Exposure of Bacillus subtilis to Low Pressure (5 Kilopascals) Induces Several Global Regulons, Including Those Involved in the SigB-Mediated General Stress Response

Abstract

Studies of how microorganisms respond to pressure have been limited mostly to the extreme high pressures of the deep sea (i.e., the piezosphere). In contrast, despite the fact that the growth of most bacteria is inhibited at pressures below ϳ2.5 kPa, little is known of microbial responses to low pressure (LP). To study the global LP response, we performed transcription microarrays on Bacillus subtilis cells grown under normal atmospheric pressure (ϳ101 kPa) and a nearly inhibitory LP (5 kPa), equivalent to the pressure found at an altitude of ϳ20 km. Microarray analysis revealed altered levels of 363 transcripts belonging to several global regulons (AbrB, CcpA, CodY, Fur, IolR, ResD, Rok, SigH, Spo0A). Notably, the highest number of upregulated genes, 86, belonged to the SigB-mediated general stress response (GSR) regulon. Upregulation of the GSR by LP was confirmed by monitoring the expression of the SigB-dependent ctc-lacZ reporter fusion. Measuring transcriptome changes resulting from exposure of bacterial cells to LP reveals insights into cellular processes that may respond to LP exposure.

RETRACTED: Twenty-Three Species of Hypobarophilic Bacteria Recovered from Diverse Ecosystems Exhibit Growth under Simulated Martian Conditions at 0.7 kPa

“…Work here with hypobarophiles at 0.7 kPa and other research with mesobarophiles down to 2.5 kPa Schuerger et al, , 2013Nicholson et al, 2010;Fajardo-Cavazos et al, 2012;Waters et al, 2014) suggests that most airborne bacteria are capable of metabolic activity and growth up to the middle troposphere where temperature, not pressure, becomes limiting at 5-8 km. This should hold for bacteria present as individual cells, aggregates of cells, cell/ aerosol assemblages, or embedded cells in ice crystals.…”

“…4). Recent data (Nicholson et al, 2010;Fajardo-Cavazos et al, 2012;Schuerger et al, 2013;Waters et al, 2014) suggest that pressures down to 5 kPa are not limiting for microbial growth for most species; thus microbial activity will be constrained by other parameters in the atmosphere such as UV irradiation, temperature, desiccation effects, and access to nutrients and liquid water. Based on temperature constraints alone, the only other plausible region in Earth's atmosphere where microbial growth might resume would be in the upper stratosphere and stratopause between 40 and 50 km in which temperature once again approaches 0°C.…”

“…and a single type-strain of Serratia liquefaciens that exhibited vigorous to moderate growth, respectively, on semisolid media incubated under Mars surface conditions of 0.7 kPa, 0°C, and CO 2 -enriched anoxic atmosphere. Taken together, a number of studies Schuerger et al, , 2013Nicholson et al, 2010Nicholson et al, , 2013Fajardo-Cavazos et al, 2012;Waters et al, 2014) have demonstrated that of over 150 bacterial strains tested under a range of decreasing pressures, most bacteria grew nominally between 10.0 and 101.3 kPa, with decreased growth rates noted for most bacteria below 10.0 kPa, and the cessation of growth for most species at 2.5-3.5 kPa. Only a few species including Carnobacterium spp.…”

“…exhibited growth down to 2.5 kPa in an Earth-normal O 2 /N 2 atmosphere . Recent papers have demonstrated microbial growth and up-regulation of the des-desKR system encoding membrane fatty acid desaturase (Fajardo-Cavazos et al, 2012), evolution (Nicholson et al, 2010), and altered global gene expression (Waters et al, 2014) of Bacillus subtilis strains cultivated under Earth-normal O 2 / N 2 atmospheres at 5 kPa. A pressure range of 2.5 to 5 kPa is equivalent to altitudes of 20 to 25 km, respectively, in Earth's atmosphere.…”

Experimental evolution of Bacillus subtilis

“…Incubation of B. subtilis at low P (5 kPa) significantly altered the expression of 10 regulons, most notably an upregulation of 86 transcripts of the General Stress Response (GSR) regulon (Waters et al, 2014). Transcription of GSR genes is controlled by RNA polymerase containing sigma-B (Esig B ), and expression of the GSR gene ctc was induced at low pressure in an Esig Bdependent manner (Waters et al, 2014).…”