Characterization of the intracellular polyphosphate granules of the phototrophic green sulfur bacterium Chlorobaculum tepidum.

The ability to generate polyphosphate (polyP) granules is important for survival for bacteria during resistance to diverse environmental stresses, however the genesis of polyP granules is poorly understood. Chlorobaculum tepidum (Cba tepidum) is a thermophilic green sulfur anoxygenic phototrophic bacterium which uses reduced sulfur compounds as electron donors. The presence of electron rich granules inside the Cba tepidum was reported, but no further information was provided. In this work we used cell thin sections at three different time points of cultivation to observe the biogenesis of the inclusions over time, and the in cell total phosphate concentration was monitored over time as well. Furthermore, the elemental analysis (EDS) of the electron rich inclusions showed the presence of phosphorus and oxygen. The existence of polyphosphate was demonstrated by 31P NMR spectroscopy of cell lysates. Finally, we show that the biogenesis of the phosphorus granules correlates with an abundance of proteins that are closely related to polyphosphate metabolism.