Resuscitation of soil microbiota after > 70-years of desiccation

The response pattern of soil bacterial communities to drought events has been characterized from short-term laboratory desiccation and in naturally arid soils, but the resistance of soil bacteria to persistently long periods of desiccation remains largely unknown. This study assessed the abundance and composition of bacteria in 24 historical soils air-dried for more than 70 years, by quantification and high-throughput sequencing analyses of 16S rRNA genes. All soils contained measurable abundances of bacteria varying from 10 ³ to 10 ⁸ gene copies g ⁻¹ soil and contrasting community compositions were observed in soils with different land histories, suggesting that the detected bacteria were indigenous to the field. A 28-day soil rewetting incubation significantly increased the bacterial gene abundance in soils, indicating some bacteria in these soils were still alive and quickly resuscitated. Among all identified taxa, Paenibacillus, Cohnella and two unclassified Bacillales genera within the phylum Firmicutes showed growth in the highest number of soils (≥12 soils), whereas Bacillales genera Tumebacillus, Alicyclobacillus and Brevibacillus displayed the strongest growth activity (>1000-fold increase in gene abundance) following rewet. Some Actinobacteria and Proteobacteria genera also showed relatively high activity following the rewet, suggesting that the tolerance to prolonged desiccation is a common trait across phylogenetically divergent microbes. The present study thus confirmed the value of desiccated soils for detecting the composition difference of bacteria, and provided evidence for strong adaptation of some bacteria to long-term desiccation and extreme osmotic change.