Conditions achieved through selleck chemicals llc clinorotation are also referred to as weightlessness, modeled reduced gravity (MRG), simulated microgravity, or low-shear
modeled microgravity and hereafter are referred to as MRG in this paper. Clinorotation provides a cost-effective, accessible approach to study these conditions relative to space-based research and has been demonstrated to serve as an effective model for examining bacterial responses [19, 21]. Previous studies have shown that bacteria grown under either actual reduced gravity or MRG conditions, surprisingly, exhibit resistance to multiple antimicrobial methods [13, 22] and become more virulent, which has important potential impacts for human health [23, 24], reviewed by . In addition, bacteria under these conditions have enhanced growth [26–28], secondary metabolite production , biofilm formation  and extracellular polysaccharide production . Other studies have examined changes
in transcription (based on microarrays and real mTOR inhibitor time quantitative PCR) and proteomes [e.g., [31–33]] revealing the large scope of responses to these environmental conditions. The mechanisms behind the responses observed are largely unstudied . Lastly, prior research has demonstrated that bacterial responses under actual reduced gravity conditions are similar to those in ground-based studies, demonstrating the effectiveness of this model [26, 27]. As noted above, a variety of metrics have been used to evaluate bacterial responses to MRG. However, few of these studies have examined cellular physiological properties or compared responses among else different bacterial
species (but see ; where growth responses of Sphingobacterium thalpophilium [a motile strain] and Ralstonia pickettii [a non-motile strain] under MRG and NG conditions were compared). Therefore, in this study we examined bacterial physiological properties under environmental conditions created by clinorotation. Specifically, Escherichia coli and Staphylococcus aureus responses to MRG and normal gravity (NG) conditions under different growth (nutrient-rich and -poor) conditions were examined by analysis of a suite of cellular parameters, including protein concentrations, cell volume, membrane potential, and membrane integrity. Parameters chosen vary with availability of nutrients [9, 10, 35, 36] and are correlated with the physiological status of the cell, including its viability [37–39]. Most of these parameters have not been studied in E. coli and S. aureus under MRG conditions and they provide critical information about bacterial “”health”" as well as microenvironmental conditions near bacteria.