CUMS alters behavioral phenotypes and gut mycobiota in mice

To investigate the effects of chronic unpredictable mild stress (CUMS) on the gut fungal community in mice and its association with anxiety-like behaviors.

C57BL/6 male mice were randomly divided into a control group and a CUMS group, with 10 mice per group. The CUMS group was exposed to a 3-week regimen of chronic stressors (damp bedding, food and water deprivation, continuous light exposure, tail pinch, cage tilting, restraint, and forced swimming). Anxiety-like behaviors were assessed using the elevated plus maze (EPM) and open field test (OFT). Colonic contents were collected for ITS high-throughput sequencing. Alterations in the gut fungal community and their correlations with behavioral parameters were evaluated through α-diversity and β-diversity analyses, LEfSe differential analysis, Spearman correlation analysis and co-occurrence network analysis.

Compared with the control group, the CUMS group showed significantly reduced percentage of open-arm entries and percentage of time spent in open arms in the EPM (P < 0.01 and P < 0.001, respectively), as well as decreased central entries in the OFT (P < 0.05), indicating successful induction of anxiety-like behaviors. α-Diversity analysis revealed lower Chao and Shannon indices in the CUMS group (P < 0.05). β-Diversity analysis demonstrated a marked separation in fungal community structure between the two groups (R = 0.9420, P = 0.001). Species composition and LEfSe analysis identified Kazachstania as the absolutely dominant genus in the CUMS group (LDA score > 5.5), with its relative abundance being highly significantly increased (P < 0.001), while the relative abundances of most other dominant genera (e.g., Aspergillus, Scopulariopsis, and Wallemia) were significantly decreased. Correlation analysis revealed that the enrichment levels of Aspergillus, Scopulariopsis, and Wallemia were positively correlated with fungal species diversity (P < 0.05), and these taxa also exhibited positive correlations with the reduction in anxiety-like behaviors. Co-occurrence network analysis indicated that Kazachstania acted as the hub taxon with the highest connectivity within the network, exhibiting extensive niche antagonism against fungal taxa including Aspergillus, Scopulariopsis, and Wallemia in the community. In contrast, other fungal groups such as Aspergillus, Scopulariopsis and Wallemia showed pairwise positive co-occurrence relationships, forming a stable fungal subcommunity with internal synergistic interactions.

This study firstly demonstrates that chronic unpredictable mild stress (CUMS) induces profound ecological remodeling of the gut fungal community, characterized by the enrichment of Kazachstania and suppression of other fungal genera. Combined with prior evidence, our results suggest CUMS enables Kazachstania to become conditionally dominant as an opportunistic fungus. We hypothesize CUMS-mediated homeostatic disturbance facilitates pathological overgrowth of Kazachstania, though this overgrowth does not directly exacerbate anxiety-like behaviors. By contrast, Aspergillus, Scopulariopsis and Wallemia may maintain intestinal homeostasis and alleviate anxiety-like phenotypes. These findings challenge the conventional view that fungal community dysbiosis is merely reflected by reduced diversity; instead, monotypic fungal dominance better mirrors pathological status. This work provides novel theoretical perspectives and research directions for exploring how CUMS shapes host health via gut mycobiota.