4. DISCUSSION
4.1 Analysis of gut microbiota composition
in different states of Catharsius
molossus
Gut microbiota, as the ”inner ecosystem” of the gut, plays a crucial
role in insects’ digestive systems that rely on limited nutrients or
hard-to-digest food sources(Tafesh-Edwards & Eleftherianos, 2023; Wang
et al., 2020). We observed stable and
enduring microbial community structures in the host, referred to as
”dominant microbial taxa.” The presence of such microbial communities is
vital for maintaining ecological balance and host health(Chen et al.,
2021). Studies have demonstrated that gut microbiota in insects likePachysoma MacLeay from arid coastal regions of southwestern
Africa and flightless Thorectes lusitanicus contain dominant taxa
such as Bacteroidetes, Firmicutes, Proteobacteria, and
Actinobacteria(Franzini et al., 2016; Hernández et al., 2015). In our
study, the predominant phyla in the gut of Catharsius molossus in
both hungry and refeeding states were Proteobacteria, Firmicutes,
Actinobacteria, and Bacteroidetes. Notably, Bacteroidetes, known as
obligate or strict anaerobes, are challenging to culture in vitro,
suggesting potential similarities in the dominant microbial taxa among
different beetle species and their significant roles in host growth and
development. After refeeding, the proportion of Firmicutes and
Bacteroidetes increased, while Proteobacteria decreased. The consistent
proportion of Actinobacteria may relate to the fiber-rich diet ofCatharsius molossus , as Firmicutes possesses genes involved in
fermenting dietary fiber and interacts with intestinal mucosa,
contributing to maintaining host equilibrium (Sun et al., 2022).
Bacteroidetes, known for polysaccharide degradation and aiding dietary
fiber energy release(Pereira et al., 2021), exhibited significant
differences between hungry and refeeding states, indicating its
potential role in polysaccharide metabolism that warrants further
experimental validation (Vera-Ponce de León et al., 2020). Regarding the
variation in Proteobacteria, previous studies have suggested that an
increase in its proportion could lead to an elevated risk of diseases,
serving as an indicator of microbial community disruption, and
potentially even as a diagnostic marker for diseases (Rizzatti et al.,
2017; Shin et al., 2015). Importantly, within the context of our study,
we have observed a relatively higher abundance of Proteobacteria within
the gut microbiota of Catharsius molossus during periods of
dietary deprivation compared to the refeeding state. This observation
provides suggestive insights that starvation could potentially induce an
unfavorable physiological state, potentially contributing to the
instability of the host’s gut microbiota ecology. Additionally, the
relatively small proportion of Dysgonomonas in our study differs
from Vagococcus and Romboutsia , which were dominant genera
according to Suarez-Moo et al. (Suárez-Moo et al., 2020).Dysgonomonas has been associated with nitrogen fixation
capabilities (Bar-Shmuel et al., 2020; Skrzypczak & Przybylski, 2022),
and its higher abundance during starvation suggests a potential role in
nitrogen fixation to sustain host survival. However, more research is
needed to explore whether Dysgonomonas assimilates nitrogen into
the beetle or its direct environment. In summary, hunger and refeeding
affect gut microbiota diversity and variability in Catharsius
molossus . Yet, the impact of changes in gut microbial abundance on host
physiological functions and their mechanisms remains to be investigated.
Our study provides valuable insights into the adaptability of gut
microbiota in beetles under unique environments and their ecological
functions.
4.2 Predictive analysis of Catharsius
molossus gut microbiota
functions
Utilizing PICRUSt, we conducted functional predictions, revealing a
higher abundance of genes related to primary metabolic pathways and
genetic information processing at the primary pathway level. At the
tertiary pathway level, the gut microbiota of hungry Catharsius
molossus showed higher gene abundances in pathways related to ansamycin
biosynthesis, vancomycin group biosynthesis, and D-glutamine and
D-glutamate metabolism, while refeeding state displayed elevated gene
abundances in pathways related to ansamycin biosynthesis, valine,
leucine, and isoleucine biosynthesis, and D-glutamine and D-glutamate
metabolism. Ansaamycins are essential antibiotics, particularly against
Mycobacterium tuberculosis(Skrzypczak & Przybylski, 2022). This
suggests that Catharsius molossus may utilize its gut
microbiota’s metabolic functions to interact with the environment,
assisting in defense against pathogen and parasite infections, which may
contribute to its unique adaptation to a diet of feces and living in
such an environment. However, it’s important to note that while our
functional predictions offer valuable clues, they are based on
predictions and don’t fully represent the actual functions of gut
microbiota. To delve into the precise roles of these gene functions inCatharsius molossus’ environmental adaptability, integration of
multi-omics data is essential. Such comprehensive research would enhance
our understanding of the physiological functions, interdependencies, and
coordination mechanisms of gut microbiota, uncovering their complex
functions and potential applications. This approach could facilitate
further resource development and utilization in the context of gut
microbiota.