Cellular Response of Shewanella oneidensis to Strontium Stress

Abstract

The physiology and transcriptome dynamics of the metal ion-reducing bacterium Shewanella oneidensis strain MR-1 in response to nonradioactive strontium (Sr) exposure were investigated. Studies indicated that MR-1 was able to grow aerobically in complex medium in the presence of 180 mM SrCl 2 but showed severe growth inhibition at levels above that concentration. Temporal gene expression profiles were generated from aerobically grown, mid-exponential-phase MR-1 cells shocked with 180 mM SrCl 2 and analyzed for significant differences in mRNA abundance with reference to data for nonstressed MR-1 cells. Genes with annotated functions in siderophore biosynthesis and iron transport were among the most highly induced (>100-fold [P < 0.05]) open reading frames in response to acute Sr stress, and a mutant (SO3032::pKNOCK) defective in siderophore production was found to be hypersensitive to SrCl 2 exposure, compared to parental and wild-type strains. Transcripts encoding multidrug and heavy metal efflux pumps, proteins involved in osmotic adaptation, sulfate ABC transporters, and assimilative sulfur metabolism enzymes also were differentially expressed following Sr exposure but at levels that were several orders of magnitude lower than those for iron transport genes. Precipitate formation was observed during aerobic growth of MR-1 in broth cultures amended with 50, 100, or 150 mM SrCl 2 but not in cultures of the SO3032::pKNOCK mutant or in the abiotic control. Chemical analysis of this precipitate using laser-induced breakdown spectroscopy and static secondary ion mass spectrometry indicated extracellular solid-phase sequestration of Sr, with at least a portion of the heavy metal associated with carbonate phases.The toxic heavy metal and radionuclide waste derived from defense-related activities and various industrial processes can seriously impact the health of ecosystems and humans. In situ bioremediation exploiting the intrinsic respiratory processes of dissimilatory metal ion-reducing bacteria (DMRB) has been proposed as a potential strategy for the reductive immobilization or detoxification of environmental contaminants. Microbial cell walls, for example, can serve as templates for nucleation of metal precipitates (4), and metal-reducing bacteria can directly convert metal pollutants from a soluble, mobile form to a sparingly soluble, less bioavailable form (28), thus facilitating contaminant removal from contained-storage and natural sites. Microbially mediated immobilization of toxic metals and radionuclides can occur as a result of precipitation through formation of metal-metabolite/ligand complexes, nonenzymatic biosorption, or bioaccumulation by energy-dependent transport systems (reviewed in references 4, 13,

Eicosapentaenoic Acid Plays a Beneficial Role in Membrane Organization and Cell Division of a Cold-Adapted Bacterium,Shewanella livingstonensisAc10

“…The purified PCR products were cloned into pCR-Blunt II-TOPO (Invitrogen Corp., Carlsbad, CA) and subcloned into the PstI and SpeI sites of pKNOCK-Km r . The plasmids obtained were introduced into competent E. coli S17-1/pir cells (7). The plasmids were transferred from the recombinant E. coli S17-1/pir cells into the rifampinresistant mutant of S. livingstonensis Ac10 by conjugation at 18°C on LB plates.…”

“…Putative EPA synthesis genes of S. livingstonensis Ac10 were disrupted by the integration of suicide plasmid pKNOCKKm r as previously reported (2,7,33). An internal fragment of each gene was amplified by PCR with the primers listed in Table 2.…”

The Response ofDesulfotomaculum reducensMI-1 to U(VI) Exposure: A Transcriptomic Study

“…Exposure of a midexponential phase culture to strontium resulted in the upregulation of genes primarily involved in siderophore-mediated iron sequestration and transport despite the presence of sufficient iron in the medium. This response was specific to Sr but it remains unclear whether it corresponded to a detoxification mechanism (i.e., through Sr 2+ complexation by siderophores) or the indirect consequence of a failure in the iron homeostasis sensor Fur (Brown et al 2006a).…”

“…In S. oneidensis, the stress response to chromium and strontium lead to the upregulation of proteins involved in ferric iron transport, specifically siderophore biosynthesis proteins and a siderophore-mediated transport protein, TonB (Brown et al 2006a(Brown et al , 2006b) as well as the global regulator for ferric uptake (Fur) (Thompson et al 2002). TonB receptors were also upregulated in response to uranium stress in C. crescentus under aerobic conditions (Hu et al 2005).…”

“…The findings were confirmed by the analysis of the phenotypes of appropriate mutants. The stress response to chromium and strontium was also studied in S. oneidensis (Brown et al 2006a(Brown et al , 2006b.…”