Parasite infection not only triggers the immune response of the host but also potentially affects the reproductive status, thereby influencing the population size. Therefore, understanding the impact of parasite infection on host immune and reproductive systems has long been an important issue in ecological research. To address this, we conducted field surveys (2021–2023) to investigate Capillaria hepatica infection status in Brandt's vole (Lasiopodomys brandtii) and performed controlled experiments in semi-natural enclosures and indoor laboratories. The results showed a negative correlation between the population size of Brandt's vole and the infection rate. To further explore the regulatory mechanisms, transcriptomic and proteomic analyses were performed on the infected BALB/c mice. The study found that post-infection with Capillaria hepatica, up-regulated genes and proteins in the mice liver were primarily associated with immune functions, while down-regulated genes and proteins were related to metabolic functions such as retinol metabolism. Through validation experiments supplementing retinol to the host infected with Capillaria hepatica, it was found that infection with Capillaria hepatica leads to a decrease in systemic available retinol levels, disrupting the expression of the hypothalamic-pituitary-gonadal (HPG) axis hormones, affecting the expression of CYP17A1, thereby regulating testosterone secretion related to spermatogenesis. This process results in abnormal spermatogenesis in the testes, thereby impacting the reproductive capacity of mice. This suggests that Capillaria hepatica regulates resource allocation in hosts, striking a “trade-off” between reproduction and survival, thereby exerting control over population size. These discoveries are crucial for comprehending the interaction between Capillaria hepatica and hosts, as well as their impacts on host reproduction and immune systems, and provide a scientific basis for controlling the transmission of Capillaria hepatica.

A Gram-stain-negative, strictly aerobic, rod-shaped bacterium, designated EGI 63066 ^T , was isolated from a saline soil of Kalidium foliatum (Pall.), collected from Wujiaqu in Xinjiang, China. Strain EGI 63066 ^T is a non-motile, rod-shaped bacterium; it forms pale yellow colonies on the marine agar and grows at 10–37 °C,at pH 6.0–9.0 and 0–10% (w/v) NaCl. The 16S rRNA sequences of the strain EGI 63066 ^T and Galbibacter mesophilus Mok-17 ^T , Robertkochia solimangrovi CL23 ^T , Robertkochia sediminum 1368 ^T and Galbibacter pacificus CMA-7 ^T share sequence similarities of 92.80%, 91.85%, 91.79% and 91.79%, respectively. Higher average amino acid identity values with Galbibacter (72.10–76.90%) than with Robertkochia (69.40–70.30%) supported the assignment of strain EGI 63066 ^T to the genus Galbibacter . Phylogenomic analysis based on core genes revealed that strain Galbibacter kalidii formed a stable clade with the four recognized species of the genus Galbibacter and the not validly published ‘ Joostella atrarenae ’ M1-2. The average nucleotide identity and digital DNA–DNA hybridization values between the strain EGI 63066 ^T and members of the genus Galbibacter were 71.10–74.15% and 18.00–19.70%, respectively. The DNA G+C content of the genome for strain EGI 63066 ^T based on genomic DNA was 39.0 mol%, and the genome size was 4.66 Mbp. The predominant fatty acids of strain EGI 63066 ^T were iso-C _{15 : 0} , iso-C _{15 : 1} G and summed feature 3 (C _{16 : 1} ω6 c and/or C _{16 : 1} ω7 c). The major respiratory quinone was menaquinone-6, and the major polar lipids were phosphatidylethanolamine, aminolipid, aminophospholipid and phospholipid. Compared to other species within the genus Galbibacter , EGI 63066 ^T exhibits distinctive features, including the production of flexirubin-type pigments, CM-cellulose hydrolysis and whole-cell protein profiles. Based on the polyphasic taxonomic analysis, strain EGI 63066 ^T represents a novel species of the genus Galbibacter , for which the name G. kalidii sp. nov. is proposed. The type strain is EGI 63066 ^T (=JCM 36938 ^T =CGMCC 1.19132 ^T ).