Selective Antagonism of Lactiplantibacillus plantarum and Pediococcus acidilactici against Vibrio and Aeromonas in the Bacterial Community of Artemia nauplii.

Empiric probiotics are commonly consumed by healthy individuals as a means of disease prevention, pathogen control, etc. However, controversy has existed for a long time regarding the safety and benefits of probiotics. Here, two candidate probiotics, Lactiplantibacillus plantarum and Pediococcus acidilactici, which are antagonistic to Vibrio and Aeromonas species in vitro, were tested on Artemia under in vivo conditions. In the bacterial community of Artemia nauplii, L. plantarum reduced the abundance of the genera Vibrio and Aeromonas and P. acidilactici significantly increased the abundance of Vibrio species in a positive dosage-dependent manner, while higher and lower dosages of P. acidilactici increased and decreased the abundance of the genus Aeromonas, respectively. Based on the liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) analyses of the metabolite of L. plantarum and P. acidilactici, pyruvic acid was used in an in vitro test to explain such selective antagonism; the results showed that pyruvic acid was conducive or suppressive to V. parahaemolyticus and beneficial to A. hydrophila. Collectively, the results of this study demonstrate the selective antagonism of probiotics on the bacterial community composition of aquatic organisms and the associated pathogens. IMPORTANCE Over the last decade, the common preventive method for controlling potential pathogens in aquaculture has been the use of probiotics. However, the mechanisms of probiotics are complicated and mostly undefined. At present, less attention has been paid to the potential risks of probiotic use in aquaculture. Here, we investigated the effects of two candidate probiotics, L. plantarum and P. acidilactici, on the bacterial community of Artemia nauplii and the in vitro interactions between these two candidate probiotics and two pathogens, Vibrio and Aeromonas species. The results demonstrated the selective antagonism of probiotics on the bacterial community composition of an aquatic organism and its associated pathogens. This research contributes to providing a basis and reference for the long-term rational use of probiotics and to reducing the inappropriate use of probiotics in aquaculture.

Complete mitochondrial genome and the phylogenetic position of the giant oarfish (Regalecus glesne).

The mitochondrial genome of Regalecus glesne was firstly elucidated and analyzed in this study. It had a double-stranded DNA molecule with the length of 16,536 bp and was made up 37 genes (13 protein-coding genes, 2 rRNA genes, and 22 tRNA genes) and one control region. Furthermore, the phylogenetic result demonstrated that R. glesne clustered with Trachipterus trachypterus and Zu cristatus. The complete mitochondrial genome provided in this work would be helpful for the genetic elucidation of the evolution of Lampriformes and other orders.

Complete mitochondrial genome and the phylogenetic position of the stellate puffer (Arothron stellatus).

The complete mitochondrial genome of the stellate puffer (Arothron stellatus) was first determined in this study. It was a 16,475 bp circular molecule and consisted of 37 genes with typical gene order in vertebrate mitogenome. Its nucleotide content was 29.0% A, 32.0% C, 15.9% G and 23.1% T. This mitogenome had 30 bp short intergenic spaces located in 12 gene junctions and 28 bp overlaps located in 7 gene junctions. In the protein-coding genes, two start codons (GTG and ATG) and two stop codons (TAG and TAA/TA/T) were found. The 22 tRNA genes ranged from 64 bp (tRNA-Cys) to 74 bp (tRNA-Leu1 and tRNA-Lys). The phylogenetic result showed that Takifugu xanthopterus was most closely related to the reef-related A. stellatus among all Tetraodontiformes species.