underinvestigated. We analysed the midgut bacterial microbiota of 45 specimens of 12 fish species collected from the Gyaros Island marine protected area (Aegean Sea, Greece). The species belong to seven taxonomic families and are either herbivores or omnivores. Mucosa midgut bacterial diversity was assessed by amplicon metabarcoding of the 16S rRNA V3-V4 gene region. A total of 854 operational taxonomic units were identified. In each fish species, between 2 and 18 OTUs dominated with cumulative relative abundance [≥]70%. Most of the dominating bacterial taxa have been reported to occur both in wild and farmed fish populations. The midgut bacterial communities were different among the 12 fish, except for Pagrus pagrus and Pagellus erythrinus, which belong to the Sparidae family. No differentiation of the midgut bacterial microbiota was found based on feeding habits, i.e., omnivorous vs. carnivorous. Comparing wild and farmed P. pagrus midgut bacterial microbiota revealed considerable variation between them. Our results expand the gut microbiota of wild fish and support the host species effect as the more likely factor shaping intestinal bacterial microbiota.

microbiology↗