Screening of potential aquatic probiotics from the major microflora of guppies (Poecilia reticulata)

Analyzing the Interaction between Tetrahymena pyriformis and Bacteria under Different Physicochemical Conditions When Infecting Guppy Using the eDNA Method

In the aquaculture system of ornamental fish, the interaction between bacterial microbiota and ciliate protozoa can prevent or promote disease outbreaks, and different physicochemical conditions will affect the relationships between them. We investigated the interaction between bacterial microbiota and the parasite Tetrahymena pyriformis when infecting Poecilia reticulata (guppy) under different physicochemical conditions. The abundance of T. pyriformis in water, the relative abundance of bacterial species, and histopathological observation were studied or monitored using environmental DNA (eDNA) extraction technology, the qPCR method, and 16s rRNA sequencing, respectively. The morphological identification and phylogenetic analysis of T. pyriformis were carried out. The infected guppy tissue was also stained by the hematoxylin and eosin methods. The results showed: (1) the bacterial communities of water samples were mainly composed of species assigned to Proteobacteria and Bacteroidetes, and Tabrizicola and Puniceicoccaceae were positively correlated with fish mortality, T. pyriformis abundance, and temperature. (2) Arcicella and Methyloversatilis universalis with different correlations between ciliates appeared in different treatment groups, the result of which proved that environmental factors affected the interaction between bacteria and T. pyriformis. (3) Lower temperatures and a higher pH were more beneficial for preventing disease outbreaks.

Partial Evaluation of Autochthonous Probiotic Potential of the Gut Microbiota of Seriola lalandi

Seriola lalandi is an economically important species that is globally distributed in temperate and subtropical marine waters. Aquaculture production of this species has had problems associated with intensive fish farming, such as disease outbreaks or nutritional deficiencies causing high mortality. Intestinal microbiota are involved in many processes that benefit a host, such as disease control, stimulation of the immune response, and the promotion of nutrient metabolism. The aim of this study is to evaluate the in vitro probiotic properties of bacteria isolated from the intestinal content of wild Seriola lalandi. The probiotic potential was evaluated in terms of (i) the antimicrobial activity against vibrios causing outbreaks in farmed fish; (ii) the ability to stimulate genes related to an innate immune response in fish; and (iii) antibiotic resistance. Nineteen isolates identified as Pseudomonas, Shewanella, Psychrobacter, and Acinetobacter showed antimicrobial activity and significant relative expression of cytokines, serum amyloid A protein (SAA), hepcidin, and lysozyme. A positive correlation was observed between the levels of expression and the bacterial load after 24 h of exposure. Pseudomonas isolates showed a level of antibiotic resistance. In conclusion, isolates of the genera Shewanella, Psychrobacter, and Acinetobacter could serve as potential probiotics in S. lalandi culture.

High-throughput sequencing-based analysis of bacterial communities associated with Barbour's seahorses (Hippocampus barbouri) from Surigao del Norte, Philippines

This study identified the bacterial community composition associated with Barbour's seahorses (Hippocampus barbouri). Seahorses and samples from the surrounding environment (sediment and water) were collected from Cantiasay Island in Surigao del Norte, Philippines. Genomic DNA was isolated from these samples, and the V1-V3 region of the 16S rRNA gene was amplified and sequenced on the Illumina MiSeq platform. There were 929 803 sequence reads corresponding to 859 operational taxonomic units (OTUs), which were obtained from the six genomic libraries. The results showed that the most abundant OTUs were affiliated to the phylum Proteobacteria, particularly those belonging to the genera Shewanella, Pseudomonas, Acinetobacter and Aeromonas, which were found to be dominant in seahorse gut samples. The only exception was for the skin of male seahorses, which was dominated by members belonging to the genus Bacillus (phylum Firmicutes). These findings on bacterial community structure and composition may shed light on therapeutic claims of Barbour's seahorses and help in the conservation of this species.

Effects of Lactococcus lactis subsp. lactis JCM5805 on colonization dynamics of gut microbiota and regulation of immunity in early ontogenetic stages of tilapia

The administration of probiotics during early ontogenetic stages can be an effective way to manipulate the gut microbiota of animals. Specifically, the administration of probiotics can enhance gut-colonization success and regulate the immune response. In this study, the effects of early contact with probiotic Lactococcus lactis subsp. lactis JCM5805 on the gut microbial assembly of larvae Nile tilapia were examined. The effects of JCM5805 on IFNα expression through the TLR7 and TLR9-dependent signal transduction pathway as well as larval disease resistance were studied. Three days postfertilization, embryos were randomly allocated into nine 30 L tanks with a concentration of 20 eggs L^-1. Triplicate tanks were performed for each treatment. Treatments included a control group (C), a low probiotic concentration group (T1), where JCM5805 was added to the water at 1 × 10⁴ cfu ml^-1, and a high probiotic concentration group (T2), where JCM5805 was added to the water at 1 × 10⁸ cfu ml^-1. Probiotics were administered continuously for 15 days. qPCR was used to analyze transcript levels of the TLR7, TLR9, MyD88, IRF7 and IFNα genes using RNA extracted from whole embryos on day 5 and 10, and from the intestine of larvae on day 15. Transcription of these genes was also measured in the intestine, liver and spleen of larvae one month after the cessation of probiotic administration. The results showed that MyD88 and IRF7 were significantly elevated on days 5 and 10 in the T2 group. TLR9 and IFNα were also significantly elevated on days 5, 10 and 15 during probiotic application of T2 (P < 0.05). One month after the cessation of probiotics administration, no significant difference was observed in the expression of these genes (P > 0.05). The larvae were fed probiotics for 15 days and were infused with Streptococcus agalactiae strain WC1535 at a final concentration of 1 × 10⁶ cfu ml^-1. The survival rate of T2 was significantly higher than that of the C group (P < 0.05). Microbial characterization by Illumina HiSeq sequencing of 16S rRNA gene amplicons showed the significantly higher presence of JCM5805 in the guts of T2 after 15 days of probiotic continuous application. Although JCM5805 was below the detection level after the cessation of probiotic for 5 days, the gut microbiota of the exposed tilapia larvae in T2 remained clearly different from that of the control treatment after the cessation of probiotic administration. These data indicated that a high concentration of the probiotic strain JCM5805 upregulated the expression of IFNα via the TLR7/TLR9-Myd88 pathway and enhanced disease resistance of larvae. JCM5805 was only transiently detected and thus was not included in the stable larval microbiota. The early microbial exposure of tilapia larvae affects the gut microbiota at later life stages. However, whether the upregulation of related genes is related to the presence of JCM5805 strain in the intestine requires further verification.

Bacterial community structure in the intestinal ecosystem of rainbow trout (Oncorhynchus mykiss) as revealed by pyrosequencing-based analysis of 16S rRNA genes

In this study, we determined the diversity and composition of bacterial communities within the intestinal ecosystem of farmed rainbow trout (Oncorhynchus mykiss). Healthy rainbow trout, weighing between 520 and 750 g, were fed a commercial diet. Subsequently, genomic DNA was isolated from the intestinal mucus (n = 16 fish samples) and combined into groups of four fish samples each for pyrosequencing analysis of bacterial 16S rRNA genes. The results revealed that the most abundant operational taxonomic units (OTUs) were affiliated to the genera Acinetobacter, Cetobacterium, Pseudomonas, and Psychrobacter, and to a lesser extent, the genera Aeromonas, Clostridium, Deefgea, Flavobacterium, Neptuniibacter, and Mycoplasma. These findings could be used as a baseline for further studies about the role of bacterial communities in normal and altered host physiological states.