Exploring the effects of environmentally relevant concentrations of tris(2-chloroethyl) phosphate on tadpole health: A comprehensive analysis of intestinal microbiota and hepatic transcriptome.

Tris(2-chloroethyl) phosphate (TCEP), a chlorinated organophosphate ester, is commonly found in aquatic environments. Due to its various toxic effects, it may pose a risk to the health of aquatic organisms. However, the potential impacts of TCEP exposure on the intestinal microbiota and hepatic function in amphibians have not been reported. This study investigated the impact of long-term exposure to environmentally relevant concentrations of TCEP (0, 3, and 90 µg/L) on the intestinal microbiota and hepatic transcriptome of Polypedates megacephalus tadpoles. The results showed that the body size of the tadpoles decreased significantly with an increase in TCEP concentration. Additionally, TCEP exposure affected the diversity and composition of the intestinal microbiota in tadpoles, leading to significant changes in the relative abundance of certain bacterial groups (the genera Aeromonas decreased and Citrobacter increased) and potentially promoting a more even distribution of microbial species, as indicated by a significant increase in the Simpson index. Moreover, the impact of TCEP on hepatic gene expression profiles in tadpoles was significant, with the majority of differentially expressed genes (DEGs) (709 out of 906 total DEGs in 3 µg/L of TCEP versus control, and 344 out of 387 DEGs in 90 µg/L of TCEP versus control) being significantly down-regulated, which were primarily related to immune response and immune system process. Notably, exposure to TCEP significantly reduced the relative abundance of the genera Aeromonas and Cetobacterium in the tadpole intestine. This reduction was positively correlated with the down-regulated expression of immune-related genes in the liver of corresponding tadpoles. In summary, these findings provide empirical evidence of the potential health risks to tadpoles exposed to TCEP at environmentally relevant concentrations.

Characterization and Comparison of the Two Mitochondrial Genomes in the Genus Rana.

The mitochondrial genome (mitogenome) possesses several invaluable attributes, including limited recombination, maternal inheritance, a fast evolutionary rate, compact size, and relatively conserved gene arrangement, all of which make it particularly useful for applications in phylogenetic reconstruction, population genetics, and evolutionary research. In this study, we aimed to determine the complete mitogenomes of two morphologically similar Rana species (Rana hanluica and Rana longicrus) using next-generation sequencing. The entire circular mitogenome was successfully identified, with a length of 19,395 bp for R. hanluica and 17,833 bp for R. longicrus. The mitogenomes of both species contained 37 genes, including 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA genes, and one control region; mitogenome size varied predominantly with the length of the control region. The two synonymous codon usages in 13 PCGs showed that T and A were used more frequently than G and C. The ratios of non-synonymous to synonymous substitutions of all 13 PCGs were <1 in the Rana species, indicating that the PCGs were under purifying selection. Finally, phylogenetic relationship analyses suggested that R. hanluica and R. longicrus were classified in the R. japonica group. Our study provides valuable reference material for the taxonomy of the genus Rana.

Host defence peptide LEAP2 contributes to antimicrobial activity in a mustache toad (Leptobrachium liui).

BACKGROUND: The liver-expressed antimicrobial peptide 2 (LEAP2) is essential in host immunity against harmful pathogens and is only known to act as an extracellular modulator to regulate embryonic development in amphibians. However, there is a dearth of information on the antimicrobial function of amphibian LEAP2. Hence, a LEAP2 homologue from Leptobrachium liui was identified, characterized, and chemically synthesized, and its antibacterial activities and mechanisms were determined. RESULTS: In this study, LEAP2 gene (Ll-LEAP2) cDNA was cloned and sequenced from the Chong'an Moustache Toad (Leptobrachium liui). The predicted amino acid sequence of Ll-LEAP2 comprises a signal peptide, a mature peptide, and a prodomain. From sequence analysis, it was revealed that Ll-LEAP2 belongs to the cluster of amphibian LEAP2 and displays high similarity to the Tropical Clawed Frog (Xenopus tropicalis)'s LEAP2. Our study revealed that LEAP2 protein was found in different tissues, with the highest concentration in the kidney and liver of L. liui; and Ll-LEAP2 mRNA transcripts were expressed in various tissues with the kidney having the highest mRNA expression level. As a result of Aeromonas hydrophila infection, Ll-LEAP2 underwent a noticeable up-regulation in the skin while it was down-regulated in the intestines. The chemically synthesized Ll-LEAP2 mature peptide was selective in its antimicrobial activity against several in vitro bacteria including both gram-positive and negative bacteria. Additionally, Ll-LEAP2 can kill specific bacteria by disrupting bacterial membrane and hydrolyzing bacterial gDNA. CONCLUSIONS: This study is the first report on the antibacterial activity and mechanism of amphibian LEAP2. With more to uncover, the immunomodulatory functions and wound-healing activities of Ll-LEAP2 holds great potential for future research.

Characterization of the complete mitochondrial genome of the Chong'an Moustache Toad, Leptobrachium liui (Pope, 1947) with a phylogenetic analysis of Megophryidae.

The Chong'an Mustache Toad, Leptobrachium liui (Pope, 1947) is a Chinese endemic species, inhabiting the mountain streams with rich vegetation in southeastern China. The first complete mitochondrial genome (mitogenome) of L. liui was assembled using the data of whole-genome sequencing. The size of the complete mitogenome for L. liui was 17,190 bp, which included 13 PCGs, 23 tRNAs with two concatenated tRNAMet genes, 2 rRNAs, a non-coding region, and a D-loop. The Bayesian tree shows that L. liui was positioned near L. leishanense within the genus Leptobrachium.