Effects of Habitat River Microbiome on the Symbiotic Microbiota and Multi-Organ Gene Expression of Captive-Bred Chinese Giant Salamander

Abstract

The reintroduction of captive-bred individuals is a primary approach to rebuild the wild populations of the Chinese giant salamander (Andrias davidianus), the largest extant amphibian species. However, the complexity of the wild habitat (e.g., diverse microorganisms and potential pathogens) potentially threatens the survival of reintroduced individuals. In this study, fresh (i.e., containing environmental microbiota) or sterilized river sediments (120°C sterilized treatment) were added to the artificial habitats to treat the larvae of the Chinese giant salamander (control group—Cnt: 20 individuals, treatment group 1 with fresh river sediments—T1: 20 individuals, and treatment group 2 with sterilized river sediments—T2: 20 individuals). The main objective of this study was to test whether this procedure could provoke their wild adaptability from the perspective of commensal microbiotas (skin, oral cavity, stomach, and gut) and larvae transcriptomes (skin, spleen, liver, and brain). Our results indicated that the presence of habitat sediments (whether fresh or sterilized) reshaped the oral bacterial community composition. Specifically, Firmicutes decreased dramatically from ~70% to ~20–25% (mainly contributed by Lactobacillaceae), while Proteobacteria increased from ~6% to ~31–36% (mainly contributed by Gammaproteobacteria). Consequently, the proportion of antifungal operational taxonomic units (OTUs) increased, and the function of oral microbiota likely shifted from growth-promoting to pathogen defense. Interestingly, the skin microbiota, rather than the colonization of habitat microbiota, was the major source of the pre-treated oral microbiota. From the host perspective, the transcriptomes of all four organs were changed for treated individuals. Specifically, the proteolysis and apoptosis in the skin were promoted, and the transcription of immune genes was activated in the skin, spleen, and liver. Importantly, more robust immune activation was detected in individuals treated with sterilized sediments. These results suggested that the pathogen defense of captive-bred individuals was improved after being treated, which may benefit their survival in the wild. Taken together, our results suggested that the pre-exposure of captive-bred Chinese giant salamander individuals to habitat sediments could be considered and added into the reintroduction processes to help them better adapt to wild conditions.

Bacterial community analysis of the skin microbiota of cultured Chinese giant salamander infected with Ranavirus

“…Proteobacteria and Firmicutes showed increased relative abundances in cultured Chinese giant salamanders infected with ADRV compared with those of healthy individuals, and the relative abundances of Bacteroidetes and Actinobacteria were lower in the diseased group. This seems to indicate that apart from Proteobacteria ( Woodhams et al, 2007 ; Zhu et al, 2022 ), Firmicutes is also related to amphibian defense and immunity. Additionally, Acidobacteria showed an increased relative abundance and ranked fifth in the diseased group, replacing Verrucomicrobiota, which ranked fifth in the healthy group and ranked down to sixth in diseased group.…”

Reintroduction modifies the intraspecific variations of symbiotic microbes in captive bred Chinese giant salamander

“…This can explain the observations that few infected CGSs were detected in the field ( Liu et al, 2021 ). Accordingly, pre-exposure to the field water conditions of CGSs before reintroduction can be an effective approach to help the colonization of diverse microbes, and thus enhance the survival of released individuals ( Zhu et al, 2022 ). This is especially true for the juveniles, as we found that released juveniles exhibited lower alpha diversity of microbiome than adults.…”

Albinism in the largest extant amphibian: A metabolic, endocrine, or immune problem?

“…The brain transcriptome was included as the brain is a central organ in the regulation of pigmentation in amphibians. Previously-described protocols were followed for RNA extraction, purification, cDNA library construction, filtration, assembly, annotation, and gene expression quantification ( 23 ). RNA-seq was performed on an Illumina HiSeq 4000 platform by Annoroad (Beijing); paired-end reads were generated.…”