Microarray analysis identifies Salmonella genes belonging to the low-shear modeled microgravity regulon

Abstract

The low-shear environment of optimized rotation suspension culture allows both eukaryotic and prokaryotic cells to assume physiologically relevant phenotypes that have led to significant advances in fundamental investigations of medical and biological importance. This culture environment has also been used to model microgravity for ground-based studies regarding the impact of space flight on eukaryotic and prokaryotic physiology. We have previously demonstrated that low-shear modeled microgravity (LSMMG) under optimized rotation suspension culture is a novel environmental signal that regulates the virulence, stress resistance, and protein expression levels of Salmonella enterica serovar Typhimurium. However, the mechanisms used by the cells of any species, including Salmonella, to sense and respond to LSMMG and identities of the genes involved are unknown. In this study, we used DNA microarrays to elucidate the global transcriptional response of Salmonella to LSMMG. When compared with identical growth conditions under normal gravity (1 ؋ g), LSMMG differentially regulated the expression of 163 genes distributed throughout the chromosome, representing functionally diverse groups including transcriptional regulators, virulence factors, lipopolysaccharide biosynthetic enzymes, iron-utilization enzymes, and proteins of unknown function. Many of the LSMMG-regulated genes were organized in clusters or operons. The microarray results were further validated by RT-PCR and phenotypic analyses, and they indicate that the ferric uptake regulator is involved in the LSMMG response. The results provide important insight about the Salmonella LSMMG response and could provide clues for the functioning of known Salmonella virulence systems or the identification of uncharacterized bacterial virulence strategies.

Growth, Morphology, Cross Stress Resistance and Antibiotic Susceptibility of K. pneumoniae Under Simulated Microgravity

“…Normal gravity grown S. typhimurium had more resistance to hydrogen peroxide than the 1Xg grown cells (Wilson et al, 2002). The genes involved in the protection of cells against oxidative stress were found to be down regulated under low shear modeled microgravity growth conditions (Wilson et al, 2002a).…”

Microbial Responses to Microgravity and Other Low-Shear Environments

“…Although it is true that the gravity force vector present in a liquid environment on Earth is very different in magnitude from that present in the space atmosphere, the low-shear buoyant sensation experienced in both environments is very similar. There is increasing evidence not only that entire organisms sense and respond physiologically to low-shear, buoyant environments but also that cells respond at the molecular level to this environment (43,52,81,106,107).…”

Effect of simulated microgravity on the virulence properties of the opportunistic bacterial pathogen Staphylococcus aureus

“…Nickerson and effect of reduced gravitational vectors on the acity of pathogenic bacteria to cause infection, a tor that may impact on the well being of flight c colleagues [15,24] have provided strong evidence that growth in LSMMG substantially increases the lethality of S. enterica for mice and increased their capacity to survive in stressed environments, including survival within macrophages. DNA microarray analysis determined that LSMMG differentially regulated the expression of a large number of genes of functional diversity; although the regulatory elements of the LSMMG-mediated phenotype have yet to be identified, there is evidence that the ferric uptake regulator fur is involved in the LSMMG response [16]. As the virulence of Gram-negative pathogens such as S. enterica is less reliant on the elaboration of extracellular proteins that damage the infected host than specialised Gram-positive pathogens such as members of the streptococci and staphylococci, we examined the effect of LSMMG on the expression of factors known to mediate the pathogenesis of S. aureus.…”

“…Nickerson and coworkers [15] determined that Salmonella enterica serovar Typhimurium grown under low-shear modelled microgravity (LSMMG) using a high aspect ratio vessel (HARV) displayed enhanced virulence for mice compared to bacteria grown under normal gravity: LSMMG-grown cells had a decreased LD 50 , produced shortened time to death of infected test animals, and more readily colonized the liver and spleen. The processes involved in LSMMG-induced gene regulation appear to be novel and may be microgravityspecific [16]. We believe that there is an urgent need for these pioneering studies to be extended to include other groups of pathogens, particularly opportunistic Gram-positive bacteria frequently associated with the human microflora and likely to pose a risk of infection on extended missions.…”