Alterations in the gastric and small intestinal microbiota of mice exposed to short-term and long-term hypoxia

Tens of millions of people worldwide travel to high-altitude regions (> 2500 m) every year for short-term work, tourism and pilgrimage. Hypoxia, resulting in a range of gastrointestinal disorders, is a significant physiological challenge in high-altitude environments. The gastrointestinal microbiota is closely linked to the mucosal barrier and our previous research found that hypoxia-induced mucosal injury mainly occurs in stomach and small intestine. This study aimed to characterize the temporal dynamics of gastric and small intestinal microbiota by directly analyzing the luminal contents to elucidate site-specific microbial alterations and their potential role in mucosal damage under hypoxic conditions. C57BL/6 J mice were randomly assigned to four groups: normoxic control, 1-day hypoxic exposure, 3-day hypoxic exposure and 12-day hypoxic exposure. Fresh gastric and small intestinal contents were collected for 16S rRNA sequencing. The operational taxonomic unit (OTU) counts, α/β-diversity and temporal microbial abundance shifts across different durations of hypoxia exposure were analyzed. Our results found that short-term hypoxia (1-3 days) significantly reduced the OTU counts and diminished α/β-diversity in the stomach and small intestine. However, prolonged hypoxia (day 12) reversed the diminished OTU counts and α/β-diversity to near-normoxic levels. In the stomach, short-term hypoxia increased the abundances of the phylum Firmicutes and genus Lactobacillus and suppressed the levels of the phyla Verrucomicrobia, Candidate_division_TM7, Tenericutes, Actinobacteria, and Bacteroidetes and genera S24-7_unclassified and Bifidobacterium. However, at 12 days of hypoxia, these phyla and genera reverted to near-normoxic levels. In the small intestine, the relative abundances of the phylum Firmicutes and genus Lactobacillus increased and those of the phyla Actinobacteria and Verrucomicrobia and genera Bifidobacterium and Akkermansia decreased during short-term hypoxia. However, these altered bacteria returned to near-normoxic levels by day 12 of hypoxia. Temporal clustering revealed persistent taxon shifts; the relative abundances of the phyla Gemmatimonadetes and Acidobacteria and genera Gemmatimonas, Kocuria, Parasutterella, and Saccharopolyspora declined steadily, while Staphylococcus increased consistently in the stomach. In the small intestine, the relative abundance of the genus Stomatobaculum consistently increased in response to prolonged hypoxia. This study provided a time-resolved overview of gastric and small intestinal microbiota adaptations to hypoxia, identified potential candidate taxa involved in mucosal injury caused by hypoxia.