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

Department of Microbiology and Immunology, Life Sciences Institute, University of British Columbia, Vancouver, Canada

^* To whom correspondence should be addressed. Email: wmohn{at}interchange.ubc.ca.

	Abstract

Rhodococcus jostii RHA1 is a soil-residing actinomycete with many favourable metabolic capabilities making it an ideal candidate for bioremediation of contaminated soils. Arguably the most basic requirement for life is water, yet some non-sporulating 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, RHA1 morphology was characterized by cryo-fixation scanning electron microscopy during each treatment. Desiccation resulted in a transcriptional response of approximately eight 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. 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, as well as two genes encoding sigma factors, SigF1 and SigF3, possibly involved in the regulatory response to desiccation. RHA1 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.