Growth capacity and mortality burden shape microbial persistence under osmotic stress in Bacteroides thetaiotaomicron

The study of microbial persistence in the gut highlights the importance of understanding the factors that influence the survival of beneficial gut bacteria. Microbial communities in the intestines interact with the host in a complex manner, making it difficult to pinpoint the specific determinants of persistence in vivo. To address this challenge, researchers employed a defined microbial consortium to examine the role of intrinsic growth capacity in Bacteroides thetaiotaomicron, a common gut bacterium.

The research revealed that as intestinal osmolality increased, intrinsic growth capacity became a more significant predictor of B. thetaiotaomicron's relative abundance in the gut. However, this was not the sole factor contributing to the bacterium's persistence. The study identified mortality as another determinant of persistence, showing that adaptation to prolonged osmotic stress led to a reduction in cell loss without a corresponding increase in growth capacity.

The adaptive phenotype observed in B. thetaiotaomicron was associated with rapid and reversible phase variation in cell surface-associated PUL78/80. This adaptation, rather than fixed de novo mutations, allowed the bacterium to survive under osmotic stress. The PUL78/80-OFF state became progressively enriched among surviving cells as mortality increased, demonstrating the bacterium's ability to modulate its persistence through reversible phase variation.

In conclusion, the findings of this study emphasize that microbial persistence in the gut is not solely determined by intrinsic growth capacity. Reduced cell loss, as a consequence of adaptive mechanisms, can provide an alternative route to microbial persistence during environmental perturbation. This research sheds light on the complex interplay between growth capacity and mortality in shaping the survival of beneficial gut bacteria like Bacteroides thetaiotaomicron.