Global response to desiccation stress in the soil actinomycete Rhodococcus jostii RHA1

Rhodococcus jostii RHA1 is a soil-residing actinomycete with many favorable metabolic capabilities that make it an ideal candidate for the bioremediation of contaminated soils. Arguably the most basic requirement for life is water, yet some nonsporulating bacteria, like RHA1, can survive lengthy droughts. Here we report the first transcriptomic analysis of a gram-positive bacterium during desiccation. Filtered RHA1 cells incubated at either low relative humidity (20%), as an air-drying treatment, or high relative humidity (100%), as a control, were transcriptionally profiled over a comprehensive time series. Also, the morphology of RHA1 cells was characterized by cryofixation scanning electron microscopy during each treatment. Desiccation resulted in a transcriptional response of approximately 8 times more differentially regulated genes than in the control (819 versus 106 genes, respectively). Genes that were differentially expressed during only the desiccation treatment primarily had expression profiles that were maximally up-regulated upon complete drying of the cells. The microarray expression ratios for some of the highly up-regulated genes were verified by reverse transcriptase quantitative PCR. These genes included dps1, encoding an oxidative stress protection protein which has not previously been directly associated with desiccation, and the two genes encoding sigma factors SigF1 and SigF3, possibly involved in the regulatory response to desiccation. RHA1 cells also induced the biosynthetic pathway for the compatible solute ectoine. These desiccation-specific responses represent the best candidates for important mechanisms of desiccation resistance in RHA1.