The role of the sulfur globule proteins of Allochromatium vinosum: mutagenesis of the sulfur globule protein genes and expression studies by real-time RT-PCR

Abstract

During oxidation of reduced sulfur compounds, the purple sulfur bacterium Allochromatium vinosum stores sulfur in the periplasm in the form of intracellular sulfur globules. The sulfur in the globules is enclosed by a protein envelope that consists of the homologous 10.5-kDa proteins SgpA and SgpB and the smaller 8.5-kDa SgpC. Reporter gene fusions of sgpA and alkaline phosphatase showed the constitutive expression of sgpA in A. vinosum and yielded additional evidence for the periplasmic localization of the sulfur globules. Expression analysis of the wild-type sgp genes by quantitative RT-PCR using the LightCycler system showed the constitutive expression of all three sgp genes. The expression of sgpB and sgpC is significantly enhanced under photolithotrophic conditions. Interestingly, sgpB is expressed ten times less than sgpA and sgpC implying that SgpA and SgpC are the "main proteins" of the sulfur globule envelope. Mutants with inactivated sgpA or sgpB did not show any differences in comparison with the wild-type, i.e., the encoded proteins can replace each other, whereas inactivation of sgpC leads to the formation of considerably smaller sulfur globules. This indicates a role of SgpC for globule expansion. A sgpBC double mutant was unable to grow on sulfide and could not form sulfur globules, showing that the protein envelope is indispensible for the formation and deposition of intracellular sulfur.

Sulfite oxidation in the purple sulfur bacterium Allochromatium vinosum: identification of SoeABC as a major player and relevance of SoxYZ in the process

“…For the insertional inactivation of Characterization of phenotypes, detection of sulfur species and protein determination. A. vinosum WT and mutant strains were characterized in batch culture experiments essentially as described previously (Prange et al, 2004;Hensen et al, 2006). Cells of A. vinosum, grown photo organoheterotrophically on malate [RCV medium (Weaver et al, 1975)] for 3 days were used as an inoculum for experiments concerned with transformation of sulfide and sulfite.…”

“…1b). Polysulfides were formed as intermediates in the process (Prange et al, 2004), but are not shown here for better clarity. In the next step, sulfite was generated in the cytoplasm by the Dsr proteins.…”

“…In A. vinosum, the sulfur globules are deposited in the same cellular compartment as the periplasmic thiosulfateand sulfide-oxidizing enzymes. This is evidenced by the presence of signal peptide-encoding sequences in the genes for the three structural proteins constituting the sulfur globule envelope (Pattaragulwanit et al, 1998;Prange et al, 2004;Frigaard & Dahl, 2008). For further oxidation of stored sulfur, the so-called Dsr system is of essential importance (Pott & Dahl, 1998;Dahl et al, 2005;Lübbe et al, 2006;Sander et al, 2006).…”

Exploiting genomic patterns to discover new supramolecular protein assemblies

“…In sulfur-oxidizing organisms, sulfur is stored in the periplasm for later oxidation in proteincoated sulfur globules. 48 In Allochromatium vinosum, the protein coat includes two paralogs, SgpA and SgpB. Although SgpA and SgpB are paralogous, they do not co-occur together in the same operon, thus evading detection by the criteria employed.…”

DsrR, a Novel IscA-Like Protein Lacking Iron- and Fe-S-Binding Functions, Involved in the Regulation of Sulfur Oxidation inAllochromatium vinosum

“…The photolithoautotrophic growth of A. vinosum wild-type and mutant strains was examined in batch culture under continuous illumination essentially as described by Prange et al (52) in a medium containing sulfide as the sole sulfur compound. Two hundred fifty milliliters of a photoheterotrophically grown stationary-phase culture was harvested (5,900 ϫ g; 10 min), and the cell material was used to inoculate 1 liter of modified Pfennig's medium (17) in a temperaturecontrolled fermentor.…”