Transcriptional and metabolic stasis define desiccation-induced dormancy in the soil bacterium Arthrobacter sp. AZCC_0090 until water vapor initiates resuscitation

TL;DR

This study shows that desiccated soil bacteria maintain stable RNA and metabolite profiles during dormancy, challenging the use of RNA as a marker of microbial activity in dry environments.

Contribution

The study reveals that mRNA and metabolite profiles remain static during desiccation-induced dormancy in Arthrobacter, with changes only during state transitions.

Findings

mRNA and metabolite profiles remain essentially unchanged during desiccation-induced dormancy.

Water vapor rehydration restores cultivability and triggers dynamic changes in RNA and metabolite profiles.

RNA-based activity assessments may be misleading in periodically dry environments due to dormancy-associated molecular preservation.

Abstract

Microbes inhabiting soils experience periodic water deprivation. The effects of desiccation on DNA, protein, and membrane integrity are well-described. However, the effects of drying and rehydration on the composition of cellular RNA and metabolites are still poorly understood. Here, we describe how slow drying and rehydration with water vapor influence the composition of RNAs and metabolites in a soil Arthrobacter. While drying reduced cultivability relative to hydrated controls, water vapor rehydration fully restored it. Ribosomal RNA proportions remained constant throughout all treatments, and mRNA profiles showed stable composition during desiccation—changing only during transitions into and out of desiccation-induced dormancy. Six transcriptional modules displayed distinct expression patterns in desiccated-rehydrated samples relative to hydrated controls, including desiccation-rehydration responsive and rehydration-specific profiles. Targeted intracellular metabolomics revealed similarly static profiles during desiccation, with a cluster of ribonucleosides and nucleobases increasing in response to desiccation and returning to baseline levels upon rehydration with water vapor. These findings demonstrate that both mRNA and metabolite profiles remain essentially frozen in desiccated Arthrobacter, with dynamic changes occurring only during state transitions. These results have important implications for environments with frequent drying cycles where stable mRNA in dormant cells combined with intracellular RNA recycling may obscure interpretations of RNA-based environmental analyses that use RNA as a marker of microbial activity. Our results suggest that RNA-based activity assessments in periodically dry environments require careful consideration of dormancy-associated molecular preservation.

Metabolic activity quickly ceases in drying bacteria as they enter desiccation-induced dormancy. We show that mRNA and metabolite profiles were variable during drying and rewetting but did not change while desiccated. Additionally, water vapor stimulated the shift from the static to active state when exiting desiccation-induced dormancy. These shifts coincided with increased cultivability, indicating water vapor resuscitated dry cells. Because RNAs are transient, labile molecules that are turned over rapidly in growing bacteria, the presence of RNA in the environment is used as a marker for microbial activity. Our research shows this assumption may not hold for desiccated cells, indicating reliance on RNA as a marker of activity in environments that experience drying may obscure estimates of in situ microbial activity.

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