R. brelichi
Wild and captive R. brelichi feed on different foods, and the
ingestion of microorganisms via food may be one of the main sources of
gut microbial colonization. In addition, these monkeys are exposed to
different microorganisms through the environmental conditions in their
habitat, including diet, water, soil, and social activities, which are
potential sources of microbes in their gut (Diaz & Reese, 2021; Sun et
al., 2023). Our study revealed strong similarities in the main gut
microbiota between wild and captive R. brelichi . Regarding the
top 10 most dominant taxa in the fecal microbiota of the two groups,
Firmicutes, Bacteroides, and Spirochaetota were the dominant phyla
common to the two groups. This is consistent with the results of
Bornbusch et al. (2022) regarding the core dominant groups ofLemur catta in wild and captive populations. These results
suggest that wild and captive R. brelichi share a potential core
gut microbiota despite their different dietary habits and living
environments. This core microbiota may be essential for maintaining body
function and can be retained even in the face of environmental changes
(Tian et al., 2020). In this study, Christensenellaceae_R_7_group,
followed by Acinetobacter and Clostridia_UCG_014 , had
the highest relative abundance in the gut microbiota of wild R.
brelichi . In addition, LEfSe analysis showed that the abundance of
these genera of wild R. brelichi was significantly higher than
that of captive R. brelichi . Christensenellaceae_R_7 group and
Clostridia_UCG_014 belong to the Firmicutes. The former primarily
participates in cellulose and hemicellulose degradation (Wang et al.,
2023), facilitating the host’s digestion of cellulosic substances and
nutrient absorption, while the latter plays a crucial role in amino acid
metabolism (Yang et al., 2021). As leaves rich in fibrous compounds
dominate the diet of wild R. brelichi (Xiang et al., 2012), the
significant increases in the abundance of both genera were also
considered a response to changes in their diet. LEfSe analysis showed
that the abundance of Fibrobacter , Ruminococcus ,UCG_005 , and Prevotellaceae_UCG_001 significantly increased in
the gut microbiota of captive R. brelichi . Ruminococcus belongs to the Ruminococcaceae. When the energy intake is low, the
increased abundance of Ruminococcaceae bacteria fermenting nonstructural
carbohydrates can provide additional energy and nutrients to supplement
the insufficient intake of energy from the diet (Amato et al., 2015).
Meanwhile, Prevotellaceae_UCG_001 belongs to the genusPrevotella . Its enzymes can degrade cellulose and xylan, and its
significant enrichment plays an important role in alleviating disordered
glucose and lipid metabolism (Tang et al., 2020). The substantial
increase in the abundance of these flora in the captive group may
partially compensate for the significant decrease in the abundance of
Christensenellaceae_R_7_group and Clostridia_UCG_014, thereby
contributing to functional balance. Previous studies have also shown
that R. brelichi has a greater capacity to use plant fiber as an
energy source than R. bieti and R. roxellanae (Xi et al.,
2023). This may be related to the wide distribution of
cellulose-degrading bacteria such as UCG-005 ,Ruminococcus , Christensenellaceae_R-7_group, andFibrobacter in the intestine.
