Shah, U. | bioRxiv Science

bioRxiv2026

Dietary fiber selectively regulates intestinal persistence of probiotic bifidobacteria

Bifidobacteria dominate the gut microbiota of breast-fed infants, and are strongly associated with human health, including immune regulation, colonization resistance, and protection against inflammation. However, bifidobacteria persist at high abundance after weaning in only a subset of individuals, and the factors that regulate intestinal persistence of bifidobacteria are poorly understood. Using gnotobiotic mouse models, we identified a common dietary fiber, raffinose, as a critical determinant of bifidobacterial persistence during microbial transitions associated with weaning. Bifidobacterial persistence depends on an intact raffinose utilization operon and is associated with disease resistance and restrained inflammation in adult mice. Specific dietary fiber recommendations commencing at weaning are a potential strategy to maintain bifidobacteria persistence beyond infancy, with potential long-term benefits for host resilience and reduced risk of inflammatory disease.

microbiology↗

bioRxiv2026

Metformin Redirects Autophagy from Bulk Turnover to Mitochondrial Clearance

Metformin is the most widely prescribed antidiabetic drug and an active candidate for repurposing in oncology. How it engages autophagy - a pathway central to both its metabolic and its anti-tumor effects - has remained unresolved, with reports of induction, suppression, and no effect. Here we show that metformin reroutes rather than induces or inhibits autophagy in human cancer cells: at therapeutic concentrations, it suppresses bulk cytosolic turnover by selectively blocking WIPI2-mediated phagophore tethering, while the ULK1 initiation complex relocates toward mitochondria and engages selective mitochondrial clearance. We trace this redirection to mitochondrial complex I inhibition, registered as a shift in the NAD+/NADH ratio before any change in the adenylate pool, and to a non-canonical reprogramming of the ULK1 complex that operates independently of mTORC1 and of the proposed PEN2-lysosomal route. AMPK is engaged in a subunit-specific manner that restrains ATG13 at initiation and enables WIPI2 displacement at maturation. The ULK1 complex is therefore the node at which metformin sets autophagic substrate selection, with direct implications for combination therapy in diabetes and cancer.

cell biology↗