Proteômica de Chromobacterium violaceum submetida à microgravidade simulada

Abstract

Chromobcterium violaceum (C.violaceum) is a Gram-negative bacteria, which has been found at tropical and subtropical regions, considered a free living model organism. Some proteomic studies performed with this bacterium have demonstrated its ability to adapt to environmental challenges such as high iron concentration and oxidative stress exposure. However, no study was made with this specie submitted to simulated microgravity (SMG), that is, under conditions in which the gravity is artificially reduced to less than 1xg. MGS studies may be important in understanding the molecular-level modulations undergone by living organisms. Therefore, the aim of this study was to characterize the response of C. violaceum, as free-living model organism, cultured at MGS, using proteomics techniques in order to understand how this bacterium response to this stress. The SMG was achieved by rotating the vessel around the horizontal axis perpendicular to the gravitational vector in Rotating Cell Culture Systems (RCCS4). SMG was conducted at a speed of 40 rpm for a period of 12 hours to obtain the growth curve every 2 hours. Total protein extraction was made in two times: 5 and 12 hours, corresponding to early (MG5) and late (MG12) exponential phase, respectively, taking the growth curve as a reference. After trypsinization, samples were analyzed with Q-TOF mass spectrometer. As a result a total of 212 proteins during 5h of growth and 192 at 12h were detected, of which 144 of them were common in both periods. We detected 155 proteins during MG5, from which 18 proteins were upregulated, 19 down-regulated and 17 proteins were exclusive when compared to GN5. In the proteome obtained in 12h of growth, 165 proteins were identified in normal gravity (GN12) and 173 in MG12, of which, 17 were upregulated, 22 were downregulated and 28 expressed only in MG12 condition. In addition, it was possible to identify 25 proteins with unknown function in MG5 and MG12. Using computational tools it was possible to construct networks of protein-protein interactions (PPI) and sub-networks containing group of proteins with correlated functions, to analyze metabolic pathways, biological processes, genomic context and search for conserved domains and homologous sequences of proteins with unknown function . As a result, we identified sub-networks related to protein biosynthesis, transcription regulation and translation, stress response and energetic metabolism, we conclude that the cellular responses associated with differential expression induced by MGS led to a decrease in the growth of C. violaceum, accompanied by the negative regulation of proteins related to transcriptional, translational and energy release by aerobic pathways and by the positive regulation of proteins involved in oxidative stress, anaerobic pathway and cell survival.