LEfSe analysis also showed that the abundance of Acinetobacter (belonging to Proteobacteria) was significantly increased in the gut of
wild R. brelichi . This is consistent with the findings of Cabana
et al. (2019), who showed that Acinetobacter was significantly
enriched in the gut of wild Nycticebus javanicus , but contrasts
with the findings of Sun et al. (2020), who revealed significant
enrichment of Proteobacteria in the gut microbiota of captiveMoschus chrysogaster . Studies have shown that environment, soil,
and animals are the natural habitats of Acinetobacter for its
growth and reproduction (Zhai et al., 2020). In humans and animals, this
is associated with diseases such as septicemia, pulmonary infections,
meningitis, and diarrhea, with susceptibility to infection being
associated with low host resistance, resulting in disease risk (Xu et
al., 2014; He et al., 2023). The abundance of this bacterial genus in
the gut of wild R. brelichi was significantly higher than that in
captivity, with such infection being suggested to occur through
contaminated food and water sources, and wild R. brelichi also
have more chances to ingest soil. There is thus a need for further
research on the imbalance of Acinetobacter in the gut microbiota
of wild R. brelichi , in combination with analyses of the
environment and feeding. LEfSe analysis showed that the potential
pathogen Treponema showed significantly increased abundance in
the gut of captive R. brelichi . Treponema is a spirochetal
bacterium that can infect a wide range of hosts and tissues (Mamuad et
al., 2020); for example, it is associated with porcine colonic
spirochetosis, a diarrheal disease that can lead to reduced
productivity. (Nguyen et al., 2023). A study by Zeng (2020) showed that
an increase in the abundance of Treponema was conducive to the
fermentation of cellulose and starch in R. roxellanae , but the
role of Treponema in the gut of snub-nosed monkeys remains
unclear. Therefore, further studies based on the physiological
characteristics of R. brelichi should be conducted.
4.3 Functional differences of the gut microbiota between wild and
captive R. brelichi
Under different environmental conditions, an increase or decrease of
certain gut microbiota can be an adaptation to the changing environment.
In this study, the potential functions of gut microbiota in R.
brelichi were predicted using PICRUSt2. KEGG database analysis showed
that functional genes of the gut microbiota in R. brelichi were
mainly associated with metabolic pathways such as metabolism, genetic
information processing, and cellular processes, which is consistent with
the results of previous studies on this species (Huang et al., 2024).
KEGG functions were also influenced by food provisioning, with wild
foraging monkeys showing higher functions of metabolism and environment
information processing, while captive food fed monkeys exhibited
increases in genetic information processing, cellular processes, and
organismal systems, which is contrary to the results of Li et al. (2024)
on Yunnan snub-nosed monkey. At the KEGG Level 2 categories, gut
microbial functions of R. brelichi were found to be mainly
enriched in carbohydrate metabolism, amino acid metabolism, and lipid
metabolism, which is consistent with the findings of most researchers on
the metabolic functions of gut microbiota in non-human primates (Sun et
al., 2016; Cheng et al., 2020; Wang et al., 2023). As a typical
leaf-eating primate, R. brelichi in the wild mainly eat large
leaves, while in captivity they ingest less cellulose and increase their
intake of carbohydrates and fats. This is consistent with a significant
increase in the abundance of carbohydrate metabolism pathways in the
captive group; the ability to digest cellulose was decreased in captiveR. brelichi due to changes in the diet, which in turn increased
its ability to digest simple carbohydrates (Wang et al., 2023); this
also reflected the significant increases of Prevotellaceae_UCG_001 andRuminococcus in the captive group. Meanwhile, captive R.
brelichi exhibited enhanced digestive and endocrine regulation
capabilities. Additionally, a significant increase in the enrichment of
metabolic pathways related to infectious diseases was identified,
suggesting a heightened risk of infectious diseases in these monkeys.
Wild R. brelichi exhibited greater ability of the xenobiotics
biodegradation and metabolism pathway, xenobiotics are manmade
refractory organic pollutants that are harmful to the health of living
organisms. Most of them can readily be found in various components of
the environment, such as soil, sediment, and water bodies (Zhang et al.,
2021). Wild R. brelichi live in more complex environments and are
more affected by exogenous pollutants than their captive counterparts;
therefore, the enhancement of this function is understandable given the
greater need to maintain gut health. In addition, the enrichment of the
metabolic pathway of lipid metabolism was significantly increased in the
gut of wild R. brelichi . This may be explained by the significant
increase in the bacterial genus Christensenellaceae_R-7_group in the
wild group, as a taxon mainly involved in host amino acid metabolism and
lipid metabolism (Jiang et al., 2023). Overall, captivity altered the
gut microbiota of R. brelichi , which in turn affected their
functions, but these changes may have helped the host to adapt to
captivity.