The research team, led by scientists at the Ocean University of China working with collaborators at the BYHEALTH Institute of Nutrition and Health and other Chinese institutions, set out to investigate whether chronic, low-level antibiotic exposure could trigger adaptive responses in this non-spore-forming bacterium. Unlike spore-forming species such as Bacillus, which can build tough, desiccated spores to ride out hostile conditions, Lactobacillus species have long been considered relatively fragile outside their comfortable niches. Bacterial dormancy offers an alternative strategy: a metabolically suppressed but fully reversible state that allows non-spore-forming bacteria to withstand adverse conditions without constructing specialized survival structures. The researchers exposed the sp1.1 strain of L. delbrueckii subsp. bulgaricus to concentrations of rifampicin that stressed but did not kill the cells, then tracked what happened to their physiology, their stress resistance, and their behavior in living animals.

The results were striking. Rifampicin-treated cells entered a state the authors characterize as dormancy, marked by sharply reduced ATP levels, the cellular energy currency, and impaired cell division. The bacteria essentially throttled themselves down, halting growth and conserving resources. Crucially, the state was reversible: when the antibiotic stress was removed, colonies recovered and normal growth resumed. This reversibility distinguishes dormancy from death and from irreversible injury, and it suggests a programmed, controlled response rather than simple damage. In the food industry, where starter cultures routinely face freezing, drying, acidification, and thermal processing steps that whittle down viable cell counts, a reversible dormant state that confers cross-tolerance to multiple stressors at once would be an enormously valuable property.

And cross-tolerance is exactly what the team observed. Dormant cells tolerated acid, alkali, and heat stress significantly better than untreated controls, meaning a single trigger, sublethal rifampicin exposure, produced broad-spectrum resistance rather than protection against just one threat. The functional consequences extended beyond the laboratory bench. When the researchers administered the treated bacteria to mice, the dormant cells persisted longer in the intestinal tract than normal cells, a property known as prolonged intestinal retention. They also exerted a greater impact on the structure of the gut microbial community, indicating that the dormant state changes not just survival but ecological behavior once the bacteria reach the gut. For probiotic formulations, where the central challenge is delivering enough live cells through gastric acid and bile to produce a benefit, these findings point to a potentially powerful new lever.

The mechanism behind this transformation turned out to be one of the most intriguing aspects of the study. When the researchers disrupted the protein aggregates that formed in the dormant cells, either by adjusting pH or by treating the cells with 1,6-hexanediol, a chemical that dissolves certain types of protein condensates, the enhanced tolerance vanished entirely. That causal experiment established that the aggregates are not a byproduct of dormancy but its functional engine. Rifampicin, which targets RNA polymerase and inhibits transcription, triggered a metabolic shift toward transcriptional and translational inhibition, and as protein synthesis slowed, proteins began to clump together into aggregates within the cells. What could have been cellular garbage, however, turned out to be something far more purposeful.

Proteomic analysis of the aggregates revealed a striking selectivity. Rather than capturing random cellular proteins, the aggregates were enriched for proteins involved in translation, RNA metabolism, and DNA repair, precisely the functions a cell would need to restart growth once conditions improve. The authors propose a model in which these aggregates function as molecular safe houses, sequestering and protecting key proteins from degradation or damage during the dormant period. By concentrating translation and DNA repair machinery in one protected location, the aggregates may locally enhance the efficiency of those processes when the cell revives, while also serving as a protein reservoir that allows rapid recovery of growth. In this view, the aggregate is less like a junk pile and more like a sealed emergency kit, packed with the tools needed for reconstruction.

Two intrinsically disordered proteins, identified in the study as Gene1622 and Gene1909, emerged as likely architects of this process. Disordered proteins lack a fixed three-dimensional structure and are known drivers of biomolecular condensate formation in many organisms. In the rifampicin-treated bacteria, both proteins were upregulated in whole-cell measurements and were enriched within the aggregates, suggesting they help nucleate or organize the condensates. The involvement of disordered proteins links this bacterial phenomenon to a broader and rapidly growing body of research on biomolecular condensates, membrane-less compartments that cells across all domains of life use to organize their biochemistry. That a food bacterium uses condensate biology to survive antibiotic stress adds a new ecological dimension to what has largely been studied in model organisms and human cells.

The study also uncovered hidden diversity within the bacterial population. Using single-cell RNA sequencing, the researchers identified a subpopulation of cells that sustained expression of alaS and gatA, genes involved in translation, even while global protein synthesis was being suppressed. These genes were downregulated in bulk RNA sequencing, which averages signals across the whole population, but single-cell analysis revealed that a distinct cluster of cells kept them active. This population heterogeneity means that not all cells respond identically to antibiotic stress; some appear to hedge their bets, maintaining critical functions while their neighbors go fully dormant. Such bet-hedging strategies are well known in microbial ecology, and this study demonstrates them at single-cell resolution in a commercially important probiotic, showing how a population can prepare for recovery even while most of its members are shut down.

The implications cut in two directions. On the constructive side, the findings provide a theoretical basis for engineering more robust starter cultures and probiotics. If manufacturers can deliberately induce and control this reversible dormant state, perhaps through stress conditioning rather than antibiotic exposure, they could produce cultures that survive processing better, retain viability longer on the shelf, and persist more effectively in the gut. The authors note that the work was supported by the National Natural Science Foundation of China and the BYHEALTH Nutrition and Health Research Foundation, reflecting industry interest in exactly these applications. On the cautionary side, the study raises ecological questions about stress-induced adaptation in the food chain. Antibiotic residues at sublethal levels are a known feature of some food production environments, and this research shows that such exposure can make food bacteria hardier and more persistent in the gut, where they exert stronger effects on microbial community structure. Whether that enhanced persistence is beneficial or disruptive to gut microbial homeostasis remains an open question, and one the authors flag explicitly. As the boundaries between food microbiology, antibiotic stewardship, and gut ecology continue to blur, this study suggests that the microbes in our yogurt may be far more adaptable, and far more responsive to their chemical environment, than anyone assumed.

Subject of Research: Sublethal antibiotic-induced dormancy and protein aggregation in Lactobacillus delbrueckii subsp. bulgaricus

Article Title: Sublethal rifampicin enhances the tolerance of Lactobacillus delbrueckii subsp. bulgaricus to food processing and intestinal retention through protein aggregation

Article References: Liu, L., Li, Z., Di, C., Ma, C., Huang, Y., Hao, X., Fu, Z., Yi, H., Zhang, Z., Li, P., Li, L., Ze, X., He, R., Zhang, L., & Gong, P. (2026). Sublethal rifampicin enhances the tolerance of Lactobacillus delbrueckii subsp. bulgaricus to food processing and intestinal retention through protein aggregation. Microbiome. https://doi.org/10.1186/s40168-026-02517-3

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02517-3

Keywords: Lactobacillus delbrueckii subsp. bulgaricus, rifampicin, bacterial dormancy, protein aggregates, probiotics, starter cultures, gut microbiome, stress tolerance, single-cell RNA sequencing, intrinsically disordered proteins, food fermentation, intestinal retention