Bacterial intracellular sulfur globules: structure and function.

Bacteria that oxidize reduced sulfur compounds like H2S often transiently store sulfur in protein membrane-bounded intracellular sulfur globules; intracellular in this case meaning found inside the cell wall. The cultured bacteria that form these globules are primarily phylogenetically classified in the Proteobacteria and are chemotrophic or photoautotrophic. The current model organism is the purple sulfur bacterium Allochromatium vinosum. Research on this bacterium has provided the groundwork for understanding the protein membranes and the sulfur contents of globules. In addition, it has demonstrated the importance of different genes (e.g. sulfur oxidizing, sox) in their formation and in the final oxidation of sulfur in the globules to sulfate (e.g. dissimilatory sulfite reductase, dsr). Pursuing the characteristics of other intracellular sulfur globule-forming bacteria through genomics, transcriptomics and proteomics will eventually lead to a complete picture of their formation and breakdown. There will be commonality to some of the genetic, physiological and morphological characteristics involved in intracellular sulfur globules of different bacteria, but there will likely be some surprises as well.