Global Response to Desiccation Stress in the Soil Actinomycete Rhodococcus jostii RHA1

Abstract

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.Fluctuation in water availability is a fundamental stress challenging soil-residing microorganisms, and desiccation tolerance is a key adaptation of many such organisms. The structural integrity and proper functioning of many proteins and other cellular macromolecules depend upon interactions with water molecules. The mechanisms by which microorganisms adapt to water limitation have been best studied in cyanobacteria. Many cyanobacteria mitigate water loss by synthesizing extracellular polysaccharides (EPS) to create a barrier between themselves and the dry environment (31). The second main strategy employed by cyanobacteria for retaining water during air drying is to increase their intracellular solute concentrations to equilibrate them with those of their increasingly hypertonic surroundings (41). The molecules either imported or synthesized for this purpose are referred to as compatible solutes because, even at high concentrations, they permit cellular machinery to function (32). In a microarray study of a desiccated cyanobacterial species, Anabaena sp. strain PCC7120, the importance of compatible solute production as a major water stress response was identified (21). Other, concurrent responses included the up-regulation of genes associated with protein stabilization (heat shock and chaperone proteins) and with countering oxidative threats (probable...

Morphological and proteomic analysis of early stage air–liquid interface biofilm formation in Mycobacterium smegmatis

“…However, some of these proteins were also recognized as multifunctional proteins involved in various types of stress response in a number of bacterial species. The propane monooxygenase hydroxylase in Rhodococcus jostii was highly overexpressed in response to organic-solvent stress and starvation stress, which suggests that this gene might be part of a general stress system (LeBlanc et al, 2008;Patrauchan et al, 2012). Another multifunctional protein is dihydrolipoamide acetyltransferase, which has been suggested to take part in antioxidant defence in Mycobacterium tuberculosis, in addition to its role in intermediary metabolism (Shi & Ehrt, 2006).…”

Formation of specialized aerial architectures by Rhodococcus during utilization of vaporized p-cresol

“…The function of these rhodococcal genes remains to be discovered. In fact, SigF1 and SigF3 have been shown to play a key role in providing resistance against desiccation in R. jostii RHA1 (LeBlanc et al, 2008).…”

“…They are widely spread throughout diverse environments, including soil and water; they are metabolically diverse and have the ability to degrade a wide range of xenobiotic and plantderived molecules, playing a vital role in the turnover of organic matter in biogeochemical cycles (Goodfellow & Williams, 1983;Larkin et al, 2005;Martinkova et al, 2009;Warhurst & Fewson, 1994). These bacteria are well adapted to carbon starvation, chemical toxicity, adverse conditions and air-borne dispersal (Alvarez et al, 2004;de Carvalho et al, 2009;LeBlanc et al, 2008;McLeod et al, 2006;Sandhu et al, 2009;Warhurst & Fewson, 1994). These bacteria are also known to have different cellular and growth patterns, showing cocci-shaped, rod-shaped and filamentous cells, with elementary branch patterns and microscopically visible hyphae (Goodfellow, 1989).…”

Monooxygenases involved in the n-alkanes metabolism by Rhodococcus sp. BCP1: molecular characterization and expression of alkB gene

“…Furthermore, a proteomic analysis was conducted by LeBlanc [143] in order to identify the genetic basis of the strategies used by RHA1 to survive desiccation treatment.…”